Index: sbin/reboot/boot_i386.8
===================================================================
--- sbin/reboot/boot_i386.8
+++ sbin/reboot/boot_i386.8
@@ -105,7 +105,7 @@
 .Ar bios_drive : interface ( unit , Oo Ar slice , Oc Ar part )
 .Ar filename
 .Sm on
-.Op Fl aCcDdghmnPprsv
+.Op Fl aCcDdghmnPpRrsv
 .Op Fl S Ns Ar speed
 .Xc
 Specify boot file and flags.
@@ -166,7 +166,7 @@
 Defaults to
 .Pa /boot/kernel/kernel .
 Symbolic links are not supported (hard links are).
-.It Xo Op Fl aCcDdghmnPpqrsv
+.It Xo Op Fl aCcDdghmnPpqRrsv
 .Op Fl S Ns Ar speed
 .Xc
 Boot flags:
@@ -230,6 +230,15 @@
 combination with the
 .Fl m
 option.
+.It Fl R
+reset the serial terminal if serial console is enabled. This option could
+help if previous boot stages (BIOS, for example) leave the serial terminal
+in an unspecified or bogus state. The reset sequence is "\ec" by default
+unless it has been overridden by setting
+.Va BOOT_COMCONSOLE_RESET_TERM_CMD
+in
+.Xr make.conf 5
+and recompiling and reinstalling the boot blocks.
 .It Fl r
 use the statically configured default for the device containing the
 root file system
Index: stand/common/rbx.h
===================================================================
--- stand/common/rbx.h
+++ stand/common/rbx.h
@@ -43,6 +43,7 @@
 #define RBX_NOINTR	0x1c	/* -n */
 /* 0x1d is reserved for log2(RB_MULTIPLE) and is just misnamed here. */
 #define RBX_DUAL	0x1d	/* -D */
+#define RBX_RTERM	0x1e	/* -R */
 /* 0x1f is reserved for log2(RB_BOOTINFO). */
 
 /* pass: -a, -s, -r, -d, -c, -v, -h, -C, -g, -m, -p, -D */
Index: stand/defs.mk
===================================================================
--- stand/defs.mk
+++ stand/defs.mk
@@ -190,6 +190,8 @@
 # Make sure we use the machine link we're about to create
 CFLAGS+=-I.
 
+BOOT_COMCONSOLE_RESET_TERM_CMD?= "\ec"
+
 all: ${PROG}
 
 CLEANFILES+= teken_state.h
Index: stand/i386/boot2/Makefile
===================================================================
--- stand/i386/boot2/Makefile
+++ stand/i386/boot2/Makefile
@@ -28,6 +28,7 @@
 	-DSIOPRT=${BOOT_COMCONSOLE_PORT} \
 	-DSIOFMT=${B2SIOFMT} \
 	-DSIOSPD=${BOOT_COMCONSOLE_SPEED} \
+	-DSIORST=\"${BOOT_COMCONSOLE_RESET_TERM_CMD}\" \
 	-I${LDRSRC} \
 	-Wall -Waggregate-return -Wbad-function-cast -Wno-cast-align \
 	-Wmissing-declarations -Wmissing-prototypes -Wnested-externs \
Index: stand/i386/boot2/boot2.c
===================================================================
--- stand/i386/boot2/boot2.c
+++ stand/i386/boot2/boot2.c
@@ -55,7 +55,7 @@
 #define SECOND		18	/* Circa that many ticks in a second. */
 
 #define ARGS		0x900
-#define NOPT		14
+#define NOPT		15
 #define NDEV		3
 #define MEM_BASE	0x12
 #define MEM_EXT 	0x15
@@ -70,7 +70,7 @@
 
 extern uint32_t _end;
 
-static const char optstr[NOPT] = "DhaCcdgmnpqrsv"; /* Also 'P', 'S' */
+static const char optstr[NOPT] = "DhaCcdgmnpqRrsv"; /* Also 'P', 'S' */
 static const unsigned char flags[NOPT] = {
 	RBX_DUAL,
 	RBX_SERIAL,
@@ -83,6 +83,7 @@
 	RBX_NOINTR,
 	RBX_PAUSE,
 	RBX_QUIET,
+	RBX_RTERM,
 	RBX_DFLTROOT,
 	RBX_SINGLE,
 	RBX_VERBOSE
@@ -107,6 +108,7 @@
 #if SERIAL
 static int comspeed = SIOSPD;
 static uint8_t ioctrl = IO_KEYBOARD;
+static const char resettermcmd[] = SIORST;
 #endif
 
