diff --git a/en/handbook/hw/chapter.sgml b/en/handbook/hw/chapter.sgml index 4554b8e7cb..d3bf2da501 100644 --- a/en/handbook/hw/chapter.sgml +++ b/en/handbook/hw/chapter.sgml @@ -1,5550 +1,5557 @@ PC Hardware compatibility Issues of hardware compatibility are among the most troublesome in the computer industry today and FreeBSD is by no means immune to trouble. In this respect, FreeBSD's advantage of being able to run on inexpensive commodity PC hardware is also its liability when it comes to support for the amazing variety of components on the market. While it would be impossible to provide a exhaustive listing of hardware that FreeBSD supports, this section serves as a catalog of the device drivers included with FreeBSD and the hardware each drivers supports. Where possible and appropriate, notes about specific products are included. You may also want to refer to the kernel configuration file section in this handbook for a list of supported devices. As FreeBSD is a volunteer project without a funded testing department, we depend on you, the user, for much of the information contained in this catalog. If you have direct experience of hardware that does or does not work with FreeBSD, please let us know by sending e-mail to the &a.doc;. Questions about supported hardware should be directed to the &a.questions; (see Mailing Lists for more information). When submitting information or asking a question, please remember to specify exactly what version of FreeBSD you are using and include as many details of your hardware as possible. Resources on the Internet The following links have proven useful in selecting hardware. Though some of what you see won't necessarily be specific (or even applicable) to FreeBSD, most of the hardware information out there is OS independent. Please check with the FreeBSD hardware guide to make sure that your chosen configuration is supported before making any purchases. The Pentium Systems Hardware Performance Guide Sample Configurations The following list of sample hardware configurations by no means constitutes an endorsement of a given hardware vendor or product by The FreeBSD Project. This information is provided only as a public service and merely catalogs some of the experiences that various individuals have had with different hardware combinations. Your mileage may vary. Slippery when wet. Beware of dog. Jordan's Picks I have had fairly good luck building workstation and server configurations with the following components. I can't guarantee that you will too, nor that any of the companies here will remain “best buys” forever. I will try, when I can, to keep this list up-to-date but cannot obviously guarantee that it will be at any given time. Motherboards For Pentium Pro (P6) systems, I'm quite fond of the Tyan S1668 dual-processor motherboard as well as the Intel PR440FX motherboard with on-board SCSI WIDE and 100/10MB Intel Etherexpress NIC. You can build a dandy little single or dual processor system (which is supported in FreeBSD 3.0) for very little cost now that the Pentium Pro 180/256K chips have fallen so greatly in price, but no telling how much longer this will last. For the Pentium II, I'm rather partial to the ASUS P2l97-S motherboard with the on-board Adaptec SCSI WIDE controller. For Pentium machines, the ASUS P55T2P4 motherboard appears to be a good choice for mid-to-high range Pentium server and workstation systems. Those wishing to build more fault-tolerant systems should also be sure to use Parity memory or, for truly 24/7 applications, ECC memory. ECC memory does involve a slight performance trade-off (which may or may not be noticeable depending on your application) but buys you significantly increased fault-tolerance to memory errors. Disk Controllers This one is a bit trickier, and while I used to recommend the Buslogic controllers unilaterally for everything from ISA to PCI, now I tend to lean towards the Adaptec 1542CF for ISA, Buslogic Bt747c for EISA and Adaptec 2940UW for PCI. The NCR/Symbios cards for PCI have also worked well for me, though you need to make sure that your motherboard supports the BIOS-less model if you're using one of those (if your card has nothing which looks even vaguely like a ROM chip on it, you've probably got one which expects its BIOS to be on your motherboard). If you should find that you need more than one SCSI controller in a PCI machine, you may wish to consider conserving your scarce PCI bus resources by buying the Adaptec 3940 card, which puts two SCSI controllers (and internal busses) in a single slot. There are two types of 3940 on the market—the older model with AIC 7880 chips on it, and hte newer one with AIC 7895 chips. The newer model requires CAM support which is not yet part of FreeBSD—you have to add it, or install from one of the CAM binary snapshot release. Disk drives In this particular game of Russian roulette, I'll make few specific recommendations except to say “SCSI over IDE whenever you can afford it.” Even in small desktop configurations, SCSI often makes more sense since it allows you to easily migrate drives from server to desktop as falling drive prices make it economical to do so. If you have more than one machine to administer then think of it not simply as storage, think of it as a food chain! For a serious server configuration, there's not even any argument—use SCSI equipment and good cables. CDROM drives My SCSI preferences extend to SCSI CDROM drives as well, and while the Toshiba drives have always been favourites of mine (in whatever speed is hot that week), I'm still fond of my good old Plextor PX-12CS drive. It's only a 12 speed, but it's offered excellent performance and reliability. Generally speaking, most SCSI CDROM drives I've seen have been of pretty solid construction and you probably won't go wrong with an HP or NEC SCSI CDROM drive either. SCSI CDROM prices also appear to have dropped considerably in the last few months and are now quite competitive with IDE CDROMs while remaining a technically superior solution. I now see no reason whatsoever to settle for an IDE CDROM drive if given a choice between the two. CD Recordable (WORM) drives At the time of this writing, FreeBSD supports 3 types of CDR drives (though I believe they all ultimately come from Phillips anyway): The Phillips CDD 522 (Acts like a Plasmon), the PLASMON RF4100 and the HP 6020i. I myself use the HP 6020i for burning CDROMs (in 2.2 and alter releases—it does not work with earlier releases of the SCSI code) and it works very well. See /usr/share/examples/worm on your 2.2 system for example scripts used to created ISO9660 filesystem images (with RockRidge extensions) and burn them onto an HP6020i CDR. Tape drives I've had pretty good luck with both 8mm drives from Exabyte and 4mm (DAT) drives from HP. For backup purposes, I'd have to give the higher recommendation to the Exabyte due to the more robust nature (and higher storage capacity) of 8mm tape. Video Cards If you can also afford to buy a commercial X server for US$99 from Xi Graphics, Inc. (formerly X Inside, Inc) then I can heartily recommend the Matrox Millenium II card. Note that support for this card is also excellent with the XFree86 server, which is now at version 3.3.2. You also certainly can't go wrong with one of Number 9's cards — their S3 Vision 868 and 968 based cards (the 9FX series) also being quite fast and very well supported by XFree86's S3 server. You can also pick up their Revolution 3D cards very cheaply these days, especially if you require a lot of video memory. Monitors I have had very good luck with the Sony Multiscan 17seII monitors, as have I with the Viewsonic offering in the same (Trinitron) tube. For larger than 17", all I can recommend at the time of this writing is to not spend any less than U.S. $2,000 for a 21" monitor or $1,700 for a 20" monitor if that's what you really need. There are good monitors available in the >=20" range and there are also cheap monitors in the >=20" range. Unfortunately, very few are both cheap and good! Networking I can recommend the Intel EtherExpress Pro/100B card first ande foremost, followed by the SMC Ultra 16 controller for any ISA application and the SMC EtherPower or Compex ENET32 cards for slightly cheaper PCI based networking. In general, any PCI NIC based around DEC's DC21041 Ethernet controller chip, such as the Zynx ZX342 or DEC DE435, will generally work quite well and can frequently be found in 2-port and 4-port version (useful for firewalls and routers), though the Pro/100MB card has the edge when it comes to providing the best performance with teh lower overhead. If what you're looking for is the cheapest possible solution then almost any NE2000 clone will do a fine job for very little cost. Serial If you're looking for high-speed serial networking solutions, then Digi International makes the SYNC/570 series, with drivers now in FreeBSD-current. Emerging Technologies also manufactures a board with T1/E1 capabilities, using software they provide. I have no direct experience using either product, however. Multiport card options are somewhat more numerous, though it has to be said that FreeBSD's support for Cyclades's products is probably the tightest, primarily as a result of that company's commitment to making sure that we are adequately supplied with evaluation boards and technical specs. I've heard that the Cyclom-16Ye offers the best price/performance, though I've not checked the prices lately. Other multiport cards I've heard good things about are the BOCA and AST cards, and Stallion Technologies apparently offers an unofficial driver for their cards at this location. Audio I currently use a Creative Labs AWE32 though just about anything from Creative Labs will generally work these days. This is not to say that other types of sound cards don't also work, simply that I have little experience with them (I was a former GUS fan, but Gravis's soundcard situation has been dire for some time). Video For video capture, there are two good choices — any card based on the Brooktree BT848 chip, such as the Hauppage or WinTV boards, will work very nicely with FreeBSD. Another board which works for me is the Matrox Meteor card. FreeBSD also supports the older video spigot card from Creative Labs, but those are getting somewhat difficult to find. Note that the Meteor frame grabber card will not work with motherboards based on the 440FX chipset! See the motherboard reference section for details. In such cases, it's better to go with a BT848 based board. Core/Processing Motherboards, busses, and chipsets * ISA * EISA * VLB PCI Contributed by &a.obrien; from postings by &a.rgrimes;. 25 April 1995. Continuing updates by &a.jkh;. Last update on 26 August 1996. Of the Intel PCI chip sets, the following list describes various types of known-brokenness and the degree of breakage, listed from worst to best. Mercury: Cache coherency problems, especially if there are ISA bus masters behind the ISA to PCI bridge chip. Hardware flaw, only known work around is to turn the cache off. Saturn-I (ie, 82424ZX at rev 0, 1 or 2): Write back cache coherency problems. Hardware flaw, only known work around is to set the external cache to write-through mode. Upgrade to Saturn-II. Saturn-II (ie, 82424ZX at rev 3 or 4): Works fine, but many MB manufactures leave out the external dirty bit SRAM needed for write back operation. Work arounds are either run it in write through mode, or get the dirty bit SRAM installed. (I have these for the ASUS PCI/I-486SP3G rev 1.6 and later boards). Neptune: Can not run more than 2 bus master devices. Admitted Intel design flaw. Workarounds include do not run more than 2 bus masters, special hardware design to replace the PCI bus arbiter (appears on Intel Altair board and several other Intel server group MB's). And of course Intel's official answer, move to the Triton chip set, we “fixed it there”. Triton (ie, 430FX): No known cache coherency or bus master problems, chip set does not implement parity checking. Workaround for parity issue. Use Triton-II based motherboards if you have the choice. Triton-II (ie, 430HX): All reports on motherboards using this chipset have been favorable so far. No known problems. Orion: Early versions of this chipset suffered from a PCI write-posting bug which can cause noticeable performance degradation in applications where large amounts of PCI bus traffic is involved. B0 stepping or later revisions of the chipset fixed this problem. 440FX: This Pentium Pro support chipset seems to work well, and does not suffer from any of the early Orion chipset problems. It also supports a wider variety of memory, including ECC and parity. The only known problem with it is that the Matrox Meteor frame grabber card doesn't like it. CPUs/FPUs Contributed by &a.asami;. 26 December 1997. P6 class (Pentium Pro/Pentium II) Both the Pentium Pro and Pentium II work fine with FreeBSD. In fact, our main ftp site ftp.freebsd.org (also known as "ftp.cdrom.com", world's largest ftp site) runs FreeBSD on a Pentium Pro. Configurations details are available for interested parties. Pentium class The Intel Pentium (P54C), Pentium MMX (P55C), AMD K6 and Cyrix/IBM 6x86MX processors are all reported to work with FreeBSD. I will not go into details of which processor is faster than what, there are zillions of web sites on the Internet that tells you one way or another. :) Various CPUs have different voltage/cooling requirements. Make sure your motherboard can supply the exact voltage needed by the CPU. For instance, many recent MMX chips require split voltage (e.g., 2.9V core, 3.3V I/O). Also, some AMD and Cyrix/IBM chips run hotter than Intel chips. In that case, make sure you have good heatsink/fans (you can get the list of certified parts from their web pages). Clock speeds Contributed by &a.rgrimes;. 1 October 1996. Updated by &a.asami;. 27 December 1997. Pentium class machines use different clock speeds for the various parts of the system. These being the speed of the CPU, external memory bus, and the PCI bus. It is not always true that a “faster” processor will make a system faster than a “slower” one, due to the various clock speeds used. Below is a table showing the differences: Rated CPU MHz External Clock and Memory Bus MHz External to Internal Clock Multiplier PCI Bus Clock MHz 60 60 1.0 30 66 66 1.0 33 75 50 1.5 25 90 60 1.5 30 100 50 2 25 100 66 1.5 33 120 60 2 30 133 66 2 33 150 60 2.5 30 (Intel, AMD) 150 75 2 37.5 (Cyrix/IBM 6x86MX) 166 66 2.5 33 180 60 3 30 200 66 3 33 233 66 3.5 33 66MHz may actually be 66.667MHz, but don't assume so. The Pentium 100 can be run at either 50MHz external clock with a multiplier of 2 or at 66MHz and a multiplier of 1.5. As can be seen the best parts to be using are the 100, 133, 166, 200 and 233, with the exception that at a multiplier of 3 or more the CPU starves for memory. The AMD K6 Bug In 1997, there have been reports of the AMD K6 seg faulting during heavy compilation. That problem has been fixed in 3Q '97. According to reports, K6 chips with date mark “9733” or larger (i.e., manufactured in the 33rd week of '97 or later) do not have this bug. * 486 class * 386 class 286 class Sorry, FreeBSD does not run on 80286 machines. It is nearly impossible to run today's large full-featured UNIXes on such hardware. * Memory The minimum amount of memory you must have to install FreeBSD is 5 MB. Once your system is up and running you can build a custom kernel that will use less memory. If you use the boot4.flp you can get away with having only 4 MB. * BIOS Input/Output Devices * Video cards * Sound cards Serial ports and multiport cards The UART: What it is and how it works Copyright © 1996 &a.uhclem;, All Rights Reserved. 13 January 1996. The Universal Asynchronous Receiver/Transmitter (UART) controller is the key component of the serial communications subsystem of a computer. The UART takes bytes of data and transmits the individual bits in a sequential fashion. At the destination, a second UART re-assembles the bits into complete bytes. Serial transmission is commonly used with modems and for non-networked communication between computers, terminals and other devices. There are two primary forms of serial transmission: Synchronous and Asynchronous. Depending on the modes that are supported by the hardware, the name of the communication sub-system will usually include a A if it supports Asynchronous communications, and a S if it supports Synchronous communications. Both forms are described below. Some common acronyms are:
UART Universal Asynchronous Receiver/Transmitter
USART Universal Synchronous-Asynchronous Receiver/Transmitter
Synchronous Serial Transmission Synchronous serial transmission requires that the sender and receiver share a clock with one another, or that the sender provide a strobe or other timing signal so that the receiver knows when to “read” the next bit of the data. In most forms of serial Synchronous communication, if there is no data available at a given instant to transmit, a fill character must be sent instead so that data is always being transmitted. Synchronous communication is usually more efficient because only data bits are transmitted between sender and receiver, and synchronous communication can be more more costly if extra wiring and circuits are required to share a clock signal between the sender and receiver. A form of Synchronous transmission is used with printers and fixed disk devices in that the data is sent on one set of wires while a clock or strobe is sent on a different wire. Printers and fixed disk devices are not normally serial devices because most fixed disk interface standards send an entire word of data for each clock or strobe signal by using a separate wire for each bit of the word. In the PC industry, these are known as Parallel devices. The standard serial communications hardware in the PC does not support Synchronous operations. This mode is described here for comparison purposes only. Asynchronous Serial Transmission Asynchronous transmission allows data to be transmitted without the sender having to send a clock signal to the receiver. Instead, the sender and receiver must agree on timing parameters in advance and special bits are added to each word which are used to synchronize the sending and receiving units. When a word is given to the UART for Asynchronous transmissions, a bit called the "Start Bit" is added to the beginning of each word that is to be transmitted. The Start Bit is used to alert the receiver that a word of data is about to be sent, and to force the clock in the receiver into synchronization with the clock in the transmitter. These two clocks must be accurate enough to not have the frequency drift by more than 10% during the transmission of the remaining bits in the word. (This requirement was set in the days of mechanical teleprinters and is easily met by modern electronic equipment.) After the Start Bit, the individual bits of the word of data are sent, with the Least Significant Bit (LSB) being sent first. Each bit in the transmission is transmitted for exactly the same amount of time as all of the other bits, and the receiver “looks” at the wire at approximately halfway through the period assigned to each bit to determine if the bit is a 1 or a 0. For example, if it takes two seconds to send each bit, the receiver will examine the signal to determine if it is a 1 or a 0 after one second has passed, then it will wait two seconds and then examine the value of the next bit, and so on. The sender does not know when the receiver has “looked” at the value of the bit. The sender only knows when the clock says to begin transmitting the next bit of the word. When the entire data word has been sent, the transmitter may add a Parity Bit that the transmitter generates. The Parity Bit may be used by the receiver to perform simple error checking. Then at least one Stop Bit is sent by the transmitter. When the receiver has received all of the bits in the data word, it may check for the Parity Bits (both sender and receiver must agree on whether a Parity Bit is to be used), and then the receiver looks for a Stop Bit. If the Stop Bit does not appear when it is supposed to, the UART considers the entire word to be garbled and will report a Framing Error to the host processor when the data word is read. The usual cause of a Framing Error is that the sender and receiver clocks were not running at the same speed, or that the signal was interrupted. Regardless of whether the data was received correctly or not, the UART automatically discards the Start, Parity and Stop bits. If the sender and receiver are configured identically, these bits are not passed to the host. If another word is ready for transmission, the Start Bit for the new word can be sent as soon as the Stop Bit for the previous word has been sent. Because asynchronous data is “self synchronizing”, if there is no data to transmit, the transmission line can be idle. Other UART Functions In addition to the basic job of converting data from parallel to serial for transmission and from serial to parallel on reception, a UART will usually provide additional circuits for signals that can be used to indicate the state of the transmission media, and to regulate the flow of data in the event that the remote device is not prepared to accept more data. For example, when the device connected to the UART is a modem, the modem may report the presence of a carrier on the phone line while the computer may be able to instruct the modem to reset itself or to not take calls by asserting or deasserting one more more of these extra signals. The function of each of these additional signals is defined in the EIA RS232-C standard. The RS232-C and V.24 Standards In most computer systems, the UART is connected to circuitry that generates signals that comply with the EIA RS232-C specification. There is also a CCITT standard named V.24 that mirrors the specifications included in RS232-C. RS232-C Bit Assignments (Marks and Spaces) In RS232-C, a value of 1 is called a Mark and a value of 0 is called a Space. When a communication line is idle, the line is said to be “Marking”, or transmitting continuous 1 values. The Start bit always has a value of 0 (a Space). The Stop Bit always has a value of 1 (a Mark). This means that there will always be a Mark (1) to Space (0) transition on the line at the start of every word, even when multiple word are transmitted back to back. This guarantees that sender and receiver can resynchronize their clocks regardless of the content of the data bits that are being transmitted. The idle time between Stop and Start bits does not have to be an exact multiple (including zero) of the bit rate of the communication link, but most UARTs are designed this way for simplicity. In RS232-C, the "Marking" signal (a 1) is represented by a voltage between -2 VDC and -12 VDC, and a "Spacing" signal (a 0) is represented by a voltage between 0 and +12 VDC. The transmitter is supposed to send +12 VDC or -12 VDC, and the receiver is supposed to allow for some voltage loss in long cables. Some transmitters in low power devices (like portable computers) sometimes use only +5 VDC and -5 VDC, but these values are still acceptable to a RS232-C receiver, provided that the cable lengths are short. RS232-C Break Signal RS232-C also specifies a signal called a Break, which is caused by sending continuous Spacing values (no Start or Stop bits). When there is no electricity present on the data circuit, the line is considered to be sending Break. The Break signal must be of a duration longer than the time it takes to send a complete byte plus Start, Stop and Parity bits. Most UARTs can distinguish between a Framing Error and a Break, but if the UART cannot do this, the Framing Error detection can be used to identify Breaks. In the days of teleprinters, when numerous printers around the country were wired in series (such as news services), any unit could cause a Break by temporarily opening the entire circuit so that no current flowed. This was used to allow a location with urgent news to interrupt some other location that was currently sending information. In modern systems there are two types of Break signals. If the Break is longer than 1.6 seconds, it is considered a "Modem Break", and some modems can be programmed to terminate the conversation and go on-hook or enter the modems' command mode when the modem detects this signal. If the Break is smaller than 1.6 seconds, it signifies a Data Break and it is up to the remote computer to respond to this signal. Sometimes this form of Break is used as an Attention or Interrupt signal and sometimes is accepted as a substitute for the ASCII CONTROL-C character. Marks and Spaces are also equivalent to “Holes” and “No Holes” in paper tape systems. Breaks cannot be generated from paper tape or from any other byte value, since bytes are always sent with Start and Stop bit. The UART is usually capable of generating the continuous Spacing signal in response to a special command from the host processor. RS232-C DTE and DCE Devices The RS232-C specification defines two types of equipment: the Data Terminal Equipment (DTE) and the Data Carrier Equipment (DCE). Usually, the DTE device is the terminal (or computer), and the DCE is a modem. Across the phone line at the other end of a conversation, the receiving modem is also a DCE device and the computer that is connected to that modem is a DTE device. The DCE device receives signals on the pins that the DTE device transmits on, and vice versa. When two devices that are both DTE or both DCE must be connected together without a modem or a similar media translater between them, a NULL modem must be used. The NULL modem electrically re-arranges the cabling so that the transmitter output is connected to the receiver input on the other device, and vice versa. Similar translations are performed on all of the control signals so that each device will see what it thinks are DCE (or DTE) signals from the other device. The number of signals generated by the DTE and DCE devices are not symmetrical. The DTE device generates fewer signals for the DCE device than the DTE device receives from the DCE. RS232-C Pin Assignments The EIA RS232-C specification (and the ITU equivalent, V.24) calls for a twenty-five pin connector (usually a DB25) and defines the purpose of most of the pins in that connector. In the IBM Personal Computer and similar systems, a subset of RS232-C signals are provided via nine pin connectors (DB9). The signals that are not included on the PC connector deal mainly with synchronous operation, and this transmission mode is not supported by the UART that IBM selected for use in the IBM PC. Depending on the computer manufacturer, a DB25, a DB9, or both types of connector may be used for RS232-C communications. (The IBM PC also uses a DB25 connector for the parallel printer interface which causes some confusion.) Below is a table of the RS232-C signal assignments in the DB25 and DB9 connectors. DB25 RS232-C Pin DB9 IBM PC Pin EIA Circuit Symbol CCITT Circuit Symbol Common Name Signal Source Description 1 - AA 101 PG/FG - Frame/Protective Ground 2 3 BA 103 TD DTE Transmit Data 3 2 BB 104 RD DCE Receive Data 4 7 CA 105 RTS DTE Request to Send 5 8 CB 106 CTS DCE Clear to Send 6 6 CC 107 DSR DCE Data Set Ready 7 5 AV 102 SG/GND - Signal Ground 8 1 CF 109 DCD/CD DCE Data Carrier Detect 9 - - - - - Reserved for Test 10 - - - - - Reserved for Test 11 - - - - - Reserved for Test 12 - CI 122 SRLSD DCE Sec. Recv. Line Signal Detector 13 - SCB 121 SCTS DCE Secondary Clear to Send 14 - SBA 118 STD DTE Secondary Transmit Data 15 - DB 114 TSET DCE Trans. Sig. Element Timing 16 - SBB 119 SRD DCE Secondary Received Data 17 - DD 115 RSET DCE Receiver Signal Element Timing 18 - - 141 LOOP DTE Local Loopback 19 - SCA 120 SRS DTE Secondary Request to Send 20 4 CD 108.2 DTR DTE Data Terminal Ready 21 - - - RDL DTE Remote Digital Loopback 22 9 CE 125 RI DCE Ring Indicator 23 - CH 111 DSRS DTE Data Signal Rate Selector 24 - DA 113 TSET DTE Trans. Sig. Element Timing 25 - - 142 - DCE Test Mode Bits, Baud and Symbols Baud is a measurement of transmission speed in asynchronous communication. Because of advances in modem communication technology, this term is frequently misused when describing the data rates in newer devices. Traditionally, a Baud Rate represents the number of bits that are actually being sent over the media, not the amount of data that is actually moved from one DTE device to the other. The Baud count includes the overhead bits Start, Stop and Parity that are generated by the sending UART and removed by the receiving UART. This means that seven-bit words of data actually take 10 bits to be completely transmitted. Therefore, a modem capable of moving 300 bits per second from one place to another can normally only move 30 7-bit words if Parity is used and one Start and Stop bit are present. If 8-bit data words are used and Parity bits are also used, the data rate falls to 27.27 words per second, because it now takes 11 bits to send the eight-bit words, and the modem still only sends 300 bits per second. The formula for converting bytes per second into a baud rate and vice versa was simple until error-correcting modems came along. These modems receive the serial stream of bits from the UART in the host computer (even when internal modems are used the data is still frequently serialized) and converts the bits back into bytes. These bytes are then combined into packets and sent over the phone line using a Synchronous transmission method. This means that the Stop, Start, and Parity bits added by the UART in the DTE (the computer) were removed by the modem before transmission by the sending modem. When these bytes are received by the remote modem, the remote modem adds Start, Stop and Parity bits to the words, converts them to a serial format and then sends them to the receiving UART in the remote computer, who then strips the Start, Stop and Parity bits. The reason all these extra conversions are done is so that the two modems can perform error correction, which means that the receiving modem is able to ask the sending modem to resend a block of data that was not received with the correct checksum. This checking is handled by the modems, and the DTE devices are usually unaware that the process is occurring. By striping the Start, Stop and Parity bits, the additional bits of data that the two modems must share between themselves to perform error-correction are mostly concealed from the effective transmission rate seen by the sending and receiving DTE equipment. For example, if a modem sends ten 7-bit words to another modem without including the Start, Stop and Parity bits, the sending modem will be able to add 30 bits of its own information that the receiving modem can use to do error-correction without impacting the transmission speed of the real data. The use of the term Baud is further confused by modems that perform compression. A single 8-bit word passed over the telephone line might represent a dozen words that were transmitted to the sending modem. The receiving modem will expand the data back to its original content and pass that data to the receiving DTE. Modern modems also include buffers that allow the rate that bits move across the phone line (DCE to DCE) to be a different speed than the speed that the bits move between the DTE and DCE on both ends of the conversation. Normally the speed between the DTE and DCE is higher than the DCE to DCE speed because of the use of compression by the modems. Because the number of bits needed to describe a byte varied during the trip between the two machines plus the differing bits-per-seconds speeds that are used present on the DTE-DCE and DCE-DCE links, the usage of the term Baud to describe the overall communication speed causes problems and can misrepresent the true transmission speed. So Bits Per Second (bps) is the correct term to use to describe the transmission rate seen at the DCE to DCE interface and Baud or Bits Per Second are acceptable terms to use when a connection is made between two systems with a wired connection, or if a modem is in use that is not performing error-correction or compression. Modern high speed modems (2400, 9600, 14,400, and 19,200bps) in reality still operate at or below 2400 baud, or more accurately, 2400 Symbols per second. High speed modem are able to encode more bits of data into each Symbol using a technique called Constellation Stuffing, which is why the effective bits per second rate of the modem is higher, but the modem continues to operate within the limited audio bandwidth that the telephone system provides. Modems operating at 28,800 and higher speeds have variable Symbol rates, but the technique is the same. The IBM Personal Computer UART Starting with the original IBM Personal Computer, IBM selected the National Semiconductor INS8250 UART for use in the IBM PC Parallel/Serial Adapter. Subsequent generations of compatible computers from IBM and other vendors continued to use the INS8250 or improved versions of the National Semiconductor UART family. National Semiconductor UART Family Tree There have been several versions and subsequent generations of the INS8250 UART. Each major version is described below. INS8250 -> INS8250B \ \ \-> INS8250A -> INS82C50A \ \ \-> NS16450 -> NS16C450 \ \ \-> NS16550 -> NS16550A -> PC16550D INS8250 This part was used in the original IBM PC and IBM PC/XT. The original name for this part was the INS8250 ACE (Asynchronous Communications Element) and it is made from NMOS technology. The 8250 uses eight I/O ports and has a one-byte send and a one-byte receive buffer. This original UART has several race conditions and other flaws. The original IBM BIOS includes code to work around these flaws, but this made the BIOS dependent on the flaws being present, so subsequent parts like the 8250A, 16450 or 16550 could not be used in the original IBM PC or IBM PC/XT. INS8250-B This is the slower speed of the INS8250 made from NMOS technology. It contains the same problems as the original INS8250. INS8250A An improved version of the INS8250 using XMOS technology with various functional flaws corrected. The INS8250A was used initially in PC clone computers by vendors who used “clean” BIOS designs. Because of the corrections in the chip, this part could not be used with a BIOS compatible with the INS8250 or INS8250B. INS82C50A This is a CMOS version (low power consumption) of the INS8250A and has similar functional characteristics. NS16450 Same as NS8250A with improvements so it can be used with faster CPU bus designs. IBM used this part in the IBM AT and updated the IBM BIOS to no longer rely on the bugs in the INS8250. NS16C450 This is a CMOS version (low power consumption) of the NS16450. NS16550 Same as NS16450 with a 16-byte send and receive buffer but the buffer design was flawed and could not be reliably be used. NS16550A Same as NS16550 with the buffer flaws corrected. The 16550A and its successors have become the most popular UART design in the PC industry, mainly due it its ability to reliably handle higher data rates on operating systems with sluggish interrupt response times. NS16C552 This component consists of two NS16C550A CMOS UARTs in a single package. PC16550D Same as NS16550A with subtle flaws corrected. This is revision D of the 16550 family and is the latest design available from National Semiconductor. The NS16550AF and the PC16550D are the same thing National reorganized their part numbering system a few years ago, and the NS16550AFN no longer exists by that name. (If you have a NS16550AFN, look at the date code on the part, which is a four digit number that usually starts with a nine. The first two digits of the number are the year, and the last two digits are the week in that year when the part was packaged. If you have a NS16550AFN, it is probably a few years old.) The new numbers are like PC16550DV, with minor differences in the suffix letters depending on the package material and its shape. (A description of the numbering system can be found below.) It is important to understand that in some stores, you may pay $15(US) for a NS16550AFN made in 1990 and in the next bin are the new PC16550DN parts with minor fixes that National has made since the AFN part was in production, the PC16550DN was probably made in the past six months and it costs half (as low as $5(US) in volume) as much as the NS16550AFN because they are readily available. As the supply of NS16550AFN chips continues to shrink, the price will probably continue to increase until more people discover and accept that the PC16550DN really has the same function as the old part number. National Semiconductor Part Numbering System The older NSnnnnnrqp part numbers are now of the format PCnnnnnrgp. The r is the revision field. The current revision of the 16550 from National Semiconductor is D. The p is the package-type field. The types are: "F" QFP (quad flat pack) L lead type "N" DIP (dual inline package) through hole straight lead type "V" LPCC (lead plastic chip carrier) J lead type The g is the product grade field. If an I precedes the package-type letter, it indicates an “industrial” grade part, which has higher specs than a standard part but not as high as Military Specification (Milspec) component. This is an optional field. So what we used to call a NS16550AFN (DIP Package) is now called a PC16550DN or PC16550DIN. Other Vendors and Similar UARTs Over the years, the 8250, 8250A, 16450 and 16550 have been licensed or copied by other chip vendors. In the case of the 8250, 8250A and 16450, the exact circuit (the “megacell”) was licensed to many vendors, including Western Digital and Intel. Other vendors reverse-engineered the part or produced emulations that had similar behavior. In internal modems, the modem designer will frequently emulate the 8250A/16450 with the modem microprocessor, and the emulated UART will frequently have a hidden buffer consisting of several hundred bytes. Because of the size of the buffer, these emulations can be as reliable as a 16550A in their ability to handle high speed data. However, most operating systems will still report that the UART is only a 8250A or 16450, and may not make effective use of the extra buffering present in the emulated UART unless special drivers are used. Some modem makers are driven by market forces to abandon a design that has hundreds of bytes of buffer and instead use a 16550A UART so that the product will compare favorably in market comparisons even though the effective performance may be lowered by this action. A common misconception is that all parts with “16550A” written on them are identical in performance. There are differences, and in some cases, outright flaws in most of these 16550A clones. When the NS16550 was developed, the National Semiconductor obtained several patents on the design and they also limited licensing, making it harder for other vendors to provide a chip with similar features. Because of the patents, reverse-engineered designs and emulations had to avoid infringing the claims covered by the patents. Subsequently, these copies almost never perform exactly the same as the NS16550A or PC16550D, which are the parts most computer and modem makers want to buy but are sometimes unwilling to pay the price required to get the genuine part. Some of the differences in the clone 16550A parts are unimportant, while others can prevent the device from being used at all with a given operating system or driver. These differences may show up when using other drivers, or when particular combinations of events occur that were not well tested or considered in the Windows driver. This is because most modem vendors and 16550-clone makers use the Microsoft drivers from Windows for Workgroups 3.11 and the Microsoft MSD utility as the primary tests for compatibility with the NS16550A. This over-simplistic criteria means that if a different operating system is used, problems could appear due to subtle differences between the clones and genuine components. National Semiconductor has made available a program named COMTEST that performs compatibility tests independent of any OS drivers. It should be remembered that the purpose of this type of program is to demonstrate the flaws in the products of the competition, so the program will report major as well as extremely subtle differences in behavior in the part being tested. In a series of tests performed by the author of this document in 1994, components made by National Semiconductor, TI, StarTech, and CMD as well as megacells and emulations embedded in internal modems were tested with COMTEST. A difference count for some of these components is listed below. Because these tests were performed in 1994, they may not reflect the current performance of the given product from a vendor. It should be noted that COMTEST normally aborts when an excessive number or certain types of problems have been detected. As part of this testing, COMTEST was modified so that it would not abort no matter how many differences were encountered. Vendor Part Number Errors (aka "differences" reported) National (PC16550DV) 0 National (NS16550AFN) 0 National (NS16C552V) 0 TI (TL16550AFN) 3 CMD (16C550PE) 19 StarTech (ST16C550J) 23 Rockwell Reference modem with internal 16550 or an emulation (RC144DPi/C3000-25) 117 Sierra Modem with an internal 16550 (SC11951/SC11351) 91 To date, the author of this document has not found any non-National parts that report zero differences using the COMTEST program. It should also be noted that National has had five versions of the 16550 over the years and the newest parts behave a bit differently than the classic NS16550AFN that is considered the benchmark for functionality. COMTEST appears to turn a blind eye to the differences within the National product line and reports no errors on the National parts (except for the original 16550) even when there are official erratas that describe bugs in the A, B and C revisions of the parts, so this bias in COMTEST must be taken into account. It is important to understand that a simple count of differences from COMTEST does not reveal a lot about what differences are important and which are not. For example, about half of the differences reported in the two modems listed above that have internal UARTs were caused by the clone UARTs not supporting five- and six-bit character modes. The real 16550, 16450, and 8250 UARTs all support these modes and COMTEST checks the functionality of these modes so over fifty differences are reported. However, almost no modern modem supports five- or six-bit characters, particularly those with error-correction and compression capabilities. This means that the differences related to five- and six-bit character modes can be discounted. Many of the differences COMTEST reports have to do with timing. In many of the clone designs, when the host reads from one port, the status bits in some other port may not update in the same amount of time (some faster, some slower) as a real NS16550AFN and COMTEST looks for these differences. This means that the number of differences can be misleading in that one device may only have one or two differences but they are extremely serious, and some other device that updates the status registers faster or slower than the reference part (that would probably never affect the operation of a properly written driver) could have dozens of differences reported. COMTEST can be used as a screening tool to alert the administrator to the presence of potentially incompatible components that might cause problems or have to be handled as a special case. If you run COMTEST on a 16550 that is in a modem or a modem is attached to the serial port, you need to first issue a ATE0&W command to the modem so that the modem will not echo any of the test characters. If you forget to do this, COMTEST will report at least this one difference: Error (6)...Timeout interrupt failed: IIR = c1 LSR = 61 8250/16450/16550 Registers The 8250/16450/16550 UART occupies eight contiguous I/O port addresses. In the IBM PC, there are two defined locations for these eight ports and they are known collectively as COM1 and COM2. The makers of PC-clones and add-on cards have created two additional areas known as COM3 and COM4, but these extra COM ports conflict with other hardware on some systems. The most common conflict is with video adapters that provide IBM 8514 emulation. COM1 is located from 0x3f8 to 0x3ff and normally uses IRQ 4 COM2 is located from 0x2f8 to 0x2ff and normally uses IRQ 3 COM3 is located from 0x3e8 to 0x3ef and has no standardized IRQ COM4 is located from 0x2e8 to 0x2ef and has no standardized IRQ. A description of the I/O ports of the 8250/16450/16550 UART is provided below. I/O Port Access Allowed Description +0x00 write (DLAB==0) Transmit Holding Register (THR).Information written to this port are treated as data words and will be transmitted by the UART. +0x00 read (DLAB==0) Receive Buffer Register (RBR).Any data words received by the UART form the serial link are accessed by the host by reading this port. +0x00 write/read (DLAB==1) Divisor Latch LSB (DLL)This value will be divided from the master input clock (in the IBM PC, the master clock is 1.8432MHz) and the resulting clock will determine the baud rate of the UART. This register holds bits 0 thru 7 of the divisor. +0x01 write/read (DLAB==1) Divisor Latch MSB (DLH)This value will be divided from the master input clock (in the IBM PC, the master clock is 1.8432MHz) and the resulting clock will determine the baud rate of the UART. This register holds bits 8 thru 15 of the divisor. +0x01 write/read (DLAB==0) Interrupt Enable Register (IER)The 8250/16450/16550 UART classifies events into one of four categories. Each category can be configured to generate an interrupt when any of the events occurs. The 8250/16450/16550 UART generates a single external interrupt signal regardless of how many events in the enabled categories have occurred. It is up to the host processor to respond to the interrupt and then poll the enabled interrupt categories (usually all categories have interrupts enabled) to determine the true cause(s) of the interrupt. Bit 7 Reserved, always 0. Bit 6 Reserved, always 0. Bit 5 Reserved, always 0. Bit 4 Reserved, always 0. Bit 3 Enable Modem Status Interrupt (EDSSI). Setting this bit to "1" allows the UART to generate an interrupt when a change occurs on one or more of the status lines. Bit 2 Enable Receiver Line Status Interrupt (ELSI) Setting this bit to "1" causes the UART to generate an interrupt when the an error (or a BREAK signal) has been detected in the incoming data. Bit 1 Enable Transmitter Holding Register Empty Interrupt (ETBEI) Setting this bit to "1" causes the UART to generate an interrupt when the UART has room for one or more additional characters that are to be transmitted. Bit 0 Enable Received Data Available Interrupt (ERBFI) Setting this bit to "1" causes the UART to generate an interrupt when the UART has received enough characters to exceed the trigger level of the FIFO, or the FIFO timer has expired (stale data), or a single character has been received when the FIFO is disabled. +0x02 write FIFO Control Register (FCR) (This port does not exist on the 8250 and 16450 UART.) Bit 7 Receiver Trigger Bit #1 Bit 6 Receiver Trigger Bit #0These two bits control at what point the receiver is to generate an interrupt when the FIFO is active. 7 6 How many words are received before an interrupt is generated 0 0 1 0 1 4 1 0 8 1 1 14 Bit 5 Reserved, always 0. Bit 4 Reserved, always 0. Bit 3 DMA Mode Select. If Bit 0 is set to "1" (FIFOs enabled), setting this bit changes the operation of the -RXRDY and -TXRDY signals from Mode 0 to Mode 1. Bit 2 Transmit FIFO Reset. When a "1" is written to this bit, the contents of the FIFO are discarded. Any word currently being transmitted will be sent intact. This function is useful in aborting transfers. Bit 1 Receiver FIFO Reset. When a "1" is written to this bit, the contents of the FIFO are discarded. Any word currently being assembled in the shift register will be received intact. Bit 0 16550 FIFO Enable. When set, both the transmit and receive FIFOs are enabled. Any contents in the holding register, shift registers or FIFOs are lost when FIFOs are enabled or disabled. +0x02 read Interrupt Identification Register Bit 7 FIFOs enabled. On the 8250/16450 UART, this bit is zero. Bit 6 FIFOs enabled. On the 8250/16450 UART, this bit is zero. Bit 5 Reserved, always 0. Bit 4 Reserved, always 0. Bit 3 Interrupt ID Bit #2. On the 8250/16450 UART, this bit is zero. Bit 2 Interrupt ID Bit #1 Bit 1 Interrupt ID Bit #0.These three bits combine to report the category of event that caused the interrupt that is in progress. These categories have priorities, so if multiple categories of events occur at the same time, the UART will report the more important events first and the host must resolve the events in the order they are reported. All events that caused the current interrupt must be resolved before any new interrupts will be generated. (This is a limitation of the PC architecture.) 2 1 0 Priority Description 0 1 1 First Received Error (OE, PE, BI, or FE) 0 1 0 Second Received Data Available 1 1 0 Second Trigger level identification (Stale data in receive buffer) 0 0 1 Third Transmitter has room for more words (THRE) 0 0 0 Fourth Modem Status Change (-CTS, -DSR, -RI, or -DCD) Bit 0 Interrupt Pending Bit. If this bit is set to "0", then at least one interrupt is pending. +0x03 write/read Line Control Register (LCR) Bit 7 Divisor Latch Access Bit (DLAB). When set, access to the data transmit/receive register (THR/RBR) and the Interrupt Enable Register (IER) is disabled. Any access to these ports is now redirected to the Divisor Latch Registers. Setting this bit, loading the Divisor Registers, and clearing DLAB should be done with interrupts disabled. Bit 6 Set Break. When set to "1", the transmitter begins to transmit continuous Spacing until this bit is set to "0". This overrides any bits of characters that are being transmitted. Bit 5 Stick Parity. When parity is enabled, setting this bit causes parity to always be "1" or "0", based on the value of Bit 4. Bit 4 Even Parity Select (EPS). When parity is enabled and Bit 5 is "0", setting this bit causes even parity to be transmitted and expected. Otherwise, odd parity is used. Bit 3 Parity Enable (PEN). When set to "1", a parity bit is inserted between the last bit of the data and the Stop Bit. The UART will also expect parity to be present in the received data. Bit 2 Number of Stop Bits (STB). If set to "1" and using 5-bit data words, 1.5 Stop Bits are transmitted and expected in each data word. For 6, 7 and 8-bit data words, 2 Stop Bits are transmitted and expected. When this bit is set to "0", one Stop Bit is used on each data word. Bit 1 Word Length Select Bit #1 (WLSB1) Bit 0 Word Length Select Bit #0 (WLSB0) Together these bits specify the number of bits in each data word. 1 0 Word Length 0 0 5 Data Bits 0 1 6 Data Bits 1 0 7 Data Bits 1 1 8 Data Bits +0x04 write/read Modem Control Register (MCR) Bit 7 Reserved, always 0. Bit 6 Reserved, always 0. Bit 5 Reserved, always 0. Bit 4 Loop-Back Enable. When set to "1", the UART transmitter and receiver are internally connected together to allow diagnostic operations. In addition, the UART modem control outputs are connected to the UART modem control inputs. CTS is connected to RTS, DTR is connected to DSR, OUT1 is connected to RI, and OUT 2 is connected to DCD. Bit 3 OUT 2. An auxiliary output that the host processor may set high or low. In the IBM PC serial adapter (and most clones), OUT 2 is used to tri-state (disable) the interrupt signal from the 8250/16450/16550 UART. Bit 2 OUT 1. An auxiliary output that the host processor may set high or low. This output is not used on the IBM PC serial adapter. Bit 1 Request to Send (RTS). When set to "1", the output of the UART -RTS line is Low (Active). Bit 0 Data Terminal Ready (DTR). When set to "1", the output of the UART -DTR line is Low (Active). +0x05 write/read Line Status Register (LSR) Bit 7 Error in Receiver FIFO. On the 8250/16450 UART, this bit is zero. This bit is set to "1" when any of the bytes in the FIFO have one or more of the following error conditions: PE, FE, or BI. Bit 6 Transmitter Empty (TEMT). When set to "1", there are no words remaining in the transmit FIFO or the transmit shift register. The transmitter is completely idle. Bit 5 Transmitter Holding Register Empty (THRE). When set to "1", the FIFO (or holding register) now has room for at least one additional word to transmit. The transmitter may still be transmitting when this bit is set to "1". Bit 4 Break Interrupt (BI). The receiver has detected a Break signal. Bit 3 Framing Error (FE). A Start Bit was detected but the Stop Bit did not appear at the expected time. The received word is probably garbled. Bit 2 Parity Error (PE). The parity bit was incorrect for the word received. Bit 1 Overrun Error (OE). A new word was received and there was no room in the receive buffer. The newly-arrived word in the shift register is discarded. On 8250/16450 UARTs, the word in the holding register is discarded and the newly- arrived word is put in the holding register. Bit 0 Data Ready (DR) One or more words are in the receive FIFO that the host may read. A word must be completely received and moved from the shift register into the FIFO (or holding register for 8250/16450 designs) before this bit is set. +0x06 write/read Modem Status Register (MSR) Bit 7 Data Carrier Detect (DCD). Reflects the state of the DCD line on the UART. Bit 6 Ring Indicator (RI). Reflects the state of the RI line on the UART. Bit 5 Data Set Ready (DSR). Reflects the state of the DSR line on the UART. Bit 4 Clear To Send (CTS). Reflects the state of the CTS line on the UART. Bit 3 Delta Data Carrier Detect (DDCD). Set to "1" if the -DCD line has changed state one more more times since the last time the MSR was read by the host. Bit 2 Trailing Edge Ring Indicator (TERI). Set to "1" if the -RI line has had a low to high transition since the last time the MSR was read by the host. Bit 1 Delta Data Set Ready (DDSR). Set to "1" if the -DSR line has changed state one more more times since the last time the MSR was read by the host. Bit 0 Delta Clear To Send (DCTS). Set to "1" if the -CTS line has changed state one more more times since the last time the MSR was read by the host. +0x07 write/read Scratch Register (SCR). This register performs no function in the UART. Any value can be written by the host to this location and read by the host later on. Beyond the 16550A UART Although National Semiconductor has not offered any components compatible with the 16550 that provide additional features, various other vendors have. Some of these components are described below. It should be understood that to effectively utilize these improvements, drivers may have to be provided by the chip vendor since most of the popular operating systems do not support features beyond those provided by the 16550. ST16650 By default this part is similar to the NS16550A, but an extended 32-byte send and receive buffer can be optionally enabled. Made by Startech. TIL16660 By default this part behaves similar to the NS16550A, but an extended 64-byte send and receive buffer can be optionally enabled. Made by Texas Instruments. Hayes ESP This proprietary plug-in card contains a 2048-byte send and receive buffer, and supports data rates to 230.4Kbit/sec. Made by Hayes. In addition to these “dumb” UARTs, many vendors produce intelligent serial communication boards. This type of design usually provides a microprocessor that interfaces with several UARTs, processes and buffers the data, and then alerts the main PC processor when necessary. Because the UARTs are not directly accessed by the PC processor in this type of communication system, it is not necessary for the vendor to use UARTs that are compatible with the 8250, 16450, or the 16550 UART. This leaves the designer free to components that may have better performance characteristics. Configuring the <devicename>sio</devicename> driver The sio driver provides support for NS8250-, NS16450-, NS16550 and NS16550A-based EIA RS-232C (CCITT V.24) communications interfaces. Several multiport cards are supported as well. See the &man.sio.4; manual page for detailed technical documentation. Digi International (DigiBoard) PC/8 Contributed by &a.awebster;. 26 August 1995. Here is a config snippet from a machine with a Digi International PC/8 with 16550. It has 8 modems connected to these 8 lines, and they work just great. Do not forget to add options COM_MULTIPORT or it will not work very well! device sio4 at isa? port 0x100 tty flags 0xb05 device sio5 at isa? port 0x108 tty flags 0xb05 device sio6 at isa? port 0x110 tty flags 0xb05 device sio7 at isa? port 0x118 tty flags 0xb05 device sio8 at isa? port 0x120 tty flags 0xb05 device sio9 at isa? port 0x128 tty flags 0xb05 device sio10 at isa? port 0x130 tty flags 0xb05 device sio11 at isa? port 0x138 tty flags 0xb05 irq 9 vector siointr The trick in setting this up is that the MSB of the flags represent the last SIO port, in this case 11 so flags are 0xb05. Boca 16 Contributed by &a.whiteside;. 26 August 1995. The procedures to make a Boca 16 port board with FreeBSD are pretty straightforward, but you will need a couple things to make it work: You either need the kernel sources installed so you can recompile the necessary options or you will need someone else to compile it for you. The 2.0.5 default kernel does not come with multiport support enabled and you will need to add a device entry for each port anyways. Two, you will need to know the interrupt and IO setting for your Boca Board so you can set these options properly in the kernel. One important note — the actual UART chips for the Boca 16 are in the connector box, not on the internal board itself. So if you have it unplugged, probes of those ports will fail. I have never tested booting with the box unplugged and plugging it back in, and I suggest you do not either. If you do not already have a custom kernel configuration file set up, refer to Kernel Configuration for general procedures. The following are the specifics for the Boca 16 board and assume you are using the kernel name MYKERNEL and editing with vi. Add the line options COM_MULTIPORT to the config file. Where the current device sion lines are, you will need to add 16 more devices. Only the last device includes the interrupt vector for the board. (See the &man.sio.4; manual page for detail as to why.) The following example is for a Boca Board with an interrupt of 3, and a base IO address 100h. The IO address for Each port is +8 hexadecimal from the previous port, thus the 100h, 108h, 110h... addresses. device sio1 at isa? port 0x100 tty flags 0x1005 device sio2 at isa? port 0x108 tty flags 0x1005 device sio3 at isa? port 0x110 tty flags 0x1005 device sio4 at isa? port 0x118 tty flags 0x1005 … device sio15 at isa? port 0x170 tty flags 0x1005 device sio16 at isa? port 0x178 tty flags 0x1005 irq 3 vector siointr The flags entry must be changed from this example unless you are using the exact same sio assignments. Flags are set according to 0xMYY where M indicates the minor number of the master port (the last port on a Boca 16) and YY indicates if FIFO is enabled or disabled(enabled), IRQ sharing is used(yes) and if there is an AST/4 compatible IRQ control register(no). In this example, flags 0x1005 indicates that the master port is sio16. If I added another board and assigned sio17 through sio28, the flags for all 16 ports on that board would be 0x1C05, where 1C indicates the minor number of the master port. Do not change the 05 setting. Save and complete the kernel configuration, recompile, install and reboot. Presuming you have successfully installed the recompiled kernel and have it set to the correct address and IRQ, your boot message should indicate the successful probe of the Boca ports as follows: (obviously the sio numbers, IO and IRQ could be different) sio1 at 0x100-0x107 flags 0x1005 on isa sio1: type 16550A (multiport) sio2 at 0x108-0x10f flags 0x1005 on isa sio2: type 16550A (multiport) sio3 at 0x110-0x117 flags 0x1005 on isa sio3: type 16550A (multiport) sio4 at 0x118-0x11f flags 0x1005 on isa sio4: type 16550A (multiport) sio5 at 0x120-0x127 flags 0x1005 on isa sio5: type 16550A (multiport) sio6 at 0x128-0x12f flags 0x1005 on isa sio6: type 16550A (multiport) sio7 at 0x130-0x137 flags 0x1005 on isa sio7: type 16550A (multiport) sio8 at 0x138-0x13f flags 0x1005 on isa sio8: type 16550A (multiport) sio9 at 0x140-0x147 flags 0x1005 on isa sio9: type 16550A (multiport) sio10 at 0x148-0x14f flags 0x1005 on isa sio10: type 16550A (multiport) sio11 at 0x150-0x157 flags 0x1005 on isa sio11: type 16550A (multiport) sio12 at 0x158-0x15f flags 0x1005 on isa sio12: type 16550A (multiport) sio13 at 0x160-0x167 flags 0x1005 on isa sio13: type 16550A (multiport) sio14 at 0x168-0x16f flags 0x1005 on isa sio14: type 16550A (multiport) sio15 at 0x170-0x177 flags 0x1005 on isa sio15: type 16550A (multiport) sio16 at 0x178-0x17f irq 3 flags 0x1005 on isa sio16: type 16550A (multiport master) If the messages go by too fast to see, &prompt.root; dmesg | more will show you the boot messages. Next, appropriate entries in /dev for the devices must be made using the /dev/MAKEDEV script. After becoming root: &prompt.root; cd /dev &prompt.root; ./MAKEDEV tty1 &prompt.root; ./MAKEDEV cua1 (everything in between) &prompt.root; ./MAKEDEV ttyg &prompt.root; ./MAKEDEV cuag If you do not want or need callout devices for some reason, you can dispense with making the cua* devices. If you want a quick and sloppy way to make sure the devices are working, you can simply plug a modem into each port and (as root) &prompt.root; echo at > ttyd* for each device you have made. You should see the RX lights flash for each working port. Configuring the <devicename>cy</devicename> driver Contributed by &a.alex;. 6 June 1996. The Cyclades multiport cards are based on the cy driver instead of the usual sio driver used by other multiport cards. Configuration is a simple matter of: Add the cy device to your kernel configuration (note that your irq and iomem settings may differ). device cy0 at isa? tty irq 10 iomem 0xd4000 iosiz 0x2000 vector cyintr Rebuild and install the new kernel. Make the device nodes by typing (the following example assumes an 8-port board): &prompt.root; cd /dev &prompt.root; for i in 0 1 2 3 4 5 6 7;do ./MAKEDEV cuac$i ttyc$i;done If appropriate, add dialup entries to /etc/ttys by duplicating serial device (ttyd) entries and using ttyc in place of ttyd. For example: ttyc0 "/usr/libexec/getty std.38400" unknown on insecure ttyc1 "/usr/libexec/getty std.38400" unknown on insecure ttyc2 "/usr/libexec/getty std.38400" unknown on insecure … ttyc7 "/usr/libexec/getty std.38400" unknown on insecure Reboot with the new kernel. - Configuring the <devicename>si</devicename> driver - - Contributed by &a.nsayer;. 25 March 1998. - - The Specialix SI/XIO and SX multiport cards use the si driver. A single - machine can have up to 4 host cards. The following host cards are supported: - - ISA SI/XIO host card (2 versions) - EISA SI/XIO host card - PCI SI/XIO host card - ISA SX host card - PCI SX host card -Although the SX and SI/XIO host cards look markedly different, their - functionality are basically the same. The host cards do not use I/O - locations, but instead require a 32K chunk of memory. The factory - configuration for ISA cards places this at 0xd0000-0xd7fff. They - also require an IRQ. PCI cards will, of course, autoconfigure themselves. - - You can attach up to 4 external modules to each host card. The external - modules contain either 4 or 8 serial ports. They come in the following - varieties: - -SI 4 or 8 port modules. Up to 57600 bps on each port supported. - XIO 8 port modules. Up to 115200 bps on each port supported. One - type of XIO module has 7 serial and 1 parallel port. - SXDC 8 port modules. Up to 921600 bps on each port supported. Like - XIO, a module is available with one parallel port as well. - + + Configuring the <devicename>si</devicename> driver + + Contributed by &a.nsayer;. 25 March + 1998. + + The Specialix SI/XIO and SX multiport cards use the si driver. A + single machine can have up to 4 host cards. The following host cards + are supported: + + + ISA SI/XIO host card (2 versions) + EISA SI/XIO host card + PCI SI/XIO host card + ISA SX host card + PCI SX host card + + Although the SX and SI/XIO host cards look markedly different, + their functionality are basically the same. The host cards do not + use I/O locations, but instead require a 32K chunk of memory. The + factory configuration for ISA cards places this at 0xd0000-0xd7fff. + They also require an IRQ. PCI cards will, of course, autoconfigure + themselves. + You can attach up to 4 external modules to each host card. The + external modules contain either 4 or 8 serial ports. They come in + the following varieties: + + + SI 4 or 8 port modules. Up to 57600 bps on each port + supported. + + XIO 8 port modules. Up to 115200 bps on each port + supported. One type of XIO module has 7 serial and 1 parallel + port. + + SXDC 8 port modules. Up to 921600 bps on each port + supported. Like XIO, a module is available with one parallel + port as well. + -To configure an ISA host card, add the following line to your - kernel configuration file, changing - the numbers as appropriate: + To configure an ISA host card, add the following line to your + kernel configuration + file, changing the numbers as appropriate: - - device si0 at isa? tty iomem 0xd0000 irq 11 - - - Valid IRQ numbers are 9, 10, 11, 12 and 15 for SX ISA host cards and - 11, 12 and 15 for SI/XIO ISA host cards. + +device si0 at isa? tty iomem 0xd0000 irq 11 + + Valid IRQ numbers are 9, 10, 11, 12 and 15 for SX ISA host cards + and 11, 12 and 15 for SI/XIO ISA host cards. - To configure an EISA or PCI host card, use this line: + To configure an EISA or PCI host card, use this line: - - device si0 - + +device si0 -After adding the configuration entry, - rebuild and install - your new kernel. - -After rebooting with the new kernel, you need to make the - device nodes - in /dev. The MAKEDEV script will take care of this for you. Count how many - total ports you have and type: + After adding the configuration entry, rebuild and install your + new kernel. - &prompt.root; cd /dev -&prompt.root; ./MAKEDEV ttyAnn cuaAnn + After rebooting with the new kernel, you need to make the device nodes in /dev. The + MAKEDEV script will take care of this for you. + Count how many total ports you have and type: - (where nn is the number of ports) + &prompt.root; cd /dev +&prompt.root; ./MAKEDEV ttyAnn cuaAnn -If you want login prompts to appear on these ports, you will need - to add lines like this to /etc/ttys: + (where nn is the number of + ports) - - ttyA01 "/usr/libexec/getty std.9600" vt100 on insecure - - -Change the terminal type as approprate. For modems, dialup or - unknown is fine. + If you want login prompts to appear on these ports, you will + need to add lines like this to /etc/ttys: + + +ttyA01 "/usr/libexec/getty std.9600" vt100 on insecure + - - - - + Change the terminal type as approprate. For modems, + dialup or unknown is + fine. * Parallel ports * Modems * Network cards * Keyboards * Mice * Other Storage Devices Using ESDI hard disks Copyright © 1995, &a.wilko;. 24 September 1995. ESDI is an acronym that means Enhanced Small Device Interface. It is loosely based on the good old ST506/412 interface originally devised by Seagate Technology, the makers of the first affordable 5.25" winchester disk. The acronym says Enhanced, and rightly so. In the first place the speed of the interface is higher, 10 or 15 Mbits/second instead of the 5 Mbits/second of ST412 interfaced drives. Secondly some higher level commands are added, making the ESDI interface somewhat 'smarter' to the operating system driver writers. It is by no means as smart as SCSI by the way. ESDI is standardized by ANSI. Capacities of the drives are boosted by putting more sectors on each track. Typical is 35 sectors per track, high capacity drives I have seen were up to 54 sectors/track. Although ESDI has been largely obsoleted by IDE and SCSI interfaces, the availability of free or cheap surplus drives makes them ideal for low (or now) budget systems. Concepts of ESDI Physical connections The ESDI interface uses two cables connected to each drive. One cable is a 34 pin flat cable edge connector that carries the command and status signals from the controller to the drive and vice-versa. The command cable is daisy chained between all the drives. So, it forms a bus onto which all drives are connected. The second cable is a 20 pin flat cable edge connector that carries the data to and from the drive. This cable is radially connected, so each drive has its own direct connection to the controller. To the best of my knowledge PC ESDI controllers are limited to using a maximum of 2 drives per controller. This is compatibility feature(?) left over from the WD1003 standard that reserves only a single bit for device addressing. Device addressing On each command cable a maximum of 7 devices and 1 controller can be present. To enable the controller to uniquely identify which drive it addresses, each ESDI device is equipped with jumpers or switches to select the devices address. On PC type controllers the first drive is set to address 0, the second disk to address 1. Always make sure you set each disk to an unique address! So, on a PC with its two drives/controller maximum the first drive is drive 0, the second is drive 1. Termination The daisy chained command cable (the 34 pin cable remember?) needs to be terminated at the last drive on the chain. For this purpose ESDI drives come with a termination resistor network that can be removed or disabled by a jumper when it is not used. So, one and only one drive, the one at the farthest end of the command cable has its terminator installed/enabled. The controller automatically terminates the other end of the cable. Please note that this implies that the controller must be at one end of the cable and not in the middle. Using ESDI disks with FreeBSD Why is ESDI such a pain to get working in the first place? People who tried ESDI disks with FreeBSD are known to have developed a profound sense of frustration. A combination of factors works against you to produce effects that are hard to understand when you have never seen them before. This has also led to the popular legend ESDI and FreeBSD is a plain NO-GO. The following sections try to list all the pitfalls and solutions. ESDI speed variants As briefly mentioned before, ESDI comes in two speed flavors. The older drives and controllers use a 10 Mbits/second data transfer rate. Newer stuff uses 15 Mbits/second. It is not hard to imagine that 15 Mbits/second drive cause problems on controllers laid out for 10 Mbits/second. As always, consult your controller and drive documentation to see if things match. Stay on track Mainstream ESDI drives use 34 to 36 sectors per track. Most (older) controllers cannot handle more than this number of sectors. Newer, higher capacity, drives use higher numbers of sectors per track. For instance, I own a 670 Mb drive that has 54 sectors per track. In my case, the controller could not handle this number of sectors. It proved to work well except that it only used 35 sectors on each track. This meant losing a lot of disk space. Once again, check the documentation of your hardware for more info. Going out-of-spec like in the example might or might not work. Give it a try or get another more capable controller. Hard or soft sectoring Most ESDI drives allow hard or soft sectoring to be selected using a jumper. Hard sectoring means that the drive will produce a sector pulse on the start of each new sector. The controller uses this pulse to tell when it should start to write or read. Hard sectoring allows a selection of sector size (normally 256, 512 or 1024 bytes per formatted sector). FreeBSD uses 512 byte sectors. The number of sectors per track also varies while still using the same number of bytes per formatted sector. The number of unformatted bytes per sector varies, dependent on your controller it needs more or less overhead bytes to work correctly. Pushing more sectors on a track of course gives you more usable space, but might give problems if your controller needs more bytes than the drive offers. In case of soft sectoring, the controller itself determines where to start/stop reading or writing. For ESDI hard sectoring is the default (at least on everything I came across). I never felt the urge to try soft sectoring. In general, experiment with sector settings before you install FreeBSD because you need to re-run the low-level format after each change. Low level formatting ESDI drives need to be low level formatted before they are usable. A reformat is needed whenever you figgle with the number of sectors/track jumpers or the physical orientation of the drive (horizontal, vertical). So, first think, then format. The format time must not be underestimated, for big disks it can take hours. After a low level format, a surface scan is done to find and flag bad sectors. Most disks have a manufacturer bad block list listed on a piece of paper or adhesive sticker. In addition, on most disks the list is also written onto the disk. Please use the manufacturer's list. It is much easier to remap a defect now than after FreeBSD is installed. Stay away from low-level formatters that mark all sectors of a track as bad as soon as they find one bad sector. Not only does this waste space, it also and more importantly causes you grief with bad144 (see the section on bad144). Translations Translations, although not exclusively a ESDI-only problem, might give you real trouble. Translations come in multiple flavors. Most of them have in common that they attempt to work around the limitations posed upon disk geometries by the original IBM PC/AT design (thanks IBM!). First of all there is the (in)famous 1024 cylinder limit. For a system to be able to boot, the stuff (whatever operating system) must be in the first 1024 cylinders of a disk. Only 10 bits are available to encode the cylinder number. For the number of sectors the limit is 64 (0-63). When you combine the 1024 cylinder limit with the 16 head limit (also a design feature) you max out at fairly limited disk sizes. To work around this problem, the manufacturers of ESDI PC controllers added a BIOS prom extension on their boards. This BIOS extension handles disk I/O for booting (and for some operating systems all disk I/O) by using translation. For instance, a big drive might be presented to the system as having 32 heads and 64 sectors/track. The result is that the number of cylinders is reduced to something below 1024 and is therefore usable by the system without problems. It is noteworthy to know that FreeBSD does not use the BIOS after its kernel has started. More on this later. A second reason for translations is the fact that most older system BIOSes could only handle drives with 17 sectors per track (the old ST412 standard). Newer system BIOSes usually have a user-defined drive type (in most cases this is drive type 47). Whatever you do to translations after reading this document, keep in mind that if you have multiple operating systems on the same disk, all must use the same translation While on the subject of translations, I have seen one controller type (but there are probably more like this) offer the option to logically split a drive in multiple partitions as a BIOS option. I had select 1 drive == 1 partition because this controller wrote this info onto the disk. On power-up it read the info and presented itself to the system based on the info from the disk. Spare sectoring Most ESDI controllers offer the possibility to remap bad sectors. During/after the low-level format of the disk bad sectors are marked as such, and a replacement sector is put in place (logically of course) of the bad one. In most cases the remapping is done by using N-1 sectors on each track for actual data storage, and sector N itself is the spare sector. N is the total number of sectors physically available on the track. The idea behind this is that the operating system sees a 'perfect' disk without bad sectors. In the case of FreeBSD this concept is not usable. The problem is that the translation from bad to good is performed by the BIOS of the ESDI controller. FreeBSD, being a true 32 bit operating system, does not use the BIOS after it has been booted. Instead, it has device drivers that talk directly to the hardware. So: don't use spare sectoring, bad block remapping or whatever it may be called by the controller manufacturer when you want to use the disk for FreeBSD. Bad block handling The preceding section leaves us with a problem. The controller's bad block handling is not usable and still FreeBSD's filesystems assume perfect media without any flaws. To solve this problem, FreeBSD use the bad144 tool. Bad144 (named after a Digital Equipment standard for bad block handling) scans a FreeBSD slice for bad blocks. Having found these bad blocks, it writes a table with the offending block numbers to the end of the FreeBSD slice. When the disk is in operation, the disk accesses are checked against the table read from the disk. Whenever a block number is requested that is in the bad144 list, a replacement block (also from the end of the FreeBSD slice) is used. In this way, the bad144 replacement scheme presents 'perfect' media to the FreeBSD filesystems. There are a number of potential pitfalls associated with the use of bad144. First of all, the slice cannot have more than 126 bad sectors. If your drive has a high number of bad sectors, you might need to divide it into multiple FreeBSD slices each containing less than 126 bad sectors. Stay away from low-level format programs that mark every sector of a track as bad when they find a flaw on the track. As you can imagine, the 126 limit is quickly reached when the low-level format is done this way. Second, if the slice contains the root filesystem, the slice should be within the 1024 cylinder BIOS limit. During the boot process the bad144 list is read using the BIOS and this only succeeds when the list is within the 1024 cylinder limit. The restriction is not that only the root filesystem must be within the 1024 cylinder limit, but rather the entire slice that contains the root filesystem. Kernel configuration ESDI disks are handled by the same wddriver as IDE and ST412 MFM disks. The wd driver should work for all WD1003 compatible interfaces. Most hardware is jumperable for one of two different I/O address ranges and IRQ lines. This allows you to have two wd type controllers in one system. When your hardware allows non-standard strappings, you can use these with FreeBSD as long as you enter the correct info into the kernel config file. An example from the kernel config file (they live in /sys/i386/conf BTW). # First WD compatible controller controller wdc0 at isa? port "IO_WD1" bio irq 14 vector wdintr disk wd0 at wdc0 drive 0 disk wd1 at wdc0 drive 1 # Second WD compatible controller controller wdc1 at isa? port "IO_WD2" bio irq 15 vector wdintr disk wd2 at wdc1 drive 0 disk wd3 at wdc1 drive 1 Particulars on ESDI hardware Adaptec 2320 controllers I successfully installed FreeBSD onto a ESDI disk controlled by a ACB-2320. No other operating system was present on the disk. To do so I low level formatted the disk using NEFMT.EXE (ftpable from www.adaptec.com) and answered NO to the question whether the disk should be formatted with a spare sector on each track. The BIOS on the ACD-2320 was disabled. I used the free configurable option in the system BIOS to allow the BIOS to boot it. Before using NEFMT.EXE I tried to format the disk using the ACB-2320 BIOS builtin formatter. This proved to be a show stopper, because it did not give me an option to disable spare sectoring. With spare sectoring enabled the FreeBSD installation process broke down on the bad144 run. Please check carefully which ACB-232xy variant you have. The x is either 0 or 2, indicating a controller without or with a floppy controller on board. The y is more interesting. It can either be a blank, a A-8 or a D. A blank indicates a plain 10 Mbits/second controller. An A-8 indicates a 15 Mbits/second controller capable of handling 52 sectors/track. A D means a 15 Mbits/second controller that can also handle drives with > 36 sectors/track (also 52 ?). All variations should be capable of using 1:1 interleaving. Use 1:1, FreeBSD is fast enough to handle it. Western Digital WD1007 controllers I successfully installed FreeBSD onto a ESDI disk controlled by a WD1007 controller. To be precise, it was a WD1007-WA2. Other variations of the WD1007 do exist. To get it to work, I had to disable the sector translation and the WD1007's onboard BIOS. This implied I could not use the low-level formatter built into this BIOS. Instead, I grabbed WDFMT.EXE from www.wdc.com Running this formatted my drive just fine. Ultrastor U14F controllers According to multiple reports from the net, Ultrastor ESDI boards work OK with FreeBSD. I lack any further info on particular settings. Further reading If you intend to do some serious ESDI hacking, you might want to have the official standard at hand: The latest ANSI X3T10 committee document is: Enhanced Small Device Interface (ESDI) [X3.170-1990/X3.170a-1991] [X3T10/792D Rev 11] On Usenet the newsgroup comp.periphs is a noteworthy place to look for more info. The World Wide Web (WWW) also proves to be a very handy info source: For info on Adaptec ESDI controllers see http://www.adaptec.com/. For info on Western Digital controllers see http://www.wdc.com/. Thanks to... Andrew Gordon for sending me an Adaptec 2320 controller and ESDI disk for testing. What is SCSI? Copyright © 1995, &a.wilko;. July 6, 1996. SCSI is an acronym for Small Computer Systems Interface. It is an ANSI standard that has become one of the leading I/O buses in the computer industry. The foundation of the SCSI standard was laid by Shugart Associates (the same guys that gave the world the first mini floppy disks) when they introduced the SASI bus (Shugart Associates Standard Interface). After some time an industry effort was started to come to a more strict standard allowing devices from different vendors to work together. This effort was recognized in the ANSI SCSI-1 standard. The SCSI-1 standard (approx 1985) is rapidly becoming obsolete. The current standard is SCSI-2 (see Further reading), with SCSI-3 on the drawing boards. In addition to a physical interconnection standard, SCSI defines a logical (command set) standard to which disk devices must adhere. This standard is called the Common Command Set (CCS) and was developed more or less in parallel with ANSI SCSI-1. SCSI-2 includes the (revised) CCS as part of the standard itself. The commands are dependent on the type of device at hand. It does not make much sense of course to define a Write command for a scanner. The SCSI bus is a parallel bus, which comes in a number of variants. The oldest and most used is an 8 bit wide bus, with single-ended signals, carried on 50 wires. (If you do not know what single-ended means, do not worry, that is what this document is all about.) Modern designs also use 16 bit wide buses, with differential signals. This allows transfer speeds of 20Mbytes/second, on cables lengths of up to 25 meters. SCSI-2 allows a maximum bus width of 32 bits, using an additional cable. Quickly emerging are Ultra SCSI (also called Fast-20) and Ultra2 (also called Fast-40). Fast-20 is 20 million transfers per second (20 Mbytes/sec on a 8 bit bus), Fast-40 is 40 million transfers per second (40 Mbytes/sec on a 8 bit bus). Most hard drives sold today are single-ended Ultra SCSI (8 or 16 bits). Of course the SCSI bus not only has data lines, but also a number of control signals. A very elaborate protocol is part of the standard to allow multiple devices to share the bus in an efficient manner. In SCSI-2, the data is always checked using a separate parity line. In pre-SCSI-2 designs parity was optional. In SCSI-3 even faster bus types are introduced, along with a serial SCSI busses that reduces the cabling overhead and allows a higher maximum bus length. You might see names like SSA and Fiberchannel in this context. None of the serial buses are currently in widespread use (especially not in the typical FreeBSD environment). For this reason the serial bus types are not discussed any further. As you could have guessed from the description above, SCSI devices are intelligent. They have to be to adhere to the SCSI standard (which is over 2 inches thick BTW). So, for a hard disk drive for instance you do not specify a head/cylinder/sector to address a particular block, but simply the number of the block you want. Elaborate caching schemes, automatic bad block replacement etc are all made possible by this 'intelligent device' approach. On a SCSI bus, each possible pair of devices can communicate. Whether their function allows this is another matter, but the standard does not restrict it. To avoid signal contention, the 2 devices have to arbitrate for the bus before using it. The philosophy of SCSI is to have a standard that allows older-standard devices to work with newer-standard ones. So, an old SCSI-1 device should normally work on a SCSI-2 bus. I say Normally, because it is not absolutely sure that the implementation of an old device follows the (old) standard closely enough to be acceptable on a new bus. Modern devices are usually more well-behaved, because the standardization has become more strict and is better adhered to by the device manufacturers. Generally speaking, the chances of getting a working set of devices on a single bus is better when all the devices are SCSI-2 or newer. This implies that you do not have to dump all your old stuff when you get that shiny 2GB disk: I own a system on which a pre-SCSI-1 disk, a SCSI-2 QIC tape unit, a SCSI-1 helical scan tape unit and 2 SCSI-1 disks work together quite happily. From a performance standpoint you might want to separate your older and newer (=faster) devices however. Components of SCSI As said before, SCSI devices are smart. The idea is to put the knowledge about intimate hardware details onto the SCSI device itself. In this way, the host system does not have to worry about things like how many heads are hard disks has, or how many tracks there are on a specific tape device. If you are curious, the standard specifies commands with which you can query your devices on their hardware particulars. FreeBSD uses this capability during boot to check out what devices are connected and whether they need any special treatment. The advantage of intelligent devices is obvious: the device drivers on the host can be made in a much more generic fashion, there is no longer a need to change (and qualify!) drivers for every odd new device that is introduced. For cabling and connectors there is a golden rule: get good stuff. With bus speeds going up all the time you will save yourself a lot of grief by using good material. So, gold plated connectors, shielded cabling, sturdy connector hoods with strain reliefs etc are the way to go. Second golden rule: do no use cables longer than necessary. I once spent 3 days hunting down a problem with a flaky machine only to discover that shortening the SCSI bus by 1 meter solved the problem. And the original bus length was well within the SCSI specification. SCSI bus types From an electrical point of view, there are two incompatible bus types: single-ended and differential. This means that there are two different main groups of SCSI devices and controllers, which cannot be mixed on the same bus. It is possible however to use special converter hardware to transform a single-ended bus into a differential one (and vice versa). The differences between the bus types are explained in the next sections. In lots of SCSI related documentation there is a sort of jargon in use to abbreviate the different bus types. A small list: FWD: Fast Wide Differential FND: Fast Narrow Differential SE: Single Ended FN: Fast Narrow etc. With a minor amount of imagination one can usually imagine what is meant. Wide is a bit ambiguous, it can indicate 16 or 32 bit buses. As far as I know, the 32 bit variant is not (yet) in use, so wide normally means 16 bit. Fast means that the timing on the bus is somewhat different, so that on a narrow (8 bit) bus 10 Mbytes/sec are possible instead of 5 Mbytes/sec for 'slow' SCSI. As discussed before, bus speeds of 20 and 40 million transfers/second are also emerging (Fast-20 == Ultra SCSI and Fast-40 == Ultra2 SCSI). The data lines > 8 are only used for data transfers and device addressing. The transfers of commands and status messages etc are only performed on the lowest 8 data lines. The standard allows narrow devices to operate on a wide bus. The usable bus width is negotiated between the devices. You have to watch your device addressing closely when mixing wide and narrow. Single ended buses A single-ended SCSI bus uses signals that are either 5 Volts or 0 Volts (indeed, TTL levels) and are relative to a COMMON ground reference. A singled ended 8 bit SCSI bus has approximately 25 ground lines, who are all tied to a single `rail' on all devices. A standard single ended bus has a maximum length of 6 meters. If the same bus is used with fast-SCSI devices, the maximum length allowed drops to 3 meters. Fast-SCSI means that instead of 5Mbytes/sec the bus allows 10Mbytes/sec transfers. Fast-20 (Ultra SCSI) and Fast-40 allow for 20 and 40 million transfers/second respectively. So, F20 is 20 Mbytes/second on a 8 bit bus, 40 Mbytes/second on a 16 bit bus etc. For F20 the max bus length is 1.5 meters, for F40 it becomes 0.75 meters. Be aware that F20 is pushing the limits quite a bit, so you will quickly find out if your SCSI bus is electrically sound. If some devices on your bus use 'fast' to communicate your bus must adhere to the length restrictions for fast buses! It is obvious that with the newer fast-SCSI devices the bus length can become a real bottleneck. This is why the differential SCSI bus was introduced in the SCSI-2 standard. For connector pinning and connector types please refer to the SCSI-2 standard (see Further reading) itself, connectors etc are listed there in painstaking detail. Beware of devices using non-standard cabling. For instance Apple uses a 25pin D-type connecter (like the one on serial ports and parallel printers). Considering that the official SCSI bus needs 50 pins you can imagine the use of this connector needs some 'creative cabling'. The reduction of the number of ground wires they used is a bad idea, you better stick to 50 pins cabling in accordance with the SCSI standard. For Fast-20 and 40 do not even think about buses like this. Differential buses A differential SCSI bus has a maximum length of 25 meters. Quite a difference from the 3 meters for a single-ended fast-SCSI bus. The idea behind differential signals is that each bus signal has its own return wire. So, each signal is carried on a (preferably twisted) pair of wires. The voltage difference between these two wires determines whether the signal is asserted or de-asserted. To a certain extent the voltage difference between ground and the signal wire pair is not relevant (do not try 10 kVolts though). It is beyond the scope of this document to explain why this differential idea is so much better. Just accept that electrically seen the use of differential signals gives a much better noise margin. You will normally find differential buses in use for inter-cabinet connections. Because of the lower cost single ended is mostly used for shorter buses like inside cabinets. There is nothing that stops you from using differential stuff with FreeBSD, as long as you use a controller that has device driver support in FreeBSD. As an example, Adaptec marketed the AHA1740 as a single ended board, whereas the AHA1744 was differential. The software interface to the host is identical for both. Terminators Terminators in SCSI terminology are resistor networks that are used to get a correct impedance matching. Impedance matching is important to get clean signals on the bus, without reflections or ringing. If you once made a long distance telephone call on a bad line you probably know what reflections are. With 20Mbytes/sec traveling over your SCSI bus, you do not want signals echoing back. Terminators come in various incarnations, with more or less sophisticated designs. Of course, there are internal and external variants. Many SCSI devices come with a number of sockets in which a number of resistor networks can (must be!) installed. If you remove terminators from a device, carefully store them. You will need them when you ever decide to reconfigure your SCSI bus. There is enough variation in even these simple tiny things to make finding the exact replacement a frustrating business. There are also SCSI devices that have a single jumper to enable or disable a built-in terminator. There are special terminators you can stick onto a flat cable bus. Others look like external connectors, or a connector hood without a cable. So, lots of choice as you can see. There is much debate going on if and when you should switch from simple resistor (passive) terminators to active terminators. Active terminators contain slightly more elaborate circuit to give cleaner bus signals. The general consensus seems to be that the usefulness of active termination increases when you have long buses and/or fast devices. If you ever have problems with your SCSI buses you might consider trying an active terminator. Try to borrow one first, they reputedly are quite expensive. Please keep in mind that terminators for differential and single-ended buses are not identical. You should not mix the two variants. OK, and now where should you install your terminators? This is by far the most misunderstood part of SCSI. And it is by far the simplest. The rule is: every single line on the SCSI bus has 2 (two) terminators, one at each end of the bus. So, two and not one or three or whatever. Do yourself a favor and stick to this rule. It will save you endless grief, because wrong termination has the potential to introduce highly mysterious bugs. (Note the “potential” here; the nastiest part is that it may or may not work.) A common pitfall is to have an internal (flat) cable in a machine and also an external cable attached to the controller. It seems almost everybody forgets to remove the terminators from the controller. The terminator must now be on the last external device, and not on the controller! In general, every reconfiguration of a SCSI bus must pay attention to this. Termination is to be done on a per-line basis. This means if you have both narrow and wide buses connected to the same host adapter, you need to enable termination on the higher 8 bits of the bus on the adapter (as well as the last devices on each bus, of course). What I did myself is remove all terminators from my SCSI devices and controllers. I own a couple of external terminators, for both the Centronics-type external cabling and for the internal flat cable connectors. This makes reconfiguration much easier. On modern devices, sometimes integrated terminators are used. These things are special purpose integrated circuits that can be dis/en-abled with a control pin. It is not necessary to physically remove them from a device. You may find them on newer host adapters, sometimes they are software configurable, using some sort of setup tool. Some will even auto-detect the cables attached to the connectors and automatically set up the termination as necessary. At any rate, consult your documentation! Terminator power The terminators discussed in the previous chapter need power to operate properly. On the SCSI bus, a line is dedicated to this purpose. So, simple huh? Not so. Each device can provide its own terminator power to the terminator sockets it has on-device. But if you have external terminators, or when the device supplying the terminator power to the SCSI bus line is switched off you are in trouble. The idea is that initiators (these are devices that initiate actions on the bus, a discussion follows) must supply terminator power. All SCSI devices are allowed (but not required) to supply terminator power. To allow for un-powered devices on a bus, the terminator power must be supplied to the bus via a diode. This prevents the backflow of current to un-powered devices. To prevent all kinds of nastiness, the terminator power is usually fused. As you can imagine, fuses might blow. This can, but does not have to, lead to a non functional bus. If multiple devices supply terminator power, a single blown fuse will not put you out of business. A single supplier with a blown fuse certainly will. Clever external terminators sometimes have a LED indication that shows whether terminator power is present. In newer designs auto-restoring fuses that 'reset' themselves after some time are sometimes used. Device addressing Because the SCSI bus is, ehh, a bus there must be a way to distinguish or address the different devices connected to it. This is done by means of the SCSI or target ID. Each device has a unique target ID. You can select the ID to which a device must respond using a set of jumpers, or a dip switch, or something similar. Some SCSI host adapters let you change the target ID from the boot menu. (Yet some others will not let you change the ID from 7.) Consult the documentation of your device for more information. Beware of multiple devices configured to use the same ID. Chaos normally reigns in this case. A pitfall is that one of the devices sharing the same ID sometimes even manages to answer to I/O requests! For an 8 bit bus, a maximum of 8 targets is possible. The maximum is 8 because the selection is done bitwise using the 8 data lines on the bus. For wide buses this increases to the number of data lines (usually 16). A narrow SCSI device can not communicate with a SCSI device with a target ID larger than 7. This means it is generally not a good idea to move your SCSI host adapter's target ID to something higher than 7 (or your CD-ROM will stop working). The higher the SCSI target ID, the higher the priority the devices has. When it comes to arbitration between devices that want to use the bus at the same time, the device that has the highest SCSI ID will win. This also means that the SCSI host adapter usually uses target ID 7. Note however that the lower 8 IDs have higher priorities than the higher 8 IDs on a wide-SCSI bus. Thus, the order of target IDs is: [7 6 .. 1 0 15 14 .. 9 8] on a wide-SCSI system. (If you you are wondering why the lower 8 have higher priority, read the previous paragraph for a hint.) For a further subdivision, the standard allows for Logical Units or LUNs for short. A single target ID may have multiple LUNs. For example, a tape device including a tape changer may have LUN 0 for the tape device itself, and LUN 1 for the tape changer. In this way, the host system can address each of the functional units of the tape changer as desired. Bus layout SCSI buses are linear. So, not shaped like Y-junctions, star topologies, rings, cobwebs or whatever else people might want to invent. One of the most common mistakes is for people with wide-SCSI host adapters to connect devices on all three connecters (external connector, internal wide connector, internal narrow connector). Don't do that. It may appear to work if you are really lucky, but I can almost guarantee that your system will stop functioning at the most unfortunate moment (this is also known as “Murphy's law”). You might notice that the terminator issue discussed earlier becomes rather hairy if your bus is not linear. Also, if you have more connectors than devices on your internal SCSI cable, make sure you attach devices on connectors on both ends instead of using the connectors in the middle and let one or both ends dangle. This will screw up the termination of the bus. The electrical characteristics, its noise margins and ultimately the reliability of it all are tightly related to linear bus rule. Stick to the linear bus rule! Using SCSI with FreeBSD About translations, BIOSes and magic... As stated before, you should first make sure that you have a electrically sound bus. When you want to use a SCSI disk on your PC as boot disk, you must aware of some quirks related to PC BIOSes. The PC BIOS in its first incarnation used a low level physical interface to the hard disk. So, you had to tell the BIOS (using a setup tool or a BIOS built-in setup) how your disk physically looked like. This involved stating number of heads, number of cylinders, number of sectors per track, obscure things like precompensation and reduced write current cylinder etc. One might be inclined to think that since SCSI disks are smart you can forget about this. Alas, the arcane setup issue is still present today. The system BIOS needs to know how to access your SCSI disk with the head/cyl/sector method in order to load the FreeBSD kernel during boot. The SCSI host adapter or SCSI controller you have put in your AT/EISA/PCI/whatever bus to connect your disk therefore has its own on-board BIOS. During system startup, the SCSI BIOS takes over the hard disk interface routines from the system BIOS. To fool the system BIOS, the system setup is normally set to No hard disk present. Obvious, isn't it? The SCSI BIOS itself presents to the system a so called translated drive. This means that a fake drive table is constructed that allows the PC to boot the drive. This translation is often (but not always) done using a pseudo drive with 64 heads and 32 sectors per track. By varying the number of cylinders, the SCSI BIOS adapts to the actual drive size. It is useful to note that 32 * 64 / 2 = the size of your drive in megabytes. The division by 2 is to get from disk blocks that are normally 512 bytes in size to Kbytes. Right. All is well now?! No, it is not. The system BIOS has another quirk you might run into. The number of cylinders of a bootable hard disk cannot be greater than 1024. Using the translation above, this is a show-stopper for disks greater than 1 GB. With disk capacities going up all the time this is causing problems. Fortunately, the solution is simple: just use another translation, e.g. with 128 heads instead of 32. In most cases new SCSI BIOS versions are available to upgrade older SCSI host adapters. Some newer adapters have an option, in the form of a jumper or software setup selection, to switch the translation the SCSI BIOS uses. It is very important that all operating systems on the disk use the same translation to get the right idea about where to find the relevant partitions. So, when installing FreeBSD you must answer any questions about heads/cylinders etc using the translated values your host adapter uses. Failing to observe the translation issue might lead to un-bootable systems or operating systems overwriting each others partitions. Using fdisk you should be able to see all partitions. You might have heard some talk of “lying” devices? Older FreeBSD kernels used to report the geometry of SCSI disks when booting. An example from one of my systems: aha0 targ 0 lun 0: <MICROP 1588-15MB1057404HSP4> sd0: 636MB (1303250 total sec), 1632 cyl, 15 head, 53 sec, bytes/sec 512 Newer kernels usually do not report this information. e.g. (bt0:0:0): "SEAGATE ST41651 7574" type 0 fixed SCSI 2 sd0(bt0:0:0): Direct-Access 1350MB (2766300 512 byte sectors) Why has this changed? This info is retrieved from the SCSI disk itself. Newer disks often use a technique called zone bit recording. The idea is that on the outer cylinders of the drive there is more space so more sectors per track can be put on them. This results in disks that have more tracks on outer cylinders than on the inner cylinders and, last but not least, have more capacity. You can imagine that the value reported by the drive when inquiring about the geometry now becomes suspect at best, and nearly always misleading. When asked for a geometry , it is nearly always better to supply the geometry used by the BIOS, or if the BIOS is never going to know about this disk, (e.g. it is not a booting disk) to supply a fictitious geometry that is convenient. SCSI subsystem design FreeBSD uses a layered SCSI subsystem. For each different controller card a device driver is written. This driver knows all the intimate details about the hardware it controls. The driver has a interface to the upper layers of the SCSI subsystem through which it receives its commands and reports back any status. On top of the card drivers there are a number of more generic drivers for a class of devices. More specific: a driver for tape devices (abbreviation: st), magnetic disks (sd), CD-ROMs (cd) etc. In case you are wondering where you can find this stuff, it all lives in /sys/scsi. See the man pages in section 4 for more details. The multi level design allows a decoupling of low-level bit banging and more high level stuff. Adding support for another piece of hardware is a much more manageable problem. Kernel configuration Dependent on your hardware, the kernel configuration file must contain one or more lines describing your host adapter(s). This includes I/O addresses, interrupts etc. Consult the man page for your adapter driver to get more info. Apart from that, check out /sys/i386/conf/LINT for an overview of a kernel config file. LINT contains every possible option you can dream of. It does not imply LINT will actually get you to a working kernel at all. Although it is probably stating the obvious: the kernel config file should reflect your actual hardware setup. So, interrupts, I/O addresses etc must match the kernel config file. During system boot messages will be displayed to indicate whether the configured hardware was actually found. Note that most of the EISA/PCI drivers (namely ahb, ahc, ncr and amd will automatically obtain the correct parameters from the host adapters themselves at boot time; thus, you just need to write, for instance, controller ahc0. An example loosely based on the FreeBSD 2.2.5-Release kernel config file LINT with some added comments (between []): # SCSI host adapters: `aha', `ahb', `aic', `bt', `nca' # # aha: Adaptec 154x # ahb: Adaptec 174x # ahc: Adaptec 274x/284x/294x # aic: Adaptec 152x and sound cards using the Adaptec AIC-6360 (slow!) # amd: AMD 53c974 based SCSI cards (e.g., Tekram DC-390 and 390T) # bt: Most Buslogic controllers # nca: ProAudioSpectrum cards using the NCR 5380 or Trantor T130 # ncr: NCR/Symbios 53c810/815/825/875 etc based SCSI cards # uha: UltraStore 14F and 34F # sea: Seagate ST01/02 8 bit controller (slow!) # wds: Western Digital WD7000 controller (no scatter/gather!). # [For an Adaptec AHA274x/284x/294x/394x etc controller] controller ahc0 [For an NCR/Symbios 53c875 based controller] controller ncr0 [For an Ultrastor adapter] controller uha0 at isa? port "IO_UHA0" bio irq ? drq 5 vector uhaintr # Map SCSI buses to specific SCSI adapters controller scbus0 at ahc0 controller scbus2 at ncr0 controller scbus1 at uha0 # The actual SCSI devices disk sd0 at scbus0 target 0 unit 0 [SCSI disk 0 is at scbus 0, LUN 0] disk sd1 at scbus0 target 1 [implicit LUN 0 if omitted] disk sd2 at scbus1 target 3 [SCSI disk on the uha0] disk sd3 at scbus2 target 4 [SCSI disk on the ncr0] tape st1 at scbus0 target 6 [SCSI tape at target 6] device cd0 at scbus? [the first ever CD-ROM found, no wiring] The example above tells the kernel to look for a ahc (Adaptec 274x) controller, then for an NCR/Symbios board, and so on. The lines following the controller specifications tell the kernel to configure specific devices but only attach them when they match the target ID and LUN specified on the corresponding bus. Wired down devices get “first shot” at the unit numbers so the first non “wired down” device, is allocated the unit number one greater than the highest “wired down” unit number for that kind of device. So, if you had a SCSI tape at target ID 2 it would be configured as st2, as the tape at target ID 6 is wired down to unit number 1. Wired down devices need not be found to get their unit number. The unit number for a wired down device is reserved for that device, even if it is turned off at boot time. This allows the device to be turned on and brought on-line at a later time, without rebooting. Notice that a device's unit number has no relationship with its target ID on the SCSI bus. Below is another example of a kernel config file as used by FreeBSD version < 2.0.5. The difference with the first example is that devices are not “wired down”. “Wired down” means that you specify which SCSI target belongs to which device. A kernel built to the config file below will attach the first SCSI disk it finds to sd0, the second disk to sd1 etc. If you ever removed or added a disk, all other devices of the same type (disk in this case) would 'move around'. This implies you have to change /etc/fstab each time. Although the old style still works, you are strongly recommended to use this new feature. It will save you a lot of grief whenever you shift your hardware around on the SCSI buses. So, when you re-use your old trusty config file after upgrading from a pre-FreeBSD2.0.5.R system check this out. [driver for Adaptec 174x] controller ahb0 at isa? bio irq 11 vector ahbintr [for Adaptec 154x] controller aha0 at isa? port "IO_AHA0" bio irq 11 drq 5 vector ahaintr [for Seagate ST01/02] controller sea0 at isa? bio irq 5 iomem 0xc8000 iosiz 0x2000 vector seaintr controller scbus0 device sd0 [support for 4 SCSI harddisks, sd0 up sd3] device st0 [support for 2 SCSI tapes] [for the CD-ROM] device cd0 #Only need one of these, the code dynamically grows Both examples support SCSI disks. If during boot more devices of a specific type (e.g. sd disks) are found than are configured in the booting kernel, the system will simply allocate more devices, incrementing the unit number starting at the last number “wired down”. If there are no “wired down” devices then counting starts at unit 0. Use man 4 scsi to check for the latest info on the SCSI subsystem. For more detailed info on host adapter drivers use eg man 4 ahc for info on the Adaptec 294x driver. Tuning your SCSI kernel setup Experience has shown that some devices are slow to respond to INQUIRY commands after a SCSI bus reset (which happens at boot time). An INQUIRY command is sent by the kernel on boot to see what kind of device (disk, tape, CD-ROM etc) is connected to a specific target ID. This process is called device probing by the way. To work around the 'slow response' problem, FreeBSD allows a tunable delay time before the SCSI devices are probed following a SCSI bus reset. You can set this delay time in your kernel configuration file using a line like: options SCSI_DELAY=15 #Be pessimistic about Joe SCSI device This line sets the delay time to 15 seconds. On my own system I had to use 3 seconds minimum to get my trusty old CD-ROM drive to be recognized. Start with a high value (say 30 seconds or so) when you have problems with device recognition. If this helps, tune it back until it just stays working. Rogue SCSI devices Although the SCSI standard tries to be complete and concise, it is a complex standard and implementing things correctly is no easy task. Some vendors do a better job then others. This is exactly where the “rogue” devices come into view. Rogues are devices that are recognized by the FreeBSD kernel as behaving slightly (...) non-standard. Rogue devices are reported by the kernel when booting. An example for two of my cartridge tape units: Feb 25 21:03:34 yedi /kernel: ahb0 targ 5 lun 0: <TANDBERG TDC 3600 -06:> Feb 25 21:03:34 yedi /kernel: st0: Tandberg tdc3600 is a known rogue Mar 29 21:16:37 yedi /kernel: aha0 targ 5 lun 0: <ARCHIVE VIPER 150 21247-005> Mar 29 21:16:37 yedi /kernel: st1: Archive Viper 150 is a known rogue For instance, there are devices that respond to all LUNs on a certain target ID, even if they are actually only one device. It is easy to see that the kernel might be fooled into believing that there are 8 LUNs at that particular target ID. The confusion this causes is left as an exercise to the reader. The SCSI subsystem of FreeBSD recognizes devices with bad habits by looking at the INQUIRY response they send when probed. Because the INQUIRY response also includes the version number of the device firmware, it is even possible that for different firmware versions different workarounds are used. See e.g. /sys/scsi/st.c and /sys/scsi/scsiconf.c for more info on how this is done. This scheme works fine, but keep in mind that it of course only works for devices that are known to be weird. If you are the first to connect your bogus Mumbletech SCSI CD-ROM you might be the one that has to define which workaround is needed. After you got your Mumbletech working, please send the required workaround to the FreeBSD development team for inclusion in the next release of FreeBSD. Other Mumbletech owners will be grateful to you. Multiple LUN devices In some cases you come across devices that use multiple logical units (LUNs) on a single SCSI ID. In most cases FreeBSD only probes devices for LUN 0. An example are so called bridge boards that connect 2 non-SCSI harddisks to a SCSI bus (e.g. an Emulex MD21 found in old Sun systems). This means that any devices with LUNs != 0 are not normally found during device probe on system boot. To work around this problem you must add an appropriate entry in /sys/scsi/scsiconf.c and rebuild your kernel. Look for a struct that is initialized like below: { T_DIRECT, T_FIXED, "MAXTOR", "XT-4170S", "B5A", "mx1", SC_ONE_LU } For you Mumbletech BRIDGE2000 that has more than one LUN, acts as a SCSI disk and has firmware revision 123 you would add something like: { T_DIRECT, T_FIXED, "MUMBLETECH", "BRIDGE2000", "123", "sd", SC_MORE_LUS } The kernel on boot scans the inquiry data it receives against the table and acts accordingly. See the source for more info. Tagged command queueing Modern SCSI devices, particularly magnetic disks, support what is called tagged command queuing (TCQ). In a nutshell, TCQ allows the device to have multiple I/O requests outstanding at the same time. Because the device is intelligent, it can optimise its operations (like head positioning) based on its own request queue. On SCSI devices like RAID (Redundant Array of Independent Disks) arrays the TCQ function is indispensable to take advantage of the device's inherent parallelism. Each I/O request is uniquely identified by a “tag” (hence the name tagged command queuing) and this tag is used by FreeBSD to see which I/O in the device drivers queue is reported as complete by the device. It should be noted however that TCQ requires device driver support and that some devices implemented it “not quite right” in their firmware. This problem bit me once, and it leads to highly mysterious problems. In such cases, try to disable TCQ. Busmaster host adapters Most, but not all, SCSI host adapters are bus mastering controllers. This means that they can do I/O on their own without putting load onto the host CPU for data movement. This is of course an advantage for a multitasking operating system like FreeBSD. It must be noted however that there might be some rough edges. For instance an Adaptec 1542 controller can be set to use different transfer speeds on the host bus (ISA or AT in this case). The controller is settable to different rates because not all motherboards can handle the higher speeds. Problems like hangups, bad data etc might be the result of using a higher data transfer rate then your motherboard can stomach. The solution is of course obvious: switch to a lower data transfer rate and try if that works better. In the case of a Adaptec 1542, there is an option that can be put into the kernel config file to allow dynamic determination of the right, read: fastest feasible, transfer rate. This option is disabled by default: options "TUNE_1542" #dynamic tune of bus DMA speed Check the man pages for the host adapter that you use. Or better still, use the ultimate documentation (read: driver source). Tracking down problems The following list is an attempt to give a guideline for the most common SCSI problems and their solutions. It is by no means complete. Check for loose connectors and cables. Check and double check the location and number of your terminators. Check if your bus has at least one supplier of terminator power (especially with external terminators. Check if no double target IDs are used. Check if all devices to be used are powered up. Make a minimal bus config with as little devices as possible. If possible, configure your host adapter to use slow bus speeds. Disable tagged command queuing to make things as simple as possible (for a NCR hostadapter based system see man ncrcontrol) If you can compile a kernel, make one with the SCSIDEBUG option, and try accessing the device with debugging turned on for that device. If your device does not even probe at startup, you may have to define the address of the device that is failing, and the desired debug level in /sys/scsi/scsidebug.h. If it probes but just does not work, you can use the &man.scsi.8; command to dynamically set a debug level to it in a running kernel (if SCSIDEBUG is defined). This will give you copious debugging output with which to confuse the gurus. See man 4 scsi for more exact information. Also look at man 8 scsi. Further reading If you intend to do some serious SCSI hacking, you might want to have the official standard at hand: Approved American National Standards can be purchased from ANSI at
13th Floor 11 West 42nd Street New York NY 10036 Sales Dept: (212) 642-4900
You can also buy many ANSI standards and most committee draft documents from Global Engineering Documents,
15 Inverness Way East Englewood CO, 80112-5704 Phone: (800) 854-7179 Outside USA and Canada: (303) 792-2181 Fax: (303) 792- 2192
Many X3T10 draft documents are available electronically on the SCSI BBS (719-574-0424) and on the ncrinfo.ncr.com anonymous ftp site. Latest X3T10 committee documents are: AT Attachment (ATA or IDE) [X3.221-1994] (Approved) ATA Extensions (ATA-2) [X3T10/948D Rev 2i] Enhanced Small Device Interface (ESDI) [X3.170-1990/X3.170a-1991] (Approved) Small Computer System Interface — 2 (SCSI-2) [X3.131-1994] (Approved) SCSI-2 Common Access Method Transport and SCSI Interface Module (CAM) [X3T10/792D Rev 11] Other publications that might provide you with additional information are: “SCSI: Understanding the Small Computer System Interface”, written by NCR Corporation. Available from: Prentice Hall, Englewood Cliffs, NJ, 07632 Phone: (201) 767-5937 ISBN 0-13-796855-8 “Basics of SCSI”, a SCSI tutorial written by Ancot Corporation Contact Ancot for availability information at: Phone: (415) 322-5322 Fax: (415) 322-0455 “SCSI Interconnection Guide Book”, an AMP publication (dated 4/93, Catalog 65237) that lists the various SCSI connectors and suggests cabling schemes. Available from AMP at (800) 522-6752 or (717) 564-0100 “Fast Track to SCSI”, A Product Guide written by Fujitsu. Available from: Prentice Hall, Englewood Cliffs, NJ, 07632 Phone: (201) 767-5937 ISBN 0-13-307000-X “The SCSI Bench Reference”, “The SCSI Encyclopedia”, and the “SCSI Tutor”, ENDL Publications, 14426 Black Walnut Court, Saratoga CA, 95070 Phone: (408) 867-6642 “Zadian SCSI Navigator” (quick ref. book) and “Discover the Power of SCSI” (First book along with a one-hour video and tutorial book), Zadian Software, Suite 214, 1210 S. Bascom Ave., San Jose, CA 92128, (408) 293-0800 On Usenet the newsgroups comp.periphs.scsi and comp.periphs are noteworthy places to look for more info. You can also find the SCSI-Faq there, which is posted periodically. Most major SCSI device and host adapter suppliers operate ftp sites and/or BBS systems. They may be valuable sources of information about the devices you own. * Disk/tape controllers * SCSI * IDE * Floppy Hard drives SCSI hard drives Contributed by &a.asami;. 17 February 1998. As mentioned in the SCSI section, virtually all SCSI hard drives sold today are SCSI-2 compliant and thus will work fine as long as you connect them to a supported SCSI host adapter. Most problems people encounter are either due to badly designed cabling (cable too long, star topology, etc.), insufficient termination, or defective parts. Please refer to the SCSI section first if your SCSI hard drive is not working. However, there are a couple of things you may want to take into account before you purchase SCSI hard drives for your system. Rotational speed Rotational speeds of SCSI drives sold today range from around 4,500RPM to 10,000RPM. Most of them are either 5,400RPM or 7,200RPM. Even though the 7,200RPM drives can generally transfer data faster, they run considerably hotter than their 5,400RPM counterparts. A large fraction of today's disk drive malfunctions are heat-related. If you do not have very good cooling in your PC case, you may want to stick with 5,400RPM or slower drives. Note that newer drives, with higher areal recording densities, can deliver much more bits per rotation than older ones. Today's top-of-line 5,400RPM drives can sustain a throughput comparable to 7,200RPM drives of one or two model generations ago. The number to find on the spec sheet for bandwidth is “internal data (or transfer) rate”. It is usually in megabits/sec so divide it by 8 and you'll get the rough approximation of how much megabytes/sec you can get out of the drive. (If you are a speed maniac and want a 10,000RPM drive for your cute little peecee, be my guest; however, those drives become extremely hot. Don't even think about it if you don't have a fan blowing air directly at the drive or a properly ventilated disk enclosure.) Obviously, the latest 10,000RPM drives and 7,200RPM drives can deliver more data than the latest 5,400RPM drives, so if absolute bandwidth is the necessity for your applications, you have little choice but to get the faster drives. Also, if you need low latency, faster drives are better; not only do they usually have lower average seek times, but also the rotational delay is one place where slow-spinning drives can never beat a faster one. (The average rotational latency is half the time it takes to rotate the drive once; thus, it's 3 milliseconds for 10,000RPM drives, 4.2ms for 7,200RPM drives and 5.6ms for 5,400RPM drives.) Latency is seek time plus rotational delay. Make sure you understand whether you need low latency or more accesses per second, though; in the latter case (e.g., news servers), it may not be optimal to purchase one big fast drive. You can achieve similar or even better results by using the ccd (concatenated disk) driver to create a striped disk array out of multiple slower drives for comparable overall cost. Make sure you have adequate air flow around the drive, especially if you are going to use a fast-spinning drive. You generally need at least 1/2" (1.25cm) of spacing above and below a drive. Understand how the air flows through your PC case. Most cases have the power supply suck the air out of the back. See where the air flows in, and put the drive where it will have the largest volume of cool air flowing around it. You may need to seal some unwanted holes or add a new fan for effective cooling. Another consideration is noise. Many 7,200 or faster drives generate a high-pitched whine which is quite unpleasant to most people. That, plus the extra fans often required for cooling, may make 7,200 or faster drives unsuitable for some office and home environments. Form factor Most SCSI drives sold today are of 3.5" form factor. They come in two different heights; 1.6" (“half-height”) or 1" (“low-profile”). The half-height drive is the same height as a CD-ROM drive. However, don't forget the spacing rule mentioned in the previous section. If you have three standard 3.5" drive bays, you will not be able to put three half-height drives in there (without frying them, that is). Interface The majority of SCSI hard drives sold today are Ultra or Ultra-wide SCSI. The maximum bandwidth of Ultra SCSI is 20MB/sec, and Ultra-wide SCSI is 40MB/sec. There is no difference in max cable length between Ultra and Ultra-wide; however, the more devices you have on the same bus, the sooner you will start having bus integrity problems. Unless you have a well-designed disk enclosure, it is not easy to make more than 5 or 6 Ultra SCSI drives work on a single bus. On the other hand, if you need to connect many drives, going for Fast-wide SCSI may not be a bad idea. That will have the same max bandwidth as Ultra (narrow) SCSI, while electronically it's much easier to get it “right”. My advice would be: if you want to connect many disks, get wide SCSI drives; they usually cost a little more but it may save you down the road. (Besides, if you can't afford the cost difference, you shouldn't be building a disk array.) There are two variant of wide SCSI drives; 68-pin and 80-pin SCA (Single Connector Attach). The SCA drives don't have a separate 4-pin power connector, and also read the SCSI ID settings through the 80-pin connector. If you are really serious about building a large storage system, get SCA drives and a good SCA enclosure (dual power supply with at least one extra fan). They are more electronically sound than 68-pin counterparts because there is no “stub” of the SCSI bus inside the disk canister as in arrays built from 68-pin drives. They are easier to install too (you just need to screw the drive in the canister, instead of trying to squeeze in your fingers in a tight place to hook up all the little cables (like the SCSI ID and disk activity LED lines). * IDE hard drives Tape drives Contributed by &a.jmb;. 2 July 1996. General tape access commands &man.mt.1; provides generic access to the tape drives. Some of the more common commands are rewind, erase, and status. See the &man.mt.1; manual page for a detailed description. Controller Interfaces There are several different interfaces that support tape drives. The interfaces are SCSI, IDE, Floppy and Parallel Port. A wide variety of tape drives are available for these interfaces. Controllers are discussed in Disk/tape controllers. SCSI drives The &man.st.4; driver provides support for 8mm (Exabyte), 4mm (DAT: Digital Audio Tape), QIC (Quarter-Inch Cartridge), DLT (Digital Linear Tape), QIC Minicartridge and 9-track (remember the big reels that you see spinning in Hollywood computer rooms) tape drives. See the &man.st.4; manual page for a detailed description. The drives listed below are currently being used by members of the FreeBSD community. They are not the only drives that will work with FreeBSD. They just happen to be the ones that we use. 4mm (DAT: Digital Audio Tape) Archive Python HP C1533A HP C1534A HP 35450A HP 35470A HP 35480A SDT-5000 Wangtek 6200 8mm (Exabyte) EXB-8200 EXB-8500 EXB-8505 QIC (Quarter-Inch Cartridge) Archive Ananconda 2750 Archive Viper 60 Archive Viper 150 Archive Viper 2525 Tandberg TDC 3600 Tandberg TDC 3620 Tandberg TDC 4222 Wangtek 5525ES DLT (Digital Linear Tape) Digital TZ87 Mini-Cartridge Conner CTMS 3200 Exabyte 2501 Autoloaders/Changers Hewlett-Packard HP C1553A Autoloading DDS2 * IDE drives Floppy drives Conner 420R * Parallel port drives Detailed Information Archive Anaconda 2750 The boot message identifier for this drive is ARCHIVE ANCDA 2750 28077 -003 type 1 removable SCSI 2 This is a QIC tape drive. Native capacity is 1.35GB when using QIC-1350 tapes. This drive will read and write QIC-150 (DC6150), QIC-250 (DC6250), and QIC-525 (DC6525) tapes as well. Data transfer rate is 350kB/s using &man.dump.8;. Rates of 530kB/s have been reported when using Amanda Production of this drive has been discontinued. The SCSI bus connector on this tape drive is reversed from that on most other SCSI devices. Make sure that you have enough SCSI cable to twist the cable one-half turn before and after the Archive Anaconda tape drive, or turn your other SCSI devices upside-down. Two kernel code changes are required to use this drive. This drive will not work as delivered. If you have a SCSI-2 controller, short jumper 6. Otherwise, the drive behaves are a SCSI-1 device. When operating as a SCSI-1 device, this drive, “locks” the SCSI bus during some tape operations, including: fsf, rewind, and rewoffl. If you are using the NCR SCSI controllers, patch the file /usr/src/sys/pci/ncr.c (as shown below). Build and install a new kernel. *** 4831,4835 **** }; ! if (np->latetime>4) { /* ** Although we tried to wake it up, --- 4831,4836 ---- }; ! if (np->latetime>1200) { /* ** Although we tried to wake it up, Reported by: &a.jmb; Archive Python The boot message identifier for this drive is ARCHIVE Python 28454-XXX4ASB type 1 removable SCSI 2 density code 0x8c, 512-byte blocks This is a DDS-1 tape drive. Native capacity is 2.5GB on 90m tapes. Data transfer rate is XXX. This drive was repackaged by Sun Microsystems as model 411. Reported by: Bob Bishop rb@gid.co.uk Archive Viper 60 The boot message identifier for this drive is ARCHIVE VIPER 60 21116 -007 type 1 removable SCSI 1 This is a QIC tape drive. Native capacity is 60MB. Data transfer rate is XXX. Production of this drive has been discontinued. Reported by: Philippe Regnauld regnauld@hsc.fr Archive Viper 150 The boot message identifier for this drive is ARCHIVE VIPER 150 21531 -004 Archive Viper 150 is a known rogue type 1 removable SCSI 1. A multitude of firmware revisions exist for this drive. Your drive may report different numbers (e.g 21247 -005. This is a QIC tape drive. Native capacity is 150/250MB. Both 150MB (DC6150) and 250MB (DC6250) tapes have the recording format. The 250MB tapes are approximately 67% longer than the 150MB tapes. This drive can read 120MB tapes as well. It can not write 120MB tapes. Data transfer rate is 100kB/s This drive reads and writes DC6150 (150MB) and DC6250 (250MB) tapes. This drives quirks are known and pre-compiled into the scsi tape device driver (&man.st.4;). Under FreeBSD 2.2-current, use mt blocksize 512 to set the blocksize. (The particular drive had firmware revision 21247 -005. Other firmware revisions may behave differently) Previous versions of FreeBSD did not have this problem. Production of this drive has been discontinued. Reported by: Pedro A M Vazquez vazquez@IQM.Unicamp.BR Mike Smith msmith@atrad.adelaide.edu.au Archive Viper 2525 The boot message identifier for this drive is ARCHIVE VIPER 2525 25462 -011 type 1 removable SCSI 1 This is a QIC tape drive. Native capacity is 525MB. Data transfer rate is 180kB/s at 90 inches/sec. The drive reads QIC-525, QIC-150, QIC-120 and QIC-24 tapes. Writes QIC-525, QIC-150, and QIC-120. Firmware revisions prior to 25462 -011 are bug ridden and will not function properly. Production of this drive has been discontinued. Conner 420R The boot message identifier for this drive is Conner tape. This is a floppy controller, minicartridge tape drive. Native capacity is XXXX Data transfer rate is XXX The drive uses QIC-80 tape cartridges. Reported by: Mark Hannon mark@seeware.DIALix.oz.au Conner CTMS 3200 The boot message identifier for this drive is CONNER CTMS 3200 7.00 type 1 removable SCSI 2. This is a minicartridge tape drive. Native capacity is XXXX Data transfer rate is XXX The drive uses QIC-3080 tape cartridges. Reported by: Thomas S. Traylor tst@titan.cs.mci.com <ulink URL="http://www.digital.com/info/Customer-Update/931206004.txt.html">DEC TZ87</ulink> The boot message identifier for this drive is DEC TZ87 (C) DEC 9206 type 1 removable SCSI 2 density code 0x19 This is a DLT tape drive. Native capacity is 10GB. This drive supports hardware data compression. Data transfer rate is 1.2MB/s. This drive is identical to the Quantum DLT2000. The drive firmware can be set to emulate several well-known drives, including an Exabyte 8mm drive. Reported by: &a.wilko; <ulink URL="http://www.Exabyte.COM:80/Products/Minicartridge/2501/Rfeatures.html">Exabyte EXB-2501</ulink> The boot message identifier for this drive is EXABYTE EXB-2501 This is a mini-cartridge tape drive. Native capacity is 1GB when using MC3000XL minicartridges. Data transfer rate is XXX This drive can read and write DC2300 (550MB), DC2750 (750MB), MC3000 (750MB), and MC3000XL (1GB) minicartridges. WARNING: This drive does not meet the SCSI-2 specifications. The drive locks up completely in response to a SCSI MODE_SELECT command unless there is a formatted tape in the drive. Before using this drive, set the tape blocksize with &prompt.root; mt -f /dev/st0ctl.0 blocksize 1024 Before using a minicartridge for the first time, the minicartridge must be formated. FreeBSD 2.1.0-RELEASE and earlier: &prompt.root; /sbin/scsi -f /dev/rst0.ctl -s 600 -c "4 0 0 0 0 0" (Alternatively, fetch a copy of the scsiformat shell script from FreeBSD 2.1.5/2.2.) FreeBSD 2.1.5 and later: &prompt.root; /sbin/scsiformat -q -w /dev/rst0.ctl Right now, this drive cannot really be recommended for FreeBSD. Reported by: Bob Beaulieu ez@eztravel.com Exabyte EXB-8200 The boot message identifier for this drive is EXABYTE EXB-8200 252X type 1 removable SCSI 1 This is an 8mm tape drive. Native capacity is 2.3GB. Data transfer rate is 270kB/s. This drive is fairly slow in responding to the SCSI bus during boot. A custom kernel may be required (set SCSI_DELAY to 10 seconds). There are a large number of firmware configurations for this drive, some have been customized to a particular vendor's hardware. The firmware can be changed via EPROM replacement. Production of this drive has been discontinued. Reported by: Mike Smith msmith@atrad.adelaide.edu.au Exabyte EXB-8500 The boot message identifier for this drive is EXABYTE EXB-8500-85Qanx0 0415 type 1 removable SCSI 2 This is an 8mm tape drive. Native capacity is 5GB. Data transfer rate is 300kB/s. Reported by: Greg Lehey grog@lemis.de <ulink URL="http://www.Exabyte.COM:80/Products/8mm/8505XL/Rfeatures.html">Exabyte EXB-8505</ulink> The boot message identifier for this drive is EXABYTE EXB-85058SQANXR1 05B0 type 1 removable SCSI 2 This is an 8mm tape drive which supports compression, and is upward compatible with the EXB-5200 and EXB-8500. Native capacity is 5GB. The drive supports hardware data compression. Data transfer rate is 300kB/s. Reported by: Glen Foster gfoster@gfoster.com Hewlett-Packard HP C1533A The boot message identifier for this drive is HP C1533A 9503 type 1 removable SCSI 2. This is a DDS-2 tape drive. DDS-2 means hardware data compression and narrower tracks for increased data capacity. Native capacity is 4GB when using 120m tapes. This drive supports hardware data compression. Data transfer rate is 510kB/s. This drive is used in Hewlett-Packard's SureStore 6000eU and 6000i tape drives and C1533A DDS-2 DAT drive. The drive has a block of 8 dip switches. The proper settings for FreeBSD are: 1 ON; 2 ON; 3 OFF; 4 ON; 5 ON; 6 ON; 7 ON; 8 ON. switch 1 switch 2 Result On On Compression enabled at power-on, with host control On Off Compression enabled at power-on, no host control Off On Compression disabled at power-on, with host control Off Off Compression disabled at power-on, no host control Switch 3 controls MRS (Media Recognition System). MRS tapes have stripes on the transparent leader. These identify the tape as DDS (Digital Data Storage) grade media. Tapes that do not have the stripes will be treated as write-protected. Switch 3 OFF enables MRS. Switch 3 ON disables MRS. See HP SureStore Tape Products and Hewlett-Packard Disk and Tape Technical Information for more information on configuring this drive. Warning: Quality control on these drives varies greatly. One FreeBSD core-team member has returned 2 of these drives. Neither lasted more than 5 months. Reported by: &a.se; Hewlett-Packard HP 1534A The boot message identifier for this drive is HP HP35470A T503 type 1 removable SCSI 2 Sequential-Access density code 0x13, variable blocks. This is a DDS-1 tape drive. DDS-1 is the original DAT tape format. Native capacity is 2GB when using 90m tapes. Data transfer rate is 183kB/s. The same mechanism is used in Hewlett-Packard's SureStore 2000i tape drive, C35470A DDS format DAT drive, C1534A DDS format DAT drive and HP C1536A DDS format DAT drive. The HP C1534A DDS format DAT drive has two indicator lights, one green and one amber. The green one indicates tape action: slow flash during load, steady when loaded, fast flash during read/write operations. The amber one indicates warnings: slow flash when cleaning is required or tape is nearing the end of its useful life, steady indicates an hard fault. (factory service required?) Reported by Gary Crutcher gcrutchr@nightflight.com Hewlett-Packard HP C1553A Autoloading DDS2 The boot message identifier for this drive is "". This is a DDS-2 tape drive with a tape changer. DDS-2 means hardware data compression and narrower tracks for increased data capacity. Native capacity is 24GB when using 120m tapes. This drive supports hardware data compression. Data transfer rate is 510kB/s (native). This drive is used in Hewlett-Packard's SureStore 12000e tape drive. The drive has two selectors on the rear panel. The selector closer to the fan is SCSI id. The other selector should be set to 7. There are four internal switches. These should be set: 1 ON; 2 ON; 3 ON; 4 OFF. At present the kernel drivers do not automatically change tapes at the end of a volume. This shell script can be used to change tapes: #!/bin/sh PATH="/sbin:/usr/sbin:/bin:/usr/bin"; export PATH usage() { echo "Usage: dds_changer [123456ne] raw-device-name echo "1..6 = Select cartridge" echo "next cartridge" echo "eject magazine" exit 2 } if [ $# -ne 2 ] ; then usage fi cdb3=0 cdb4=0 cdb5=0 case $1 in [123456]) cdb3=$1 cdb4=1 ;; n) ;; e) cdb5=0x80 ;; ?) usage ;; esac scsi -f $2 -s 100 -c "1b 0 0 $cdb3 $cdb4 $cdb5" Hewlett-Packard HP 35450A The boot message identifier for this drive is HP HP35450A -A C620 type 1 removable SCSI 2 Sequential-Access density code 0x13 This is a DDS-1 tape drive. DDS-1 is the original DAT tape format. Native capacity is 1.2GB. Data transfer rate is 160kB/s. Reported by: mark thompson mark.a.thompson@pobox.com Hewlett-Packard HP 35470A The boot message identifier for this drive is HP HP35470A 9 09 type 1 removable SCSI 2 This is a DDS-1 tape drive. DDS-1 is the original DAT tape format. Native capacity is 2GB when using 90m tapes. Data transfer rate is 183kB/s. The same mechanism is used in Hewlett-Packard's SureStore 2000i tape drive, C35470A DDS format DAT drive, C1534A DDS format DAT drive, and HP C1536A DDS format DAT drive. Warning: Quality control on these drives varies greatly. One FreeBSD core-team member has returned 5 of these drives. None lasted more than 9 months. Reported by: David Dawes dawes@rf900.physics.usyd.edu.au (9 09) Hewlett-Packard HP 35480A The boot message identifier for this drive is HP HP35480A 1009 type 1 removable SCSI 2 Sequential-Access density code 0x13. This is a DDS-DC tape drive. DDS-DC is DDS-1 with hardware data compression. DDS-1 is the original DAT tape format. Native capacity is 2GB when using 90m tapes. It cannot handle 120m tapes. This drive supports hardware data compression. Please refer to the section on HP C1533A for the proper switch settings. Data transfer rate is 183kB/s. This drive is used in Hewlett-Packard's SureStore 5000eU and 5000i tape drives and C35480A DDS format DAT drive.. This drive will occasionally hang during a tape eject operation (mt offline). Pressing the front panel button will eject the tape and bring the tape drive back to life. WARNING: HP 35480-03110 only. On at least two occasions this tape drive when used with FreeBSD 2.1.0, an IBM Server 320 and an 2940W SCSI controller resulted in all SCSI disk partitions being lost. The problem has not be analyzed or resolved at this time. <ulink URL="http://www.sel.sony.com/SEL/ccpg/storage/tape/t5000.html">Sony SDT-5000</ulink> There are at least two significantly different models: one is a DDS-1 and the other DDS-2. The DDS-1 version is SDT-5000 3.02. The DDS-2 version is SONY SDT-5000 327M. The DDS-2 version has a 1MB cache. This cache is able to keep the tape streaming in almost any circumstances. The boot message identifier for this drive is SONY SDT-5000 3.02 type 1 removable SCSI 2 Sequential-Access density code 0x13 Native capacity is 4GB when using 120m tapes. This drive supports hardware data compression. Data transfer rate is depends upon the model or the drive. The rate is 630kB/s for the SONY SDT-5000 327M while compressing the data. For the SONY SDT-5000 3.02, the data transfer rate is 225kB/s. In order to get this drive to stream, set the blocksize to 512 bytes (mt blocksize 512) reported by Kenneth Merry ken@ulc199.residence.gatech.edu SONY SDT-5000 327M information reported by Charles Henrich henrich@msu.edu Reported by: &a.jmz; Tandberg TDC 3600 The boot message identifier for this drive is TANDBERG TDC 3600 =08: type 1 removable SCSI 2 This is a QIC tape drive. Native capacity is 150/250MB. This drive has quirks which are known and work around code is present in the scsi tape device driver (&man.st.4;). Upgrading the firmware to XXX version will fix the quirks and provide SCSI 2 capabilities. Data transfer rate is 80kB/s. IBM and Emerald units will not work. Replacing the firmware EPROM of these units will solve the problem. Reported by: Michael Smith msmith@atrad.adelaide.edu.au Tandberg TDC 3620 This is very similar to the Tandberg TDC 3600 drive. Reported by: &a.joerg; Tandberg TDC 4222 The boot message identifier for this drive is TANDBERG TDC 4222 =07 type 1 removable SCSI 2 This is a QIC tape drive. Native capacity is 2.5GB. The drive will read all cartridges from the 60 MB (DC600A) upwards, and write 150 MB (DC6150) upwards. Hardware compression is optionally supported for the 2.5 GB cartridges. This drives quirks are known and pre-compiled into the scsi tape device driver (&man.st.4;) beginning with FreeBSD 2.2-current. For previous versions of FreeBSD, use mt to read one block from the tape, rewind the tape, and then execute the backup program (mt fsr 1; mt rewind; dump ...) Data transfer rate is 600kB/s (vendor claim with compression), 350 KB/s can even be reached in start/stop mode. The rate decreases for smaller cartridges. Reported by: &a.joerg; Wangtek 5525ES The boot message identifier for this drive is WANGTEK 5525ES SCSI REV7 3R1 type 1 removable SCSI 1 density code 0x11, 1024-byte blocks This is a QIC tape drive. Native capacity is 525MB. Data transfer rate is 180kB/s. The drive reads 60, 120, 150, and 525MB tapes. The drive will not write 60MB (DC600 cartridge) tapes. In order to overwrite 120 and 150 tapes reliably, first erase (mt erase) the tape. 120 and 150 tapes used a wider track (fewer tracks per tape) than 525MB tapes. The “extra” width of the previous tracks is not overwritten, as a result the new data lies in a band surrounded on both sides by the previous data unless the tape have been erased. This drives quirks are known and pre-compiled into the scsi tape device driver (&man.st.4;). Other firmware revisions that are known to work are: M75D Reported by: Marc van Kempen marc@bowtie.nl REV73R1 Andrew Gordon Andrew.Gordon@net-tel.co.uk M75D Wangtek 6200 The boot message identifier for this drive is WANGTEK 6200-HS 4B18 type 1 removable SCSI 2 Sequential-Access density code 0x13 This is a DDS-1 tape drive. Native capacity is 2GB using 90m tapes. Data transfer rate is 150kB/s. Reported by: Tony Kimball alk@Think.COM * Problem drives CD-ROM drives Contributed by &a.obrien;. 23 November 1997. As mentioned in Jordan's Picks Generally speaking those in The FreeBSD Project prefer SCSI CDROM drives over IDE CDROM drives. However not all SCSI CDROM drives are equal. Some feel the quality of some SCSI CDROM drives have been deteriorating to that of IDE CDROM drives. Toshiba used to be the favored stand-by, but many on the SCSI mailing list have found displeasure with the 12x speed XM-5701TA as its volume (when playing audio CDROMs) is not controllable by the various audio player software. Another area where SCSI CDROM manufacturers are cutting corners is adhearance to the SCSI specification. Many SCSI CDROMs will respond to multiple LUNs for its target address. Known violators include the 6x Teac CD-56S 1.0D. * Other * Other * PCMCIA diff --git a/en_US.ISO8859-1/books/handbook/hw/chapter.sgml b/en_US.ISO8859-1/books/handbook/hw/chapter.sgml index 4554b8e7cb..d3bf2da501 100644 --- a/en_US.ISO8859-1/books/handbook/hw/chapter.sgml +++ b/en_US.ISO8859-1/books/handbook/hw/chapter.sgml @@ -1,5550 +1,5557 @@ PC Hardware compatibility Issues of hardware compatibility are among the most troublesome in the computer industry today and FreeBSD is by no means immune to trouble. In this respect, FreeBSD's advantage of being able to run on inexpensive commodity PC hardware is also its liability when it comes to support for the amazing variety of components on the market. While it would be impossible to provide a exhaustive listing of hardware that FreeBSD supports, this section serves as a catalog of the device drivers included with FreeBSD and the hardware each drivers supports. Where possible and appropriate, notes about specific products are included. You may also want to refer to the kernel configuration file section in this handbook for a list of supported devices. As FreeBSD is a volunteer project without a funded testing department, we depend on you, the user, for much of the information contained in this catalog. If you have direct experience of hardware that does or does not work with FreeBSD, please let us know by sending e-mail to the &a.doc;. Questions about supported hardware should be directed to the &a.questions; (see Mailing Lists for more information). When submitting information or asking a question, please remember to specify exactly what version of FreeBSD you are using and include as many details of your hardware as possible. Resources on the Internet The following links have proven useful in selecting hardware. Though some of what you see won't necessarily be specific (or even applicable) to FreeBSD, most of the hardware information out there is OS independent. Please check with the FreeBSD hardware guide to make sure that your chosen configuration is supported before making any purchases. The Pentium Systems Hardware Performance Guide Sample Configurations The following list of sample hardware configurations by no means constitutes an endorsement of a given hardware vendor or product by The FreeBSD Project. This information is provided only as a public service and merely catalogs some of the experiences that various individuals have had with different hardware combinations. Your mileage may vary. Slippery when wet. Beware of dog. Jordan's Picks I have had fairly good luck building workstation and server configurations with the following components. I can't guarantee that you will too, nor that any of the companies here will remain “best buys” forever. I will try, when I can, to keep this list up-to-date but cannot obviously guarantee that it will be at any given time. Motherboards For Pentium Pro (P6) systems, I'm quite fond of the Tyan S1668 dual-processor motherboard as well as the Intel PR440FX motherboard with on-board SCSI WIDE and 100/10MB Intel Etherexpress NIC. You can build a dandy little single or dual processor system (which is supported in FreeBSD 3.0) for very little cost now that the Pentium Pro 180/256K chips have fallen so greatly in price, but no telling how much longer this will last. For the Pentium II, I'm rather partial to the ASUS P2l97-S motherboard with the on-board Adaptec SCSI WIDE controller. For Pentium machines, the ASUS P55T2P4 motherboard appears to be a good choice for mid-to-high range Pentium server and workstation systems. Those wishing to build more fault-tolerant systems should also be sure to use Parity memory or, for truly 24/7 applications, ECC memory. ECC memory does involve a slight performance trade-off (which may or may not be noticeable depending on your application) but buys you significantly increased fault-tolerance to memory errors. Disk Controllers This one is a bit trickier, and while I used to recommend the Buslogic controllers unilaterally for everything from ISA to PCI, now I tend to lean towards the Adaptec 1542CF for ISA, Buslogic Bt747c for EISA and Adaptec 2940UW for PCI. The NCR/Symbios cards for PCI have also worked well for me, though you need to make sure that your motherboard supports the BIOS-less model if you're using one of those (if your card has nothing which looks even vaguely like a ROM chip on it, you've probably got one which expects its BIOS to be on your motherboard). If you should find that you need more than one SCSI controller in a PCI machine, you may wish to consider conserving your scarce PCI bus resources by buying the Adaptec 3940 card, which puts two SCSI controllers (and internal busses) in a single slot. There are two types of 3940 on the market—the older model with AIC 7880 chips on it, and hte newer one with AIC 7895 chips. The newer model requires CAM support which is not yet part of FreeBSD—you have to add it, or install from one of the CAM binary snapshot release. Disk drives In this particular game of Russian roulette, I'll make few specific recommendations except to say “SCSI over IDE whenever you can afford it.” Even in small desktop configurations, SCSI often makes more sense since it allows you to easily migrate drives from server to desktop as falling drive prices make it economical to do so. If you have more than one machine to administer then think of it not simply as storage, think of it as a food chain! For a serious server configuration, there's not even any argument—use SCSI equipment and good cables. CDROM drives My SCSI preferences extend to SCSI CDROM drives as well, and while the Toshiba drives have always been favourites of mine (in whatever speed is hot that week), I'm still fond of my good old Plextor PX-12CS drive. It's only a 12 speed, but it's offered excellent performance and reliability. Generally speaking, most SCSI CDROM drives I've seen have been of pretty solid construction and you probably won't go wrong with an HP or NEC SCSI CDROM drive either. SCSI CDROM prices also appear to have dropped considerably in the last few months and are now quite competitive with IDE CDROMs while remaining a technically superior solution. I now see no reason whatsoever to settle for an IDE CDROM drive if given a choice between the two. CD Recordable (WORM) drives At the time of this writing, FreeBSD supports 3 types of CDR drives (though I believe they all ultimately come from Phillips anyway): The Phillips CDD 522 (Acts like a Plasmon), the PLASMON RF4100 and the HP 6020i. I myself use the HP 6020i for burning CDROMs (in 2.2 and alter releases—it does not work with earlier releases of the SCSI code) and it works very well. See /usr/share/examples/worm on your 2.2 system for example scripts used to created ISO9660 filesystem images (with RockRidge extensions) and burn them onto an HP6020i CDR. Tape drives I've had pretty good luck with both 8mm drives from Exabyte and 4mm (DAT) drives from HP. For backup purposes, I'd have to give the higher recommendation to the Exabyte due to the more robust nature (and higher storage capacity) of 8mm tape. Video Cards If you can also afford to buy a commercial X server for US$99 from Xi Graphics, Inc. (formerly X Inside, Inc) then I can heartily recommend the Matrox Millenium II card. Note that support for this card is also excellent with the XFree86 server, which is now at version 3.3.2. You also certainly can't go wrong with one of Number 9's cards — their S3 Vision 868 and 968 based cards (the 9FX series) also being quite fast and very well supported by XFree86's S3 server. You can also pick up their Revolution 3D cards very cheaply these days, especially if you require a lot of video memory. Monitors I have had very good luck with the Sony Multiscan 17seII monitors, as have I with the Viewsonic offering in the same (Trinitron) tube. For larger than 17", all I can recommend at the time of this writing is to not spend any less than U.S. $2,000 for a 21" monitor or $1,700 for a 20" monitor if that's what you really need. There are good monitors available in the >=20" range and there are also cheap monitors in the >=20" range. Unfortunately, very few are both cheap and good! Networking I can recommend the Intel EtherExpress Pro/100B card first ande foremost, followed by the SMC Ultra 16 controller for any ISA application and the SMC EtherPower or Compex ENET32 cards for slightly cheaper PCI based networking. In general, any PCI NIC based around DEC's DC21041 Ethernet controller chip, such as the Zynx ZX342 or DEC DE435, will generally work quite well and can frequently be found in 2-port and 4-port version (useful for firewalls and routers), though the Pro/100MB card has the edge when it comes to providing the best performance with teh lower overhead. If what you're looking for is the cheapest possible solution then almost any NE2000 clone will do a fine job for very little cost. Serial If you're looking for high-speed serial networking solutions, then Digi International makes the SYNC/570 series, with drivers now in FreeBSD-current. Emerging Technologies also manufactures a board with T1/E1 capabilities, using software they provide. I have no direct experience using either product, however. Multiport card options are somewhat more numerous, though it has to be said that FreeBSD's support for Cyclades's products is probably the tightest, primarily as a result of that company's commitment to making sure that we are adequately supplied with evaluation boards and technical specs. I've heard that the Cyclom-16Ye offers the best price/performance, though I've not checked the prices lately. Other multiport cards I've heard good things about are the BOCA and AST cards, and Stallion Technologies apparently offers an unofficial driver for their cards at this location. Audio I currently use a Creative Labs AWE32 though just about anything from Creative Labs will generally work these days. This is not to say that other types of sound cards don't also work, simply that I have little experience with them (I was a former GUS fan, but Gravis's soundcard situation has been dire for some time). Video For video capture, there are two good choices — any card based on the Brooktree BT848 chip, such as the Hauppage or WinTV boards, will work very nicely with FreeBSD. Another board which works for me is the Matrox Meteor card. FreeBSD also supports the older video spigot card from Creative Labs, but those are getting somewhat difficult to find. Note that the Meteor frame grabber card will not work with motherboards based on the 440FX chipset! See the motherboard reference section for details. In such cases, it's better to go with a BT848 based board. Core/Processing Motherboards, busses, and chipsets * ISA * EISA * VLB PCI Contributed by &a.obrien; from postings by &a.rgrimes;. 25 April 1995. Continuing updates by &a.jkh;. Last update on 26 August 1996. Of the Intel PCI chip sets, the following list describes various types of known-brokenness and the degree of breakage, listed from worst to best. Mercury: Cache coherency problems, especially if there are ISA bus masters behind the ISA to PCI bridge chip. Hardware flaw, only known work around is to turn the cache off. Saturn-I (ie, 82424ZX at rev 0, 1 or 2): Write back cache coherency problems. Hardware flaw, only known work around is to set the external cache to write-through mode. Upgrade to Saturn-II. Saturn-II (ie, 82424ZX at rev 3 or 4): Works fine, but many MB manufactures leave out the external dirty bit SRAM needed for write back operation. Work arounds are either run it in write through mode, or get the dirty bit SRAM installed. (I have these for the ASUS PCI/I-486SP3G rev 1.6 and later boards). Neptune: Can not run more than 2 bus master devices. Admitted Intel design flaw. Workarounds include do not run more than 2 bus masters, special hardware design to replace the PCI bus arbiter (appears on Intel Altair board and several other Intel server group MB's). And of course Intel's official answer, move to the Triton chip set, we “fixed it there”. Triton (ie, 430FX): No known cache coherency or bus master problems, chip set does not implement parity checking. Workaround for parity issue. Use Triton-II based motherboards if you have the choice. Triton-II (ie, 430HX): All reports on motherboards using this chipset have been favorable so far. No known problems. Orion: Early versions of this chipset suffered from a PCI write-posting bug which can cause noticeable performance degradation in applications where large amounts of PCI bus traffic is involved. B0 stepping or later revisions of the chipset fixed this problem. 440FX: This Pentium Pro support chipset seems to work well, and does not suffer from any of the early Orion chipset problems. It also supports a wider variety of memory, including ECC and parity. The only known problem with it is that the Matrox Meteor frame grabber card doesn't like it. CPUs/FPUs Contributed by &a.asami;. 26 December 1997. P6 class (Pentium Pro/Pentium II) Both the Pentium Pro and Pentium II work fine with FreeBSD. In fact, our main ftp site ftp.freebsd.org (also known as "ftp.cdrom.com", world's largest ftp site) runs FreeBSD on a Pentium Pro. Configurations details are available for interested parties. Pentium class The Intel Pentium (P54C), Pentium MMX (P55C), AMD K6 and Cyrix/IBM 6x86MX processors are all reported to work with FreeBSD. I will not go into details of which processor is faster than what, there are zillions of web sites on the Internet that tells you one way or another. :) Various CPUs have different voltage/cooling requirements. Make sure your motherboard can supply the exact voltage needed by the CPU. For instance, many recent MMX chips require split voltage (e.g., 2.9V core, 3.3V I/O). Also, some AMD and Cyrix/IBM chips run hotter than Intel chips. In that case, make sure you have good heatsink/fans (you can get the list of certified parts from their web pages). Clock speeds Contributed by &a.rgrimes;. 1 October 1996. Updated by &a.asami;. 27 December 1997. Pentium class machines use different clock speeds for the various parts of the system. These being the speed of the CPU, external memory bus, and the PCI bus. It is not always true that a “faster” processor will make a system faster than a “slower” one, due to the various clock speeds used. Below is a table showing the differences: Rated CPU MHz External Clock and Memory Bus MHz External to Internal Clock Multiplier PCI Bus Clock MHz 60 60 1.0 30 66 66 1.0 33 75 50 1.5 25 90 60 1.5 30 100 50 2 25 100 66 1.5 33 120 60 2 30 133 66 2 33 150 60 2.5 30 (Intel, AMD) 150 75 2 37.5 (Cyrix/IBM 6x86MX) 166 66 2.5 33 180 60 3 30 200 66 3 33 233 66 3.5 33 66MHz may actually be 66.667MHz, but don't assume so. The Pentium 100 can be run at either 50MHz external clock with a multiplier of 2 or at 66MHz and a multiplier of 1.5. As can be seen the best parts to be using are the 100, 133, 166, 200 and 233, with the exception that at a multiplier of 3 or more the CPU starves for memory. The AMD K6 Bug In 1997, there have been reports of the AMD K6 seg faulting during heavy compilation. That problem has been fixed in 3Q '97. According to reports, K6 chips with date mark “9733” or larger (i.e., manufactured in the 33rd week of '97 or later) do not have this bug. * 486 class * 386 class 286 class Sorry, FreeBSD does not run on 80286 machines. It is nearly impossible to run today's large full-featured UNIXes on such hardware. * Memory The minimum amount of memory you must have to install FreeBSD is 5 MB. Once your system is up and running you can build a custom kernel that will use less memory. If you use the boot4.flp you can get away with having only 4 MB. * BIOS Input/Output Devices * Video cards * Sound cards Serial ports and multiport cards The UART: What it is and how it works Copyright © 1996 &a.uhclem;, All Rights Reserved. 13 January 1996. The Universal Asynchronous Receiver/Transmitter (UART) controller is the key component of the serial communications subsystem of a computer. The UART takes bytes of data and transmits the individual bits in a sequential fashion. At the destination, a second UART re-assembles the bits into complete bytes. Serial transmission is commonly used with modems and for non-networked communication between computers, terminals and other devices. There are two primary forms of serial transmission: Synchronous and Asynchronous. Depending on the modes that are supported by the hardware, the name of the communication sub-system will usually include a A if it supports Asynchronous communications, and a S if it supports Synchronous communications. Both forms are described below. Some common acronyms are:
UART Universal Asynchronous Receiver/Transmitter
USART Universal Synchronous-Asynchronous Receiver/Transmitter
Synchronous Serial Transmission Synchronous serial transmission requires that the sender and receiver share a clock with one another, or that the sender provide a strobe or other timing signal so that the receiver knows when to “read” the next bit of the data. In most forms of serial Synchronous communication, if there is no data available at a given instant to transmit, a fill character must be sent instead so that data is always being transmitted. Synchronous communication is usually more efficient because only data bits are transmitted between sender and receiver, and synchronous communication can be more more costly if extra wiring and circuits are required to share a clock signal between the sender and receiver. A form of Synchronous transmission is used with printers and fixed disk devices in that the data is sent on one set of wires while a clock or strobe is sent on a different wire. Printers and fixed disk devices are not normally serial devices because most fixed disk interface standards send an entire word of data for each clock or strobe signal by using a separate wire for each bit of the word. In the PC industry, these are known as Parallel devices. The standard serial communications hardware in the PC does not support Synchronous operations. This mode is described here for comparison purposes only. Asynchronous Serial Transmission Asynchronous transmission allows data to be transmitted without the sender having to send a clock signal to the receiver. Instead, the sender and receiver must agree on timing parameters in advance and special bits are added to each word which are used to synchronize the sending and receiving units. When a word is given to the UART for Asynchronous transmissions, a bit called the "Start Bit" is added to the beginning of each word that is to be transmitted. The Start Bit is used to alert the receiver that a word of data is about to be sent, and to force the clock in the receiver into synchronization with the clock in the transmitter. These two clocks must be accurate enough to not have the frequency drift by more than 10% during the transmission of the remaining bits in the word. (This requirement was set in the days of mechanical teleprinters and is easily met by modern electronic equipment.) After the Start Bit, the individual bits of the word of data are sent, with the Least Significant Bit (LSB) being sent first. Each bit in the transmission is transmitted for exactly the same amount of time as all of the other bits, and the receiver “looks” at the wire at approximately halfway through the period assigned to each bit to determine if the bit is a 1 or a 0. For example, if it takes two seconds to send each bit, the receiver will examine the signal to determine if it is a 1 or a 0 after one second has passed, then it will wait two seconds and then examine the value of the next bit, and so on. The sender does not know when the receiver has “looked” at the value of the bit. The sender only knows when the clock says to begin transmitting the next bit of the word. When the entire data word has been sent, the transmitter may add a Parity Bit that the transmitter generates. The Parity Bit may be used by the receiver to perform simple error checking. Then at least one Stop Bit is sent by the transmitter. When the receiver has received all of the bits in the data word, it may check for the Parity Bits (both sender and receiver must agree on whether a Parity Bit is to be used), and then the receiver looks for a Stop Bit. If the Stop Bit does not appear when it is supposed to, the UART considers the entire word to be garbled and will report a Framing Error to the host processor when the data word is read. The usual cause of a Framing Error is that the sender and receiver clocks were not running at the same speed, or that the signal was interrupted. Regardless of whether the data was received correctly or not, the UART automatically discards the Start, Parity and Stop bits. If the sender and receiver are configured identically, these bits are not passed to the host. If another word is ready for transmission, the Start Bit for the new word can be sent as soon as the Stop Bit for the previous word has been sent. Because asynchronous data is “self synchronizing”, if there is no data to transmit, the transmission line can be idle. Other UART Functions In addition to the basic job of converting data from parallel to serial for transmission and from serial to parallel on reception, a UART will usually provide additional circuits for signals that can be used to indicate the state of the transmission media, and to regulate the flow of data in the event that the remote device is not prepared to accept more data. For example, when the device connected to the UART is a modem, the modem may report the presence of a carrier on the phone line while the computer may be able to instruct the modem to reset itself or to not take calls by asserting or deasserting one more more of these extra signals. The function of each of these additional signals is defined in the EIA RS232-C standard. The RS232-C and V.24 Standards In most computer systems, the UART is connected to circuitry that generates signals that comply with the EIA RS232-C specification. There is also a CCITT standard named V.24 that mirrors the specifications included in RS232-C. RS232-C Bit Assignments (Marks and Spaces) In RS232-C, a value of 1 is called a Mark and a value of 0 is called a Space. When a communication line is idle, the line is said to be “Marking”, or transmitting continuous 1 values. The Start bit always has a value of 0 (a Space). The Stop Bit always has a value of 1 (a Mark). This means that there will always be a Mark (1) to Space (0) transition on the line at the start of every word, even when multiple word are transmitted back to back. This guarantees that sender and receiver can resynchronize their clocks regardless of the content of the data bits that are being transmitted. The idle time between Stop and Start bits does not have to be an exact multiple (including zero) of the bit rate of the communication link, but most UARTs are designed this way for simplicity. In RS232-C, the "Marking" signal (a 1) is represented by a voltage between -2 VDC and -12 VDC, and a "Spacing" signal (a 0) is represented by a voltage between 0 and +12 VDC. The transmitter is supposed to send +12 VDC or -12 VDC, and the receiver is supposed to allow for some voltage loss in long cables. Some transmitters in low power devices (like portable computers) sometimes use only +5 VDC and -5 VDC, but these values are still acceptable to a RS232-C receiver, provided that the cable lengths are short. RS232-C Break Signal RS232-C also specifies a signal called a Break, which is caused by sending continuous Spacing values (no Start or Stop bits). When there is no electricity present on the data circuit, the line is considered to be sending Break. The Break signal must be of a duration longer than the time it takes to send a complete byte plus Start, Stop and Parity bits. Most UARTs can distinguish between a Framing Error and a Break, but if the UART cannot do this, the Framing Error detection can be used to identify Breaks. In the days of teleprinters, when numerous printers around the country were wired in series (such as news services), any unit could cause a Break by temporarily opening the entire circuit so that no current flowed. This was used to allow a location with urgent news to interrupt some other location that was currently sending information. In modern systems there are two types of Break signals. If the Break is longer than 1.6 seconds, it is considered a "Modem Break", and some modems can be programmed to terminate the conversation and go on-hook or enter the modems' command mode when the modem detects this signal. If the Break is smaller than 1.6 seconds, it signifies a Data Break and it is up to the remote computer to respond to this signal. Sometimes this form of Break is used as an Attention or Interrupt signal and sometimes is accepted as a substitute for the ASCII CONTROL-C character. Marks and Spaces are also equivalent to “Holes” and “No Holes” in paper tape systems. Breaks cannot be generated from paper tape or from any other byte value, since bytes are always sent with Start and Stop bit. The UART is usually capable of generating the continuous Spacing signal in response to a special command from the host processor. RS232-C DTE and DCE Devices The RS232-C specification defines two types of equipment: the Data Terminal Equipment (DTE) and the Data Carrier Equipment (DCE). Usually, the DTE device is the terminal (or computer), and the DCE is a modem. Across the phone line at the other end of a conversation, the receiving modem is also a DCE device and the computer that is connected to that modem is a DTE device. The DCE device receives signals on the pins that the DTE device transmits on, and vice versa. When two devices that are both DTE or both DCE must be connected together without a modem or a similar media translater between them, a NULL modem must be used. The NULL modem electrically re-arranges the cabling so that the transmitter output is connected to the receiver input on the other device, and vice versa. Similar translations are performed on all of the control signals so that each device will see what it thinks are DCE (or DTE) signals from the other device. The number of signals generated by the DTE and DCE devices are not symmetrical. The DTE device generates fewer signals for the DCE device than the DTE device receives from the DCE. RS232-C Pin Assignments The EIA RS232-C specification (and the ITU equivalent, V.24) calls for a twenty-five pin connector (usually a DB25) and defines the purpose of most of the pins in that connector. In the IBM Personal Computer and similar systems, a subset of RS232-C signals are provided via nine pin connectors (DB9). The signals that are not included on the PC connector deal mainly with synchronous operation, and this transmission mode is not supported by the UART that IBM selected for use in the IBM PC. Depending on the computer manufacturer, a DB25, a DB9, or both types of connector may be used for RS232-C communications. (The IBM PC also uses a DB25 connector for the parallel printer interface which causes some confusion.) Below is a table of the RS232-C signal assignments in the DB25 and DB9 connectors. DB25 RS232-C Pin DB9 IBM PC Pin EIA Circuit Symbol CCITT Circuit Symbol Common Name Signal Source Description 1 - AA 101 PG/FG - Frame/Protective Ground 2 3 BA 103 TD DTE Transmit Data 3 2 BB 104 RD DCE Receive Data 4 7 CA 105 RTS DTE Request to Send 5 8 CB 106 CTS DCE Clear to Send 6 6 CC 107 DSR DCE Data Set Ready 7 5 AV 102 SG/GND - Signal Ground 8 1 CF 109 DCD/CD DCE Data Carrier Detect 9 - - - - - Reserved for Test 10 - - - - - Reserved for Test 11 - - - - - Reserved for Test 12 - CI 122 SRLSD DCE Sec. Recv. Line Signal Detector 13 - SCB 121 SCTS DCE Secondary Clear to Send 14 - SBA 118 STD DTE Secondary Transmit Data 15 - DB 114 TSET DCE Trans. Sig. Element Timing 16 - SBB 119 SRD DCE Secondary Received Data 17 - DD 115 RSET DCE Receiver Signal Element Timing 18 - - 141 LOOP DTE Local Loopback 19 - SCA 120 SRS DTE Secondary Request to Send 20 4 CD 108.2 DTR DTE Data Terminal Ready 21 - - - RDL DTE Remote Digital Loopback 22 9 CE 125 RI DCE Ring Indicator 23 - CH 111 DSRS DTE Data Signal Rate Selector 24 - DA 113 TSET DTE Trans. Sig. Element Timing 25 - - 142 - DCE Test Mode Bits, Baud and Symbols Baud is a measurement of transmission speed in asynchronous communication. Because of advances in modem communication technology, this term is frequently misused when describing the data rates in newer devices. Traditionally, a Baud Rate represents the number of bits that are actually being sent over the media, not the amount of data that is actually moved from one DTE device to the other. The Baud count includes the overhead bits Start, Stop and Parity that are generated by the sending UART and removed by the receiving UART. This means that seven-bit words of data actually take 10 bits to be completely transmitted. Therefore, a modem capable of moving 300 bits per second from one place to another can normally only move 30 7-bit words if Parity is used and one Start and Stop bit are present. If 8-bit data words are used and Parity bits are also used, the data rate falls to 27.27 words per second, because it now takes 11 bits to send the eight-bit words, and the modem still only sends 300 bits per second. The formula for converting bytes per second into a baud rate and vice versa was simple until error-correcting modems came along. These modems receive the serial stream of bits from the UART in the host computer (even when internal modems are used the data is still frequently serialized) and converts the bits back into bytes. These bytes are then combined into packets and sent over the phone line using a Synchronous transmission method. This means that the Stop, Start, and Parity bits added by the UART in the DTE (the computer) were removed by the modem before transmission by the sending modem. When these bytes are received by the remote modem, the remote modem adds Start, Stop and Parity bits to the words, converts them to a serial format and then sends them to the receiving UART in the remote computer, who then strips the Start, Stop and Parity bits. The reason all these extra conversions are done is so that the two modems can perform error correction, which means that the receiving modem is able to ask the sending modem to resend a block of data that was not received with the correct checksum. This checking is handled by the modems, and the DTE devices are usually unaware that the process is occurring. By striping the Start, Stop and Parity bits, the additional bits of data that the two modems must share between themselves to perform error-correction are mostly concealed from the effective transmission rate seen by the sending and receiving DTE equipment. For example, if a modem sends ten 7-bit words to another modem without including the Start, Stop and Parity bits, the sending modem will be able to add 30 bits of its own information that the receiving modem can use to do error-correction without impacting the transmission speed of the real data. The use of the term Baud is further confused by modems that perform compression. A single 8-bit word passed over the telephone line might represent a dozen words that were transmitted to the sending modem. The receiving modem will expand the data back to its original content and pass that data to the receiving DTE. Modern modems also include buffers that allow the rate that bits move across the phone line (DCE to DCE) to be a different speed than the speed that the bits move between the DTE and DCE on both ends of the conversation. Normally the speed between the DTE and DCE is higher than the DCE to DCE speed because of the use of compression by the modems. Because the number of bits needed to describe a byte varied during the trip between the two machines plus the differing bits-per-seconds speeds that are used present on the DTE-DCE and DCE-DCE links, the usage of the term Baud to describe the overall communication speed causes problems and can misrepresent the true transmission speed. So Bits Per Second (bps) is the correct term to use to describe the transmission rate seen at the DCE to DCE interface and Baud or Bits Per Second are acceptable terms to use when a connection is made between two systems with a wired connection, or if a modem is in use that is not performing error-correction or compression. Modern high speed modems (2400, 9600, 14,400, and 19,200bps) in reality still operate at or below 2400 baud, or more accurately, 2400 Symbols per second. High speed modem are able to encode more bits of data into each Symbol using a technique called Constellation Stuffing, which is why the effective bits per second rate of the modem is higher, but the modem continues to operate within the limited audio bandwidth that the telephone system provides. Modems operating at 28,800 and higher speeds have variable Symbol rates, but the technique is the same. The IBM Personal Computer UART Starting with the original IBM Personal Computer, IBM selected the National Semiconductor INS8250 UART for use in the IBM PC Parallel/Serial Adapter. Subsequent generations of compatible computers from IBM and other vendors continued to use the INS8250 or improved versions of the National Semiconductor UART family. National Semiconductor UART Family Tree There have been several versions and subsequent generations of the INS8250 UART. Each major version is described below. INS8250 -> INS8250B \ \ \-> INS8250A -> INS82C50A \ \ \-> NS16450 -> NS16C450 \ \ \-> NS16550 -> NS16550A -> PC16550D INS8250 This part was used in the original IBM PC and IBM PC/XT. The original name for this part was the INS8250 ACE (Asynchronous Communications Element) and it is made from NMOS technology. The 8250 uses eight I/O ports and has a one-byte send and a one-byte receive buffer. This original UART has several race conditions and other flaws. The original IBM BIOS includes code to work around these flaws, but this made the BIOS dependent on the flaws being present, so subsequent parts like the 8250A, 16450 or 16550 could not be used in the original IBM PC or IBM PC/XT. INS8250-B This is the slower speed of the INS8250 made from NMOS technology. It contains the same problems as the original INS8250. INS8250A An improved version of the INS8250 using XMOS technology with various functional flaws corrected. The INS8250A was used initially in PC clone computers by vendors who used “clean” BIOS designs. Because of the corrections in the chip, this part could not be used with a BIOS compatible with the INS8250 or INS8250B. INS82C50A This is a CMOS version (low power consumption) of the INS8250A and has similar functional characteristics. NS16450 Same as NS8250A with improvements so it can be used with faster CPU bus designs. IBM used this part in the IBM AT and updated the IBM BIOS to no longer rely on the bugs in the INS8250. NS16C450 This is a CMOS version (low power consumption) of the NS16450. NS16550 Same as NS16450 with a 16-byte send and receive buffer but the buffer design was flawed and could not be reliably be used. NS16550A Same as NS16550 with the buffer flaws corrected. The 16550A and its successors have become the most popular UART design in the PC industry, mainly due it its ability to reliably handle higher data rates on operating systems with sluggish interrupt response times. NS16C552 This component consists of two NS16C550A CMOS UARTs in a single package. PC16550D Same as NS16550A with subtle flaws corrected. This is revision D of the 16550 family and is the latest design available from National Semiconductor. The NS16550AF and the PC16550D are the same thing National reorganized their part numbering system a few years ago, and the NS16550AFN no longer exists by that name. (If you have a NS16550AFN, look at the date code on the part, which is a four digit number that usually starts with a nine. The first two digits of the number are the year, and the last two digits are the week in that year when the part was packaged. If you have a NS16550AFN, it is probably a few years old.) The new numbers are like PC16550DV, with minor differences in the suffix letters depending on the package material and its shape. (A description of the numbering system can be found below.) It is important to understand that in some stores, you may pay $15(US) for a NS16550AFN made in 1990 and in the next bin are the new PC16550DN parts with minor fixes that National has made since the AFN part was in production, the PC16550DN was probably made in the past six months and it costs half (as low as $5(US) in volume) as much as the NS16550AFN because they are readily available. As the supply of NS16550AFN chips continues to shrink, the price will probably continue to increase until more people discover and accept that the PC16550DN really has the same function as the old part number. National Semiconductor Part Numbering System The older NSnnnnnrqp part numbers are now of the format PCnnnnnrgp. The r is the revision field. The current revision of the 16550 from National Semiconductor is D. The p is the package-type field. The types are: "F" QFP (quad flat pack) L lead type "N" DIP (dual inline package) through hole straight lead type "V" LPCC (lead plastic chip carrier) J lead type The g is the product grade field. If an I precedes the package-type letter, it indicates an “industrial” grade part, which has higher specs than a standard part but not as high as Military Specification (Milspec) component. This is an optional field. So what we used to call a NS16550AFN (DIP Package) is now called a PC16550DN or PC16550DIN. Other Vendors and Similar UARTs Over the years, the 8250, 8250A, 16450 and 16550 have been licensed or copied by other chip vendors. In the case of the 8250, 8250A and 16450, the exact circuit (the “megacell”) was licensed to many vendors, including Western Digital and Intel. Other vendors reverse-engineered the part or produced emulations that had similar behavior. In internal modems, the modem designer will frequently emulate the 8250A/16450 with the modem microprocessor, and the emulated UART will frequently have a hidden buffer consisting of several hundred bytes. Because of the size of the buffer, these emulations can be as reliable as a 16550A in their ability to handle high speed data. However, most operating systems will still report that the UART is only a 8250A or 16450, and may not make effective use of the extra buffering present in the emulated UART unless special drivers are used. Some modem makers are driven by market forces to abandon a design that has hundreds of bytes of buffer and instead use a 16550A UART so that the product will compare favorably in market comparisons even though the effective performance may be lowered by this action. A common misconception is that all parts with “16550A” written on them are identical in performance. There are differences, and in some cases, outright flaws in most of these 16550A clones. When the NS16550 was developed, the National Semiconductor obtained several patents on the design and they also limited licensing, making it harder for other vendors to provide a chip with similar features. Because of the patents, reverse-engineered designs and emulations had to avoid infringing the claims covered by the patents. Subsequently, these copies almost never perform exactly the same as the NS16550A or PC16550D, which are the parts most computer and modem makers want to buy but are sometimes unwilling to pay the price required to get the genuine part. Some of the differences in the clone 16550A parts are unimportant, while others can prevent the device from being used at all with a given operating system or driver. These differences may show up when using other drivers, or when particular combinations of events occur that were not well tested or considered in the Windows driver. This is because most modem vendors and 16550-clone makers use the Microsoft drivers from Windows for Workgroups 3.11 and the Microsoft MSD utility as the primary tests for compatibility with the NS16550A. This over-simplistic criteria means that if a different operating system is used, problems could appear due to subtle differences between the clones and genuine components. National Semiconductor has made available a program named COMTEST that performs compatibility tests independent of any OS drivers. It should be remembered that the purpose of this type of program is to demonstrate the flaws in the products of the competition, so the program will report major as well as extremely subtle differences in behavior in the part being tested. In a series of tests performed by the author of this document in 1994, components made by National Semiconductor, TI, StarTech, and CMD as well as megacells and emulations embedded in internal modems were tested with COMTEST. A difference count for some of these components is listed below. Because these tests were performed in 1994, they may not reflect the current performance of the given product from a vendor. It should be noted that COMTEST normally aborts when an excessive number or certain types of problems have been detected. As part of this testing, COMTEST was modified so that it would not abort no matter how many differences were encountered. Vendor Part Number Errors (aka "differences" reported) National (PC16550DV) 0 National (NS16550AFN) 0 National (NS16C552V) 0 TI (TL16550AFN) 3 CMD (16C550PE) 19 StarTech (ST16C550J) 23 Rockwell Reference modem with internal 16550 or an emulation (RC144DPi/C3000-25) 117 Sierra Modem with an internal 16550 (SC11951/SC11351) 91 To date, the author of this document has not found any non-National parts that report zero differences using the COMTEST program. It should also be noted that National has had five versions of the 16550 over the years and the newest parts behave a bit differently than the classic NS16550AFN that is considered the benchmark for functionality. COMTEST appears to turn a blind eye to the differences within the National product line and reports no errors on the National parts (except for the original 16550) even when there are official erratas that describe bugs in the A, B and C revisions of the parts, so this bias in COMTEST must be taken into account. It is important to understand that a simple count of differences from COMTEST does not reveal a lot about what differences are important and which are not. For example, about half of the differences reported in the two modems listed above that have internal UARTs were caused by the clone UARTs not supporting five- and six-bit character modes. The real 16550, 16450, and 8250 UARTs all support these modes and COMTEST checks the functionality of these modes so over fifty differences are reported. However, almost no modern modem supports five- or six-bit characters, particularly those with error-correction and compression capabilities. This means that the differences related to five- and six-bit character modes can be discounted. Many of the differences COMTEST reports have to do with timing. In many of the clone designs, when the host reads from one port, the status bits in some other port may not update in the same amount of time (some faster, some slower) as a real NS16550AFN and COMTEST looks for these differences. This means that the number of differences can be misleading in that one device may only have one or two differences but they are extremely serious, and some other device that updates the status registers faster or slower than the reference part (that would probably never affect the operation of a properly written driver) could have dozens of differences reported. COMTEST can be used as a screening tool to alert the administrator to the presence of potentially incompatible components that might cause problems or have to be handled as a special case. If you run COMTEST on a 16550 that is in a modem or a modem is attached to the serial port, you need to first issue a ATE0&W command to the modem so that the modem will not echo any of the test characters. If you forget to do this, COMTEST will report at least this one difference: Error (6)...Timeout interrupt failed: IIR = c1 LSR = 61 8250/16450/16550 Registers The 8250/16450/16550 UART occupies eight contiguous I/O port addresses. In the IBM PC, there are two defined locations for these eight ports and they are known collectively as COM1 and COM2. The makers of PC-clones and add-on cards have created two additional areas known as COM3 and COM4, but these extra COM ports conflict with other hardware on some systems. The most common conflict is with video adapters that provide IBM 8514 emulation. COM1 is located from 0x3f8 to 0x3ff and normally uses IRQ 4 COM2 is located from 0x2f8 to 0x2ff and normally uses IRQ 3 COM3 is located from 0x3e8 to 0x3ef and has no standardized IRQ COM4 is located from 0x2e8 to 0x2ef and has no standardized IRQ. A description of the I/O ports of the 8250/16450/16550 UART is provided below. I/O Port Access Allowed Description +0x00 write (DLAB==0) Transmit Holding Register (THR).Information written to this port are treated as data words and will be transmitted by the UART. +0x00 read (DLAB==0) Receive Buffer Register (RBR).Any data words received by the UART form the serial link are accessed by the host by reading this port. +0x00 write/read (DLAB==1) Divisor Latch LSB (DLL)This value will be divided from the master input clock (in the IBM PC, the master clock is 1.8432MHz) and the resulting clock will determine the baud rate of the UART. This register holds bits 0 thru 7 of the divisor. +0x01 write/read (DLAB==1) Divisor Latch MSB (DLH)This value will be divided from the master input clock (in the IBM PC, the master clock is 1.8432MHz) and the resulting clock will determine the baud rate of the UART. This register holds bits 8 thru 15 of the divisor. +0x01 write/read (DLAB==0) Interrupt Enable Register (IER)The 8250/16450/16550 UART classifies events into one of four categories. Each category can be configured to generate an interrupt when any of the events occurs. The 8250/16450/16550 UART generates a single external interrupt signal regardless of how many events in the enabled categories have occurred. It is up to the host processor to respond to the interrupt and then poll the enabled interrupt categories (usually all categories have interrupts enabled) to determine the true cause(s) of the interrupt. Bit 7 Reserved, always 0. Bit 6 Reserved, always 0. Bit 5 Reserved, always 0. Bit 4 Reserved, always 0. Bit 3 Enable Modem Status Interrupt (EDSSI). Setting this bit to "1" allows the UART to generate an interrupt when a change occurs on one or more of the status lines. Bit 2 Enable Receiver Line Status Interrupt (ELSI) Setting this bit to "1" causes the UART to generate an interrupt when the an error (or a BREAK signal) has been detected in the incoming data. Bit 1 Enable Transmitter Holding Register Empty Interrupt (ETBEI) Setting this bit to "1" causes the UART to generate an interrupt when the UART has room for one or more additional characters that are to be transmitted. Bit 0 Enable Received Data Available Interrupt (ERBFI) Setting this bit to "1" causes the UART to generate an interrupt when the UART has received enough characters to exceed the trigger level of the FIFO, or the FIFO timer has expired (stale data), or a single character has been received when the FIFO is disabled. +0x02 write FIFO Control Register (FCR) (This port does not exist on the 8250 and 16450 UART.) Bit 7 Receiver Trigger Bit #1 Bit 6 Receiver Trigger Bit #0These two bits control at what point the receiver is to generate an interrupt when the FIFO is active. 7 6 How many words are received before an interrupt is generated 0 0 1 0 1 4 1 0 8 1 1 14 Bit 5 Reserved, always 0. Bit 4 Reserved, always 0. Bit 3 DMA Mode Select. If Bit 0 is set to "1" (FIFOs enabled), setting this bit changes the operation of the -RXRDY and -TXRDY signals from Mode 0 to Mode 1. Bit 2 Transmit FIFO Reset. When a "1" is written to this bit, the contents of the FIFO are discarded. Any word currently being transmitted will be sent intact. This function is useful in aborting transfers. Bit 1 Receiver FIFO Reset. When a "1" is written to this bit, the contents of the FIFO are discarded. Any word currently being assembled in the shift register will be received intact. Bit 0 16550 FIFO Enable. When set, both the transmit and receive FIFOs are enabled. Any contents in the holding register, shift registers or FIFOs are lost when FIFOs are enabled or disabled. +0x02 read Interrupt Identification Register Bit 7 FIFOs enabled. On the 8250/16450 UART, this bit is zero. Bit 6 FIFOs enabled. On the 8250/16450 UART, this bit is zero. Bit 5 Reserved, always 0. Bit 4 Reserved, always 0. Bit 3 Interrupt ID Bit #2. On the 8250/16450 UART, this bit is zero. Bit 2 Interrupt ID Bit #1 Bit 1 Interrupt ID Bit #0.These three bits combine to report the category of event that caused the interrupt that is in progress. These categories have priorities, so if multiple categories of events occur at the same time, the UART will report the more important events first and the host must resolve the events in the order they are reported. All events that caused the current interrupt must be resolved before any new interrupts will be generated. (This is a limitation of the PC architecture.) 2 1 0 Priority Description 0 1 1 First Received Error (OE, PE, BI, or FE) 0 1 0 Second Received Data Available 1 1 0 Second Trigger level identification (Stale data in receive buffer) 0 0 1 Third Transmitter has room for more words (THRE) 0 0 0 Fourth Modem Status Change (-CTS, -DSR, -RI, or -DCD) Bit 0 Interrupt Pending Bit. If this bit is set to "0", then at least one interrupt is pending. +0x03 write/read Line Control Register (LCR) Bit 7 Divisor Latch Access Bit (DLAB). When set, access to the data transmit/receive register (THR/RBR) and the Interrupt Enable Register (IER) is disabled. Any access to these ports is now redirected to the Divisor Latch Registers. Setting this bit, loading the Divisor Registers, and clearing DLAB should be done with interrupts disabled. Bit 6 Set Break. When set to "1", the transmitter begins to transmit continuous Spacing until this bit is set to "0". This overrides any bits of characters that are being transmitted. Bit 5 Stick Parity. When parity is enabled, setting this bit causes parity to always be "1" or "0", based on the value of Bit 4. Bit 4 Even Parity Select (EPS). When parity is enabled and Bit 5 is "0", setting this bit causes even parity to be transmitted and expected. Otherwise, odd parity is used. Bit 3 Parity Enable (PEN). When set to "1", a parity bit is inserted between the last bit of the data and the Stop Bit. The UART will also expect parity to be present in the received data. Bit 2 Number of Stop Bits (STB). If set to "1" and using 5-bit data words, 1.5 Stop Bits are transmitted and expected in each data word. For 6, 7 and 8-bit data words, 2 Stop Bits are transmitted and expected. When this bit is set to "0", one Stop Bit is used on each data word. Bit 1 Word Length Select Bit #1 (WLSB1) Bit 0 Word Length Select Bit #0 (WLSB0) Together these bits specify the number of bits in each data word. 1 0 Word Length 0 0 5 Data Bits 0 1 6 Data Bits 1 0 7 Data Bits 1 1 8 Data Bits +0x04 write/read Modem Control Register (MCR) Bit 7 Reserved, always 0. Bit 6 Reserved, always 0. Bit 5 Reserved, always 0. Bit 4 Loop-Back Enable. When set to "1", the UART transmitter and receiver are internally connected together to allow diagnostic operations. In addition, the UART modem control outputs are connected to the UART modem control inputs. CTS is connected to RTS, DTR is connected to DSR, OUT1 is connected to RI, and OUT 2 is connected to DCD. Bit 3 OUT 2. An auxiliary output that the host processor may set high or low. In the IBM PC serial adapter (and most clones), OUT 2 is used to tri-state (disable) the interrupt signal from the 8250/16450/16550 UART. Bit 2 OUT 1. An auxiliary output that the host processor may set high or low. This output is not used on the IBM PC serial adapter. Bit 1 Request to Send (RTS). When set to "1", the output of the UART -RTS line is Low (Active). Bit 0 Data Terminal Ready (DTR). When set to "1", the output of the UART -DTR line is Low (Active). +0x05 write/read Line Status Register (LSR) Bit 7 Error in Receiver FIFO. On the 8250/16450 UART, this bit is zero. This bit is set to "1" when any of the bytes in the FIFO have one or more of the following error conditions: PE, FE, or BI. Bit 6 Transmitter Empty (TEMT). When set to "1", there are no words remaining in the transmit FIFO or the transmit shift register. The transmitter is completely idle. Bit 5 Transmitter Holding Register Empty (THRE). When set to "1", the FIFO (or holding register) now has room for at least one additional word to transmit. The transmitter may still be transmitting when this bit is set to "1". Bit 4 Break Interrupt (BI). The receiver has detected a Break signal. Bit 3 Framing Error (FE). A Start Bit was detected but the Stop Bit did not appear at the expected time. The received word is probably garbled. Bit 2 Parity Error (PE). The parity bit was incorrect for the word received. Bit 1 Overrun Error (OE). A new word was received and there was no room in the receive buffer. The newly-arrived word in the shift register is discarded. On 8250/16450 UARTs, the word in the holding register is discarded and the newly- arrived word is put in the holding register. Bit 0 Data Ready (DR) One or more words are in the receive FIFO that the host may read. A word must be completely received and moved from the shift register into the FIFO (or holding register for 8250/16450 designs) before this bit is set. +0x06 write/read Modem Status Register (MSR) Bit 7 Data Carrier Detect (DCD). Reflects the state of the DCD line on the UART. Bit 6 Ring Indicator (RI). Reflects the state of the RI line on the UART. Bit 5 Data Set Ready (DSR). Reflects the state of the DSR line on the UART. Bit 4 Clear To Send (CTS). Reflects the state of the CTS line on the UART. Bit 3 Delta Data Carrier Detect (DDCD). Set to "1" if the -DCD line has changed state one more more times since the last time the MSR was read by the host. Bit 2 Trailing Edge Ring Indicator (TERI). Set to "1" if the -RI line has had a low to high transition since the last time the MSR was read by the host. Bit 1 Delta Data Set Ready (DDSR). Set to "1" if the -DSR line has changed state one more more times since the last time the MSR was read by the host. Bit 0 Delta Clear To Send (DCTS). Set to "1" if the -CTS line has changed state one more more times since the last time the MSR was read by the host. +0x07 write/read Scratch Register (SCR). This register performs no function in the UART. Any value can be written by the host to this location and read by the host later on. Beyond the 16550A UART Although National Semiconductor has not offered any components compatible with the 16550 that provide additional features, various other vendors have. Some of these components are described below. It should be understood that to effectively utilize these improvements, drivers may have to be provided by the chip vendor since most of the popular operating systems do not support features beyond those provided by the 16550. ST16650 By default this part is similar to the NS16550A, but an extended 32-byte send and receive buffer can be optionally enabled. Made by Startech. TIL16660 By default this part behaves similar to the NS16550A, but an extended 64-byte send and receive buffer can be optionally enabled. Made by Texas Instruments. Hayes ESP This proprietary plug-in card contains a 2048-byte send and receive buffer, and supports data rates to 230.4Kbit/sec. Made by Hayes. In addition to these “dumb” UARTs, many vendors produce intelligent serial communication boards. This type of design usually provides a microprocessor that interfaces with several UARTs, processes and buffers the data, and then alerts the main PC processor when necessary. Because the UARTs are not directly accessed by the PC processor in this type of communication system, it is not necessary for the vendor to use UARTs that are compatible with the 8250, 16450, or the 16550 UART. This leaves the designer free to components that may have better performance characteristics. Configuring the <devicename>sio</devicename> driver The sio driver provides support for NS8250-, NS16450-, NS16550 and NS16550A-based EIA RS-232C (CCITT V.24) communications interfaces. Several multiport cards are supported as well. See the &man.sio.4; manual page for detailed technical documentation. Digi International (DigiBoard) PC/8 Contributed by &a.awebster;. 26 August 1995. Here is a config snippet from a machine with a Digi International PC/8 with 16550. It has 8 modems connected to these 8 lines, and they work just great. Do not forget to add options COM_MULTIPORT or it will not work very well! device sio4 at isa? port 0x100 tty flags 0xb05 device sio5 at isa? port 0x108 tty flags 0xb05 device sio6 at isa? port 0x110 tty flags 0xb05 device sio7 at isa? port 0x118 tty flags 0xb05 device sio8 at isa? port 0x120 tty flags 0xb05 device sio9 at isa? port 0x128 tty flags 0xb05 device sio10 at isa? port 0x130 tty flags 0xb05 device sio11 at isa? port 0x138 tty flags 0xb05 irq 9 vector siointr The trick in setting this up is that the MSB of the flags represent the last SIO port, in this case 11 so flags are 0xb05. Boca 16 Contributed by &a.whiteside;. 26 August 1995. The procedures to make a Boca 16 port board with FreeBSD are pretty straightforward, but you will need a couple things to make it work: You either need the kernel sources installed so you can recompile the necessary options or you will need someone else to compile it for you. The 2.0.5 default kernel does not come with multiport support enabled and you will need to add a device entry for each port anyways. Two, you will need to know the interrupt and IO setting for your Boca Board so you can set these options properly in the kernel. One important note — the actual UART chips for the Boca 16 are in the connector box, not on the internal board itself. So if you have it unplugged, probes of those ports will fail. I have never tested booting with the box unplugged and plugging it back in, and I suggest you do not either. If you do not already have a custom kernel configuration file set up, refer to Kernel Configuration for general procedures. The following are the specifics for the Boca 16 board and assume you are using the kernel name MYKERNEL and editing with vi. Add the line options COM_MULTIPORT to the config file. Where the current device sion lines are, you will need to add 16 more devices. Only the last device includes the interrupt vector for the board. (See the &man.sio.4; manual page for detail as to why.) The following example is for a Boca Board with an interrupt of 3, and a base IO address 100h. The IO address for Each port is +8 hexadecimal from the previous port, thus the 100h, 108h, 110h... addresses. device sio1 at isa? port 0x100 tty flags 0x1005 device sio2 at isa? port 0x108 tty flags 0x1005 device sio3 at isa? port 0x110 tty flags 0x1005 device sio4 at isa? port 0x118 tty flags 0x1005 … device sio15 at isa? port 0x170 tty flags 0x1005 device sio16 at isa? port 0x178 tty flags 0x1005 irq 3 vector siointr The flags entry must be changed from this example unless you are using the exact same sio assignments. Flags are set according to 0xMYY where M indicates the minor number of the master port (the last port on a Boca 16) and YY indicates if FIFO is enabled or disabled(enabled), IRQ sharing is used(yes) and if there is an AST/4 compatible IRQ control register(no). In this example, flags 0x1005 indicates that the master port is sio16. If I added another board and assigned sio17 through sio28, the flags for all 16 ports on that board would be 0x1C05, where 1C indicates the minor number of the master port. Do not change the 05 setting. Save and complete the kernel configuration, recompile, install and reboot. Presuming you have successfully installed the recompiled kernel and have it set to the correct address and IRQ, your boot message should indicate the successful probe of the Boca ports as follows: (obviously the sio numbers, IO and IRQ could be different) sio1 at 0x100-0x107 flags 0x1005 on isa sio1: type 16550A (multiport) sio2 at 0x108-0x10f flags 0x1005 on isa sio2: type 16550A (multiport) sio3 at 0x110-0x117 flags 0x1005 on isa sio3: type 16550A (multiport) sio4 at 0x118-0x11f flags 0x1005 on isa sio4: type 16550A (multiport) sio5 at 0x120-0x127 flags 0x1005 on isa sio5: type 16550A (multiport) sio6 at 0x128-0x12f flags 0x1005 on isa sio6: type 16550A (multiport) sio7 at 0x130-0x137 flags 0x1005 on isa sio7: type 16550A (multiport) sio8 at 0x138-0x13f flags 0x1005 on isa sio8: type 16550A (multiport) sio9 at 0x140-0x147 flags 0x1005 on isa sio9: type 16550A (multiport) sio10 at 0x148-0x14f flags 0x1005 on isa sio10: type 16550A (multiport) sio11 at 0x150-0x157 flags 0x1005 on isa sio11: type 16550A (multiport) sio12 at 0x158-0x15f flags 0x1005 on isa sio12: type 16550A (multiport) sio13 at 0x160-0x167 flags 0x1005 on isa sio13: type 16550A (multiport) sio14 at 0x168-0x16f flags 0x1005 on isa sio14: type 16550A (multiport) sio15 at 0x170-0x177 flags 0x1005 on isa sio15: type 16550A (multiport) sio16 at 0x178-0x17f irq 3 flags 0x1005 on isa sio16: type 16550A (multiport master) If the messages go by too fast to see, &prompt.root; dmesg | more will show you the boot messages. Next, appropriate entries in /dev for the devices must be made using the /dev/MAKEDEV script. After becoming root: &prompt.root; cd /dev &prompt.root; ./MAKEDEV tty1 &prompt.root; ./MAKEDEV cua1 (everything in between) &prompt.root; ./MAKEDEV ttyg &prompt.root; ./MAKEDEV cuag If you do not want or need callout devices for some reason, you can dispense with making the cua* devices. If you want a quick and sloppy way to make sure the devices are working, you can simply plug a modem into each port and (as root) &prompt.root; echo at > ttyd* for each device you have made. You should see the RX lights flash for each working port. Configuring the <devicename>cy</devicename> driver Contributed by &a.alex;. 6 June 1996. The Cyclades multiport cards are based on the cy driver instead of the usual sio driver used by other multiport cards. Configuration is a simple matter of: Add the cy device to your kernel configuration (note that your irq and iomem settings may differ). device cy0 at isa? tty irq 10 iomem 0xd4000 iosiz 0x2000 vector cyintr Rebuild and install the new kernel. Make the device nodes by typing (the following example assumes an 8-port board): &prompt.root; cd /dev &prompt.root; for i in 0 1 2 3 4 5 6 7;do ./MAKEDEV cuac$i ttyc$i;done If appropriate, add dialup entries to /etc/ttys by duplicating serial device (ttyd) entries and using ttyc in place of ttyd. For example: ttyc0 "/usr/libexec/getty std.38400" unknown on insecure ttyc1 "/usr/libexec/getty std.38400" unknown on insecure ttyc2 "/usr/libexec/getty std.38400" unknown on insecure … ttyc7 "/usr/libexec/getty std.38400" unknown on insecure Reboot with the new kernel. - Configuring the <devicename>si</devicename> driver - - Contributed by &a.nsayer;. 25 March 1998. - - The Specialix SI/XIO and SX multiport cards use the si driver. A single - machine can have up to 4 host cards. The following host cards are supported: - - ISA SI/XIO host card (2 versions) - EISA SI/XIO host card - PCI SI/XIO host card - ISA SX host card - PCI SX host card -Although the SX and SI/XIO host cards look markedly different, their - functionality are basically the same. The host cards do not use I/O - locations, but instead require a 32K chunk of memory. The factory - configuration for ISA cards places this at 0xd0000-0xd7fff. They - also require an IRQ. PCI cards will, of course, autoconfigure themselves. - - You can attach up to 4 external modules to each host card. The external - modules contain either 4 or 8 serial ports. They come in the following - varieties: - -SI 4 or 8 port modules. Up to 57600 bps on each port supported. - XIO 8 port modules. Up to 115200 bps on each port supported. One - type of XIO module has 7 serial and 1 parallel port. - SXDC 8 port modules. Up to 921600 bps on each port supported. Like - XIO, a module is available with one parallel port as well. - + + Configuring the <devicename>si</devicename> driver + + Contributed by &a.nsayer;. 25 March + 1998. + + The Specialix SI/XIO and SX multiport cards use the si driver. A + single machine can have up to 4 host cards. The following host cards + are supported: + + + ISA SI/XIO host card (2 versions) + EISA SI/XIO host card + PCI SI/XIO host card + ISA SX host card + PCI SX host card + + Although the SX and SI/XIO host cards look markedly different, + their functionality are basically the same. The host cards do not + use I/O locations, but instead require a 32K chunk of memory. The + factory configuration for ISA cards places this at 0xd0000-0xd7fff. + They also require an IRQ. PCI cards will, of course, autoconfigure + themselves. + You can attach up to 4 external modules to each host card. The + external modules contain either 4 or 8 serial ports. They come in + the following varieties: + + + SI 4 or 8 port modules. Up to 57600 bps on each port + supported. + + XIO 8 port modules. Up to 115200 bps on each port + supported. One type of XIO module has 7 serial and 1 parallel + port. + + SXDC 8 port modules. Up to 921600 bps on each port + supported. Like XIO, a module is available with one parallel + port as well. + -To configure an ISA host card, add the following line to your - kernel configuration file, changing - the numbers as appropriate: + To configure an ISA host card, add the following line to your + kernel configuration + file, changing the numbers as appropriate: - - device si0 at isa? tty iomem 0xd0000 irq 11 - - - Valid IRQ numbers are 9, 10, 11, 12 and 15 for SX ISA host cards and - 11, 12 and 15 for SI/XIO ISA host cards. + +device si0 at isa? tty iomem 0xd0000 irq 11 + + Valid IRQ numbers are 9, 10, 11, 12 and 15 for SX ISA host cards + and 11, 12 and 15 for SI/XIO ISA host cards. - To configure an EISA or PCI host card, use this line: + To configure an EISA or PCI host card, use this line: - - device si0 - + +device si0 -After adding the configuration entry, - rebuild and install - your new kernel. - -After rebooting with the new kernel, you need to make the - device nodes - in /dev. The MAKEDEV script will take care of this for you. Count how many - total ports you have and type: + After adding the configuration entry, rebuild and install your + new kernel. - &prompt.root; cd /dev -&prompt.root; ./MAKEDEV ttyAnn cuaAnn + After rebooting with the new kernel, you need to make the device nodes in /dev. The + MAKEDEV script will take care of this for you. + Count how many total ports you have and type: - (where nn is the number of ports) + &prompt.root; cd /dev +&prompt.root; ./MAKEDEV ttyAnn cuaAnn -If you want login prompts to appear on these ports, you will need - to add lines like this to /etc/ttys: + (where nn is the number of + ports) - - ttyA01 "/usr/libexec/getty std.9600" vt100 on insecure - - -Change the terminal type as approprate. For modems, dialup or - unknown is fine. + If you want login prompts to appear on these ports, you will + need to add lines like this to /etc/ttys: + + +ttyA01 "/usr/libexec/getty std.9600" vt100 on insecure + - - - - + Change the terminal type as approprate. For modems, + dialup or unknown is + fine. * Parallel ports * Modems * Network cards * Keyboards * Mice * Other Storage Devices Using ESDI hard disks Copyright © 1995, &a.wilko;. 24 September 1995. ESDI is an acronym that means Enhanced Small Device Interface. It is loosely based on the good old ST506/412 interface originally devised by Seagate Technology, the makers of the first affordable 5.25" winchester disk. The acronym says Enhanced, and rightly so. In the first place the speed of the interface is higher, 10 or 15 Mbits/second instead of the 5 Mbits/second of ST412 interfaced drives. Secondly some higher level commands are added, making the ESDI interface somewhat 'smarter' to the operating system driver writers. It is by no means as smart as SCSI by the way. ESDI is standardized by ANSI. Capacities of the drives are boosted by putting more sectors on each track. Typical is 35 sectors per track, high capacity drives I have seen were up to 54 sectors/track. Although ESDI has been largely obsoleted by IDE and SCSI interfaces, the availability of free or cheap surplus drives makes them ideal for low (or now) budget systems. Concepts of ESDI Physical connections The ESDI interface uses two cables connected to each drive. One cable is a 34 pin flat cable edge connector that carries the command and status signals from the controller to the drive and vice-versa. The command cable is daisy chained between all the drives. So, it forms a bus onto which all drives are connected. The second cable is a 20 pin flat cable edge connector that carries the data to and from the drive. This cable is radially connected, so each drive has its own direct connection to the controller. To the best of my knowledge PC ESDI controllers are limited to using a maximum of 2 drives per controller. This is compatibility feature(?) left over from the WD1003 standard that reserves only a single bit for device addressing. Device addressing On each command cable a maximum of 7 devices and 1 controller can be present. To enable the controller to uniquely identify which drive it addresses, each ESDI device is equipped with jumpers or switches to select the devices address. On PC type controllers the first drive is set to address 0, the second disk to address 1. Always make sure you set each disk to an unique address! So, on a PC with its two drives/controller maximum the first drive is drive 0, the second is drive 1. Termination The daisy chained command cable (the 34 pin cable remember?) needs to be terminated at the last drive on the chain. For this purpose ESDI drives come with a termination resistor network that can be removed or disabled by a jumper when it is not used. So, one and only one drive, the one at the farthest end of the command cable has its terminator installed/enabled. The controller automatically terminates the other end of the cable. Please note that this implies that the controller must be at one end of the cable and not in the middle. Using ESDI disks with FreeBSD Why is ESDI such a pain to get working in the first place? People who tried ESDI disks with FreeBSD are known to have developed a profound sense of frustration. A combination of factors works against you to produce effects that are hard to understand when you have never seen them before. This has also led to the popular legend ESDI and FreeBSD is a plain NO-GO. The following sections try to list all the pitfalls and solutions. ESDI speed variants As briefly mentioned before, ESDI comes in two speed flavors. The older drives and controllers use a 10 Mbits/second data transfer rate. Newer stuff uses 15 Mbits/second. It is not hard to imagine that 15 Mbits/second drive cause problems on controllers laid out for 10 Mbits/second. As always, consult your controller and drive documentation to see if things match. Stay on track Mainstream ESDI drives use 34 to 36 sectors per track. Most (older) controllers cannot handle more than this number of sectors. Newer, higher capacity, drives use higher numbers of sectors per track. For instance, I own a 670 Mb drive that has 54 sectors per track. In my case, the controller could not handle this number of sectors. It proved to work well except that it only used 35 sectors on each track. This meant losing a lot of disk space. Once again, check the documentation of your hardware for more info. Going out-of-spec like in the example might or might not work. Give it a try or get another more capable controller. Hard or soft sectoring Most ESDI drives allow hard or soft sectoring to be selected using a jumper. Hard sectoring means that the drive will produce a sector pulse on the start of each new sector. The controller uses this pulse to tell when it should start to write or read. Hard sectoring allows a selection of sector size (normally 256, 512 or 1024 bytes per formatted sector). FreeBSD uses 512 byte sectors. The number of sectors per track also varies while still using the same number of bytes per formatted sector. The number of unformatted bytes per sector varies, dependent on your controller it needs more or less overhead bytes to work correctly. Pushing more sectors on a track of course gives you more usable space, but might give problems if your controller needs more bytes than the drive offers. In case of soft sectoring, the controller itself determines where to start/stop reading or writing. For ESDI hard sectoring is the default (at least on everything I came across). I never felt the urge to try soft sectoring. In general, experiment with sector settings before you install FreeBSD because you need to re-run the low-level format after each change. Low level formatting ESDI drives need to be low level formatted before they are usable. A reformat is needed whenever you figgle with the number of sectors/track jumpers or the physical orientation of the drive (horizontal, vertical). So, first think, then format. The format time must not be underestimated, for big disks it can take hours. After a low level format, a surface scan is done to find and flag bad sectors. Most disks have a manufacturer bad block list listed on a piece of paper or adhesive sticker. In addition, on most disks the list is also written onto the disk. Please use the manufacturer's list. It is much easier to remap a defect now than after FreeBSD is installed. Stay away from low-level formatters that mark all sectors of a track as bad as soon as they find one bad sector. Not only does this waste space, it also and more importantly causes you grief with bad144 (see the section on bad144). Translations Translations, although not exclusively a ESDI-only problem, might give you real trouble. Translations come in multiple flavors. Most of them have in common that they attempt to work around the limitations posed upon disk geometries by the original IBM PC/AT design (thanks IBM!). First of all there is the (in)famous 1024 cylinder limit. For a system to be able to boot, the stuff (whatever operating system) must be in the first 1024 cylinders of a disk. Only 10 bits are available to encode the cylinder number. For the number of sectors the limit is 64 (0-63). When you combine the 1024 cylinder limit with the 16 head limit (also a design feature) you max out at fairly limited disk sizes. To work around this problem, the manufacturers of ESDI PC controllers added a BIOS prom extension on their boards. This BIOS extension handles disk I/O for booting (and for some operating systems all disk I/O) by using translation. For instance, a big drive might be presented to the system as having 32 heads and 64 sectors/track. The result is that the number of cylinders is reduced to something below 1024 and is therefore usable by the system without problems. It is noteworthy to know that FreeBSD does not use the BIOS after its kernel has started. More on this later. A second reason for translations is the fact that most older system BIOSes could only handle drives with 17 sectors per track (the old ST412 standard). Newer system BIOSes usually have a user-defined drive type (in most cases this is drive type 47). Whatever you do to translations after reading this document, keep in mind that if you have multiple operating systems on the same disk, all must use the same translation While on the subject of translations, I have seen one controller type (but there are probably more like this) offer the option to logically split a drive in multiple partitions as a BIOS option. I had select 1 drive == 1 partition because this controller wrote this info onto the disk. On power-up it read the info and presented itself to the system based on the info from the disk. Spare sectoring Most ESDI controllers offer the possibility to remap bad sectors. During/after the low-level format of the disk bad sectors are marked as such, and a replacement sector is put in place (logically of course) of the bad one. In most cases the remapping is done by using N-1 sectors on each track for actual data storage, and sector N itself is the spare sector. N is the total number of sectors physically available on the track. The idea behind this is that the operating system sees a 'perfect' disk without bad sectors. In the case of FreeBSD this concept is not usable. The problem is that the translation from bad to good is performed by the BIOS of the ESDI controller. FreeBSD, being a true 32 bit operating system, does not use the BIOS after it has been booted. Instead, it has device drivers that talk directly to the hardware. So: don't use spare sectoring, bad block remapping or whatever it may be called by the controller manufacturer when you want to use the disk for FreeBSD. Bad block handling The preceding section leaves us with a problem. The controller's bad block handling is not usable and still FreeBSD's filesystems assume perfect media without any flaws. To solve this problem, FreeBSD use the bad144 tool. Bad144 (named after a Digital Equipment standard for bad block handling) scans a FreeBSD slice for bad blocks. Having found these bad blocks, it writes a table with the offending block numbers to the end of the FreeBSD slice. When the disk is in operation, the disk accesses are checked against the table read from the disk. Whenever a block number is requested that is in the bad144 list, a replacement block (also from the end of the FreeBSD slice) is used. In this way, the bad144 replacement scheme presents 'perfect' media to the FreeBSD filesystems. There are a number of potential pitfalls associated with the use of bad144. First of all, the slice cannot have more than 126 bad sectors. If your drive has a high number of bad sectors, you might need to divide it into multiple FreeBSD slices each containing less than 126 bad sectors. Stay away from low-level format programs that mark every sector of a track as bad when they find a flaw on the track. As you can imagine, the 126 limit is quickly reached when the low-level format is done this way. Second, if the slice contains the root filesystem, the slice should be within the 1024 cylinder BIOS limit. During the boot process the bad144 list is read using the BIOS and this only succeeds when the list is within the 1024 cylinder limit. The restriction is not that only the root filesystem must be within the 1024 cylinder limit, but rather the entire slice that contains the root filesystem. Kernel configuration ESDI disks are handled by the same wddriver as IDE and ST412 MFM disks. The wd driver should work for all WD1003 compatible interfaces. Most hardware is jumperable for one of two different I/O address ranges and IRQ lines. This allows you to have two wd type controllers in one system. When your hardware allows non-standard strappings, you can use these with FreeBSD as long as you enter the correct info into the kernel config file. An example from the kernel config file (they live in /sys/i386/conf BTW). # First WD compatible controller controller wdc0 at isa? port "IO_WD1" bio irq 14 vector wdintr disk wd0 at wdc0 drive 0 disk wd1 at wdc0 drive 1 # Second WD compatible controller controller wdc1 at isa? port "IO_WD2" bio irq 15 vector wdintr disk wd2 at wdc1 drive 0 disk wd3 at wdc1 drive 1 Particulars on ESDI hardware Adaptec 2320 controllers I successfully installed FreeBSD onto a ESDI disk controlled by a ACB-2320. No other operating system was present on the disk. To do so I low level formatted the disk using NEFMT.EXE (ftpable from www.adaptec.com) and answered NO to the question whether the disk should be formatted with a spare sector on each track. The BIOS on the ACD-2320 was disabled. I used the free configurable option in the system BIOS to allow the BIOS to boot it. Before using NEFMT.EXE I tried to format the disk using the ACB-2320 BIOS builtin formatter. This proved to be a show stopper, because it did not give me an option to disable spare sectoring. With spare sectoring enabled the FreeBSD installation process broke down on the bad144 run. Please check carefully which ACB-232xy variant you have. The x is either 0 or 2, indicating a controller without or with a floppy controller on board. The y is more interesting. It can either be a blank, a A-8 or a D. A blank indicates a plain 10 Mbits/second controller. An A-8 indicates a 15 Mbits/second controller capable of handling 52 sectors/track. A D means a 15 Mbits/second controller that can also handle drives with > 36 sectors/track (also 52 ?). All variations should be capable of using 1:1 interleaving. Use 1:1, FreeBSD is fast enough to handle it. Western Digital WD1007 controllers I successfully installed FreeBSD onto a ESDI disk controlled by a WD1007 controller. To be precise, it was a WD1007-WA2. Other variations of the WD1007 do exist. To get it to work, I had to disable the sector translation and the WD1007's onboard BIOS. This implied I could not use the low-level formatter built into this BIOS. Instead, I grabbed WDFMT.EXE from www.wdc.com Running this formatted my drive just fine. Ultrastor U14F controllers According to multiple reports from the net, Ultrastor ESDI boards work OK with FreeBSD. I lack any further info on particular settings. Further reading If you intend to do some serious ESDI hacking, you might want to have the official standard at hand: The latest ANSI X3T10 committee document is: Enhanced Small Device Interface (ESDI) [X3.170-1990/X3.170a-1991] [X3T10/792D Rev 11] On Usenet the newsgroup comp.periphs is a noteworthy place to look for more info. The World Wide Web (WWW) also proves to be a very handy info source: For info on Adaptec ESDI controllers see http://www.adaptec.com/. For info on Western Digital controllers see http://www.wdc.com/. Thanks to... Andrew Gordon for sending me an Adaptec 2320 controller and ESDI disk for testing. What is SCSI? Copyright © 1995, &a.wilko;. July 6, 1996. SCSI is an acronym for Small Computer Systems Interface. It is an ANSI standard that has become one of the leading I/O buses in the computer industry. The foundation of the SCSI standard was laid by Shugart Associates (the same guys that gave the world the first mini floppy disks) when they introduced the SASI bus (Shugart Associates Standard Interface). After some time an industry effort was started to come to a more strict standard allowing devices from different vendors to work together. This effort was recognized in the ANSI SCSI-1 standard. The SCSI-1 standard (approx 1985) is rapidly becoming obsolete. The current standard is SCSI-2 (see Further reading), with SCSI-3 on the drawing boards. In addition to a physical interconnection standard, SCSI defines a logical (command set) standard to which disk devices must adhere. This standard is called the Common Command Set (CCS) and was developed more or less in parallel with ANSI SCSI-1. SCSI-2 includes the (revised) CCS as part of the standard itself. The commands are dependent on the type of device at hand. It does not make much sense of course to define a Write command for a scanner. The SCSI bus is a parallel bus, which comes in a number of variants. The oldest and most used is an 8 bit wide bus, with single-ended signals, carried on 50 wires. (If you do not know what single-ended means, do not worry, that is what this document is all about.) Modern designs also use 16 bit wide buses, with differential signals. This allows transfer speeds of 20Mbytes/second, on cables lengths of up to 25 meters. SCSI-2 allows a maximum bus width of 32 bits, using an additional cable. Quickly emerging are Ultra SCSI (also called Fast-20) and Ultra2 (also called Fast-40). Fast-20 is 20 million transfers per second (20 Mbytes/sec on a 8 bit bus), Fast-40 is 40 million transfers per second (40 Mbytes/sec on a 8 bit bus). Most hard drives sold today are single-ended Ultra SCSI (8 or 16 bits). Of course the SCSI bus not only has data lines, but also a number of control signals. A very elaborate protocol is part of the standard to allow multiple devices to share the bus in an efficient manner. In SCSI-2, the data is always checked using a separate parity line. In pre-SCSI-2 designs parity was optional. In SCSI-3 even faster bus types are introduced, along with a serial SCSI busses that reduces the cabling overhead and allows a higher maximum bus length. You might see names like SSA and Fiberchannel in this context. None of the serial buses are currently in widespread use (especially not in the typical FreeBSD environment). For this reason the serial bus types are not discussed any further. As you could have guessed from the description above, SCSI devices are intelligent. They have to be to adhere to the SCSI standard (which is over 2 inches thick BTW). So, for a hard disk drive for instance you do not specify a head/cylinder/sector to address a particular block, but simply the number of the block you want. Elaborate caching schemes, automatic bad block replacement etc are all made possible by this 'intelligent device' approach. On a SCSI bus, each possible pair of devices can communicate. Whether their function allows this is another matter, but the standard does not restrict it. To avoid signal contention, the 2 devices have to arbitrate for the bus before using it. The philosophy of SCSI is to have a standard that allows older-standard devices to work with newer-standard ones. So, an old SCSI-1 device should normally work on a SCSI-2 bus. I say Normally, because it is not absolutely sure that the implementation of an old device follows the (old) standard closely enough to be acceptable on a new bus. Modern devices are usually more well-behaved, because the standardization has become more strict and is better adhered to by the device manufacturers. Generally speaking, the chances of getting a working set of devices on a single bus is better when all the devices are SCSI-2 or newer. This implies that you do not have to dump all your old stuff when you get that shiny 2GB disk: I own a system on which a pre-SCSI-1 disk, a SCSI-2 QIC tape unit, a SCSI-1 helical scan tape unit and 2 SCSI-1 disks work together quite happily. From a performance standpoint you might want to separate your older and newer (=faster) devices however. Components of SCSI As said before, SCSI devices are smart. The idea is to put the knowledge about intimate hardware details onto the SCSI device itself. In this way, the host system does not have to worry about things like how many heads are hard disks has, or how many tracks there are on a specific tape device. If you are curious, the standard specifies commands with which you can query your devices on their hardware particulars. FreeBSD uses this capability during boot to check out what devices are connected and whether they need any special treatment. The advantage of intelligent devices is obvious: the device drivers on the host can be made in a much more generic fashion, there is no longer a need to change (and qualify!) drivers for every odd new device that is introduced. For cabling and connectors there is a golden rule: get good stuff. With bus speeds going up all the time you will save yourself a lot of grief by using good material. So, gold plated connectors, shielded cabling, sturdy connector hoods with strain reliefs etc are the way to go. Second golden rule: do no use cables longer than necessary. I once spent 3 days hunting down a problem with a flaky machine only to discover that shortening the SCSI bus by 1 meter solved the problem. And the original bus length was well within the SCSI specification. SCSI bus types From an electrical point of view, there are two incompatible bus types: single-ended and differential. This means that there are two different main groups of SCSI devices and controllers, which cannot be mixed on the same bus. It is possible however to use special converter hardware to transform a single-ended bus into a differential one (and vice versa). The differences between the bus types are explained in the next sections. In lots of SCSI related documentation there is a sort of jargon in use to abbreviate the different bus types. A small list: FWD: Fast Wide Differential FND: Fast Narrow Differential SE: Single Ended FN: Fast Narrow etc. With a minor amount of imagination one can usually imagine what is meant. Wide is a bit ambiguous, it can indicate 16 or 32 bit buses. As far as I know, the 32 bit variant is not (yet) in use, so wide normally means 16 bit. Fast means that the timing on the bus is somewhat different, so that on a narrow (8 bit) bus 10 Mbytes/sec are possible instead of 5 Mbytes/sec for 'slow' SCSI. As discussed before, bus speeds of 20 and 40 million transfers/second are also emerging (Fast-20 == Ultra SCSI and Fast-40 == Ultra2 SCSI). The data lines > 8 are only used for data transfers and device addressing. The transfers of commands and status messages etc are only performed on the lowest 8 data lines. The standard allows narrow devices to operate on a wide bus. The usable bus width is negotiated between the devices. You have to watch your device addressing closely when mixing wide and narrow. Single ended buses A single-ended SCSI bus uses signals that are either 5 Volts or 0 Volts (indeed, TTL levels) and are relative to a COMMON ground reference. A singled ended 8 bit SCSI bus has approximately 25 ground lines, who are all tied to a single `rail' on all devices. A standard single ended bus has a maximum length of 6 meters. If the same bus is used with fast-SCSI devices, the maximum length allowed drops to 3 meters. Fast-SCSI means that instead of 5Mbytes/sec the bus allows 10Mbytes/sec transfers. Fast-20 (Ultra SCSI) and Fast-40 allow for 20 and 40 million transfers/second respectively. So, F20 is 20 Mbytes/second on a 8 bit bus, 40 Mbytes/second on a 16 bit bus etc. For F20 the max bus length is 1.5 meters, for F40 it becomes 0.75 meters. Be aware that F20 is pushing the limits quite a bit, so you will quickly find out if your SCSI bus is electrically sound. If some devices on your bus use 'fast' to communicate your bus must adhere to the length restrictions for fast buses! It is obvious that with the newer fast-SCSI devices the bus length can become a real bottleneck. This is why the differential SCSI bus was introduced in the SCSI-2 standard. For connector pinning and connector types please refer to the SCSI-2 standard (see Further reading) itself, connectors etc are listed there in painstaking detail. Beware of devices using non-standard cabling. For instance Apple uses a 25pin D-type connecter (like the one on serial ports and parallel printers). Considering that the official SCSI bus needs 50 pins you can imagine the use of this connector needs some 'creative cabling'. The reduction of the number of ground wires they used is a bad idea, you better stick to 50 pins cabling in accordance with the SCSI standard. For Fast-20 and 40 do not even think about buses like this. Differential buses A differential SCSI bus has a maximum length of 25 meters. Quite a difference from the 3 meters for a single-ended fast-SCSI bus. The idea behind differential signals is that each bus signal has its own return wire. So, each signal is carried on a (preferably twisted) pair of wires. The voltage difference between these two wires determines whether the signal is asserted or de-asserted. To a certain extent the voltage difference between ground and the signal wire pair is not relevant (do not try 10 kVolts though). It is beyond the scope of this document to explain why this differential idea is so much better. Just accept that electrically seen the use of differential signals gives a much better noise margin. You will normally find differential buses in use for inter-cabinet connections. Because of the lower cost single ended is mostly used for shorter buses like inside cabinets. There is nothing that stops you from using differential stuff with FreeBSD, as long as you use a controller that has device driver support in FreeBSD. As an example, Adaptec marketed the AHA1740 as a single ended board, whereas the AHA1744 was differential. The software interface to the host is identical for both. Terminators Terminators in SCSI terminology are resistor networks that are used to get a correct impedance matching. Impedance matching is important to get clean signals on the bus, without reflections or ringing. If you once made a long distance telephone call on a bad line you probably know what reflections are. With 20Mbytes/sec traveling over your SCSI bus, you do not want signals echoing back. Terminators come in various incarnations, with more or less sophisticated designs. Of course, there are internal and external variants. Many SCSI devices come with a number of sockets in which a number of resistor networks can (must be!) installed. If you remove terminators from a device, carefully store them. You will need them when you ever decide to reconfigure your SCSI bus. There is enough variation in even these simple tiny things to make finding the exact replacement a frustrating business. There are also SCSI devices that have a single jumper to enable or disable a built-in terminator. There are special terminators you can stick onto a flat cable bus. Others look like external connectors, or a connector hood without a cable. So, lots of choice as you can see. There is much debate going on if and when you should switch from simple resistor (passive) terminators to active terminators. Active terminators contain slightly more elaborate circuit to give cleaner bus signals. The general consensus seems to be that the usefulness of active termination increases when you have long buses and/or fast devices. If you ever have problems with your SCSI buses you might consider trying an active terminator. Try to borrow one first, they reputedly are quite expensive. Please keep in mind that terminators for differential and single-ended buses are not identical. You should not mix the two variants. OK, and now where should you install your terminators? This is by far the most misunderstood part of SCSI. And it is by far the simplest. The rule is: every single line on the SCSI bus has 2 (two) terminators, one at each end of the bus. So, two and not one or three or whatever. Do yourself a favor and stick to this rule. It will save you endless grief, because wrong termination has the potential to introduce highly mysterious bugs. (Note the “potential” here; the nastiest part is that it may or may not work.) A common pitfall is to have an internal (flat) cable in a machine and also an external cable attached to the controller. It seems almost everybody forgets to remove the terminators from the controller. The terminator must now be on the last external device, and not on the controller! In general, every reconfiguration of a SCSI bus must pay attention to this. Termination is to be done on a per-line basis. This means if you have both narrow and wide buses connected to the same host adapter, you need to enable termination on the higher 8 bits of the bus on the adapter (as well as the last devices on each bus, of course). What I did myself is remove all terminators from my SCSI devices and controllers. I own a couple of external terminators, for both the Centronics-type external cabling and for the internal flat cable connectors. This makes reconfiguration much easier. On modern devices, sometimes integrated terminators are used. These things are special purpose integrated circuits that can be dis/en-abled with a control pin. It is not necessary to physically remove them from a device. You may find them on newer host adapters, sometimes they are software configurable, using some sort of setup tool. Some will even auto-detect the cables attached to the connectors and automatically set up the termination as necessary. At any rate, consult your documentation! Terminator power The terminators discussed in the previous chapter need power to operate properly. On the SCSI bus, a line is dedicated to this purpose. So, simple huh? Not so. Each device can provide its own terminator power to the terminator sockets it has on-device. But if you have external terminators, or when the device supplying the terminator power to the SCSI bus line is switched off you are in trouble. The idea is that initiators (these are devices that initiate actions on the bus, a discussion follows) must supply terminator power. All SCSI devices are allowed (but not required) to supply terminator power. To allow for un-powered devices on a bus, the terminator power must be supplied to the bus via a diode. This prevents the backflow of current to un-powered devices. To prevent all kinds of nastiness, the terminator power is usually fused. As you can imagine, fuses might blow. This can, but does not have to, lead to a non functional bus. If multiple devices supply terminator power, a single blown fuse will not put you out of business. A single supplier with a blown fuse certainly will. Clever external terminators sometimes have a LED indication that shows whether terminator power is present. In newer designs auto-restoring fuses that 'reset' themselves after some time are sometimes used. Device addressing Because the SCSI bus is, ehh, a bus there must be a way to distinguish or address the different devices connected to it. This is done by means of the SCSI or target ID. Each device has a unique target ID. You can select the ID to which a device must respond using a set of jumpers, or a dip switch, or something similar. Some SCSI host adapters let you change the target ID from the boot menu. (Yet some others will not let you change the ID from 7.) Consult the documentation of your device for more information. Beware of multiple devices configured to use the same ID. Chaos normally reigns in this case. A pitfall is that one of the devices sharing the same ID sometimes even manages to answer to I/O requests! For an 8 bit bus, a maximum of 8 targets is possible. The maximum is 8 because the selection is done bitwise using the 8 data lines on the bus. For wide buses this increases to the number of data lines (usually 16). A narrow SCSI device can not communicate with a SCSI device with a target ID larger than 7. This means it is generally not a good idea to move your SCSI host adapter's target ID to something higher than 7 (or your CD-ROM will stop working). The higher the SCSI target ID, the higher the priority the devices has. When it comes to arbitration between devices that want to use the bus at the same time, the device that has the highest SCSI ID will win. This also means that the SCSI host adapter usually uses target ID 7. Note however that the lower 8 IDs have higher priorities than the higher 8 IDs on a wide-SCSI bus. Thus, the order of target IDs is: [7 6 .. 1 0 15 14 .. 9 8] on a wide-SCSI system. (If you you are wondering why the lower 8 have higher priority, read the previous paragraph for a hint.) For a further subdivision, the standard allows for Logical Units or LUNs for short. A single target ID may have multiple LUNs. For example, a tape device including a tape changer may have LUN 0 for the tape device itself, and LUN 1 for the tape changer. In this way, the host system can address each of the functional units of the tape changer as desired. Bus layout SCSI buses are linear. So, not shaped like Y-junctions, star topologies, rings, cobwebs or whatever else people might want to invent. One of the most common mistakes is for people with wide-SCSI host adapters to connect devices on all three connecters (external connector, internal wide connector, internal narrow connector). Don't do that. It may appear to work if you are really lucky, but I can almost guarantee that your system will stop functioning at the most unfortunate moment (this is also known as “Murphy's law”). You might notice that the terminator issue discussed earlier becomes rather hairy if your bus is not linear. Also, if you have more connectors than devices on your internal SCSI cable, make sure you attach devices on connectors on both ends instead of using the connectors in the middle and let one or both ends dangle. This will screw up the termination of the bus. The electrical characteristics, its noise margins and ultimately the reliability of it all are tightly related to linear bus rule. Stick to the linear bus rule! Using SCSI with FreeBSD About translations, BIOSes and magic... As stated before, you should first make sure that you have a electrically sound bus. When you want to use a SCSI disk on your PC as boot disk, you must aware of some quirks related to PC BIOSes. The PC BIOS in its first incarnation used a low level physical interface to the hard disk. So, you had to tell the BIOS (using a setup tool or a BIOS built-in setup) how your disk physically looked like. This involved stating number of heads, number of cylinders, number of sectors per track, obscure things like precompensation and reduced write current cylinder etc. One might be inclined to think that since SCSI disks are smart you can forget about this. Alas, the arcane setup issue is still present today. The system BIOS needs to know how to access your SCSI disk with the head/cyl/sector method in order to load the FreeBSD kernel during boot. The SCSI host adapter or SCSI controller you have put in your AT/EISA/PCI/whatever bus to connect your disk therefore has its own on-board BIOS. During system startup, the SCSI BIOS takes over the hard disk interface routines from the system BIOS. To fool the system BIOS, the system setup is normally set to No hard disk present. Obvious, isn't it? The SCSI BIOS itself presents to the system a so called translated drive. This means that a fake drive table is constructed that allows the PC to boot the drive. This translation is often (but not always) done using a pseudo drive with 64 heads and 32 sectors per track. By varying the number of cylinders, the SCSI BIOS adapts to the actual drive size. It is useful to note that 32 * 64 / 2 = the size of your drive in megabytes. The division by 2 is to get from disk blocks that are normally 512 bytes in size to Kbytes. Right. All is well now?! No, it is not. The system BIOS has another quirk you might run into. The number of cylinders of a bootable hard disk cannot be greater than 1024. Using the translation above, this is a show-stopper for disks greater than 1 GB. With disk capacities going up all the time this is causing problems. Fortunately, the solution is simple: just use another translation, e.g. with 128 heads instead of 32. In most cases new SCSI BIOS versions are available to upgrade older SCSI host adapters. Some newer adapters have an option, in the form of a jumper or software setup selection, to switch the translation the SCSI BIOS uses. It is very important that all operating systems on the disk use the same translation to get the right idea about where to find the relevant partitions. So, when installing FreeBSD you must answer any questions about heads/cylinders etc using the translated values your host adapter uses. Failing to observe the translation issue might lead to un-bootable systems or operating systems overwriting each others partitions. Using fdisk you should be able to see all partitions. You might have heard some talk of “lying” devices? Older FreeBSD kernels used to report the geometry of SCSI disks when booting. An example from one of my systems: aha0 targ 0 lun 0: <MICROP 1588-15MB1057404HSP4> sd0: 636MB (1303250 total sec), 1632 cyl, 15 head, 53 sec, bytes/sec 512 Newer kernels usually do not report this information. e.g. (bt0:0:0): "SEAGATE ST41651 7574" type 0 fixed SCSI 2 sd0(bt0:0:0): Direct-Access 1350MB (2766300 512 byte sectors) Why has this changed? This info is retrieved from the SCSI disk itself. Newer disks often use a technique called zone bit recording. The idea is that on the outer cylinders of the drive there is more space so more sectors per track can be put on them. This results in disks that have more tracks on outer cylinders than on the inner cylinders and, last but not least, have more capacity. You can imagine that the value reported by the drive when inquiring about the geometry now becomes suspect at best, and nearly always misleading. When asked for a geometry , it is nearly always better to supply the geometry used by the BIOS, or if the BIOS is never going to know about this disk, (e.g. it is not a booting disk) to supply a fictitious geometry that is convenient. SCSI subsystem design FreeBSD uses a layered SCSI subsystem. For each different controller card a device driver is written. This driver knows all the intimate details about the hardware it controls. The driver has a interface to the upper layers of the SCSI subsystem through which it receives its commands and reports back any status. On top of the card drivers there are a number of more generic drivers for a class of devices. More specific: a driver for tape devices (abbreviation: st), magnetic disks (sd), CD-ROMs (cd) etc. In case you are wondering where you can find this stuff, it all lives in /sys/scsi. See the man pages in section 4 for more details. The multi level design allows a decoupling of low-level bit banging and more high level stuff. Adding support for another piece of hardware is a much more manageable problem. Kernel configuration Dependent on your hardware, the kernel configuration file must contain one or more lines describing your host adapter(s). This includes I/O addresses, interrupts etc. Consult the man page for your adapter driver to get more info. Apart from that, check out /sys/i386/conf/LINT for an overview of a kernel config file. LINT contains every possible option you can dream of. It does not imply LINT will actually get you to a working kernel at all. Although it is probably stating the obvious: the kernel config file should reflect your actual hardware setup. So, interrupts, I/O addresses etc must match the kernel config file. During system boot messages will be displayed to indicate whether the configured hardware was actually found. Note that most of the EISA/PCI drivers (namely ahb, ahc, ncr and amd will automatically obtain the correct parameters from the host adapters themselves at boot time; thus, you just need to write, for instance, controller ahc0. An example loosely based on the FreeBSD 2.2.5-Release kernel config file LINT with some added comments (between []): # SCSI host adapters: `aha', `ahb', `aic', `bt', `nca' # # aha: Adaptec 154x # ahb: Adaptec 174x # ahc: Adaptec 274x/284x/294x # aic: Adaptec 152x and sound cards using the Adaptec AIC-6360 (slow!) # amd: AMD 53c974 based SCSI cards (e.g., Tekram DC-390 and 390T) # bt: Most Buslogic controllers # nca: ProAudioSpectrum cards using the NCR 5380 or Trantor T130 # ncr: NCR/Symbios 53c810/815/825/875 etc based SCSI cards # uha: UltraStore 14F and 34F # sea: Seagate ST01/02 8 bit controller (slow!) # wds: Western Digital WD7000 controller (no scatter/gather!). # [For an Adaptec AHA274x/284x/294x/394x etc controller] controller ahc0 [For an NCR/Symbios 53c875 based controller] controller ncr0 [For an Ultrastor adapter] controller uha0 at isa? port "IO_UHA0" bio irq ? drq 5 vector uhaintr # Map SCSI buses to specific SCSI adapters controller scbus0 at ahc0 controller scbus2 at ncr0 controller scbus1 at uha0 # The actual SCSI devices disk sd0 at scbus0 target 0 unit 0 [SCSI disk 0 is at scbus 0, LUN 0] disk sd1 at scbus0 target 1 [implicit LUN 0 if omitted] disk sd2 at scbus1 target 3 [SCSI disk on the uha0] disk sd3 at scbus2 target 4 [SCSI disk on the ncr0] tape st1 at scbus0 target 6 [SCSI tape at target 6] device cd0 at scbus? [the first ever CD-ROM found, no wiring] The example above tells the kernel to look for a ahc (Adaptec 274x) controller, then for an NCR/Symbios board, and so on. The lines following the controller specifications tell the kernel to configure specific devices but only attach them when they match the target ID and LUN specified on the corresponding bus. Wired down devices get “first shot” at the unit numbers so the first non “wired down” device, is allocated the unit number one greater than the highest “wired down” unit number for that kind of device. So, if you had a SCSI tape at target ID 2 it would be configured as st2, as the tape at target ID 6 is wired down to unit number 1. Wired down devices need not be found to get their unit number. The unit number for a wired down device is reserved for that device, even if it is turned off at boot time. This allows the device to be turned on and brought on-line at a later time, without rebooting. Notice that a device's unit number has no relationship with its target ID on the SCSI bus. Below is another example of a kernel config file as used by FreeBSD version < 2.0.5. The difference with the first example is that devices are not “wired down”. “Wired down” means that you specify which SCSI target belongs to which device. A kernel built to the config file below will attach the first SCSI disk it finds to sd0, the second disk to sd1 etc. If you ever removed or added a disk, all other devices of the same type (disk in this case) would 'move around'. This implies you have to change /etc/fstab each time. Although the old style still works, you are strongly recommended to use this new feature. It will save you a lot of grief whenever you shift your hardware around on the SCSI buses. So, when you re-use your old trusty config file after upgrading from a pre-FreeBSD2.0.5.R system check this out. [driver for Adaptec 174x] controller ahb0 at isa? bio irq 11 vector ahbintr [for Adaptec 154x] controller aha0 at isa? port "IO_AHA0" bio irq 11 drq 5 vector ahaintr [for Seagate ST01/02] controller sea0 at isa? bio irq 5 iomem 0xc8000 iosiz 0x2000 vector seaintr controller scbus0 device sd0 [support for 4 SCSI harddisks, sd0 up sd3] device st0 [support for 2 SCSI tapes] [for the CD-ROM] device cd0 #Only need one of these, the code dynamically grows Both examples support SCSI disks. If during boot more devices of a specific type (e.g. sd disks) are found than are configured in the booting kernel, the system will simply allocate more devices, incrementing the unit number starting at the last number “wired down”. If there are no “wired down” devices then counting starts at unit 0. Use man 4 scsi to check for the latest info on the SCSI subsystem. For more detailed info on host adapter drivers use eg man 4 ahc for info on the Adaptec 294x driver. Tuning your SCSI kernel setup Experience has shown that some devices are slow to respond to INQUIRY commands after a SCSI bus reset (which happens at boot time). An INQUIRY command is sent by the kernel on boot to see what kind of device (disk, tape, CD-ROM etc) is connected to a specific target ID. This process is called device probing by the way. To work around the 'slow response' problem, FreeBSD allows a tunable delay time before the SCSI devices are probed following a SCSI bus reset. You can set this delay time in your kernel configuration file using a line like: options SCSI_DELAY=15 #Be pessimistic about Joe SCSI device This line sets the delay time to 15 seconds. On my own system I had to use 3 seconds minimum to get my trusty old CD-ROM drive to be recognized. Start with a high value (say 30 seconds or so) when you have problems with device recognition. If this helps, tune it back until it just stays working. Rogue SCSI devices Although the SCSI standard tries to be complete and concise, it is a complex standard and implementing things correctly is no easy task. Some vendors do a better job then others. This is exactly where the “rogue” devices come into view. Rogues are devices that are recognized by the FreeBSD kernel as behaving slightly (...) non-standard. Rogue devices are reported by the kernel when booting. An example for two of my cartridge tape units: Feb 25 21:03:34 yedi /kernel: ahb0 targ 5 lun 0: <TANDBERG TDC 3600 -06:> Feb 25 21:03:34 yedi /kernel: st0: Tandberg tdc3600 is a known rogue Mar 29 21:16:37 yedi /kernel: aha0 targ 5 lun 0: <ARCHIVE VIPER 150 21247-005> Mar 29 21:16:37 yedi /kernel: st1: Archive Viper 150 is a known rogue For instance, there are devices that respond to all LUNs on a certain target ID, even if they are actually only one device. It is easy to see that the kernel might be fooled into believing that there are 8 LUNs at that particular target ID. The confusion this causes is left as an exercise to the reader. The SCSI subsystem of FreeBSD recognizes devices with bad habits by looking at the INQUIRY response they send when probed. Because the INQUIRY response also includes the version number of the device firmware, it is even possible that for different firmware versions different workarounds are used. See e.g. /sys/scsi/st.c and /sys/scsi/scsiconf.c for more info on how this is done. This scheme works fine, but keep in mind that it of course only works for devices that are known to be weird. If you are the first to connect your bogus Mumbletech SCSI CD-ROM you might be the one that has to define which workaround is needed. After you got your Mumbletech working, please send the required workaround to the FreeBSD development team for inclusion in the next release of FreeBSD. Other Mumbletech owners will be grateful to you. Multiple LUN devices In some cases you come across devices that use multiple logical units (LUNs) on a single SCSI ID. In most cases FreeBSD only probes devices for LUN 0. An example are so called bridge boards that connect 2 non-SCSI harddisks to a SCSI bus (e.g. an Emulex MD21 found in old Sun systems). This means that any devices with LUNs != 0 are not normally found during device probe on system boot. To work around this problem you must add an appropriate entry in /sys/scsi/scsiconf.c and rebuild your kernel. Look for a struct that is initialized like below: { T_DIRECT, T_FIXED, "MAXTOR", "XT-4170S", "B5A", "mx1", SC_ONE_LU } For you Mumbletech BRIDGE2000 that has more than one LUN, acts as a SCSI disk and has firmware revision 123 you would add something like: { T_DIRECT, T_FIXED, "MUMBLETECH", "BRIDGE2000", "123", "sd", SC_MORE_LUS } The kernel on boot scans the inquiry data it receives against the table and acts accordingly. See the source for more info. Tagged command queueing Modern SCSI devices, particularly magnetic disks, support what is called tagged command queuing (TCQ). In a nutshell, TCQ allows the device to have multiple I/O requests outstanding at the same time. Because the device is intelligent, it can optimise its operations (like head positioning) based on its own request queue. On SCSI devices like RAID (Redundant Array of Independent Disks) arrays the TCQ function is indispensable to take advantage of the device's inherent parallelism. Each I/O request is uniquely identified by a “tag” (hence the name tagged command queuing) and this tag is used by FreeBSD to see which I/O in the device drivers queue is reported as complete by the device. It should be noted however that TCQ requires device driver support and that some devices implemented it “not quite right” in their firmware. This problem bit me once, and it leads to highly mysterious problems. In such cases, try to disable TCQ. Busmaster host adapters Most, but not all, SCSI host adapters are bus mastering controllers. This means that they can do I/O on their own without putting load onto the host CPU for data movement. This is of course an advantage for a multitasking operating system like FreeBSD. It must be noted however that there might be some rough edges. For instance an Adaptec 1542 controller can be set to use different transfer speeds on the host bus (ISA or AT in this case). The controller is settable to different rates because not all motherboards can handle the higher speeds. Problems like hangups, bad data etc might be the result of using a higher data transfer rate then your motherboard can stomach. The solution is of course obvious: switch to a lower data transfer rate and try if that works better. In the case of a Adaptec 1542, there is an option that can be put into the kernel config file to allow dynamic determination of the right, read: fastest feasible, transfer rate. This option is disabled by default: options "TUNE_1542" #dynamic tune of bus DMA speed Check the man pages for the host adapter that you use. Or better still, use the ultimate documentation (read: driver source). Tracking down problems The following list is an attempt to give a guideline for the most common SCSI problems and their solutions. It is by no means complete. Check for loose connectors and cables. Check and double check the location and number of your terminators. Check if your bus has at least one supplier of terminator power (especially with external terminators. Check if no double target IDs are used. Check if all devices to be used are powered up. Make a minimal bus config with as little devices as possible. If possible, configure your host adapter to use slow bus speeds. Disable tagged command queuing to make things as simple as possible (for a NCR hostadapter based system see man ncrcontrol) If you can compile a kernel, make one with the SCSIDEBUG option, and try accessing the device with debugging turned on for that device. If your device does not even probe at startup, you may have to define the address of the device that is failing, and the desired debug level in /sys/scsi/scsidebug.h. If it probes but just does not work, you can use the &man.scsi.8; command to dynamically set a debug level to it in a running kernel (if SCSIDEBUG is defined). This will give you copious debugging output with which to confuse the gurus. See man 4 scsi for more exact information. Also look at man 8 scsi. Further reading If you intend to do some serious SCSI hacking, you might want to have the official standard at hand: Approved American National Standards can be purchased from ANSI at
13th Floor 11 West 42nd Street New York NY 10036 Sales Dept: (212) 642-4900
You can also buy many ANSI standards and most committee draft documents from Global Engineering Documents,
15 Inverness Way East Englewood CO, 80112-5704 Phone: (800) 854-7179 Outside USA and Canada: (303) 792-2181 Fax: (303) 792- 2192
Many X3T10 draft documents are available electronically on the SCSI BBS (719-574-0424) and on the ncrinfo.ncr.com anonymous ftp site. Latest X3T10 committee documents are: AT Attachment (ATA or IDE) [X3.221-1994] (Approved) ATA Extensions (ATA-2) [X3T10/948D Rev 2i] Enhanced Small Device Interface (ESDI) [X3.170-1990/X3.170a-1991] (Approved) Small Computer System Interface — 2 (SCSI-2) [X3.131-1994] (Approved) SCSI-2 Common Access Method Transport and SCSI Interface Module (CAM) [X3T10/792D Rev 11] Other publications that might provide you with additional information are: “SCSI: Understanding the Small Computer System Interface”, written by NCR Corporation. Available from: Prentice Hall, Englewood Cliffs, NJ, 07632 Phone: (201) 767-5937 ISBN 0-13-796855-8 “Basics of SCSI”, a SCSI tutorial written by Ancot Corporation Contact Ancot for availability information at: Phone: (415) 322-5322 Fax: (415) 322-0455 “SCSI Interconnection Guide Book”, an AMP publication (dated 4/93, Catalog 65237) that lists the various SCSI connectors and suggests cabling schemes. Available from AMP at (800) 522-6752 or (717) 564-0100 “Fast Track to SCSI”, A Product Guide written by Fujitsu. Available from: Prentice Hall, Englewood Cliffs, NJ, 07632 Phone: (201) 767-5937 ISBN 0-13-307000-X “The SCSI Bench Reference”, “The SCSI Encyclopedia”, and the “SCSI Tutor”, ENDL Publications, 14426 Black Walnut Court, Saratoga CA, 95070 Phone: (408) 867-6642 “Zadian SCSI Navigator” (quick ref. book) and “Discover the Power of SCSI” (First book along with a one-hour video and tutorial book), Zadian Software, Suite 214, 1210 S. Bascom Ave., San Jose, CA 92128, (408) 293-0800 On Usenet the newsgroups comp.periphs.scsi and comp.periphs are noteworthy places to look for more info. You can also find the SCSI-Faq there, which is posted periodically. Most major SCSI device and host adapter suppliers operate ftp sites and/or BBS systems. They may be valuable sources of information about the devices you own. * Disk/tape controllers * SCSI * IDE * Floppy Hard drives SCSI hard drives Contributed by &a.asami;. 17 February 1998. As mentioned in the SCSI section, virtually all SCSI hard drives sold today are SCSI-2 compliant and thus will work fine as long as you connect them to a supported SCSI host adapter. Most problems people encounter are either due to badly designed cabling (cable too long, star topology, etc.), insufficient termination, or defective parts. Please refer to the SCSI section first if your SCSI hard drive is not working. However, there are a couple of things you may want to take into account before you purchase SCSI hard drives for your system. Rotational speed Rotational speeds of SCSI drives sold today range from around 4,500RPM to 10,000RPM. Most of them are either 5,400RPM or 7,200RPM. Even though the 7,200RPM drives can generally transfer data faster, they run considerably hotter than their 5,400RPM counterparts. A large fraction of today's disk drive malfunctions are heat-related. If you do not have very good cooling in your PC case, you may want to stick with 5,400RPM or slower drives. Note that newer drives, with higher areal recording densities, can deliver much more bits per rotation than older ones. Today's top-of-line 5,400RPM drives can sustain a throughput comparable to 7,200RPM drives of one or two model generations ago. The number to find on the spec sheet for bandwidth is “internal data (or transfer) rate”. It is usually in megabits/sec so divide it by 8 and you'll get the rough approximation of how much megabytes/sec you can get out of the drive. (If you are a speed maniac and want a 10,000RPM drive for your cute little peecee, be my guest; however, those drives become extremely hot. Don't even think about it if you don't have a fan blowing air directly at the drive or a properly ventilated disk enclosure.) Obviously, the latest 10,000RPM drives and 7,200RPM drives can deliver more data than the latest 5,400RPM drives, so if absolute bandwidth is the necessity for your applications, you have little choice but to get the faster drives. Also, if you need low latency, faster drives are better; not only do they usually have lower average seek times, but also the rotational delay is one place where slow-spinning drives can never beat a faster one. (The average rotational latency is half the time it takes to rotate the drive once; thus, it's 3 milliseconds for 10,000RPM drives, 4.2ms for 7,200RPM drives and 5.6ms for 5,400RPM drives.) Latency is seek time plus rotational delay. Make sure you understand whether you need low latency or more accesses per second, though; in the latter case (e.g., news servers), it may not be optimal to purchase one big fast drive. You can achieve similar or even better results by using the ccd (concatenated disk) driver to create a striped disk array out of multiple slower drives for comparable overall cost. Make sure you have adequate air flow around the drive, especially if you are going to use a fast-spinning drive. You generally need at least 1/2" (1.25cm) of spacing above and below a drive. Understand how the air flows through your PC case. Most cases have the power supply suck the air out of the back. See where the air flows in, and put the drive where it will have the largest volume of cool air flowing around it. You may need to seal some unwanted holes or add a new fan for effective cooling. Another consideration is noise. Many 7,200 or faster drives generate a high-pitched whine which is quite unpleasant to most people. That, plus the extra fans often required for cooling, may make 7,200 or faster drives unsuitable for some office and home environments. Form factor Most SCSI drives sold today are of 3.5" form factor. They come in two different heights; 1.6" (“half-height”) or 1" (“low-profile”). The half-height drive is the same height as a CD-ROM drive. However, don't forget the spacing rule mentioned in the previous section. If you have three standard 3.5" drive bays, you will not be able to put three half-height drives in there (without frying them, that is). Interface The majority of SCSI hard drives sold today are Ultra or Ultra-wide SCSI. The maximum bandwidth of Ultra SCSI is 20MB/sec, and Ultra-wide SCSI is 40MB/sec. There is no difference in max cable length between Ultra and Ultra-wide; however, the more devices you have on the same bus, the sooner you will start having bus integrity problems. Unless you have a well-designed disk enclosure, it is not easy to make more than 5 or 6 Ultra SCSI drives work on a single bus. On the other hand, if you need to connect many drives, going for Fast-wide SCSI may not be a bad idea. That will have the same max bandwidth as Ultra (narrow) SCSI, while electronically it's much easier to get it “right”. My advice would be: if you want to connect many disks, get wide SCSI drives; they usually cost a little more but it may save you down the road. (Besides, if you can't afford the cost difference, you shouldn't be building a disk array.) There are two variant of wide SCSI drives; 68-pin and 80-pin SCA (Single Connector Attach). The SCA drives don't have a separate 4-pin power connector, and also read the SCSI ID settings through the 80-pin connector. If you are really serious about building a large storage system, get SCA drives and a good SCA enclosure (dual power supply with at least one extra fan). They are more electronically sound than 68-pin counterparts because there is no “stub” of the SCSI bus inside the disk canister as in arrays built from 68-pin drives. They are easier to install too (you just need to screw the drive in the canister, instead of trying to squeeze in your fingers in a tight place to hook up all the little cables (like the SCSI ID and disk activity LED lines). * IDE hard drives Tape drives Contributed by &a.jmb;. 2 July 1996. General tape access commands &man.mt.1; provides generic access to the tape drives. Some of the more common commands are rewind, erase, and status. See the &man.mt.1; manual page for a detailed description. Controller Interfaces There are several different interfaces that support tape drives. The interfaces are SCSI, IDE, Floppy and Parallel Port. A wide variety of tape drives are available for these interfaces. Controllers are discussed in Disk/tape controllers. SCSI drives The &man.st.4; driver provides support for 8mm (Exabyte), 4mm (DAT: Digital Audio Tape), QIC (Quarter-Inch Cartridge), DLT (Digital Linear Tape), QIC Minicartridge and 9-track (remember the big reels that you see spinning in Hollywood computer rooms) tape drives. See the &man.st.4; manual page for a detailed description. The drives listed below are currently being used by members of the FreeBSD community. They are not the only drives that will work with FreeBSD. They just happen to be the ones that we use. 4mm (DAT: Digital Audio Tape) Archive Python HP C1533A HP C1534A HP 35450A HP 35470A HP 35480A SDT-5000 Wangtek 6200 8mm (Exabyte) EXB-8200 EXB-8500 EXB-8505 QIC (Quarter-Inch Cartridge) Archive Ananconda 2750 Archive Viper 60 Archive Viper 150 Archive Viper 2525 Tandberg TDC 3600 Tandberg TDC 3620 Tandberg TDC 4222 Wangtek 5525ES DLT (Digital Linear Tape) Digital TZ87 Mini-Cartridge Conner CTMS 3200 Exabyte 2501 Autoloaders/Changers Hewlett-Packard HP C1553A Autoloading DDS2 * IDE drives Floppy drives Conner 420R * Parallel port drives Detailed Information Archive Anaconda 2750 The boot message identifier for this drive is ARCHIVE ANCDA 2750 28077 -003 type 1 removable SCSI 2 This is a QIC tape drive. Native capacity is 1.35GB when using QIC-1350 tapes. This drive will read and write QIC-150 (DC6150), QIC-250 (DC6250), and QIC-525 (DC6525) tapes as well. Data transfer rate is 350kB/s using &man.dump.8;. Rates of 530kB/s have been reported when using Amanda Production of this drive has been discontinued. The SCSI bus connector on this tape drive is reversed from that on most other SCSI devices. Make sure that you have enough SCSI cable to twist the cable one-half turn before and after the Archive Anaconda tape drive, or turn your other SCSI devices upside-down. Two kernel code changes are required to use this drive. This drive will not work as delivered. If you have a SCSI-2 controller, short jumper 6. Otherwise, the drive behaves are a SCSI-1 device. When operating as a SCSI-1 device, this drive, “locks” the SCSI bus during some tape operations, including: fsf, rewind, and rewoffl. If you are using the NCR SCSI controllers, patch the file /usr/src/sys/pci/ncr.c (as shown below). Build and install a new kernel. *** 4831,4835 **** }; ! if (np->latetime>4) { /* ** Although we tried to wake it up, --- 4831,4836 ---- }; ! if (np->latetime>1200) { /* ** Although we tried to wake it up, Reported by: &a.jmb; Archive Python The boot message identifier for this drive is ARCHIVE Python 28454-XXX4ASB type 1 removable SCSI 2 density code 0x8c, 512-byte blocks This is a DDS-1 tape drive. Native capacity is 2.5GB on 90m tapes. Data transfer rate is XXX. This drive was repackaged by Sun Microsystems as model 411. Reported by: Bob Bishop rb@gid.co.uk Archive Viper 60 The boot message identifier for this drive is ARCHIVE VIPER 60 21116 -007 type 1 removable SCSI 1 This is a QIC tape drive. Native capacity is 60MB. Data transfer rate is XXX. Production of this drive has been discontinued. Reported by: Philippe Regnauld regnauld@hsc.fr Archive Viper 150 The boot message identifier for this drive is ARCHIVE VIPER 150 21531 -004 Archive Viper 150 is a known rogue type 1 removable SCSI 1. A multitude of firmware revisions exist for this drive. Your drive may report different numbers (e.g 21247 -005. This is a QIC tape drive. Native capacity is 150/250MB. Both 150MB (DC6150) and 250MB (DC6250) tapes have the recording format. The 250MB tapes are approximately 67% longer than the 150MB tapes. This drive can read 120MB tapes as well. It can not write 120MB tapes. Data transfer rate is 100kB/s This drive reads and writes DC6150 (150MB) and DC6250 (250MB) tapes. This drives quirks are known and pre-compiled into the scsi tape device driver (&man.st.4;). Under FreeBSD 2.2-current, use mt blocksize 512 to set the blocksize. (The particular drive had firmware revision 21247 -005. Other firmware revisions may behave differently) Previous versions of FreeBSD did not have this problem. Production of this drive has been discontinued. Reported by: Pedro A M Vazquez vazquez@IQM.Unicamp.BR Mike Smith msmith@atrad.adelaide.edu.au Archive Viper 2525 The boot message identifier for this drive is ARCHIVE VIPER 2525 25462 -011 type 1 removable SCSI 1 This is a QIC tape drive. Native capacity is 525MB. Data transfer rate is 180kB/s at 90 inches/sec. The drive reads QIC-525, QIC-150, QIC-120 and QIC-24 tapes. Writes QIC-525, QIC-150, and QIC-120. Firmware revisions prior to 25462 -011 are bug ridden and will not function properly. Production of this drive has been discontinued. Conner 420R The boot message identifier for this drive is Conner tape. This is a floppy controller, minicartridge tape drive. Native capacity is XXXX Data transfer rate is XXX The drive uses QIC-80 tape cartridges. Reported by: Mark Hannon mark@seeware.DIALix.oz.au Conner CTMS 3200 The boot message identifier for this drive is CONNER CTMS 3200 7.00 type 1 removable SCSI 2. This is a minicartridge tape drive. Native capacity is XXXX Data transfer rate is XXX The drive uses QIC-3080 tape cartridges. Reported by: Thomas S. Traylor tst@titan.cs.mci.com <ulink URL="http://www.digital.com/info/Customer-Update/931206004.txt.html">DEC TZ87</ulink> The boot message identifier for this drive is DEC TZ87 (C) DEC 9206 type 1 removable SCSI 2 density code 0x19 This is a DLT tape drive. Native capacity is 10GB. This drive supports hardware data compression. Data transfer rate is 1.2MB/s. This drive is identical to the Quantum DLT2000. The drive firmware can be set to emulate several well-known drives, including an Exabyte 8mm drive. Reported by: &a.wilko; <ulink URL="http://www.Exabyte.COM:80/Products/Minicartridge/2501/Rfeatures.html">Exabyte EXB-2501</ulink> The boot message identifier for this drive is EXABYTE EXB-2501 This is a mini-cartridge tape drive. Native capacity is 1GB when using MC3000XL minicartridges. Data transfer rate is XXX This drive can read and write DC2300 (550MB), DC2750 (750MB), MC3000 (750MB), and MC3000XL (1GB) minicartridges. WARNING: This drive does not meet the SCSI-2 specifications. The drive locks up completely in response to a SCSI MODE_SELECT command unless there is a formatted tape in the drive. Before using this drive, set the tape blocksize with &prompt.root; mt -f /dev/st0ctl.0 blocksize 1024 Before using a minicartridge for the first time, the minicartridge must be formated. FreeBSD 2.1.0-RELEASE and earlier: &prompt.root; /sbin/scsi -f /dev/rst0.ctl -s 600 -c "4 0 0 0 0 0" (Alternatively, fetch a copy of the scsiformat shell script from FreeBSD 2.1.5/2.2.) FreeBSD 2.1.5 and later: &prompt.root; /sbin/scsiformat -q -w /dev/rst0.ctl Right now, this drive cannot really be recommended for FreeBSD. Reported by: Bob Beaulieu ez@eztravel.com Exabyte EXB-8200 The boot message identifier for this drive is EXABYTE EXB-8200 252X type 1 removable SCSI 1 This is an 8mm tape drive. Native capacity is 2.3GB. Data transfer rate is 270kB/s. This drive is fairly slow in responding to the SCSI bus during boot. A custom kernel may be required (set SCSI_DELAY to 10 seconds). There are a large number of firmware configurations for this drive, some have been customized to a particular vendor's hardware. The firmware can be changed via EPROM replacement. Production of this drive has been discontinued. Reported by: Mike Smith msmith@atrad.adelaide.edu.au Exabyte EXB-8500 The boot message identifier for this drive is EXABYTE EXB-8500-85Qanx0 0415 type 1 removable SCSI 2 This is an 8mm tape drive. Native capacity is 5GB. Data transfer rate is 300kB/s. Reported by: Greg Lehey grog@lemis.de <ulink URL="http://www.Exabyte.COM:80/Products/8mm/8505XL/Rfeatures.html">Exabyte EXB-8505</ulink> The boot message identifier for this drive is EXABYTE EXB-85058SQANXR1 05B0 type 1 removable SCSI 2 This is an 8mm tape drive which supports compression, and is upward compatible with the EXB-5200 and EXB-8500. Native capacity is 5GB. The drive supports hardware data compression. Data transfer rate is 300kB/s. Reported by: Glen Foster gfoster@gfoster.com Hewlett-Packard HP C1533A The boot message identifier for this drive is HP C1533A 9503 type 1 removable SCSI 2. This is a DDS-2 tape drive. DDS-2 means hardware data compression and narrower tracks for increased data capacity. Native capacity is 4GB when using 120m tapes. This drive supports hardware data compression. Data transfer rate is 510kB/s. This drive is used in Hewlett-Packard's SureStore 6000eU and 6000i tape drives and C1533A DDS-2 DAT drive. The drive has a block of 8 dip switches. The proper settings for FreeBSD are: 1 ON; 2 ON; 3 OFF; 4 ON; 5 ON; 6 ON; 7 ON; 8 ON. switch 1 switch 2 Result On On Compression enabled at power-on, with host control On Off Compression enabled at power-on, no host control Off On Compression disabled at power-on, with host control Off Off Compression disabled at power-on, no host control Switch 3 controls MRS (Media Recognition System). MRS tapes have stripes on the transparent leader. These identify the tape as DDS (Digital Data Storage) grade media. Tapes that do not have the stripes will be treated as write-protected. Switch 3 OFF enables MRS. Switch 3 ON disables MRS. See HP SureStore Tape Products and Hewlett-Packard Disk and Tape Technical Information for more information on configuring this drive. Warning: Quality control on these drives varies greatly. One FreeBSD core-team member has returned 2 of these drives. Neither lasted more than 5 months. Reported by: &a.se; Hewlett-Packard HP 1534A The boot message identifier for this drive is HP HP35470A T503 type 1 removable SCSI 2 Sequential-Access density code 0x13, variable blocks. This is a DDS-1 tape drive. DDS-1 is the original DAT tape format. Native capacity is 2GB when using 90m tapes. Data transfer rate is 183kB/s. The same mechanism is used in Hewlett-Packard's SureStore 2000i tape drive, C35470A DDS format DAT drive, C1534A DDS format DAT drive and HP C1536A DDS format DAT drive. The HP C1534A DDS format DAT drive has two indicator lights, one green and one amber. The green one indicates tape action: slow flash during load, steady when loaded, fast flash during read/write operations. The amber one indicates warnings: slow flash when cleaning is required or tape is nearing the end of its useful life, steady indicates an hard fault. (factory service required?) Reported by Gary Crutcher gcrutchr@nightflight.com Hewlett-Packard HP C1553A Autoloading DDS2 The boot message identifier for this drive is "". This is a DDS-2 tape drive with a tape changer. DDS-2 means hardware data compression and narrower tracks for increased data capacity. Native capacity is 24GB when using 120m tapes. This drive supports hardware data compression. Data transfer rate is 510kB/s (native). This drive is used in Hewlett-Packard's SureStore 12000e tape drive. The drive has two selectors on the rear panel. The selector closer to the fan is SCSI id. The other selector should be set to 7. There are four internal switches. These should be set: 1 ON; 2 ON; 3 ON; 4 OFF. At present the kernel drivers do not automatically change tapes at the end of a volume. This shell script can be used to change tapes: #!/bin/sh PATH="/sbin:/usr/sbin:/bin:/usr/bin"; export PATH usage() { echo "Usage: dds_changer [123456ne] raw-device-name echo "1..6 = Select cartridge" echo "next cartridge" echo "eject magazine" exit 2 } if [ $# -ne 2 ] ; then usage fi cdb3=0 cdb4=0 cdb5=0 case $1 in [123456]) cdb3=$1 cdb4=1 ;; n) ;; e) cdb5=0x80 ;; ?) usage ;; esac scsi -f $2 -s 100 -c "1b 0 0 $cdb3 $cdb4 $cdb5" Hewlett-Packard HP 35450A The boot message identifier for this drive is HP HP35450A -A C620 type 1 removable SCSI 2 Sequential-Access density code 0x13 This is a DDS-1 tape drive. DDS-1 is the original DAT tape format. Native capacity is 1.2GB. Data transfer rate is 160kB/s. Reported by: mark thompson mark.a.thompson@pobox.com Hewlett-Packard HP 35470A The boot message identifier for this drive is HP HP35470A 9 09 type 1 removable SCSI 2 This is a DDS-1 tape drive. DDS-1 is the original DAT tape format. Native capacity is 2GB when using 90m tapes. Data transfer rate is 183kB/s. The same mechanism is used in Hewlett-Packard's SureStore 2000i tape drive, C35470A DDS format DAT drive, C1534A DDS format DAT drive, and HP C1536A DDS format DAT drive. Warning: Quality control on these drives varies greatly. One FreeBSD core-team member has returned 5 of these drives. None lasted more than 9 months. Reported by: David Dawes dawes@rf900.physics.usyd.edu.au (9 09) Hewlett-Packard HP 35480A The boot message identifier for this drive is HP HP35480A 1009 type 1 removable SCSI 2 Sequential-Access density code 0x13. This is a DDS-DC tape drive. DDS-DC is DDS-1 with hardware data compression. DDS-1 is the original DAT tape format. Native capacity is 2GB when using 90m tapes. It cannot handle 120m tapes. This drive supports hardware data compression. Please refer to the section on HP C1533A for the proper switch settings. Data transfer rate is 183kB/s. This drive is used in Hewlett-Packard's SureStore 5000eU and 5000i tape drives and C35480A DDS format DAT drive.. This drive will occasionally hang during a tape eject operation (mt offline). Pressing the front panel button will eject the tape and bring the tape drive back to life. WARNING: HP 35480-03110 only. On at least two occasions this tape drive when used with FreeBSD 2.1.0, an IBM Server 320 and an 2940W SCSI controller resulted in all SCSI disk partitions being lost. The problem has not be analyzed or resolved at this time. <ulink URL="http://www.sel.sony.com/SEL/ccpg/storage/tape/t5000.html">Sony SDT-5000</ulink> There are at least two significantly different models: one is a DDS-1 and the other DDS-2. The DDS-1 version is SDT-5000 3.02. The DDS-2 version is SONY SDT-5000 327M. The DDS-2 version has a 1MB cache. This cache is able to keep the tape streaming in almost any circumstances. The boot message identifier for this drive is SONY SDT-5000 3.02 type 1 removable SCSI 2 Sequential-Access density code 0x13 Native capacity is 4GB when using 120m tapes. This drive supports hardware data compression. Data transfer rate is depends upon the model or the drive. The rate is 630kB/s for the SONY SDT-5000 327M while compressing the data. For the SONY SDT-5000 3.02, the data transfer rate is 225kB/s. In order to get this drive to stream, set the blocksize to 512 bytes (mt blocksize 512) reported by Kenneth Merry ken@ulc199.residence.gatech.edu SONY SDT-5000 327M information reported by Charles Henrich henrich@msu.edu Reported by: &a.jmz; Tandberg TDC 3600 The boot message identifier for this drive is TANDBERG TDC 3600 =08: type 1 removable SCSI 2 This is a QIC tape drive. Native capacity is 150/250MB. This drive has quirks which are known and work around code is present in the scsi tape device driver (&man.st.4;). Upgrading the firmware to XXX version will fix the quirks and provide SCSI 2 capabilities. Data transfer rate is 80kB/s. IBM and Emerald units will not work. Replacing the firmware EPROM of these units will solve the problem. Reported by: Michael Smith msmith@atrad.adelaide.edu.au Tandberg TDC 3620 This is very similar to the Tandberg TDC 3600 drive. Reported by: &a.joerg; Tandberg TDC 4222 The boot message identifier for this drive is TANDBERG TDC 4222 =07 type 1 removable SCSI 2 This is a QIC tape drive. Native capacity is 2.5GB. The drive will read all cartridges from the 60 MB (DC600A) upwards, and write 150 MB (DC6150) upwards. Hardware compression is optionally supported for the 2.5 GB cartridges. This drives quirks are known and pre-compiled into the scsi tape device driver (&man.st.4;) beginning with FreeBSD 2.2-current. For previous versions of FreeBSD, use mt to read one block from the tape, rewind the tape, and then execute the backup program (mt fsr 1; mt rewind; dump ...) Data transfer rate is 600kB/s (vendor claim with compression), 350 KB/s can even be reached in start/stop mode. The rate decreases for smaller cartridges. Reported by: &a.joerg; Wangtek 5525ES The boot message identifier for this drive is WANGTEK 5525ES SCSI REV7 3R1 type 1 removable SCSI 1 density code 0x11, 1024-byte blocks This is a QIC tape drive. Native capacity is 525MB. Data transfer rate is 180kB/s. The drive reads 60, 120, 150, and 525MB tapes. The drive will not write 60MB (DC600 cartridge) tapes. In order to overwrite 120 and 150 tapes reliably, first erase (mt erase) the tape. 120 and 150 tapes used a wider track (fewer tracks per tape) than 525MB tapes. The “extra” width of the previous tracks is not overwritten, as a result the new data lies in a band surrounded on both sides by the previous data unless the tape have been erased. This drives quirks are known and pre-compiled into the scsi tape device driver (&man.st.4;). Other firmware revisions that are known to work are: M75D Reported by: Marc van Kempen marc@bowtie.nl REV73R1 Andrew Gordon Andrew.Gordon@net-tel.co.uk M75D Wangtek 6200 The boot message identifier for this drive is WANGTEK 6200-HS 4B18 type 1 removable SCSI 2 Sequential-Access density code 0x13 This is a DDS-1 tape drive. Native capacity is 2GB using 90m tapes. Data transfer rate is 150kB/s. Reported by: Tony Kimball alk@Think.COM * Problem drives CD-ROM drives Contributed by &a.obrien;. 23 November 1997. As mentioned in Jordan's Picks Generally speaking those in The FreeBSD Project prefer SCSI CDROM drives over IDE CDROM drives. However not all SCSI CDROM drives are equal. Some feel the quality of some SCSI CDROM drives have been deteriorating to that of IDE CDROM drives. Toshiba used to be the favored stand-by, but many on the SCSI mailing list have found displeasure with the 12x speed XM-5701TA as its volume (when playing audio CDROMs) is not controllable by the various audio player software. Another area where SCSI CDROM manufacturers are cutting corners is adhearance to the SCSI specification. Many SCSI CDROMs will respond to multiple LUNs for its target address. Known violators include the 6x Teac CD-56S 1.0D. * Other * Other * PCMCIA diff --git a/en_US.ISO_8859-1/books/handbook/hw/chapter.sgml b/en_US.ISO_8859-1/books/handbook/hw/chapter.sgml index 4554b8e7cb..d3bf2da501 100644 --- a/en_US.ISO_8859-1/books/handbook/hw/chapter.sgml +++ b/en_US.ISO_8859-1/books/handbook/hw/chapter.sgml @@ -1,5550 +1,5557 @@ PC Hardware compatibility Issues of hardware compatibility are among the most troublesome in the computer industry today and FreeBSD is by no means immune to trouble. In this respect, FreeBSD's advantage of being able to run on inexpensive commodity PC hardware is also its liability when it comes to support for the amazing variety of components on the market. While it would be impossible to provide a exhaustive listing of hardware that FreeBSD supports, this section serves as a catalog of the device drivers included with FreeBSD and the hardware each drivers supports. Where possible and appropriate, notes about specific products are included. You may also want to refer to the kernel configuration file section in this handbook for a list of supported devices. As FreeBSD is a volunteer project without a funded testing department, we depend on you, the user, for much of the information contained in this catalog. If you have direct experience of hardware that does or does not work with FreeBSD, please let us know by sending e-mail to the &a.doc;. Questions about supported hardware should be directed to the &a.questions; (see Mailing Lists for more information). When submitting information or asking a question, please remember to specify exactly what version of FreeBSD you are using and include as many details of your hardware as possible. Resources on the Internet The following links have proven useful in selecting hardware. Though some of what you see won't necessarily be specific (or even applicable) to FreeBSD, most of the hardware information out there is OS independent. Please check with the FreeBSD hardware guide to make sure that your chosen configuration is supported before making any purchases. The Pentium Systems Hardware Performance Guide Sample Configurations The following list of sample hardware configurations by no means constitutes an endorsement of a given hardware vendor or product by The FreeBSD Project. This information is provided only as a public service and merely catalogs some of the experiences that various individuals have had with different hardware combinations. Your mileage may vary. Slippery when wet. Beware of dog. Jordan's Picks I have had fairly good luck building workstation and server configurations with the following components. I can't guarantee that you will too, nor that any of the companies here will remain “best buys” forever. I will try, when I can, to keep this list up-to-date but cannot obviously guarantee that it will be at any given time. Motherboards For Pentium Pro (P6) systems, I'm quite fond of the Tyan S1668 dual-processor motherboard as well as the Intel PR440FX motherboard with on-board SCSI WIDE and 100/10MB Intel Etherexpress NIC. You can build a dandy little single or dual processor system (which is supported in FreeBSD 3.0) for very little cost now that the Pentium Pro 180/256K chips have fallen so greatly in price, but no telling how much longer this will last. For the Pentium II, I'm rather partial to the ASUS P2l97-S motherboard with the on-board Adaptec SCSI WIDE controller. For Pentium machines, the ASUS P55T2P4 motherboard appears to be a good choice for mid-to-high range Pentium server and workstation systems. Those wishing to build more fault-tolerant systems should also be sure to use Parity memory or, for truly 24/7 applications, ECC memory. ECC memory does involve a slight performance trade-off (which may or may not be noticeable depending on your application) but buys you significantly increased fault-tolerance to memory errors. Disk Controllers This one is a bit trickier, and while I used to recommend the Buslogic controllers unilaterally for everything from ISA to PCI, now I tend to lean towards the Adaptec 1542CF for ISA, Buslogic Bt747c for EISA and Adaptec 2940UW for PCI. The NCR/Symbios cards for PCI have also worked well for me, though you need to make sure that your motherboard supports the BIOS-less model if you're using one of those (if your card has nothing which looks even vaguely like a ROM chip on it, you've probably got one which expects its BIOS to be on your motherboard). If you should find that you need more than one SCSI controller in a PCI machine, you may wish to consider conserving your scarce PCI bus resources by buying the Adaptec 3940 card, which puts two SCSI controllers (and internal busses) in a single slot. There are two types of 3940 on the market—the older model with AIC 7880 chips on it, and hte newer one with AIC 7895 chips. The newer model requires CAM support which is not yet part of FreeBSD—you have to add it, or install from one of the CAM binary snapshot release. Disk drives In this particular game of Russian roulette, I'll make few specific recommendations except to say “SCSI over IDE whenever you can afford it.” Even in small desktop configurations, SCSI often makes more sense since it allows you to easily migrate drives from server to desktop as falling drive prices make it economical to do so. If you have more than one machine to administer then think of it not simply as storage, think of it as a food chain! For a serious server configuration, there's not even any argument—use SCSI equipment and good cables. CDROM drives My SCSI preferences extend to SCSI CDROM drives as well, and while the Toshiba drives have always been favourites of mine (in whatever speed is hot that week), I'm still fond of my good old Plextor PX-12CS drive. It's only a 12 speed, but it's offered excellent performance and reliability. Generally speaking, most SCSI CDROM drives I've seen have been of pretty solid construction and you probably won't go wrong with an HP or NEC SCSI CDROM drive either. SCSI CDROM prices also appear to have dropped considerably in the last few months and are now quite competitive with IDE CDROMs while remaining a technically superior solution. I now see no reason whatsoever to settle for an IDE CDROM drive if given a choice between the two. CD Recordable (WORM) drives At the time of this writing, FreeBSD supports 3 types of CDR drives (though I believe they all ultimately come from Phillips anyway): The Phillips CDD 522 (Acts like a Plasmon), the PLASMON RF4100 and the HP 6020i. I myself use the HP 6020i for burning CDROMs (in 2.2 and alter releases—it does not work with earlier releases of the SCSI code) and it works very well. See /usr/share/examples/worm on your 2.2 system for example scripts used to created ISO9660 filesystem images (with RockRidge extensions) and burn them onto an HP6020i CDR. Tape drives I've had pretty good luck with both 8mm drives from Exabyte and 4mm (DAT) drives from HP. For backup purposes, I'd have to give the higher recommendation to the Exabyte due to the more robust nature (and higher storage capacity) of 8mm tape. Video Cards If you can also afford to buy a commercial X server for US$99 from Xi Graphics, Inc. (formerly X Inside, Inc) then I can heartily recommend the Matrox Millenium II card. Note that support for this card is also excellent with the XFree86 server, which is now at version 3.3.2. You also certainly can't go wrong with one of Number 9's cards — their S3 Vision 868 and 968 based cards (the 9FX series) also being quite fast and very well supported by XFree86's S3 server. You can also pick up their Revolution 3D cards very cheaply these days, especially if you require a lot of video memory. Monitors I have had very good luck with the Sony Multiscan 17seII monitors, as have I with the Viewsonic offering in the same (Trinitron) tube. For larger than 17", all I can recommend at the time of this writing is to not spend any less than U.S. $2,000 for a 21" monitor or $1,700 for a 20" monitor if that's what you really need. There are good monitors available in the >=20" range and there are also cheap monitors in the >=20" range. Unfortunately, very few are both cheap and good! Networking I can recommend the Intel EtherExpress Pro/100B card first ande foremost, followed by the SMC Ultra 16 controller for any ISA application and the SMC EtherPower or Compex ENET32 cards for slightly cheaper PCI based networking. In general, any PCI NIC based around DEC's DC21041 Ethernet controller chip, such as the Zynx ZX342 or DEC DE435, will generally work quite well and can frequently be found in 2-port and 4-port version (useful for firewalls and routers), though the Pro/100MB card has the edge when it comes to providing the best performance with teh lower overhead. If what you're looking for is the cheapest possible solution then almost any NE2000 clone will do a fine job for very little cost. Serial If you're looking for high-speed serial networking solutions, then Digi International makes the SYNC/570 series, with drivers now in FreeBSD-current. Emerging Technologies also manufactures a board with T1/E1 capabilities, using software they provide. I have no direct experience using either product, however. Multiport card options are somewhat more numerous, though it has to be said that FreeBSD's support for Cyclades's products is probably the tightest, primarily as a result of that company's commitment to making sure that we are adequately supplied with evaluation boards and technical specs. I've heard that the Cyclom-16Ye offers the best price/performance, though I've not checked the prices lately. Other multiport cards I've heard good things about are the BOCA and AST cards, and Stallion Technologies apparently offers an unofficial driver for their cards at this location. Audio I currently use a Creative Labs AWE32 though just about anything from Creative Labs will generally work these days. This is not to say that other types of sound cards don't also work, simply that I have little experience with them (I was a former GUS fan, but Gravis's soundcard situation has been dire for some time). Video For video capture, there are two good choices — any card based on the Brooktree BT848 chip, such as the Hauppage or WinTV boards, will work very nicely with FreeBSD. Another board which works for me is the Matrox Meteor card. FreeBSD also supports the older video spigot card from Creative Labs, but those are getting somewhat difficult to find. Note that the Meteor frame grabber card will not work with motherboards based on the 440FX chipset! See the motherboard reference section for details. In such cases, it's better to go with a BT848 based board. Core/Processing Motherboards, busses, and chipsets * ISA * EISA * VLB PCI Contributed by &a.obrien; from postings by &a.rgrimes;. 25 April 1995. Continuing updates by &a.jkh;. Last update on 26 August 1996. Of the Intel PCI chip sets, the following list describes various types of known-brokenness and the degree of breakage, listed from worst to best. Mercury: Cache coherency problems, especially if there are ISA bus masters behind the ISA to PCI bridge chip. Hardware flaw, only known work around is to turn the cache off. Saturn-I (ie, 82424ZX at rev 0, 1 or 2): Write back cache coherency problems. Hardware flaw, only known work around is to set the external cache to write-through mode. Upgrade to Saturn-II. Saturn-II (ie, 82424ZX at rev 3 or 4): Works fine, but many MB manufactures leave out the external dirty bit SRAM needed for write back operation. Work arounds are either run it in write through mode, or get the dirty bit SRAM installed. (I have these for the ASUS PCI/I-486SP3G rev 1.6 and later boards). Neptune: Can not run more than 2 bus master devices. Admitted Intel design flaw. Workarounds include do not run more than 2 bus masters, special hardware design to replace the PCI bus arbiter (appears on Intel Altair board and several other Intel server group MB's). And of course Intel's official answer, move to the Triton chip set, we “fixed it there”. Triton (ie, 430FX): No known cache coherency or bus master problems, chip set does not implement parity checking. Workaround for parity issue. Use Triton-II based motherboards if you have the choice. Triton-II (ie, 430HX): All reports on motherboards using this chipset have been favorable so far. No known problems. Orion: Early versions of this chipset suffered from a PCI write-posting bug which can cause noticeable performance degradation in applications where large amounts of PCI bus traffic is involved. B0 stepping or later revisions of the chipset fixed this problem. 440FX: This Pentium Pro support chipset seems to work well, and does not suffer from any of the early Orion chipset problems. It also supports a wider variety of memory, including ECC and parity. The only known problem with it is that the Matrox Meteor frame grabber card doesn't like it. CPUs/FPUs Contributed by &a.asami;. 26 December 1997. P6 class (Pentium Pro/Pentium II) Both the Pentium Pro and Pentium II work fine with FreeBSD. In fact, our main ftp site ftp.freebsd.org (also known as "ftp.cdrom.com", world's largest ftp site) runs FreeBSD on a Pentium Pro. Configurations details are available for interested parties. Pentium class The Intel Pentium (P54C), Pentium MMX (P55C), AMD K6 and Cyrix/IBM 6x86MX processors are all reported to work with FreeBSD. I will not go into details of which processor is faster than what, there are zillions of web sites on the Internet that tells you one way or another. :) Various CPUs have different voltage/cooling requirements. Make sure your motherboard can supply the exact voltage needed by the CPU. For instance, many recent MMX chips require split voltage (e.g., 2.9V core, 3.3V I/O). Also, some AMD and Cyrix/IBM chips run hotter than Intel chips. In that case, make sure you have good heatsink/fans (you can get the list of certified parts from their web pages). Clock speeds Contributed by &a.rgrimes;. 1 October 1996. Updated by &a.asami;. 27 December 1997. Pentium class machines use different clock speeds for the various parts of the system. These being the speed of the CPU, external memory bus, and the PCI bus. It is not always true that a “faster” processor will make a system faster than a “slower” one, due to the various clock speeds used. Below is a table showing the differences: Rated CPU MHz External Clock and Memory Bus MHz External to Internal Clock Multiplier PCI Bus Clock MHz 60 60 1.0 30 66 66 1.0 33 75 50 1.5 25 90 60 1.5 30 100 50 2 25 100 66 1.5 33 120 60 2 30 133 66 2 33 150 60 2.5 30 (Intel, AMD) 150 75 2 37.5 (Cyrix/IBM 6x86MX) 166 66 2.5 33 180 60 3 30 200 66 3 33 233 66 3.5 33 66MHz may actually be 66.667MHz, but don't assume so. The Pentium 100 can be run at either 50MHz external clock with a multiplier of 2 or at 66MHz and a multiplier of 1.5. As can be seen the best parts to be using are the 100, 133, 166, 200 and 233, with the exception that at a multiplier of 3 or more the CPU starves for memory. The AMD K6 Bug In 1997, there have been reports of the AMD K6 seg faulting during heavy compilation. That problem has been fixed in 3Q '97. According to reports, K6 chips with date mark “9733” or larger (i.e., manufactured in the 33rd week of '97 or later) do not have this bug. * 486 class * 386 class 286 class Sorry, FreeBSD does not run on 80286 machines. It is nearly impossible to run today's large full-featured UNIXes on such hardware. * Memory The minimum amount of memory you must have to install FreeBSD is 5 MB. Once your system is up and running you can build a custom kernel that will use less memory. If you use the boot4.flp you can get away with having only 4 MB. * BIOS Input/Output Devices * Video cards * Sound cards Serial ports and multiport cards The UART: What it is and how it works Copyright © 1996 &a.uhclem;, All Rights Reserved. 13 January 1996. The Universal Asynchronous Receiver/Transmitter (UART) controller is the key component of the serial communications subsystem of a computer. The UART takes bytes of data and transmits the individual bits in a sequential fashion. At the destination, a second UART re-assembles the bits into complete bytes. Serial transmission is commonly used with modems and for non-networked communication between computers, terminals and other devices. There are two primary forms of serial transmission: Synchronous and Asynchronous. Depending on the modes that are supported by the hardware, the name of the communication sub-system will usually include a A if it supports Asynchronous communications, and a S if it supports Synchronous communications. Both forms are described below. Some common acronyms are:
UART Universal Asynchronous Receiver/Transmitter
USART Universal Synchronous-Asynchronous Receiver/Transmitter
Synchronous Serial Transmission Synchronous serial transmission requires that the sender and receiver share a clock with one another, or that the sender provide a strobe or other timing signal so that the receiver knows when to “read” the next bit of the data. In most forms of serial Synchronous communication, if there is no data available at a given instant to transmit, a fill character must be sent instead so that data is always being transmitted. Synchronous communication is usually more efficient because only data bits are transmitted between sender and receiver, and synchronous communication can be more more costly if extra wiring and circuits are required to share a clock signal between the sender and receiver. A form of Synchronous transmission is used with printers and fixed disk devices in that the data is sent on one set of wires while a clock or strobe is sent on a different wire. Printers and fixed disk devices are not normally serial devices because most fixed disk interface standards send an entire word of data for each clock or strobe signal by using a separate wire for each bit of the word. In the PC industry, these are known as Parallel devices. The standard serial communications hardware in the PC does not support Synchronous operations. This mode is described here for comparison purposes only. Asynchronous Serial Transmission Asynchronous transmission allows data to be transmitted without the sender having to send a clock signal to the receiver. Instead, the sender and receiver must agree on timing parameters in advance and special bits are added to each word which are used to synchronize the sending and receiving units. When a word is given to the UART for Asynchronous transmissions, a bit called the "Start Bit" is added to the beginning of each word that is to be transmitted. The Start Bit is used to alert the receiver that a word of data is about to be sent, and to force the clock in the receiver into synchronization with the clock in the transmitter. These two clocks must be accurate enough to not have the frequency drift by more than 10% during the transmission of the remaining bits in the word. (This requirement was set in the days of mechanical teleprinters and is easily met by modern electronic equipment.) After the Start Bit, the individual bits of the word of data are sent, with the Least Significant Bit (LSB) being sent first. Each bit in the transmission is transmitted for exactly the same amount of time as all of the other bits, and the receiver “looks” at the wire at approximately halfway through the period assigned to each bit to determine if the bit is a 1 or a 0. For example, if it takes two seconds to send each bit, the receiver will examine the signal to determine if it is a 1 or a 0 after one second has passed, then it will wait two seconds and then examine the value of the next bit, and so on. The sender does not know when the receiver has “looked” at the value of the bit. The sender only knows when the clock says to begin transmitting the next bit of the word. When the entire data word has been sent, the transmitter may add a Parity Bit that the transmitter generates. The Parity Bit may be used by the receiver to perform simple error checking. Then at least one Stop Bit is sent by the transmitter. When the receiver has received all of the bits in the data word, it may check for the Parity Bits (both sender and receiver must agree on whether a Parity Bit is to be used), and then the receiver looks for a Stop Bit. If the Stop Bit does not appear when it is supposed to, the UART considers the entire word to be garbled and will report a Framing Error to the host processor when the data word is read. The usual cause of a Framing Error is that the sender and receiver clocks were not running at the same speed, or that the signal was interrupted. Regardless of whether the data was received correctly or not, the UART automatically discards the Start, Parity and Stop bits. If the sender and receiver are configured identically, these bits are not passed to the host. If another word is ready for transmission, the Start Bit for the new word can be sent as soon as the Stop Bit for the previous word has been sent. Because asynchronous data is “self synchronizing”, if there is no data to transmit, the transmission line can be idle. Other UART Functions In addition to the basic job of converting data from parallel to serial for transmission and from serial to parallel on reception, a UART will usually provide additional circuits for signals that can be used to indicate the state of the transmission media, and to regulate the flow of data in the event that the remote device is not prepared to accept more data. For example, when the device connected to the UART is a modem, the modem may report the presence of a carrier on the phone line while the computer may be able to instruct the modem to reset itself or to not take calls by asserting or deasserting one more more of these extra signals. The function of each of these additional signals is defined in the EIA RS232-C standard. The RS232-C and V.24 Standards In most computer systems, the UART is connected to circuitry that generates signals that comply with the EIA RS232-C specification. There is also a CCITT standard named V.24 that mirrors the specifications included in RS232-C. RS232-C Bit Assignments (Marks and Spaces) In RS232-C, a value of 1 is called a Mark and a value of 0 is called a Space. When a communication line is idle, the line is said to be “Marking”, or transmitting continuous 1 values. The Start bit always has a value of 0 (a Space). The Stop Bit always has a value of 1 (a Mark). This means that there will always be a Mark (1) to Space (0) transition on the line at the start of every word, even when multiple word are transmitted back to back. This guarantees that sender and receiver can resynchronize their clocks regardless of the content of the data bits that are being transmitted. The idle time between Stop and Start bits does not have to be an exact multiple (including zero) of the bit rate of the communication link, but most UARTs are designed this way for simplicity. In RS232-C, the "Marking" signal (a 1) is represented by a voltage between -2 VDC and -12 VDC, and a "Spacing" signal (a 0) is represented by a voltage between 0 and +12 VDC. The transmitter is supposed to send +12 VDC or -12 VDC, and the receiver is supposed to allow for some voltage loss in long cables. Some transmitters in low power devices (like portable computers) sometimes use only +5 VDC and -5 VDC, but these values are still acceptable to a RS232-C receiver, provided that the cable lengths are short. RS232-C Break Signal RS232-C also specifies a signal called a Break, which is caused by sending continuous Spacing values (no Start or Stop bits). When there is no electricity present on the data circuit, the line is considered to be sending Break. The Break signal must be of a duration longer than the time it takes to send a complete byte plus Start, Stop and Parity bits. Most UARTs can distinguish between a Framing Error and a Break, but if the UART cannot do this, the Framing Error detection can be used to identify Breaks. In the days of teleprinters, when numerous printers around the country were wired in series (such as news services), any unit could cause a Break by temporarily opening the entire circuit so that no current flowed. This was used to allow a location with urgent news to interrupt some other location that was currently sending information. In modern systems there are two types of Break signals. If the Break is longer than 1.6 seconds, it is considered a "Modem Break", and some modems can be programmed to terminate the conversation and go on-hook or enter the modems' command mode when the modem detects this signal. If the Break is smaller than 1.6 seconds, it signifies a Data Break and it is up to the remote computer to respond to this signal. Sometimes this form of Break is used as an Attention or Interrupt signal and sometimes is accepted as a substitute for the ASCII CONTROL-C character. Marks and Spaces are also equivalent to “Holes” and “No Holes” in paper tape systems. Breaks cannot be generated from paper tape or from any other byte value, since bytes are always sent with Start and Stop bit. The UART is usually capable of generating the continuous Spacing signal in response to a special command from the host processor. RS232-C DTE and DCE Devices The RS232-C specification defines two types of equipment: the Data Terminal Equipment (DTE) and the Data Carrier Equipment (DCE). Usually, the DTE device is the terminal (or computer), and the DCE is a modem. Across the phone line at the other end of a conversation, the receiving modem is also a DCE device and the computer that is connected to that modem is a DTE device. The DCE device receives signals on the pins that the DTE device transmits on, and vice versa. When two devices that are both DTE or both DCE must be connected together without a modem or a similar media translater between them, a NULL modem must be used. The NULL modem electrically re-arranges the cabling so that the transmitter output is connected to the receiver input on the other device, and vice versa. Similar translations are performed on all of the control signals so that each device will see what it thinks are DCE (or DTE) signals from the other device. The number of signals generated by the DTE and DCE devices are not symmetrical. The DTE device generates fewer signals for the DCE device than the DTE device receives from the DCE. RS232-C Pin Assignments The EIA RS232-C specification (and the ITU equivalent, V.24) calls for a twenty-five pin connector (usually a DB25) and defines the purpose of most of the pins in that connector. In the IBM Personal Computer and similar systems, a subset of RS232-C signals are provided via nine pin connectors (DB9). The signals that are not included on the PC connector deal mainly with synchronous operation, and this transmission mode is not supported by the UART that IBM selected for use in the IBM PC. Depending on the computer manufacturer, a DB25, a DB9, or both types of connector may be used for RS232-C communications. (The IBM PC also uses a DB25 connector for the parallel printer interface which causes some confusion.) Below is a table of the RS232-C signal assignments in the DB25 and DB9 connectors. DB25 RS232-C Pin DB9 IBM PC Pin EIA Circuit Symbol CCITT Circuit Symbol Common Name Signal Source Description 1 - AA 101 PG/FG - Frame/Protective Ground 2 3 BA 103 TD DTE Transmit Data 3 2 BB 104 RD DCE Receive Data 4 7 CA 105 RTS DTE Request to Send 5 8 CB 106 CTS DCE Clear to Send 6 6 CC 107 DSR DCE Data Set Ready 7 5 AV 102 SG/GND - Signal Ground 8 1 CF 109 DCD/CD DCE Data Carrier Detect 9 - - - - - Reserved for Test 10 - - - - - Reserved for Test 11 - - - - - Reserved for Test 12 - CI 122 SRLSD DCE Sec. Recv. Line Signal Detector 13 - SCB 121 SCTS DCE Secondary Clear to Send 14 - SBA 118 STD DTE Secondary Transmit Data 15 - DB 114 TSET DCE Trans. Sig. Element Timing 16 - SBB 119 SRD DCE Secondary Received Data 17 - DD 115 RSET DCE Receiver Signal Element Timing 18 - - 141 LOOP DTE Local Loopback 19 - SCA 120 SRS DTE Secondary Request to Send 20 4 CD 108.2 DTR DTE Data Terminal Ready 21 - - - RDL DTE Remote Digital Loopback 22 9 CE 125 RI DCE Ring Indicator 23 - CH 111 DSRS DTE Data Signal Rate Selector 24 - DA 113 TSET DTE Trans. Sig. Element Timing 25 - - 142 - DCE Test Mode Bits, Baud and Symbols Baud is a measurement of transmission speed in asynchronous communication. Because of advances in modem communication technology, this term is frequently misused when describing the data rates in newer devices. Traditionally, a Baud Rate represents the number of bits that are actually being sent over the media, not the amount of data that is actually moved from one DTE device to the other. The Baud count includes the overhead bits Start, Stop and Parity that are generated by the sending UART and removed by the receiving UART. This means that seven-bit words of data actually take 10 bits to be completely transmitted. Therefore, a modem capable of moving 300 bits per second from one place to another can normally only move 30 7-bit words if Parity is used and one Start and Stop bit are present. If 8-bit data words are used and Parity bits are also used, the data rate falls to 27.27 words per second, because it now takes 11 bits to send the eight-bit words, and the modem still only sends 300 bits per second. The formula for converting bytes per second into a baud rate and vice versa was simple until error-correcting modems came along. These modems receive the serial stream of bits from the UART in the host computer (even when internal modems are used the data is still frequently serialized) and converts the bits back into bytes. These bytes are then combined into packets and sent over the phone line using a Synchronous transmission method. This means that the Stop, Start, and Parity bits added by the UART in the DTE (the computer) were removed by the modem before transmission by the sending modem. When these bytes are received by the remote modem, the remote modem adds Start, Stop and Parity bits to the words, converts them to a serial format and then sends them to the receiving UART in the remote computer, who then strips the Start, Stop and Parity bits. The reason all these extra conversions are done is so that the two modems can perform error correction, which means that the receiving modem is able to ask the sending modem to resend a block of data that was not received with the correct checksum. This checking is handled by the modems, and the DTE devices are usually unaware that the process is occurring. By striping the Start, Stop and Parity bits, the additional bits of data that the two modems must share between themselves to perform error-correction are mostly concealed from the effective transmission rate seen by the sending and receiving DTE equipment. For example, if a modem sends ten 7-bit words to another modem without including the Start, Stop and Parity bits, the sending modem will be able to add 30 bits of its own information that the receiving modem can use to do error-correction without impacting the transmission speed of the real data. The use of the term Baud is further confused by modems that perform compression. A single 8-bit word passed over the telephone line might represent a dozen words that were transmitted to the sending modem. The receiving modem will expand the data back to its original content and pass that data to the receiving DTE. Modern modems also include buffers that allow the rate that bits move across the phone line (DCE to DCE) to be a different speed than the speed that the bits move between the DTE and DCE on both ends of the conversation. Normally the speed between the DTE and DCE is higher than the DCE to DCE speed because of the use of compression by the modems. Because the number of bits needed to describe a byte varied during the trip between the two machines plus the differing bits-per-seconds speeds that are used present on the DTE-DCE and DCE-DCE links, the usage of the term Baud to describe the overall communication speed causes problems and can misrepresent the true transmission speed. So Bits Per Second (bps) is the correct term to use to describe the transmission rate seen at the DCE to DCE interface and Baud or Bits Per Second are acceptable terms to use when a connection is made between two systems with a wired connection, or if a modem is in use that is not performing error-correction or compression. Modern high speed modems (2400, 9600, 14,400, and 19,200bps) in reality still operate at or below 2400 baud, or more accurately, 2400 Symbols per second. High speed modem are able to encode more bits of data into each Symbol using a technique called Constellation Stuffing, which is why the effective bits per second rate of the modem is higher, but the modem continues to operate within the limited audio bandwidth that the telephone system provides. Modems operating at 28,800 and higher speeds have variable Symbol rates, but the technique is the same. The IBM Personal Computer UART Starting with the original IBM Personal Computer, IBM selected the National Semiconductor INS8250 UART for use in the IBM PC Parallel/Serial Adapter. Subsequent generations of compatible computers from IBM and other vendors continued to use the INS8250 or improved versions of the National Semiconductor UART family. National Semiconductor UART Family Tree There have been several versions and subsequent generations of the INS8250 UART. Each major version is described below. INS8250 -> INS8250B \ \ \-> INS8250A -> INS82C50A \ \ \-> NS16450 -> NS16C450 \ \ \-> NS16550 -> NS16550A -> PC16550D INS8250 This part was used in the original IBM PC and IBM PC/XT. The original name for this part was the INS8250 ACE (Asynchronous Communications Element) and it is made from NMOS technology. The 8250 uses eight I/O ports and has a one-byte send and a one-byte receive buffer. This original UART has several race conditions and other flaws. The original IBM BIOS includes code to work around these flaws, but this made the BIOS dependent on the flaws being present, so subsequent parts like the 8250A, 16450 or 16550 could not be used in the original IBM PC or IBM PC/XT. INS8250-B This is the slower speed of the INS8250 made from NMOS technology. It contains the same problems as the original INS8250. INS8250A An improved version of the INS8250 using XMOS technology with various functional flaws corrected. The INS8250A was used initially in PC clone computers by vendors who used “clean” BIOS designs. Because of the corrections in the chip, this part could not be used with a BIOS compatible with the INS8250 or INS8250B. INS82C50A This is a CMOS version (low power consumption) of the INS8250A and has similar functional characteristics. NS16450 Same as NS8250A with improvements so it can be used with faster CPU bus designs. IBM used this part in the IBM AT and updated the IBM BIOS to no longer rely on the bugs in the INS8250. NS16C450 This is a CMOS version (low power consumption) of the NS16450. NS16550 Same as NS16450 with a 16-byte send and receive buffer but the buffer design was flawed and could not be reliably be used. NS16550A Same as NS16550 with the buffer flaws corrected. The 16550A and its successors have become the most popular UART design in the PC industry, mainly due it its ability to reliably handle higher data rates on operating systems with sluggish interrupt response times. NS16C552 This component consists of two NS16C550A CMOS UARTs in a single package. PC16550D Same as NS16550A with subtle flaws corrected. This is revision D of the 16550 family and is the latest design available from National Semiconductor. The NS16550AF and the PC16550D are the same thing National reorganized their part numbering system a few years ago, and the NS16550AFN no longer exists by that name. (If you have a NS16550AFN, look at the date code on the part, which is a four digit number that usually starts with a nine. The first two digits of the number are the year, and the last two digits are the week in that year when the part was packaged. If you have a NS16550AFN, it is probably a few years old.) The new numbers are like PC16550DV, with minor differences in the suffix letters depending on the package material and its shape. (A description of the numbering system can be found below.) It is important to understand that in some stores, you may pay $15(US) for a NS16550AFN made in 1990 and in the next bin are the new PC16550DN parts with minor fixes that National has made since the AFN part was in production, the PC16550DN was probably made in the past six months and it costs half (as low as $5(US) in volume) as much as the NS16550AFN because they are readily available. As the supply of NS16550AFN chips continues to shrink, the price will probably continue to increase until more people discover and accept that the PC16550DN really has the same function as the old part number. National Semiconductor Part Numbering System The older NSnnnnnrqp part numbers are now of the format PCnnnnnrgp. The r is the revision field. The current revision of the 16550 from National Semiconductor is D. The p is the package-type field. The types are: "F" QFP (quad flat pack) L lead type "N" DIP (dual inline package) through hole straight lead type "V" LPCC (lead plastic chip carrier) J lead type The g is the product grade field. If an I precedes the package-type letter, it indicates an “industrial” grade part, which has higher specs than a standard part but not as high as Military Specification (Milspec) component. This is an optional field. So what we used to call a NS16550AFN (DIP Package) is now called a PC16550DN or PC16550DIN. Other Vendors and Similar UARTs Over the years, the 8250, 8250A, 16450 and 16550 have been licensed or copied by other chip vendors. In the case of the 8250, 8250A and 16450, the exact circuit (the “megacell”) was licensed to many vendors, including Western Digital and Intel. Other vendors reverse-engineered the part or produced emulations that had similar behavior. In internal modems, the modem designer will frequently emulate the 8250A/16450 with the modem microprocessor, and the emulated UART will frequently have a hidden buffer consisting of several hundred bytes. Because of the size of the buffer, these emulations can be as reliable as a 16550A in their ability to handle high speed data. However, most operating systems will still report that the UART is only a 8250A or 16450, and may not make effective use of the extra buffering present in the emulated UART unless special drivers are used. Some modem makers are driven by market forces to abandon a design that has hundreds of bytes of buffer and instead use a 16550A UART so that the product will compare favorably in market comparisons even though the effective performance may be lowered by this action. A common misconception is that all parts with “16550A” written on them are identical in performance. There are differences, and in some cases, outright flaws in most of these 16550A clones. When the NS16550 was developed, the National Semiconductor obtained several patents on the design and they also limited licensing, making it harder for other vendors to provide a chip with similar features. Because of the patents, reverse-engineered designs and emulations had to avoid infringing the claims covered by the patents. Subsequently, these copies almost never perform exactly the same as the NS16550A or PC16550D, which are the parts most computer and modem makers want to buy but are sometimes unwilling to pay the price required to get the genuine part. Some of the differences in the clone 16550A parts are unimportant, while others can prevent the device from being used at all with a given operating system or driver. These differences may show up when using other drivers, or when particular combinations of events occur that were not well tested or considered in the Windows driver. This is because most modem vendors and 16550-clone makers use the Microsoft drivers from Windows for Workgroups 3.11 and the Microsoft MSD utility as the primary tests for compatibility with the NS16550A. This over-simplistic criteria means that if a different operating system is used, problems could appear due to subtle differences between the clones and genuine components. National Semiconductor has made available a program named COMTEST that performs compatibility tests independent of any OS drivers. It should be remembered that the purpose of this type of program is to demonstrate the flaws in the products of the competition, so the program will report major as well as extremely subtle differences in behavior in the part being tested. In a series of tests performed by the author of this document in 1994, components made by National Semiconductor, TI, StarTech, and CMD as well as megacells and emulations embedded in internal modems were tested with COMTEST. A difference count for some of these components is listed below. Because these tests were performed in 1994, they may not reflect the current performance of the given product from a vendor. It should be noted that COMTEST normally aborts when an excessive number or certain types of problems have been detected. As part of this testing, COMTEST was modified so that it would not abort no matter how many differences were encountered. Vendor Part Number Errors (aka "differences" reported) National (PC16550DV) 0 National (NS16550AFN) 0 National (NS16C552V) 0 TI (TL16550AFN) 3 CMD (16C550PE) 19 StarTech (ST16C550J) 23 Rockwell Reference modem with internal 16550 or an emulation (RC144DPi/C3000-25) 117 Sierra Modem with an internal 16550 (SC11951/SC11351) 91 To date, the author of this document has not found any non-National parts that report zero differences using the COMTEST program. It should also be noted that National has had five versions of the 16550 over the years and the newest parts behave a bit differently than the classic NS16550AFN that is considered the benchmark for functionality. COMTEST appears to turn a blind eye to the differences within the National product line and reports no errors on the National parts (except for the original 16550) even when there are official erratas that describe bugs in the A, B and C revisions of the parts, so this bias in COMTEST must be taken into account. It is important to understand that a simple count of differences from COMTEST does not reveal a lot about what differences are important and which are not. For example, about half of the differences reported in the two modems listed above that have internal UARTs were caused by the clone UARTs not supporting five- and six-bit character modes. The real 16550, 16450, and 8250 UARTs all support these modes and COMTEST checks the functionality of these modes so over fifty differences are reported. However, almost no modern modem supports five- or six-bit characters, particularly those with error-correction and compression capabilities. This means that the differences related to five- and six-bit character modes can be discounted. Many of the differences COMTEST reports have to do with timing. In many of the clone designs, when the host reads from one port, the status bits in some other port may not update in the same amount of time (some faster, some slower) as a real NS16550AFN and COMTEST looks for these differences. This means that the number of differences can be misleading in that one device may only have one or two differences but they are extremely serious, and some other device that updates the status registers faster or slower than the reference part (that would probably never affect the operation of a properly written driver) could have dozens of differences reported. COMTEST can be used as a screening tool to alert the administrator to the presence of potentially incompatible components that might cause problems or have to be handled as a special case. If you run COMTEST on a 16550 that is in a modem or a modem is attached to the serial port, you need to first issue a ATE0&W command to the modem so that the modem will not echo any of the test characters. If you forget to do this, COMTEST will report at least this one difference: Error (6)...Timeout interrupt failed: IIR = c1 LSR = 61 8250/16450/16550 Registers The 8250/16450/16550 UART occupies eight contiguous I/O port addresses. In the IBM PC, there are two defined locations for these eight ports and they are known collectively as COM1 and COM2. The makers of PC-clones and add-on cards have created two additional areas known as COM3 and COM4, but these extra COM ports conflict with other hardware on some systems. The most common conflict is with video adapters that provide IBM 8514 emulation. COM1 is located from 0x3f8 to 0x3ff and normally uses IRQ 4 COM2 is located from 0x2f8 to 0x2ff and normally uses IRQ 3 COM3 is located from 0x3e8 to 0x3ef and has no standardized IRQ COM4 is located from 0x2e8 to 0x2ef and has no standardized IRQ. A description of the I/O ports of the 8250/16450/16550 UART is provided below. I/O Port Access Allowed Description +0x00 write (DLAB==0) Transmit Holding Register (THR).Information written to this port are treated as data words and will be transmitted by the UART. +0x00 read (DLAB==0) Receive Buffer Register (RBR).Any data words received by the UART form the serial link are accessed by the host by reading this port. +0x00 write/read (DLAB==1) Divisor Latch LSB (DLL)This value will be divided from the master input clock (in the IBM PC, the master clock is 1.8432MHz) and the resulting clock will determine the baud rate of the UART. This register holds bits 0 thru 7 of the divisor. +0x01 write/read (DLAB==1) Divisor Latch MSB (DLH)This value will be divided from the master input clock (in the IBM PC, the master clock is 1.8432MHz) and the resulting clock will determine the baud rate of the UART. This register holds bits 8 thru 15 of the divisor. +0x01 write/read (DLAB==0) Interrupt Enable Register (IER)The 8250/16450/16550 UART classifies events into one of four categories. Each category can be configured to generate an interrupt when any of the events occurs. The 8250/16450/16550 UART generates a single external interrupt signal regardless of how many events in the enabled categories have occurred. It is up to the host processor to respond to the interrupt and then poll the enabled interrupt categories (usually all categories have interrupts enabled) to determine the true cause(s) of the interrupt. Bit 7 Reserved, always 0. Bit 6 Reserved, always 0. Bit 5 Reserved, always 0. Bit 4 Reserved, always 0. Bit 3 Enable Modem Status Interrupt (EDSSI). Setting this bit to "1" allows the UART to generate an interrupt when a change occurs on one or more of the status lines. Bit 2 Enable Receiver Line Status Interrupt (ELSI) Setting this bit to "1" causes the UART to generate an interrupt when the an error (or a BREAK signal) has been detected in the incoming data. Bit 1 Enable Transmitter Holding Register Empty Interrupt (ETBEI) Setting this bit to "1" causes the UART to generate an interrupt when the UART has room for one or more additional characters that are to be transmitted. Bit 0 Enable Received Data Available Interrupt (ERBFI) Setting this bit to "1" causes the UART to generate an interrupt when the UART has received enough characters to exceed the trigger level of the FIFO, or the FIFO timer has expired (stale data), or a single character has been received when the FIFO is disabled. +0x02 write FIFO Control Register (FCR) (This port does not exist on the 8250 and 16450 UART.) Bit 7 Receiver Trigger Bit #1 Bit 6 Receiver Trigger Bit #0These two bits control at what point the receiver is to generate an interrupt when the FIFO is active. 7 6 How many words are received before an interrupt is generated 0 0 1 0 1 4 1 0 8 1 1 14 Bit 5 Reserved, always 0. Bit 4 Reserved, always 0. Bit 3 DMA Mode Select. If Bit 0 is set to "1" (FIFOs enabled), setting this bit changes the operation of the -RXRDY and -TXRDY signals from Mode 0 to Mode 1. Bit 2 Transmit FIFO Reset. When a "1" is written to this bit, the contents of the FIFO are discarded. Any word currently being transmitted will be sent intact. This function is useful in aborting transfers. Bit 1 Receiver FIFO Reset. When a "1" is written to this bit, the contents of the FIFO are discarded. Any word currently being assembled in the shift register will be received intact. Bit 0 16550 FIFO Enable. When set, both the transmit and receive FIFOs are enabled. Any contents in the holding register, shift registers or FIFOs are lost when FIFOs are enabled or disabled. +0x02 read Interrupt Identification Register Bit 7 FIFOs enabled. On the 8250/16450 UART, this bit is zero. Bit 6 FIFOs enabled. On the 8250/16450 UART, this bit is zero. Bit 5 Reserved, always 0. Bit 4 Reserved, always 0. Bit 3 Interrupt ID Bit #2. On the 8250/16450 UART, this bit is zero. Bit 2 Interrupt ID Bit #1 Bit 1 Interrupt ID Bit #0.These three bits combine to report the category of event that caused the interrupt that is in progress. These categories have priorities, so if multiple categories of events occur at the same time, the UART will report the more important events first and the host must resolve the events in the order they are reported. All events that caused the current interrupt must be resolved before any new interrupts will be generated. (This is a limitation of the PC architecture.) 2 1 0 Priority Description 0 1 1 First Received Error (OE, PE, BI, or FE) 0 1 0 Second Received Data Available 1 1 0 Second Trigger level identification (Stale data in receive buffer) 0 0 1 Third Transmitter has room for more words (THRE) 0 0 0 Fourth Modem Status Change (-CTS, -DSR, -RI, or -DCD) Bit 0 Interrupt Pending Bit. If this bit is set to "0", then at least one interrupt is pending. +0x03 write/read Line Control Register (LCR) Bit 7 Divisor Latch Access Bit (DLAB). When set, access to the data transmit/receive register (THR/RBR) and the Interrupt Enable Register (IER) is disabled. Any access to these ports is now redirected to the Divisor Latch Registers. Setting this bit, loading the Divisor Registers, and clearing DLAB should be done with interrupts disabled. Bit 6 Set Break. When set to "1", the transmitter begins to transmit continuous Spacing until this bit is set to "0". This overrides any bits of characters that are being transmitted. Bit 5 Stick Parity. When parity is enabled, setting this bit causes parity to always be "1" or "0", based on the value of Bit 4. Bit 4 Even Parity Select (EPS). When parity is enabled and Bit 5 is "0", setting this bit causes even parity to be transmitted and expected. Otherwise, odd parity is used. Bit 3 Parity Enable (PEN). When set to "1", a parity bit is inserted between the last bit of the data and the Stop Bit. The UART will also expect parity to be present in the received data. Bit 2 Number of Stop Bits (STB). If set to "1" and using 5-bit data words, 1.5 Stop Bits are transmitted and expected in each data word. For 6, 7 and 8-bit data words, 2 Stop Bits are transmitted and expected. When this bit is set to "0", one Stop Bit is used on each data word. Bit 1 Word Length Select Bit #1 (WLSB1) Bit 0 Word Length Select Bit #0 (WLSB0) Together these bits specify the number of bits in each data word. 1 0 Word Length 0 0 5 Data Bits 0 1 6 Data Bits 1 0 7 Data Bits 1 1 8 Data Bits +0x04 write/read Modem Control Register (MCR) Bit 7 Reserved, always 0. Bit 6 Reserved, always 0. Bit 5 Reserved, always 0. Bit 4 Loop-Back Enable. When set to "1", the UART transmitter and receiver are internally connected together to allow diagnostic operations. In addition, the UART modem control outputs are connected to the UART modem control inputs. CTS is connected to RTS, DTR is connected to DSR, OUT1 is connected to RI, and OUT 2 is connected to DCD. Bit 3 OUT 2. An auxiliary output that the host processor may set high or low. In the IBM PC serial adapter (and most clones), OUT 2 is used to tri-state (disable) the interrupt signal from the 8250/16450/16550 UART. Bit 2 OUT 1. An auxiliary output that the host processor may set high or low. This output is not used on the IBM PC serial adapter. Bit 1 Request to Send (RTS). When set to "1", the output of the UART -RTS line is Low (Active). Bit 0 Data Terminal Ready (DTR). When set to "1", the output of the UART -DTR line is Low (Active). +0x05 write/read Line Status Register (LSR) Bit 7 Error in Receiver FIFO. On the 8250/16450 UART, this bit is zero. This bit is set to "1" when any of the bytes in the FIFO have one or more of the following error conditions: PE, FE, or BI. Bit 6 Transmitter Empty (TEMT). When set to "1", there are no words remaining in the transmit FIFO or the transmit shift register. The transmitter is completely idle. Bit 5 Transmitter Holding Register Empty (THRE). When set to "1", the FIFO (or holding register) now has room for at least one additional word to transmit. The transmitter may still be transmitting when this bit is set to "1". Bit 4 Break Interrupt (BI). The receiver has detected a Break signal. Bit 3 Framing Error (FE). A Start Bit was detected but the Stop Bit did not appear at the expected time. The received word is probably garbled. Bit 2 Parity Error (PE). The parity bit was incorrect for the word received. Bit 1 Overrun Error (OE). A new word was received and there was no room in the receive buffer. The newly-arrived word in the shift register is discarded. On 8250/16450 UARTs, the word in the holding register is discarded and the newly- arrived word is put in the holding register. Bit 0 Data Ready (DR) One or more words are in the receive FIFO that the host may read. A word must be completely received and moved from the shift register into the FIFO (or holding register for 8250/16450 designs) before this bit is set. +0x06 write/read Modem Status Register (MSR) Bit 7 Data Carrier Detect (DCD). Reflects the state of the DCD line on the UART. Bit 6 Ring Indicator (RI). Reflects the state of the RI line on the UART. Bit 5 Data Set Ready (DSR). Reflects the state of the DSR line on the UART. Bit 4 Clear To Send (CTS). Reflects the state of the CTS line on the UART. Bit 3 Delta Data Carrier Detect (DDCD). Set to "1" if the -DCD line has changed state one more more times since the last time the MSR was read by the host. Bit 2 Trailing Edge Ring Indicator (TERI). Set to "1" if the -RI line has had a low to high transition since the last time the MSR was read by the host. Bit 1 Delta Data Set Ready (DDSR). Set to "1" if the -DSR line has changed state one more more times since the last time the MSR was read by the host. Bit 0 Delta Clear To Send (DCTS). Set to "1" if the -CTS line has changed state one more more times since the last time the MSR was read by the host. +0x07 write/read Scratch Register (SCR). This register performs no function in the UART. Any value can be written by the host to this location and read by the host later on. Beyond the 16550A UART Although National Semiconductor has not offered any components compatible with the 16550 that provide additional features, various other vendors have. Some of these components are described below. It should be understood that to effectively utilize these improvements, drivers may have to be provided by the chip vendor since most of the popular operating systems do not support features beyond those provided by the 16550. ST16650 By default this part is similar to the NS16550A, but an extended 32-byte send and receive buffer can be optionally enabled. Made by Startech. TIL16660 By default this part behaves similar to the NS16550A, but an extended 64-byte send and receive buffer can be optionally enabled. Made by Texas Instruments. Hayes ESP This proprietary plug-in card contains a 2048-byte send and receive buffer, and supports data rates to 230.4Kbit/sec. Made by Hayes. In addition to these “dumb” UARTs, many vendors produce intelligent serial communication boards. This type of design usually provides a microprocessor that interfaces with several UARTs, processes and buffers the data, and then alerts the main PC processor when necessary. Because the UARTs are not directly accessed by the PC processor in this type of communication system, it is not necessary for the vendor to use UARTs that are compatible with the 8250, 16450, or the 16550 UART. This leaves the designer free to components that may have better performance characteristics. Configuring the <devicename>sio</devicename> driver The sio driver provides support for NS8250-, NS16450-, NS16550 and NS16550A-based EIA RS-232C (CCITT V.24) communications interfaces. Several multiport cards are supported as well. See the &man.sio.4; manual page for detailed technical documentation. Digi International (DigiBoard) PC/8 Contributed by &a.awebster;. 26 August 1995. Here is a config snippet from a machine with a Digi International PC/8 with 16550. It has 8 modems connected to these 8 lines, and they work just great. Do not forget to add options COM_MULTIPORT or it will not work very well! device sio4 at isa? port 0x100 tty flags 0xb05 device sio5 at isa? port 0x108 tty flags 0xb05 device sio6 at isa? port 0x110 tty flags 0xb05 device sio7 at isa? port 0x118 tty flags 0xb05 device sio8 at isa? port 0x120 tty flags 0xb05 device sio9 at isa? port 0x128 tty flags 0xb05 device sio10 at isa? port 0x130 tty flags 0xb05 device sio11 at isa? port 0x138 tty flags 0xb05 irq 9 vector siointr The trick in setting this up is that the MSB of the flags represent the last SIO port, in this case 11 so flags are 0xb05. Boca 16 Contributed by &a.whiteside;. 26 August 1995. The procedures to make a Boca 16 port board with FreeBSD are pretty straightforward, but you will need a couple things to make it work: You either need the kernel sources installed so you can recompile the necessary options or you will need someone else to compile it for you. The 2.0.5 default kernel does not come with multiport support enabled and you will need to add a device entry for each port anyways. Two, you will need to know the interrupt and IO setting for your Boca Board so you can set these options properly in the kernel. One important note — the actual UART chips for the Boca 16 are in the connector box, not on the internal board itself. So if you have it unplugged, probes of those ports will fail. I have never tested booting with the box unplugged and plugging it back in, and I suggest you do not either. If you do not already have a custom kernel configuration file set up, refer to Kernel Configuration for general procedures. The following are the specifics for the Boca 16 board and assume you are using the kernel name MYKERNEL and editing with vi. Add the line options COM_MULTIPORT to the config file. Where the current device sion lines are, you will need to add 16 more devices. Only the last device includes the interrupt vector for the board. (See the &man.sio.4; manual page for detail as to why.) The following example is for a Boca Board with an interrupt of 3, and a base IO address 100h. The IO address for Each port is +8 hexadecimal from the previous port, thus the 100h, 108h, 110h... addresses. device sio1 at isa? port 0x100 tty flags 0x1005 device sio2 at isa? port 0x108 tty flags 0x1005 device sio3 at isa? port 0x110 tty flags 0x1005 device sio4 at isa? port 0x118 tty flags 0x1005 … device sio15 at isa? port 0x170 tty flags 0x1005 device sio16 at isa? port 0x178 tty flags 0x1005 irq 3 vector siointr The flags entry must be changed from this example unless you are using the exact same sio assignments. Flags are set according to 0xMYY where M indicates the minor number of the master port (the last port on a Boca 16) and YY indicates if FIFO is enabled or disabled(enabled), IRQ sharing is used(yes) and if there is an AST/4 compatible IRQ control register(no). In this example, flags 0x1005 indicates that the master port is sio16. If I added another board and assigned sio17 through sio28, the flags for all 16 ports on that board would be 0x1C05, where 1C indicates the minor number of the master port. Do not change the 05 setting. Save and complete the kernel configuration, recompile, install and reboot. Presuming you have successfully installed the recompiled kernel and have it set to the correct address and IRQ, your boot message should indicate the successful probe of the Boca ports as follows: (obviously the sio numbers, IO and IRQ could be different) sio1 at 0x100-0x107 flags 0x1005 on isa sio1: type 16550A (multiport) sio2 at 0x108-0x10f flags 0x1005 on isa sio2: type 16550A (multiport) sio3 at 0x110-0x117 flags 0x1005 on isa sio3: type 16550A (multiport) sio4 at 0x118-0x11f flags 0x1005 on isa sio4: type 16550A (multiport) sio5 at 0x120-0x127 flags 0x1005 on isa sio5: type 16550A (multiport) sio6 at 0x128-0x12f flags 0x1005 on isa sio6: type 16550A (multiport) sio7 at 0x130-0x137 flags 0x1005 on isa sio7: type 16550A (multiport) sio8 at 0x138-0x13f flags 0x1005 on isa sio8: type 16550A (multiport) sio9 at 0x140-0x147 flags 0x1005 on isa sio9: type 16550A (multiport) sio10 at 0x148-0x14f flags 0x1005 on isa sio10: type 16550A (multiport) sio11 at 0x150-0x157 flags 0x1005 on isa sio11: type 16550A (multiport) sio12 at 0x158-0x15f flags 0x1005 on isa sio12: type 16550A (multiport) sio13 at 0x160-0x167 flags 0x1005 on isa sio13: type 16550A (multiport) sio14 at 0x168-0x16f flags 0x1005 on isa sio14: type 16550A (multiport) sio15 at 0x170-0x177 flags 0x1005 on isa sio15: type 16550A (multiport) sio16 at 0x178-0x17f irq 3 flags 0x1005 on isa sio16: type 16550A (multiport master) If the messages go by too fast to see, &prompt.root; dmesg | more will show you the boot messages. Next, appropriate entries in /dev for the devices must be made using the /dev/MAKEDEV script. After becoming root: &prompt.root; cd /dev &prompt.root; ./MAKEDEV tty1 &prompt.root; ./MAKEDEV cua1 (everything in between) &prompt.root; ./MAKEDEV ttyg &prompt.root; ./MAKEDEV cuag If you do not want or need callout devices for some reason, you can dispense with making the cua* devices. If you want a quick and sloppy way to make sure the devices are working, you can simply plug a modem into each port and (as root) &prompt.root; echo at > ttyd* for each device you have made. You should see the RX lights flash for each working port. Configuring the <devicename>cy</devicename> driver Contributed by &a.alex;. 6 June 1996. The Cyclades multiport cards are based on the cy driver instead of the usual sio driver used by other multiport cards. Configuration is a simple matter of: Add the cy device to your kernel configuration (note that your irq and iomem settings may differ). device cy0 at isa? tty irq 10 iomem 0xd4000 iosiz 0x2000 vector cyintr Rebuild and install the new kernel. Make the device nodes by typing (the following example assumes an 8-port board): &prompt.root; cd /dev &prompt.root; for i in 0 1 2 3 4 5 6 7;do ./MAKEDEV cuac$i ttyc$i;done If appropriate, add dialup entries to /etc/ttys by duplicating serial device (ttyd) entries and using ttyc in place of ttyd. For example: ttyc0 "/usr/libexec/getty std.38400" unknown on insecure ttyc1 "/usr/libexec/getty std.38400" unknown on insecure ttyc2 "/usr/libexec/getty std.38400" unknown on insecure … ttyc7 "/usr/libexec/getty std.38400" unknown on insecure Reboot with the new kernel. - Configuring the <devicename>si</devicename> driver - - Contributed by &a.nsayer;. 25 March 1998. - - The Specialix SI/XIO and SX multiport cards use the si driver. A single - machine can have up to 4 host cards. The following host cards are supported: - - ISA SI/XIO host card (2 versions) - EISA SI/XIO host card - PCI SI/XIO host card - ISA SX host card - PCI SX host card -Although the SX and SI/XIO host cards look markedly different, their - functionality are basically the same. The host cards do not use I/O - locations, but instead require a 32K chunk of memory. The factory - configuration for ISA cards places this at 0xd0000-0xd7fff. They - also require an IRQ. PCI cards will, of course, autoconfigure themselves. - - You can attach up to 4 external modules to each host card. The external - modules contain either 4 or 8 serial ports. They come in the following - varieties: - -SI 4 or 8 port modules. Up to 57600 bps on each port supported. - XIO 8 port modules. Up to 115200 bps on each port supported. One - type of XIO module has 7 serial and 1 parallel port. - SXDC 8 port modules. Up to 921600 bps on each port supported. Like - XIO, a module is available with one parallel port as well. - + + Configuring the <devicename>si</devicename> driver + + Contributed by &a.nsayer;. 25 March + 1998. + + The Specialix SI/XIO and SX multiport cards use the si driver. A + single machine can have up to 4 host cards. The following host cards + are supported: + + + ISA SI/XIO host card (2 versions) + EISA SI/XIO host card + PCI SI/XIO host card + ISA SX host card + PCI SX host card + + Although the SX and SI/XIO host cards look markedly different, + their functionality are basically the same. The host cards do not + use I/O locations, but instead require a 32K chunk of memory. The + factory configuration for ISA cards places this at 0xd0000-0xd7fff. + They also require an IRQ. PCI cards will, of course, autoconfigure + themselves. + You can attach up to 4 external modules to each host card. The + external modules contain either 4 or 8 serial ports. They come in + the following varieties: + + + SI 4 or 8 port modules. Up to 57600 bps on each port + supported. + + XIO 8 port modules. Up to 115200 bps on each port + supported. One type of XIO module has 7 serial and 1 parallel + port. + + SXDC 8 port modules. Up to 921600 bps on each port + supported. Like XIO, a module is available with one parallel + port as well. + -To configure an ISA host card, add the following line to your - kernel configuration file, changing - the numbers as appropriate: + To configure an ISA host card, add the following line to your + kernel configuration + file, changing the numbers as appropriate: - - device si0 at isa? tty iomem 0xd0000 irq 11 - - - Valid IRQ numbers are 9, 10, 11, 12 and 15 for SX ISA host cards and - 11, 12 and 15 for SI/XIO ISA host cards. + +device si0 at isa? tty iomem 0xd0000 irq 11 + + Valid IRQ numbers are 9, 10, 11, 12 and 15 for SX ISA host cards + and 11, 12 and 15 for SI/XIO ISA host cards. - To configure an EISA or PCI host card, use this line: + To configure an EISA or PCI host card, use this line: - - device si0 - + +device si0 -After adding the configuration entry, - rebuild and install - your new kernel. - -After rebooting with the new kernel, you need to make the - device nodes - in /dev. The MAKEDEV script will take care of this for you. Count how many - total ports you have and type: + After adding the configuration entry, rebuild and install your + new kernel. - &prompt.root; cd /dev -&prompt.root; ./MAKEDEV ttyAnn cuaAnn + After rebooting with the new kernel, you need to make the device nodes in /dev. The + MAKEDEV script will take care of this for you. + Count how many total ports you have and type: - (where nn is the number of ports) + &prompt.root; cd /dev +&prompt.root; ./MAKEDEV ttyAnn cuaAnn -If you want login prompts to appear on these ports, you will need - to add lines like this to /etc/ttys: + (where nn is the number of + ports) - - ttyA01 "/usr/libexec/getty std.9600" vt100 on insecure - - -Change the terminal type as approprate. For modems, dialup or - unknown is fine. + If you want login prompts to appear on these ports, you will + need to add lines like this to /etc/ttys: + + +ttyA01 "/usr/libexec/getty std.9600" vt100 on insecure + - - - - + Change the terminal type as approprate. For modems, + dialup or unknown is + fine. * Parallel ports * Modems * Network cards * Keyboards * Mice * Other Storage Devices Using ESDI hard disks Copyright © 1995, &a.wilko;. 24 September 1995. ESDI is an acronym that means Enhanced Small Device Interface. It is loosely based on the good old ST506/412 interface originally devised by Seagate Technology, the makers of the first affordable 5.25" winchester disk. The acronym says Enhanced, and rightly so. In the first place the speed of the interface is higher, 10 or 15 Mbits/second instead of the 5 Mbits/second of ST412 interfaced drives. Secondly some higher level commands are added, making the ESDI interface somewhat 'smarter' to the operating system driver writers. It is by no means as smart as SCSI by the way. ESDI is standardized by ANSI. Capacities of the drives are boosted by putting more sectors on each track. Typical is 35 sectors per track, high capacity drives I have seen were up to 54 sectors/track. Although ESDI has been largely obsoleted by IDE and SCSI interfaces, the availability of free or cheap surplus drives makes them ideal for low (or now) budget systems. Concepts of ESDI Physical connections The ESDI interface uses two cables connected to each drive. One cable is a 34 pin flat cable edge connector that carries the command and status signals from the controller to the drive and vice-versa. The command cable is daisy chained between all the drives. So, it forms a bus onto which all drives are connected. The second cable is a 20 pin flat cable edge connector that carries the data to and from the drive. This cable is radially connected, so each drive has its own direct connection to the controller. To the best of my knowledge PC ESDI controllers are limited to using a maximum of 2 drives per controller. This is compatibility feature(?) left over from the WD1003 standard that reserves only a single bit for device addressing. Device addressing On each command cable a maximum of 7 devices and 1 controller can be present. To enable the controller to uniquely identify which drive it addresses, each ESDI device is equipped with jumpers or switches to select the devices address. On PC type controllers the first drive is set to address 0, the second disk to address 1. Always make sure you set each disk to an unique address! So, on a PC with its two drives/controller maximum the first drive is drive 0, the second is drive 1. Termination The daisy chained command cable (the 34 pin cable remember?) needs to be terminated at the last drive on the chain. For this purpose ESDI drives come with a termination resistor network that can be removed or disabled by a jumper when it is not used. So, one and only one drive, the one at the farthest end of the command cable has its terminator installed/enabled. The controller automatically terminates the other end of the cable. Please note that this implies that the controller must be at one end of the cable and not in the middle. Using ESDI disks with FreeBSD Why is ESDI such a pain to get working in the first place? People who tried ESDI disks with FreeBSD are known to have developed a profound sense of frustration. A combination of factors works against you to produce effects that are hard to understand when you have never seen them before. This has also led to the popular legend ESDI and FreeBSD is a plain NO-GO. The following sections try to list all the pitfalls and solutions. ESDI speed variants As briefly mentioned before, ESDI comes in two speed flavors. The older drives and controllers use a 10 Mbits/second data transfer rate. Newer stuff uses 15 Mbits/second. It is not hard to imagine that 15 Mbits/second drive cause problems on controllers laid out for 10 Mbits/second. As always, consult your controller and drive documentation to see if things match. Stay on track Mainstream ESDI drives use 34 to 36 sectors per track. Most (older) controllers cannot handle more than this number of sectors. Newer, higher capacity, drives use higher numbers of sectors per track. For instance, I own a 670 Mb drive that has 54 sectors per track. In my case, the controller could not handle this number of sectors. It proved to work well except that it only used 35 sectors on each track. This meant losing a lot of disk space. Once again, check the documentation of your hardware for more info. Going out-of-spec like in the example might or might not work. Give it a try or get another more capable controller. Hard or soft sectoring Most ESDI drives allow hard or soft sectoring to be selected using a jumper. Hard sectoring means that the drive will produce a sector pulse on the start of each new sector. The controller uses this pulse to tell when it should start to write or read. Hard sectoring allows a selection of sector size (normally 256, 512 or 1024 bytes per formatted sector). FreeBSD uses 512 byte sectors. The number of sectors per track also varies while still using the same number of bytes per formatted sector. The number of unformatted bytes per sector varies, dependent on your controller it needs more or less overhead bytes to work correctly. Pushing more sectors on a track of course gives you more usable space, but might give problems if your controller needs more bytes than the drive offers. In case of soft sectoring, the controller itself determines where to start/stop reading or writing. For ESDI hard sectoring is the default (at least on everything I came across). I never felt the urge to try soft sectoring. In general, experiment with sector settings before you install FreeBSD because you need to re-run the low-level format after each change. Low level formatting ESDI drives need to be low level formatted before they are usable. A reformat is needed whenever you figgle with the number of sectors/track jumpers or the physical orientation of the drive (horizontal, vertical). So, first think, then format. The format time must not be underestimated, for big disks it can take hours. After a low level format, a surface scan is done to find and flag bad sectors. Most disks have a manufacturer bad block list listed on a piece of paper or adhesive sticker. In addition, on most disks the list is also written onto the disk. Please use the manufacturer's list. It is much easier to remap a defect now than after FreeBSD is installed. Stay away from low-level formatters that mark all sectors of a track as bad as soon as they find one bad sector. Not only does this waste space, it also and more importantly causes you grief with bad144 (see the section on bad144). Translations Translations, although not exclusively a ESDI-only problem, might give you real trouble. Translations come in multiple flavors. Most of them have in common that they attempt to work around the limitations posed upon disk geometries by the original IBM PC/AT design (thanks IBM!). First of all there is the (in)famous 1024 cylinder limit. For a system to be able to boot, the stuff (whatever operating system) must be in the first 1024 cylinders of a disk. Only 10 bits are available to encode the cylinder number. For the number of sectors the limit is 64 (0-63). When you combine the 1024 cylinder limit with the 16 head limit (also a design feature) you max out at fairly limited disk sizes. To work around this problem, the manufacturers of ESDI PC controllers added a BIOS prom extension on their boards. This BIOS extension handles disk I/O for booting (and for some operating systems all disk I/O) by using translation. For instance, a big drive might be presented to the system as having 32 heads and 64 sectors/track. The result is that the number of cylinders is reduced to something below 1024 and is therefore usable by the system without problems. It is noteworthy to know that FreeBSD does not use the BIOS after its kernel has started. More on this later. A second reason for translations is the fact that most older system BIOSes could only handle drives with 17 sectors per track (the old ST412 standard). Newer system BIOSes usually have a user-defined drive type (in most cases this is drive type 47). Whatever you do to translations after reading this document, keep in mind that if you have multiple operating systems on the same disk, all must use the same translation While on the subject of translations, I have seen one controller type (but there are probably more like this) offer the option to logically split a drive in multiple partitions as a BIOS option. I had select 1 drive == 1 partition because this controller wrote this info onto the disk. On power-up it read the info and presented itself to the system based on the info from the disk. Spare sectoring Most ESDI controllers offer the possibility to remap bad sectors. During/after the low-level format of the disk bad sectors are marked as such, and a replacement sector is put in place (logically of course) of the bad one. In most cases the remapping is done by using N-1 sectors on each track for actual data storage, and sector N itself is the spare sector. N is the total number of sectors physically available on the track. The idea behind this is that the operating system sees a 'perfect' disk without bad sectors. In the case of FreeBSD this concept is not usable. The problem is that the translation from bad to good is performed by the BIOS of the ESDI controller. FreeBSD, being a true 32 bit operating system, does not use the BIOS after it has been booted. Instead, it has device drivers that talk directly to the hardware. So: don't use spare sectoring, bad block remapping or whatever it may be called by the controller manufacturer when you want to use the disk for FreeBSD. Bad block handling The preceding section leaves us with a problem. The controller's bad block handling is not usable and still FreeBSD's filesystems assume perfect media without any flaws. To solve this problem, FreeBSD use the bad144 tool. Bad144 (named after a Digital Equipment standard for bad block handling) scans a FreeBSD slice for bad blocks. Having found these bad blocks, it writes a table with the offending block numbers to the end of the FreeBSD slice. When the disk is in operation, the disk accesses are checked against the table read from the disk. Whenever a block number is requested that is in the bad144 list, a replacement block (also from the end of the FreeBSD slice) is used. In this way, the bad144 replacement scheme presents 'perfect' media to the FreeBSD filesystems. There are a number of potential pitfalls associated with the use of bad144. First of all, the slice cannot have more than 126 bad sectors. If your drive has a high number of bad sectors, you might need to divide it into multiple FreeBSD slices each containing less than 126 bad sectors. Stay away from low-level format programs that mark every sector of a track as bad when they find a flaw on the track. As you can imagine, the 126 limit is quickly reached when the low-level format is done this way. Second, if the slice contains the root filesystem, the slice should be within the 1024 cylinder BIOS limit. During the boot process the bad144 list is read using the BIOS and this only succeeds when the list is within the 1024 cylinder limit. The restriction is not that only the root filesystem must be within the 1024 cylinder limit, but rather the entire slice that contains the root filesystem. Kernel configuration ESDI disks are handled by the same wddriver as IDE and ST412 MFM disks. The wd driver should work for all WD1003 compatible interfaces. Most hardware is jumperable for one of two different I/O address ranges and IRQ lines. This allows you to have two wd type controllers in one system. When your hardware allows non-standard strappings, you can use these with FreeBSD as long as you enter the correct info into the kernel config file. An example from the kernel config file (they live in /sys/i386/conf BTW). # First WD compatible controller controller wdc0 at isa? port "IO_WD1" bio irq 14 vector wdintr disk wd0 at wdc0 drive 0 disk wd1 at wdc0 drive 1 # Second WD compatible controller controller wdc1 at isa? port "IO_WD2" bio irq 15 vector wdintr disk wd2 at wdc1 drive 0 disk wd3 at wdc1 drive 1 Particulars on ESDI hardware Adaptec 2320 controllers I successfully installed FreeBSD onto a ESDI disk controlled by a ACB-2320. No other operating system was present on the disk. To do so I low level formatted the disk using NEFMT.EXE (ftpable from www.adaptec.com) and answered NO to the question whether the disk should be formatted with a spare sector on each track. The BIOS on the ACD-2320 was disabled. I used the free configurable option in the system BIOS to allow the BIOS to boot it. Before using NEFMT.EXE I tried to format the disk using the ACB-2320 BIOS builtin formatter. This proved to be a show stopper, because it did not give me an option to disable spare sectoring. With spare sectoring enabled the FreeBSD installation process broke down on the bad144 run. Please check carefully which ACB-232xy variant you have. The x is either 0 or 2, indicating a controller without or with a floppy controller on board. The y is more interesting. It can either be a blank, a A-8 or a D. A blank indicates a plain 10 Mbits/second controller. An A-8 indicates a 15 Mbits/second controller capable of handling 52 sectors/track. A D means a 15 Mbits/second controller that can also handle drives with > 36 sectors/track (also 52 ?). All variations should be capable of using 1:1 interleaving. Use 1:1, FreeBSD is fast enough to handle it. Western Digital WD1007 controllers I successfully installed FreeBSD onto a ESDI disk controlled by a WD1007 controller. To be precise, it was a WD1007-WA2. Other variations of the WD1007 do exist. To get it to work, I had to disable the sector translation and the WD1007's onboard BIOS. This implied I could not use the low-level formatter built into this BIOS. Instead, I grabbed WDFMT.EXE from www.wdc.com Running this formatted my drive just fine. Ultrastor U14F controllers According to multiple reports from the net, Ultrastor ESDI boards work OK with FreeBSD. I lack any further info on particular settings. Further reading If you intend to do some serious ESDI hacking, you might want to have the official standard at hand: The latest ANSI X3T10 committee document is: Enhanced Small Device Interface (ESDI) [X3.170-1990/X3.170a-1991] [X3T10/792D Rev 11] On Usenet the newsgroup comp.periphs is a noteworthy place to look for more info. The World Wide Web (WWW) also proves to be a very handy info source: For info on Adaptec ESDI controllers see http://www.adaptec.com/. For info on Western Digital controllers see http://www.wdc.com/. Thanks to... Andrew Gordon for sending me an Adaptec 2320 controller and ESDI disk for testing. What is SCSI? Copyright © 1995, &a.wilko;. July 6, 1996. SCSI is an acronym for Small Computer Systems Interface. It is an ANSI standard that has become one of the leading I/O buses in the computer industry. The foundation of the SCSI standard was laid by Shugart Associates (the same guys that gave the world the first mini floppy disks) when they introduced the SASI bus (Shugart Associates Standard Interface). After some time an industry effort was started to come to a more strict standard allowing devices from different vendors to work together. This effort was recognized in the ANSI SCSI-1 standard. The SCSI-1 standard (approx 1985) is rapidly becoming obsolete. The current standard is SCSI-2 (see Further reading), with SCSI-3 on the drawing boards. In addition to a physical interconnection standard, SCSI defines a logical (command set) standard to which disk devices must adhere. This standard is called the Common Command Set (CCS) and was developed more or less in parallel with ANSI SCSI-1. SCSI-2 includes the (revised) CCS as part of the standard itself. The commands are dependent on the type of device at hand. It does not make much sense of course to define a Write command for a scanner. The SCSI bus is a parallel bus, which comes in a number of variants. The oldest and most used is an 8 bit wide bus, with single-ended signals, carried on 50 wires. (If you do not know what single-ended means, do not worry, that is what this document is all about.) Modern designs also use 16 bit wide buses, with differential signals. This allows transfer speeds of 20Mbytes/second, on cables lengths of up to 25 meters. SCSI-2 allows a maximum bus width of 32 bits, using an additional cable. Quickly emerging are Ultra SCSI (also called Fast-20) and Ultra2 (also called Fast-40). Fast-20 is 20 million transfers per second (20 Mbytes/sec on a 8 bit bus), Fast-40 is 40 million transfers per second (40 Mbytes/sec on a 8 bit bus). Most hard drives sold today are single-ended Ultra SCSI (8 or 16 bits). Of course the SCSI bus not only has data lines, but also a number of control signals. A very elaborate protocol is part of the standard to allow multiple devices to share the bus in an efficient manner. In SCSI-2, the data is always checked using a separate parity line. In pre-SCSI-2 designs parity was optional. In SCSI-3 even faster bus types are introduced, along with a serial SCSI busses that reduces the cabling overhead and allows a higher maximum bus length. You might see names like SSA and Fiberchannel in this context. None of the serial buses are currently in widespread use (especially not in the typical FreeBSD environment). For this reason the serial bus types are not discussed any further. As you could have guessed from the description above, SCSI devices are intelligent. They have to be to adhere to the SCSI standard (which is over 2 inches thick BTW). So, for a hard disk drive for instance you do not specify a head/cylinder/sector to address a particular block, but simply the number of the block you want. Elaborate caching schemes, automatic bad block replacement etc are all made possible by this 'intelligent device' approach. On a SCSI bus, each possible pair of devices can communicate. Whether their function allows this is another matter, but the standard does not restrict it. To avoid signal contention, the 2 devices have to arbitrate for the bus before using it. The philosophy of SCSI is to have a standard that allows older-standard devices to work with newer-standard ones. So, an old SCSI-1 device should normally work on a SCSI-2 bus. I say Normally, because it is not absolutely sure that the implementation of an old device follows the (old) standard closely enough to be acceptable on a new bus. Modern devices are usually more well-behaved, because the standardization has become more strict and is better adhered to by the device manufacturers. Generally speaking, the chances of getting a working set of devices on a single bus is better when all the devices are SCSI-2 or newer. This implies that you do not have to dump all your old stuff when you get that shiny 2GB disk: I own a system on which a pre-SCSI-1 disk, a SCSI-2 QIC tape unit, a SCSI-1 helical scan tape unit and 2 SCSI-1 disks work together quite happily. From a performance standpoint you might want to separate your older and newer (=faster) devices however. Components of SCSI As said before, SCSI devices are smart. The idea is to put the knowledge about intimate hardware details onto the SCSI device itself. In this way, the host system does not have to worry about things like how many heads are hard disks has, or how many tracks there are on a specific tape device. If you are curious, the standard specifies commands with which you can query your devices on their hardware particulars. FreeBSD uses this capability during boot to check out what devices are connected and whether they need any special treatment. The advantage of intelligent devices is obvious: the device drivers on the host can be made in a much more generic fashion, there is no longer a need to change (and qualify!) drivers for every odd new device that is introduced. For cabling and connectors there is a golden rule: get good stuff. With bus speeds going up all the time you will save yourself a lot of grief by using good material. So, gold plated connectors, shielded cabling, sturdy connector hoods with strain reliefs etc are the way to go. Second golden rule: do no use cables longer than necessary. I once spent 3 days hunting down a problem with a flaky machine only to discover that shortening the SCSI bus by 1 meter solved the problem. And the original bus length was well within the SCSI specification. SCSI bus types From an electrical point of view, there are two incompatible bus types: single-ended and differential. This means that there are two different main groups of SCSI devices and controllers, which cannot be mixed on the same bus. It is possible however to use special converter hardware to transform a single-ended bus into a differential one (and vice versa). The differences between the bus types are explained in the next sections. In lots of SCSI related documentation there is a sort of jargon in use to abbreviate the different bus types. A small list: FWD: Fast Wide Differential FND: Fast Narrow Differential SE: Single Ended FN: Fast Narrow etc. With a minor amount of imagination one can usually imagine what is meant. Wide is a bit ambiguous, it can indicate 16 or 32 bit buses. As far as I know, the 32 bit variant is not (yet) in use, so wide normally means 16 bit. Fast means that the timing on the bus is somewhat different, so that on a narrow (8 bit) bus 10 Mbytes/sec are possible instead of 5 Mbytes/sec for 'slow' SCSI. As discussed before, bus speeds of 20 and 40 million transfers/second are also emerging (Fast-20 == Ultra SCSI and Fast-40 == Ultra2 SCSI). The data lines > 8 are only used for data transfers and device addressing. The transfers of commands and status messages etc are only performed on the lowest 8 data lines. The standard allows narrow devices to operate on a wide bus. The usable bus width is negotiated between the devices. You have to watch your device addressing closely when mixing wide and narrow. Single ended buses A single-ended SCSI bus uses signals that are either 5 Volts or 0 Volts (indeed, TTL levels) and are relative to a COMMON ground reference. A singled ended 8 bit SCSI bus has approximately 25 ground lines, who are all tied to a single `rail' on all devices. A standard single ended bus has a maximum length of 6 meters. If the same bus is used with fast-SCSI devices, the maximum length allowed drops to 3 meters. Fast-SCSI means that instead of 5Mbytes/sec the bus allows 10Mbytes/sec transfers. Fast-20 (Ultra SCSI) and Fast-40 allow for 20 and 40 million transfers/second respectively. So, F20 is 20 Mbytes/second on a 8 bit bus, 40 Mbytes/second on a 16 bit bus etc. For F20 the max bus length is 1.5 meters, for F40 it becomes 0.75 meters. Be aware that F20 is pushing the limits quite a bit, so you will quickly find out if your SCSI bus is electrically sound. If some devices on your bus use 'fast' to communicate your bus must adhere to the length restrictions for fast buses! It is obvious that with the newer fast-SCSI devices the bus length can become a real bottleneck. This is why the differential SCSI bus was introduced in the SCSI-2 standard. For connector pinning and connector types please refer to the SCSI-2 standard (see Further reading) itself, connectors etc are listed there in painstaking detail. Beware of devices using non-standard cabling. For instance Apple uses a 25pin D-type connecter (like the one on serial ports and parallel printers). Considering that the official SCSI bus needs 50 pins you can imagine the use of this connector needs some 'creative cabling'. The reduction of the number of ground wires they used is a bad idea, you better stick to 50 pins cabling in accordance with the SCSI standard. For Fast-20 and 40 do not even think about buses like this. Differential buses A differential SCSI bus has a maximum length of 25 meters. Quite a difference from the 3 meters for a single-ended fast-SCSI bus. The idea behind differential signals is that each bus signal has its own return wire. So, each signal is carried on a (preferably twisted) pair of wires. The voltage difference between these two wires determines whether the signal is asserted or de-asserted. To a certain extent the voltage difference between ground and the signal wire pair is not relevant (do not try 10 kVolts though). It is beyond the scope of this document to explain why this differential idea is so much better. Just accept that electrically seen the use of differential signals gives a much better noise margin. You will normally find differential buses in use for inter-cabinet connections. Because of the lower cost single ended is mostly used for shorter buses like inside cabinets. There is nothing that stops you from using differential stuff with FreeBSD, as long as you use a controller that has device driver support in FreeBSD. As an example, Adaptec marketed the AHA1740 as a single ended board, whereas the AHA1744 was differential. The software interface to the host is identical for both. Terminators Terminators in SCSI terminology are resistor networks that are used to get a correct impedance matching. Impedance matching is important to get clean signals on the bus, without reflections or ringing. If you once made a long distance telephone call on a bad line you probably know what reflections are. With 20Mbytes/sec traveling over your SCSI bus, you do not want signals echoing back. Terminators come in various incarnations, with more or less sophisticated designs. Of course, there are internal and external variants. Many SCSI devices come with a number of sockets in which a number of resistor networks can (must be!) installed. If you remove terminators from a device, carefully store them. You will need them when you ever decide to reconfigure your SCSI bus. There is enough variation in even these simple tiny things to make finding the exact replacement a frustrating business. There are also SCSI devices that have a single jumper to enable or disable a built-in terminator. There are special terminators you can stick onto a flat cable bus. Others look like external connectors, or a connector hood without a cable. So, lots of choice as you can see. There is much debate going on if and when you should switch from simple resistor (passive) terminators to active terminators. Active terminators contain slightly more elaborate circuit to give cleaner bus signals. The general consensus seems to be that the usefulness of active termination increases when you have long buses and/or fast devices. If you ever have problems with your SCSI buses you might consider trying an active terminator. Try to borrow one first, they reputedly are quite expensive. Please keep in mind that terminators for differential and single-ended buses are not identical. You should not mix the two variants. OK, and now where should you install your terminators? This is by far the most misunderstood part of SCSI. And it is by far the simplest. The rule is: every single line on the SCSI bus has 2 (two) terminators, one at each end of the bus. So, two and not one or three or whatever. Do yourself a favor and stick to this rule. It will save you endless grief, because wrong termination has the potential to introduce highly mysterious bugs. (Note the “potential” here; the nastiest part is that it may or may not work.) A common pitfall is to have an internal (flat) cable in a machine and also an external cable attached to the controller. It seems almost everybody forgets to remove the terminators from the controller. The terminator must now be on the last external device, and not on the controller! In general, every reconfiguration of a SCSI bus must pay attention to this. Termination is to be done on a per-line basis. This means if you have both narrow and wide buses connected to the same host adapter, you need to enable termination on the higher 8 bits of the bus on the adapter (as well as the last devices on each bus, of course). What I did myself is remove all terminators from my SCSI devices and controllers. I own a couple of external terminators, for both the Centronics-type external cabling and for the internal flat cable connectors. This makes reconfiguration much easier. On modern devices, sometimes integrated terminators are used. These things are special purpose integrated circuits that can be dis/en-abled with a control pin. It is not necessary to physically remove them from a device. You may find them on newer host adapters, sometimes they are software configurable, using some sort of setup tool. Some will even auto-detect the cables attached to the connectors and automatically set up the termination as necessary. At any rate, consult your documentation! Terminator power The terminators discussed in the previous chapter need power to operate properly. On the SCSI bus, a line is dedicated to this purpose. So, simple huh? Not so. Each device can provide its own terminator power to the terminator sockets it has on-device. But if you have external terminators, or when the device supplying the terminator power to the SCSI bus line is switched off you are in trouble. The idea is that initiators (these are devices that initiate actions on the bus, a discussion follows) must supply terminator power. All SCSI devices are allowed (but not required) to supply terminator power. To allow for un-powered devices on a bus, the terminator power must be supplied to the bus via a diode. This prevents the backflow of current to un-powered devices. To prevent all kinds of nastiness, the terminator power is usually fused. As you can imagine, fuses might blow. This can, but does not have to, lead to a non functional bus. If multiple devices supply terminator power, a single blown fuse will not put you out of business. A single supplier with a blown fuse certainly will. Clever external terminators sometimes have a LED indication that shows whether terminator power is present. In newer designs auto-restoring fuses that 'reset' themselves after some time are sometimes used. Device addressing Because the SCSI bus is, ehh, a bus there must be a way to distinguish or address the different devices connected to it. This is done by means of the SCSI or target ID. Each device has a unique target ID. You can select the ID to which a device must respond using a set of jumpers, or a dip switch, or something similar. Some SCSI host adapters let you change the target ID from the boot menu. (Yet some others will not let you change the ID from 7.) Consult the documentation of your device for more information. Beware of multiple devices configured to use the same ID. Chaos normally reigns in this case. A pitfall is that one of the devices sharing the same ID sometimes even manages to answer to I/O requests! For an 8 bit bus, a maximum of 8 targets is possible. The maximum is 8 because the selection is done bitwise using the 8 data lines on the bus. For wide buses this increases to the number of data lines (usually 16). A narrow SCSI device can not communicate with a SCSI device with a target ID larger than 7. This means it is generally not a good idea to move your SCSI host adapter's target ID to something higher than 7 (or your CD-ROM will stop working). The higher the SCSI target ID, the higher the priority the devices has. When it comes to arbitration between devices that want to use the bus at the same time, the device that has the highest SCSI ID will win. This also means that the SCSI host adapter usually uses target ID 7. Note however that the lower 8 IDs have higher priorities than the higher 8 IDs on a wide-SCSI bus. Thus, the order of target IDs is: [7 6 .. 1 0 15 14 .. 9 8] on a wide-SCSI system. (If you you are wondering why the lower 8 have higher priority, read the previous paragraph for a hint.) For a further subdivision, the standard allows for Logical Units or LUNs for short. A single target ID may have multiple LUNs. For example, a tape device including a tape changer may have LUN 0 for the tape device itself, and LUN 1 for the tape changer. In this way, the host system can address each of the functional units of the tape changer as desired. Bus layout SCSI buses are linear. So, not shaped like Y-junctions, star topologies, rings, cobwebs or whatever else people might want to invent. One of the most common mistakes is for people with wide-SCSI host adapters to connect devices on all three connecters (external connector, internal wide connector, internal narrow connector). Don't do that. It may appear to work if you are really lucky, but I can almost guarantee that your system will stop functioning at the most unfortunate moment (this is also known as “Murphy's law”). You might notice that the terminator issue discussed earlier becomes rather hairy if your bus is not linear. Also, if you have more connectors than devices on your internal SCSI cable, make sure you attach devices on connectors on both ends instead of using the connectors in the middle and let one or both ends dangle. This will screw up the termination of the bus. The electrical characteristics, its noise margins and ultimately the reliability of it all are tightly related to linear bus rule. Stick to the linear bus rule! Using SCSI with FreeBSD About translations, BIOSes and magic... As stated before, you should first make sure that you have a electrically sound bus. When you want to use a SCSI disk on your PC as boot disk, you must aware of some quirks related to PC BIOSes. The PC BIOS in its first incarnation used a low level physical interface to the hard disk. So, you had to tell the BIOS (using a setup tool or a BIOS built-in setup) how your disk physically looked like. This involved stating number of heads, number of cylinders, number of sectors per track, obscure things like precompensation and reduced write current cylinder etc. One might be inclined to think that since SCSI disks are smart you can forget about this. Alas, the arcane setup issue is still present today. The system BIOS needs to know how to access your SCSI disk with the head/cyl/sector method in order to load the FreeBSD kernel during boot. The SCSI host adapter or SCSI controller you have put in your AT/EISA/PCI/whatever bus to connect your disk therefore has its own on-board BIOS. During system startup, the SCSI BIOS takes over the hard disk interface routines from the system BIOS. To fool the system BIOS, the system setup is normally set to No hard disk present. Obvious, isn't it? The SCSI BIOS itself presents to the system a so called translated drive. This means that a fake drive table is constructed that allows the PC to boot the drive. This translation is often (but not always) done using a pseudo drive with 64 heads and 32 sectors per track. By varying the number of cylinders, the SCSI BIOS adapts to the actual drive size. It is useful to note that 32 * 64 / 2 = the size of your drive in megabytes. The division by 2 is to get from disk blocks that are normally 512 bytes in size to Kbytes. Right. All is well now?! No, it is not. The system BIOS has another quirk you might run into. The number of cylinders of a bootable hard disk cannot be greater than 1024. Using the translation above, this is a show-stopper for disks greater than 1 GB. With disk capacities going up all the time this is causing problems. Fortunately, the solution is simple: just use another translation, e.g. with 128 heads instead of 32. In most cases new SCSI BIOS versions are available to upgrade older SCSI host adapters. Some newer adapters have an option, in the form of a jumper or software setup selection, to switch the translation the SCSI BIOS uses. It is very important that all operating systems on the disk use the same translation to get the right idea about where to find the relevant partitions. So, when installing FreeBSD you must answer any questions about heads/cylinders etc using the translated values your host adapter uses. Failing to observe the translation issue might lead to un-bootable systems or operating systems overwriting each others partitions. Using fdisk you should be able to see all partitions. You might have heard some talk of “lying” devices? Older FreeBSD kernels used to report the geometry of SCSI disks when booting. An example from one of my systems: aha0 targ 0 lun 0: <MICROP 1588-15MB1057404HSP4> sd0: 636MB (1303250 total sec), 1632 cyl, 15 head, 53 sec, bytes/sec 512 Newer kernels usually do not report this information. e.g. (bt0:0:0): "SEAGATE ST41651 7574" type 0 fixed SCSI 2 sd0(bt0:0:0): Direct-Access 1350MB (2766300 512 byte sectors) Why has this changed? This info is retrieved from the SCSI disk itself. Newer disks often use a technique called zone bit recording. The idea is that on the outer cylinders of the drive there is more space so more sectors per track can be put on them. This results in disks that have more tracks on outer cylinders than on the inner cylinders and, last but not least, have more capacity. You can imagine that the value reported by the drive when inquiring about the geometry now becomes suspect at best, and nearly always misleading. When asked for a geometry , it is nearly always better to supply the geometry used by the BIOS, or if the BIOS is never going to know about this disk, (e.g. it is not a booting disk) to supply a fictitious geometry that is convenient. SCSI subsystem design FreeBSD uses a layered SCSI subsystem. For each different controller card a device driver is written. This driver knows all the intimate details about the hardware it controls. The driver has a interface to the upper layers of the SCSI subsystem through which it receives its commands and reports back any status. On top of the card drivers there are a number of more generic drivers for a class of devices. More specific: a driver for tape devices (abbreviation: st), magnetic disks (sd), CD-ROMs (cd) etc. In case you are wondering where you can find this stuff, it all lives in /sys/scsi. See the man pages in section 4 for more details. The multi level design allows a decoupling of low-level bit banging and more high level stuff. Adding support for another piece of hardware is a much more manageable problem. Kernel configuration Dependent on your hardware, the kernel configuration file must contain one or more lines describing your host adapter(s). This includes I/O addresses, interrupts etc. Consult the man page for your adapter driver to get more info. Apart from that, check out /sys/i386/conf/LINT for an overview of a kernel config file. LINT contains every possible option you can dream of. It does not imply LINT will actually get you to a working kernel at all. Although it is probably stating the obvious: the kernel config file should reflect your actual hardware setup. So, interrupts, I/O addresses etc must match the kernel config file. During system boot messages will be displayed to indicate whether the configured hardware was actually found. Note that most of the EISA/PCI drivers (namely ahb, ahc, ncr and amd will automatically obtain the correct parameters from the host adapters themselves at boot time; thus, you just need to write, for instance, controller ahc0. An example loosely based on the FreeBSD 2.2.5-Release kernel config file LINT with some added comments (between []): # SCSI host adapters: `aha', `ahb', `aic', `bt', `nca' # # aha: Adaptec 154x # ahb: Adaptec 174x # ahc: Adaptec 274x/284x/294x # aic: Adaptec 152x and sound cards using the Adaptec AIC-6360 (slow!) # amd: AMD 53c974 based SCSI cards (e.g., Tekram DC-390 and 390T) # bt: Most Buslogic controllers # nca: ProAudioSpectrum cards using the NCR 5380 or Trantor T130 # ncr: NCR/Symbios 53c810/815/825/875 etc based SCSI cards # uha: UltraStore 14F and 34F # sea: Seagate ST01/02 8 bit controller (slow!) # wds: Western Digital WD7000 controller (no scatter/gather!). # [For an Adaptec AHA274x/284x/294x/394x etc controller] controller ahc0 [For an NCR/Symbios 53c875 based controller] controller ncr0 [For an Ultrastor adapter] controller uha0 at isa? port "IO_UHA0" bio irq ? drq 5 vector uhaintr # Map SCSI buses to specific SCSI adapters controller scbus0 at ahc0 controller scbus2 at ncr0 controller scbus1 at uha0 # The actual SCSI devices disk sd0 at scbus0 target 0 unit 0 [SCSI disk 0 is at scbus 0, LUN 0] disk sd1 at scbus0 target 1 [implicit LUN 0 if omitted] disk sd2 at scbus1 target 3 [SCSI disk on the uha0] disk sd3 at scbus2 target 4 [SCSI disk on the ncr0] tape st1 at scbus0 target 6 [SCSI tape at target 6] device cd0 at scbus? [the first ever CD-ROM found, no wiring] The example above tells the kernel to look for a ahc (Adaptec 274x) controller, then for an NCR/Symbios board, and so on. The lines following the controller specifications tell the kernel to configure specific devices but only attach them when they match the target ID and LUN specified on the corresponding bus. Wired down devices get “first shot” at the unit numbers so the first non “wired down” device, is allocated the unit number one greater than the highest “wired down” unit number for that kind of device. So, if you had a SCSI tape at target ID 2 it would be configured as st2, as the tape at target ID 6 is wired down to unit number 1. Wired down devices need not be found to get their unit number. The unit number for a wired down device is reserved for that device, even if it is turned off at boot time. This allows the device to be turned on and brought on-line at a later time, without rebooting. Notice that a device's unit number has no relationship with its target ID on the SCSI bus. Below is another example of a kernel config file as used by FreeBSD version < 2.0.5. The difference with the first example is that devices are not “wired down”. “Wired down” means that you specify which SCSI target belongs to which device. A kernel built to the config file below will attach the first SCSI disk it finds to sd0, the second disk to sd1 etc. If you ever removed or added a disk, all other devices of the same type (disk in this case) would 'move around'. This implies you have to change /etc/fstab each time. Although the old style still works, you are strongly recommended to use this new feature. It will save you a lot of grief whenever you shift your hardware around on the SCSI buses. So, when you re-use your old trusty config file after upgrading from a pre-FreeBSD2.0.5.R system check this out. [driver for Adaptec 174x] controller ahb0 at isa? bio irq 11 vector ahbintr [for Adaptec 154x] controller aha0 at isa? port "IO_AHA0" bio irq 11 drq 5 vector ahaintr [for Seagate ST01/02] controller sea0 at isa? bio irq 5 iomem 0xc8000 iosiz 0x2000 vector seaintr controller scbus0 device sd0 [support for 4 SCSI harddisks, sd0 up sd3] device st0 [support for 2 SCSI tapes] [for the CD-ROM] device cd0 #Only need one of these, the code dynamically grows Both examples support SCSI disks. If during boot more devices of a specific type (e.g. sd disks) are found than are configured in the booting kernel, the system will simply allocate more devices, incrementing the unit number starting at the last number “wired down”. If there are no “wired down” devices then counting starts at unit 0. Use man 4 scsi to check for the latest info on the SCSI subsystem. For more detailed info on host adapter drivers use eg man 4 ahc for info on the Adaptec 294x driver. Tuning your SCSI kernel setup Experience has shown that some devices are slow to respond to INQUIRY commands after a SCSI bus reset (which happens at boot time). An INQUIRY command is sent by the kernel on boot to see what kind of device (disk, tape, CD-ROM etc) is connected to a specific target ID. This process is called device probing by the way. To work around the 'slow response' problem, FreeBSD allows a tunable delay time before the SCSI devices are probed following a SCSI bus reset. You can set this delay time in your kernel configuration file using a line like: options SCSI_DELAY=15 #Be pessimistic about Joe SCSI device This line sets the delay time to 15 seconds. On my own system I had to use 3 seconds minimum to get my trusty old CD-ROM drive to be recognized. Start with a high value (say 30 seconds or so) when you have problems with device recognition. If this helps, tune it back until it just stays working. Rogue SCSI devices Although the SCSI standard tries to be complete and concise, it is a complex standard and implementing things correctly is no easy task. Some vendors do a better job then others. This is exactly where the “rogue” devices come into view. Rogues are devices that are recognized by the FreeBSD kernel as behaving slightly (...) non-standard. Rogue devices are reported by the kernel when booting. An example for two of my cartridge tape units: Feb 25 21:03:34 yedi /kernel: ahb0 targ 5 lun 0: <TANDBERG TDC 3600 -06:> Feb 25 21:03:34 yedi /kernel: st0: Tandberg tdc3600 is a known rogue Mar 29 21:16:37 yedi /kernel: aha0 targ 5 lun 0: <ARCHIVE VIPER 150 21247-005> Mar 29 21:16:37 yedi /kernel: st1: Archive Viper 150 is a known rogue For instance, there are devices that respond to all LUNs on a certain target ID, even if they are actually only one device. It is easy to see that the kernel might be fooled into believing that there are 8 LUNs at that particular target ID. The confusion this causes is left as an exercise to the reader. The SCSI subsystem of FreeBSD recognizes devices with bad habits by looking at the INQUIRY response they send when probed. Because the INQUIRY response also includes the version number of the device firmware, it is even possible that for different firmware versions different workarounds are used. See e.g. /sys/scsi/st.c and /sys/scsi/scsiconf.c for more info on how this is done. This scheme works fine, but keep in mind that it of course only works for devices that are known to be weird. If you are the first to connect your bogus Mumbletech SCSI CD-ROM you might be the one that has to define which workaround is needed. After you got your Mumbletech working, please send the required workaround to the FreeBSD development team for inclusion in the next release of FreeBSD. Other Mumbletech owners will be grateful to you. Multiple LUN devices In some cases you come across devices that use multiple logical units (LUNs) on a single SCSI ID. In most cases FreeBSD only probes devices for LUN 0. An example are so called bridge boards that connect 2 non-SCSI harddisks to a SCSI bus (e.g. an Emulex MD21 found in old Sun systems). This means that any devices with LUNs != 0 are not normally found during device probe on system boot. To work around this problem you must add an appropriate entry in /sys/scsi/scsiconf.c and rebuild your kernel. Look for a struct that is initialized like below: { T_DIRECT, T_FIXED, "MAXTOR", "XT-4170S", "B5A", "mx1", SC_ONE_LU } For you Mumbletech BRIDGE2000 that has more than one LUN, acts as a SCSI disk and has firmware revision 123 you would add something like: { T_DIRECT, T_FIXED, "MUMBLETECH", "BRIDGE2000", "123", "sd", SC_MORE_LUS } The kernel on boot scans the inquiry data it receives against the table and acts accordingly. See the source for more info. Tagged command queueing Modern SCSI devices, particularly magnetic disks, support what is called tagged command queuing (TCQ). In a nutshell, TCQ allows the device to have multiple I/O requests outstanding at the same time. Because the device is intelligent, it can optimise its operations (like head positioning) based on its own request queue. On SCSI devices like RAID (Redundant Array of Independent Disks) arrays the TCQ function is indispensable to take advantage of the device's inherent parallelism. Each I/O request is uniquely identified by a “tag” (hence the name tagged command queuing) and this tag is used by FreeBSD to see which I/O in the device drivers queue is reported as complete by the device. It should be noted however that TCQ requires device driver support and that some devices implemented it “not quite right” in their firmware. This problem bit me once, and it leads to highly mysterious problems. In such cases, try to disable TCQ. Busmaster host adapters Most, but not all, SCSI host adapters are bus mastering controllers. This means that they can do I/O on their own without putting load onto the host CPU for data movement. This is of course an advantage for a multitasking operating system like FreeBSD. It must be noted however that there might be some rough edges. For instance an Adaptec 1542 controller can be set to use different transfer speeds on the host bus (ISA or AT in this case). The controller is settable to different rates because not all motherboards can handle the higher speeds. Problems like hangups, bad data etc might be the result of using a higher data transfer rate then your motherboard can stomach. The solution is of course obvious: switch to a lower data transfer rate and try if that works better. In the case of a Adaptec 1542, there is an option that can be put into the kernel config file to allow dynamic determination of the right, read: fastest feasible, transfer rate. This option is disabled by default: options "TUNE_1542" #dynamic tune of bus DMA speed Check the man pages for the host adapter that you use. Or better still, use the ultimate documentation (read: driver source). Tracking down problems The following list is an attempt to give a guideline for the most common SCSI problems and their solutions. It is by no means complete. Check for loose connectors and cables. Check and double check the location and number of your terminators. Check if your bus has at least one supplier of terminator power (especially with external terminators. Check if no double target IDs are used. Check if all devices to be used are powered up. Make a minimal bus config with as little devices as possible. If possible, configure your host adapter to use slow bus speeds. Disable tagged command queuing to make things as simple as possible (for a NCR hostadapter based system see man ncrcontrol) If you can compile a kernel, make one with the SCSIDEBUG option, and try accessing the device with debugging turned on for that device. If your device does not even probe at startup, you may have to define the address of the device that is failing, and the desired debug level in /sys/scsi/scsidebug.h. If it probes but just does not work, you can use the &man.scsi.8; command to dynamically set a debug level to it in a running kernel (if SCSIDEBUG is defined). This will give you copious debugging output with which to confuse the gurus. See man 4 scsi for more exact information. Also look at man 8 scsi. Further reading If you intend to do some serious SCSI hacking, you might want to have the official standard at hand: Approved American National Standards can be purchased from ANSI at
13th Floor 11 West 42nd Street New York NY 10036 Sales Dept: (212) 642-4900
You can also buy many ANSI standards and most committee draft documents from Global Engineering Documents,
15 Inverness Way East Englewood CO, 80112-5704 Phone: (800) 854-7179 Outside USA and Canada: (303) 792-2181 Fax: (303) 792- 2192
Many X3T10 draft documents are available electronically on the SCSI BBS (719-574-0424) and on the ncrinfo.ncr.com anonymous ftp site. Latest X3T10 committee documents are: AT Attachment (ATA or IDE) [X3.221-1994] (Approved) ATA Extensions (ATA-2) [X3T10/948D Rev 2i] Enhanced Small Device Interface (ESDI) [X3.170-1990/X3.170a-1991] (Approved) Small Computer System Interface — 2 (SCSI-2) [X3.131-1994] (Approved) SCSI-2 Common Access Method Transport and SCSI Interface Module (CAM) [X3T10/792D Rev 11] Other publications that might provide you with additional information are: “SCSI: Understanding the Small Computer System Interface”, written by NCR Corporation. Available from: Prentice Hall, Englewood Cliffs, NJ, 07632 Phone: (201) 767-5937 ISBN 0-13-796855-8 “Basics of SCSI”, a SCSI tutorial written by Ancot Corporation Contact Ancot for availability information at: Phone: (415) 322-5322 Fax: (415) 322-0455 “SCSI Interconnection Guide Book”, an AMP publication (dated 4/93, Catalog 65237) that lists the various SCSI connectors and suggests cabling schemes. Available from AMP at (800) 522-6752 or (717) 564-0100 “Fast Track to SCSI”, A Product Guide written by Fujitsu. Available from: Prentice Hall, Englewood Cliffs, NJ, 07632 Phone: (201) 767-5937 ISBN 0-13-307000-X “The SCSI Bench Reference”, “The SCSI Encyclopedia”, and the “SCSI Tutor”, ENDL Publications, 14426 Black Walnut Court, Saratoga CA, 95070 Phone: (408) 867-6642 “Zadian SCSI Navigator” (quick ref. book) and “Discover the Power of SCSI” (First book along with a one-hour video and tutorial book), Zadian Software, Suite 214, 1210 S. Bascom Ave., San Jose, CA 92128, (408) 293-0800 On Usenet the newsgroups comp.periphs.scsi and comp.periphs are noteworthy places to look for more info. You can also find the SCSI-Faq there, which is posted periodically. Most major SCSI device and host adapter suppliers operate ftp sites and/or BBS systems. They may be valuable sources of information about the devices you own. * Disk/tape controllers * SCSI * IDE * Floppy Hard drives SCSI hard drives Contributed by &a.asami;. 17 February 1998. As mentioned in the SCSI section, virtually all SCSI hard drives sold today are SCSI-2 compliant and thus will work fine as long as you connect them to a supported SCSI host adapter. Most problems people encounter are either due to badly designed cabling (cable too long, star topology, etc.), insufficient termination, or defective parts. Please refer to the SCSI section first if your SCSI hard drive is not working. However, there are a couple of things you may want to take into account before you purchase SCSI hard drives for your system. Rotational speed Rotational speeds of SCSI drives sold today range from around 4,500RPM to 10,000RPM. Most of them are either 5,400RPM or 7,200RPM. Even though the 7,200RPM drives can generally transfer data faster, they run considerably hotter than their 5,400RPM counterparts. A large fraction of today's disk drive malfunctions are heat-related. If you do not have very good cooling in your PC case, you may want to stick with 5,400RPM or slower drives. Note that newer drives, with higher areal recording densities, can deliver much more bits per rotation than older ones. Today's top-of-line 5,400RPM drives can sustain a throughput comparable to 7,200RPM drives of one or two model generations ago. The number to find on the spec sheet for bandwidth is “internal data (or transfer) rate”. It is usually in megabits/sec so divide it by 8 and you'll get the rough approximation of how much megabytes/sec you can get out of the drive. (If you are a speed maniac and want a 10,000RPM drive for your cute little peecee, be my guest; however, those drives become extremely hot. Don't even think about it if you don't have a fan blowing air directly at the drive or a properly ventilated disk enclosure.) Obviously, the latest 10,000RPM drives and 7,200RPM drives can deliver more data than the latest 5,400RPM drives, so if absolute bandwidth is the necessity for your applications, you have little choice but to get the faster drives. Also, if you need low latency, faster drives are better; not only do they usually have lower average seek times, but also the rotational delay is one place where slow-spinning drives can never beat a faster one. (The average rotational latency is half the time it takes to rotate the drive once; thus, it's 3 milliseconds for 10,000RPM drives, 4.2ms for 7,200RPM drives and 5.6ms for 5,400RPM drives.) Latency is seek time plus rotational delay. Make sure you understand whether you need low latency or more accesses per second, though; in the latter case (e.g., news servers), it may not be optimal to purchase one big fast drive. You can achieve similar or even better results by using the ccd (concatenated disk) driver to create a striped disk array out of multiple slower drives for comparable overall cost. Make sure you have adequate air flow around the drive, especially if you are going to use a fast-spinning drive. You generally need at least 1/2" (1.25cm) of spacing above and below a drive. Understand how the air flows through your PC case. Most cases have the power supply suck the air out of the back. See where the air flows in, and put the drive where it will have the largest volume of cool air flowing around it. You may need to seal some unwanted holes or add a new fan for effective cooling. Another consideration is noise. Many 7,200 or faster drives generate a high-pitched whine which is quite unpleasant to most people. That, plus the extra fans often required for cooling, may make 7,200 or faster drives unsuitable for some office and home environments. Form factor Most SCSI drives sold today are of 3.5" form factor. They come in two different heights; 1.6" (“half-height”) or 1" (“low-profile”). The half-height drive is the same height as a CD-ROM drive. However, don't forget the spacing rule mentioned in the previous section. If you have three standard 3.5" drive bays, you will not be able to put three half-height drives in there (without frying them, that is). Interface The majority of SCSI hard drives sold today are Ultra or Ultra-wide SCSI. The maximum bandwidth of Ultra SCSI is 20MB/sec, and Ultra-wide SCSI is 40MB/sec. There is no difference in max cable length between Ultra and Ultra-wide; however, the more devices you have on the same bus, the sooner you will start having bus integrity problems. Unless you have a well-designed disk enclosure, it is not easy to make more than 5 or 6 Ultra SCSI drives work on a single bus. On the other hand, if you need to connect many drives, going for Fast-wide SCSI may not be a bad idea. That will have the same max bandwidth as Ultra (narrow) SCSI, while electronically it's much easier to get it “right”. My advice would be: if you want to connect many disks, get wide SCSI drives; they usually cost a little more but it may save you down the road. (Besides, if you can't afford the cost difference, you shouldn't be building a disk array.) There are two variant of wide SCSI drives; 68-pin and 80-pin SCA (Single Connector Attach). The SCA drives don't have a separate 4-pin power connector, and also read the SCSI ID settings through the 80-pin connector. If you are really serious about building a large storage system, get SCA drives and a good SCA enclosure (dual power supply with at least one extra fan). They are more electronically sound than 68-pin counterparts because there is no “stub” of the SCSI bus inside the disk canister as in arrays built from 68-pin drives. They are easier to install too (you just need to screw the drive in the canister, instead of trying to squeeze in your fingers in a tight place to hook up all the little cables (like the SCSI ID and disk activity LED lines). * IDE hard drives Tape drives Contributed by &a.jmb;. 2 July 1996. General tape access commands &man.mt.1; provides generic access to the tape drives. Some of the more common commands are rewind, erase, and status. See the &man.mt.1; manual page for a detailed description. Controller Interfaces There are several different interfaces that support tape drives. The interfaces are SCSI, IDE, Floppy and Parallel Port. A wide variety of tape drives are available for these interfaces. Controllers are discussed in Disk/tape controllers. SCSI drives The &man.st.4; driver provides support for 8mm (Exabyte), 4mm (DAT: Digital Audio Tape), QIC (Quarter-Inch Cartridge), DLT (Digital Linear Tape), QIC Minicartridge and 9-track (remember the big reels that you see spinning in Hollywood computer rooms) tape drives. See the &man.st.4; manual page for a detailed description. The drives listed below are currently being used by members of the FreeBSD community. They are not the only drives that will work with FreeBSD. They just happen to be the ones that we use. 4mm (DAT: Digital Audio Tape) Archive Python HP C1533A HP C1534A HP 35450A HP 35470A HP 35480A SDT-5000 Wangtek 6200 8mm (Exabyte) EXB-8200 EXB-8500 EXB-8505 QIC (Quarter-Inch Cartridge) Archive Ananconda 2750 Archive Viper 60 Archive Viper 150 Archive Viper 2525 Tandberg TDC 3600 Tandberg TDC 3620 Tandberg TDC 4222 Wangtek 5525ES DLT (Digital Linear Tape) Digital TZ87 Mini-Cartridge Conner CTMS 3200 Exabyte 2501 Autoloaders/Changers Hewlett-Packard HP C1553A Autoloading DDS2 * IDE drives Floppy drives Conner 420R * Parallel port drives Detailed Information Archive Anaconda 2750 The boot message identifier for this drive is ARCHIVE ANCDA 2750 28077 -003 type 1 removable SCSI 2 This is a QIC tape drive. Native capacity is 1.35GB when using QIC-1350 tapes. This drive will read and write QIC-150 (DC6150), QIC-250 (DC6250), and QIC-525 (DC6525) tapes as well. Data transfer rate is 350kB/s using &man.dump.8;. Rates of 530kB/s have been reported when using Amanda Production of this drive has been discontinued. The SCSI bus connector on this tape drive is reversed from that on most other SCSI devices. Make sure that you have enough SCSI cable to twist the cable one-half turn before and after the Archive Anaconda tape drive, or turn your other SCSI devices upside-down. Two kernel code changes are required to use this drive. This drive will not work as delivered. If you have a SCSI-2 controller, short jumper 6. Otherwise, the drive behaves are a SCSI-1 device. When operating as a SCSI-1 device, this drive, “locks” the SCSI bus during some tape operations, including: fsf, rewind, and rewoffl. If you are using the NCR SCSI controllers, patch the file /usr/src/sys/pci/ncr.c (as shown below). Build and install a new kernel. *** 4831,4835 **** }; ! if (np->latetime>4) { /* ** Although we tried to wake it up, --- 4831,4836 ---- }; ! if (np->latetime>1200) { /* ** Although we tried to wake it up, Reported by: &a.jmb; Archive Python The boot message identifier for this drive is ARCHIVE Python 28454-XXX4ASB type 1 removable SCSI 2 density code 0x8c, 512-byte blocks This is a DDS-1 tape drive. Native capacity is 2.5GB on 90m tapes. Data transfer rate is XXX. This drive was repackaged by Sun Microsystems as model 411. Reported by: Bob Bishop rb@gid.co.uk Archive Viper 60 The boot message identifier for this drive is ARCHIVE VIPER 60 21116 -007 type 1 removable SCSI 1 This is a QIC tape drive. Native capacity is 60MB. Data transfer rate is XXX. Production of this drive has been discontinued. Reported by: Philippe Regnauld regnauld@hsc.fr Archive Viper 150 The boot message identifier for this drive is ARCHIVE VIPER 150 21531 -004 Archive Viper 150 is a known rogue type 1 removable SCSI 1. A multitude of firmware revisions exist for this drive. Your drive may report different numbers (e.g 21247 -005. This is a QIC tape drive. Native capacity is 150/250MB. Both 150MB (DC6150) and 250MB (DC6250) tapes have the recording format. The 250MB tapes are approximately 67% longer than the 150MB tapes. This drive can read 120MB tapes as well. It can not write 120MB tapes. Data transfer rate is 100kB/s This drive reads and writes DC6150 (150MB) and DC6250 (250MB) tapes. This drives quirks are known and pre-compiled into the scsi tape device driver (&man.st.4;). Under FreeBSD 2.2-current, use mt blocksize 512 to set the blocksize. (The particular drive had firmware revision 21247 -005. Other firmware revisions may behave differently) Previous versions of FreeBSD did not have this problem. Production of this drive has been discontinued. Reported by: Pedro A M Vazquez vazquez@IQM.Unicamp.BR Mike Smith msmith@atrad.adelaide.edu.au Archive Viper 2525 The boot message identifier for this drive is ARCHIVE VIPER 2525 25462 -011 type 1 removable SCSI 1 This is a QIC tape drive. Native capacity is 525MB. Data transfer rate is 180kB/s at 90 inches/sec. The drive reads QIC-525, QIC-150, QIC-120 and QIC-24 tapes. Writes QIC-525, QIC-150, and QIC-120. Firmware revisions prior to 25462 -011 are bug ridden and will not function properly. Production of this drive has been discontinued. Conner 420R The boot message identifier for this drive is Conner tape. This is a floppy controller, minicartridge tape drive. Native capacity is XXXX Data transfer rate is XXX The drive uses QIC-80 tape cartridges. Reported by: Mark Hannon mark@seeware.DIALix.oz.au Conner CTMS 3200 The boot message identifier for this drive is CONNER CTMS 3200 7.00 type 1 removable SCSI 2. This is a minicartridge tape drive. Native capacity is XXXX Data transfer rate is XXX The drive uses QIC-3080 tape cartridges. Reported by: Thomas S. Traylor tst@titan.cs.mci.com <ulink URL="http://www.digital.com/info/Customer-Update/931206004.txt.html">DEC TZ87</ulink> The boot message identifier for this drive is DEC TZ87 (C) DEC 9206 type 1 removable SCSI 2 density code 0x19 This is a DLT tape drive. Native capacity is 10GB. This drive supports hardware data compression. Data transfer rate is 1.2MB/s. This drive is identical to the Quantum DLT2000. The drive firmware can be set to emulate several well-known drives, including an Exabyte 8mm drive. Reported by: &a.wilko; <ulink URL="http://www.Exabyte.COM:80/Products/Minicartridge/2501/Rfeatures.html">Exabyte EXB-2501</ulink> The boot message identifier for this drive is EXABYTE EXB-2501 This is a mini-cartridge tape drive. Native capacity is 1GB when using MC3000XL minicartridges. Data transfer rate is XXX This drive can read and write DC2300 (550MB), DC2750 (750MB), MC3000 (750MB), and MC3000XL (1GB) minicartridges. WARNING: This drive does not meet the SCSI-2 specifications. The drive locks up completely in response to a SCSI MODE_SELECT command unless there is a formatted tape in the drive. Before using this drive, set the tape blocksize with &prompt.root; mt -f /dev/st0ctl.0 blocksize 1024 Before using a minicartridge for the first time, the minicartridge must be formated. FreeBSD 2.1.0-RELEASE and earlier: &prompt.root; /sbin/scsi -f /dev/rst0.ctl -s 600 -c "4 0 0 0 0 0" (Alternatively, fetch a copy of the scsiformat shell script from FreeBSD 2.1.5/2.2.) FreeBSD 2.1.5 and later: &prompt.root; /sbin/scsiformat -q -w /dev/rst0.ctl Right now, this drive cannot really be recommended for FreeBSD. Reported by: Bob Beaulieu ez@eztravel.com Exabyte EXB-8200 The boot message identifier for this drive is EXABYTE EXB-8200 252X type 1 removable SCSI 1 This is an 8mm tape drive. Native capacity is 2.3GB. Data transfer rate is 270kB/s. This drive is fairly slow in responding to the SCSI bus during boot. A custom kernel may be required (set SCSI_DELAY to 10 seconds). There are a large number of firmware configurations for this drive, some have been customized to a particular vendor's hardware. The firmware can be changed via EPROM replacement. Production of this drive has been discontinued. Reported by: Mike Smith msmith@atrad.adelaide.edu.au Exabyte EXB-8500 The boot message identifier for this drive is EXABYTE EXB-8500-85Qanx0 0415 type 1 removable SCSI 2 This is an 8mm tape drive. Native capacity is 5GB. Data transfer rate is 300kB/s. Reported by: Greg Lehey grog@lemis.de <ulink URL="http://www.Exabyte.COM:80/Products/8mm/8505XL/Rfeatures.html">Exabyte EXB-8505</ulink> The boot message identifier for this drive is EXABYTE EXB-85058SQANXR1 05B0 type 1 removable SCSI 2 This is an 8mm tape drive which supports compression, and is upward compatible with the EXB-5200 and EXB-8500. Native capacity is 5GB. The drive supports hardware data compression. Data transfer rate is 300kB/s. Reported by: Glen Foster gfoster@gfoster.com Hewlett-Packard HP C1533A The boot message identifier for this drive is HP C1533A 9503 type 1 removable SCSI 2. This is a DDS-2 tape drive. DDS-2 means hardware data compression and narrower tracks for increased data capacity. Native capacity is 4GB when using 120m tapes. This drive supports hardware data compression. Data transfer rate is 510kB/s. This drive is used in Hewlett-Packard's SureStore 6000eU and 6000i tape drives and C1533A DDS-2 DAT drive. The drive has a block of 8 dip switches. The proper settings for FreeBSD are: 1 ON; 2 ON; 3 OFF; 4 ON; 5 ON; 6 ON; 7 ON; 8 ON. switch 1 switch 2 Result On On Compression enabled at power-on, with host control On Off Compression enabled at power-on, no host control Off On Compression disabled at power-on, with host control Off Off Compression disabled at power-on, no host control Switch 3 controls MRS (Media Recognition System). MRS tapes have stripes on the transparent leader. These identify the tape as DDS (Digital Data Storage) grade media. Tapes that do not have the stripes will be treated as write-protected. Switch 3 OFF enables MRS. Switch 3 ON disables MRS. See HP SureStore Tape Products and Hewlett-Packard Disk and Tape Technical Information for more information on configuring this drive. Warning: Quality control on these drives varies greatly. One FreeBSD core-team member has returned 2 of these drives. Neither lasted more than 5 months. Reported by: &a.se; Hewlett-Packard HP 1534A The boot message identifier for this drive is HP HP35470A T503 type 1 removable SCSI 2 Sequential-Access density code 0x13, variable blocks. This is a DDS-1 tape drive. DDS-1 is the original DAT tape format. Native capacity is 2GB when using 90m tapes. Data transfer rate is 183kB/s. The same mechanism is used in Hewlett-Packard's SureStore 2000i tape drive, C35470A DDS format DAT drive, C1534A DDS format DAT drive and HP C1536A DDS format DAT drive. The HP C1534A DDS format DAT drive has two indicator lights, one green and one amber. The green one indicates tape action: slow flash during load, steady when loaded, fast flash during read/write operations. The amber one indicates warnings: slow flash when cleaning is required or tape is nearing the end of its useful life, steady indicates an hard fault. (factory service required?) Reported by Gary Crutcher gcrutchr@nightflight.com Hewlett-Packard HP C1553A Autoloading DDS2 The boot message identifier for this drive is "". This is a DDS-2 tape drive with a tape changer. DDS-2 means hardware data compression and narrower tracks for increased data capacity. Native capacity is 24GB when using 120m tapes. This drive supports hardware data compression. Data transfer rate is 510kB/s (native). This drive is used in Hewlett-Packard's SureStore 12000e tape drive. The drive has two selectors on the rear panel. The selector closer to the fan is SCSI id. The other selector should be set to 7. There are four internal switches. These should be set: 1 ON; 2 ON; 3 ON; 4 OFF. At present the kernel drivers do not automatically change tapes at the end of a volume. This shell script can be used to change tapes: #!/bin/sh PATH="/sbin:/usr/sbin:/bin:/usr/bin"; export PATH usage() { echo "Usage: dds_changer [123456ne] raw-device-name echo "1..6 = Select cartridge" echo "next cartridge" echo "eject magazine" exit 2 } if [ $# -ne 2 ] ; then usage fi cdb3=0 cdb4=0 cdb5=0 case $1 in [123456]) cdb3=$1 cdb4=1 ;; n) ;; e) cdb5=0x80 ;; ?) usage ;; esac scsi -f $2 -s 100 -c "1b 0 0 $cdb3 $cdb4 $cdb5" Hewlett-Packard HP 35450A The boot message identifier for this drive is HP HP35450A -A C620 type 1 removable SCSI 2 Sequential-Access density code 0x13 This is a DDS-1 tape drive. DDS-1 is the original DAT tape format. Native capacity is 1.2GB. Data transfer rate is 160kB/s. Reported by: mark thompson mark.a.thompson@pobox.com Hewlett-Packard HP 35470A The boot message identifier for this drive is HP HP35470A 9 09 type 1 removable SCSI 2 This is a DDS-1 tape drive. DDS-1 is the original DAT tape format. Native capacity is 2GB when using 90m tapes. Data transfer rate is 183kB/s. The same mechanism is used in Hewlett-Packard's SureStore 2000i tape drive, C35470A DDS format DAT drive, C1534A DDS format DAT drive, and HP C1536A DDS format DAT drive. Warning: Quality control on these drives varies greatly. One FreeBSD core-team member has returned 5 of these drives. None lasted more than 9 months. Reported by: David Dawes dawes@rf900.physics.usyd.edu.au (9 09) Hewlett-Packard HP 35480A The boot message identifier for this drive is HP HP35480A 1009 type 1 removable SCSI 2 Sequential-Access density code 0x13. This is a DDS-DC tape drive. DDS-DC is DDS-1 with hardware data compression. DDS-1 is the original DAT tape format. Native capacity is 2GB when using 90m tapes. It cannot handle 120m tapes. This drive supports hardware data compression. Please refer to the section on HP C1533A for the proper switch settings. Data transfer rate is 183kB/s. This drive is used in Hewlett-Packard's SureStore 5000eU and 5000i tape drives and C35480A DDS format DAT drive.. This drive will occasionally hang during a tape eject operation (mt offline). Pressing the front panel button will eject the tape and bring the tape drive back to life. WARNING: HP 35480-03110 only. On at least two occasions this tape drive when used with FreeBSD 2.1.0, an IBM Server 320 and an 2940W SCSI controller resulted in all SCSI disk partitions being lost. The problem has not be analyzed or resolved at this time. <ulink URL="http://www.sel.sony.com/SEL/ccpg/storage/tape/t5000.html">Sony SDT-5000</ulink> There are at least two significantly different models: one is a DDS-1 and the other DDS-2. The DDS-1 version is SDT-5000 3.02. The DDS-2 version is SONY SDT-5000 327M. The DDS-2 version has a 1MB cache. This cache is able to keep the tape streaming in almost any circumstances. The boot message identifier for this drive is SONY SDT-5000 3.02 type 1 removable SCSI 2 Sequential-Access density code 0x13 Native capacity is 4GB when using 120m tapes. This drive supports hardware data compression. Data transfer rate is depends upon the model or the drive. The rate is 630kB/s for the SONY SDT-5000 327M while compressing the data. For the SONY SDT-5000 3.02, the data transfer rate is 225kB/s. In order to get this drive to stream, set the blocksize to 512 bytes (mt blocksize 512) reported by Kenneth Merry ken@ulc199.residence.gatech.edu SONY SDT-5000 327M information reported by Charles Henrich henrich@msu.edu Reported by: &a.jmz; Tandberg TDC 3600 The boot message identifier for this drive is TANDBERG TDC 3600 =08: type 1 removable SCSI 2 This is a QIC tape drive. Native capacity is 150/250MB. This drive has quirks which are known and work around code is present in the scsi tape device driver (&man.st.4;). Upgrading the firmware to XXX version will fix the quirks and provide SCSI 2 capabilities. Data transfer rate is 80kB/s. IBM and Emerald units will not work. Replacing the firmware EPROM of these units will solve the problem. Reported by: Michael Smith msmith@atrad.adelaide.edu.au Tandberg TDC 3620 This is very similar to the Tandberg TDC 3600 drive. Reported by: &a.joerg; Tandberg TDC 4222 The boot message identifier for this drive is TANDBERG TDC 4222 =07 type 1 removable SCSI 2 This is a QIC tape drive. Native capacity is 2.5GB. The drive will read all cartridges from the 60 MB (DC600A) upwards, and write 150 MB (DC6150) upwards. Hardware compression is optionally supported for the 2.5 GB cartridges. This drives quirks are known and pre-compiled into the scsi tape device driver (&man.st.4;) beginning with FreeBSD 2.2-current. For previous versions of FreeBSD, use mt to read one block from the tape, rewind the tape, and then execute the backup program (mt fsr 1; mt rewind; dump ...) Data transfer rate is 600kB/s (vendor claim with compression), 350 KB/s can even be reached in start/stop mode. The rate decreases for smaller cartridges. Reported by: &a.joerg; Wangtek 5525ES The boot message identifier for this drive is WANGTEK 5525ES SCSI REV7 3R1 type 1 removable SCSI 1 density code 0x11, 1024-byte blocks This is a QIC tape drive. Native capacity is 525MB. Data transfer rate is 180kB/s. The drive reads 60, 120, 150, and 525MB tapes. The drive will not write 60MB (DC600 cartridge) tapes. In order to overwrite 120 and 150 tapes reliably, first erase (mt erase) the tape. 120 and 150 tapes used a wider track (fewer tracks per tape) than 525MB tapes. The “extra” width of the previous tracks is not overwritten, as a result the new data lies in a band surrounded on both sides by the previous data unless the tape have been erased. This drives quirks are known and pre-compiled into the scsi tape device driver (&man.st.4;). Other firmware revisions that are known to work are: M75D Reported by: Marc van Kempen marc@bowtie.nl REV73R1 Andrew Gordon Andrew.Gordon@net-tel.co.uk M75D Wangtek 6200 The boot message identifier for this drive is WANGTEK 6200-HS 4B18 type 1 removable SCSI 2 Sequential-Access density code 0x13 This is a DDS-1 tape drive. Native capacity is 2GB using 90m tapes. Data transfer rate is 150kB/s. Reported by: Tony Kimball alk@Think.COM * Problem drives CD-ROM drives Contributed by &a.obrien;. 23 November 1997. As mentioned in Jordan's Picks Generally speaking those in The FreeBSD Project prefer SCSI CDROM drives over IDE CDROM drives. However not all SCSI CDROM drives are equal. Some feel the quality of some SCSI CDROM drives have been deteriorating to that of IDE CDROM drives. Toshiba used to be the favored stand-by, but many on the SCSI mailing list have found displeasure with the 12x speed XM-5701TA as its volume (when playing audio CDROMs) is not controllable by the various audio player software. Another area where SCSI CDROM manufacturers are cutting corners is adhearance to the SCSI specification. Many SCSI CDROMs will respond to multiple LUNs for its target address. Known violators include the 6x Teac CD-56S 1.0D. * Other * Other * PCMCIA