 int main(void);
@@ -408,8 +410,13 @@
 			ioctrl = OPT_CHECK(RBX_DUAL) ? (IO_SERIAL|IO_KEYBOARD) :
 			    OPT_CHECK(RBX_SERIAL) ? IO_SERIAL : IO_KEYBOARD;
 			if (DO_SIO) {
-				if (sio_init(115200 / comspeed) != 0)
+				if (sio_init(115200 / comspeed) != 0) {
 					ioctrl &= ~IO_SERIAL;
+				} else if (OPT_CHECK(RBX_RTERM)) {
+					for (i = 0; resettermcmd[i]; i++)
+						sio_putc(resettermcmd[i]);
+					sio_flush();
+				}
 			}
 #endif
 		} else {
Index: stand/i386/gptboot/Makefile
===================================================================
--- stand/i386/gptboot/Makefile
+++ stand/i386/gptboot/Makefile
@@ -27,6 +27,7 @@
 	-DSIOPRT=${BOOT_COMCONSOLE_PORT} \
 	-DSIOFMT=${B2SIOFMT} \
 	-DSIOSPD=${BOOT_COMCONSOLE_SPEED} \
+	-DSIORST=\"${BOOT_COMCONSOLE_RESET_TERM_CMD}\" \
 	-I${LDRSRC} \
 	-I${BOOTSRC}/i386/common \
 	-I${BOOTSRC}/i386/boot2 \
Index: stand/i386/gptboot/gptboot.c
===================================================================
--- stand/i386/gptboot/gptboot.c
+++ stand/i386/gptboot/gptboot.c
@@ -43,7 +43,7 @@
 #include "paths.h"
 
 #define ARGS		0x900
-#define NOPT		14
+#define NOPT		15
 #define NDEV		3
 #define MEM_BASE	0x12
 #define MEM_EXT 	0x15
@@ -59,7 +59,7 @@
 extern uint32_t _end;
 
 static const uuid_t freebsd_ufs_uuid = GPT_ENT_TYPE_FREEBSD_UFS;
-static const char optstr[NOPT] = "DhaCcdgmnpqrsv"; /* Also 'P', 'S' */
+static const char optstr[NOPT] = "DhaCcdgmnpqRrsv"; /* Also 'P', 'S' */
 static const unsigned char flags[NOPT] = {
 	RBX_DUAL,
 	RBX_SERIAL,
@@ -72,6 +72,7 @@
 	RBX_NOINTR,
 	RBX_PAUSE,
 	RBX_QUIET,
+	RBX_RTERM,
 	RBX_DFLTROOT,
 	RBX_SINGLE,
 	RBX_VERBOSE
@@ -83,6 +84,7 @@
 
 static char kname[1024];
 static int comspeed = SIOSPD;
+static const char resettermcmd[] = SIORST;
 static struct bootinfo bootinfo;
 #ifdef LOADER_GELI_SUPPORT
 static struct geli_boot_args geliargs;
@@ -549,8 +551,13 @@
 			ioctrl = OPT_CHECK(RBX_DUAL) ? (IO_SERIAL|IO_KEYBOARD) :
 			    OPT_CHECK(RBX_SERIAL) ? IO_SERIAL : IO_KEYBOARD;
 			if (ioctrl & IO_SERIAL) {
-				if (sio_init(115200 / comspeed) != 0)
+				if (sio_init(115200 / comspeed) != 0) {
 					ioctrl &= ~IO_SERIAL;
+				} else if (OPT_CHECK(RBX_RTERM)) {
+					for (i = 0; resettermcmd[i]; i++)
+						sio_putc(resettermcmd[i]);
+					sio_flush();
+				}
 			}
 		} else {
 			for (q = arg--; *q && *q != '('; q++);
Index: stand/i386/gptzfsboot/Makefile
===================================================================
--- stand/i386/gptzfsboot/Makefile
+++ stand/i386/gptzfsboot/Makefile
@@ -26,6 +26,7 @@
 	-DSIOPRT=${BOOT_COMCONSOLE_PORT} \
 	-DSIOFMT=${B2SIOFMT} \
 	-DSIOSPD=${BOOT_COMCONSOLE_SPEED} \
+	-DSIORST=\"${BOOT_COMCONSOLE_RESET_TERM_CMD}\" \
 	-I${LDRSRC} \
 	-I${BOOTSRC}/i386/common \
 	-I${BOOTSRC}/i386/libi386 \
Index: stand/i386/isoboot/Makefile
===================================================================
--- stand/i386/isoboot/Makefile
+++ stand/i386/isoboot/Makefile
@@ -23,6 +23,7 @@
 	-DSIOPRT=${BOOT_COMCONSOLE_PORT} \
 	-DSIOFMT=${B2SIOFMT} \
 	-DSIOSPD=${BOOT_COMCONSOLE_SPEED} \
+	-DSIORST=\"${BOOT_COMCONSOLE_RESET_TERM_CMD}\" \
 	-I${LDRSRC} \
 	-I${BOOTSRC}/i386/common \
 	-I${BOOTSRC}/i386/boot2 \
Index: stand/i386/isoboot/isoboot.c
===================================================================
--- stand/i386/isoboot/isoboot.c
+++ stand/i386/isoboot/isoboot.c
@@ -43,7 +43,7 @@
 #include "paths.h"
 
 #define ARGS		0x900
-#define NOPT		14
+#define NOPT		15
 #define NDEV		3
 #define MEM_BASE	0x12
 #define MEM_EXT 	0x15
@@ -58,7 +58,7 @@
 
 extern uint32_t _end;
 
-static const char optstr[NOPT] = "DhaCcdgmnpqrsv"; /* Also 'P', 'S' */
+static const char optstr[NOPT] = "DhaCcdgmnpqRrsv"; /* Also 'P', 'S' */
 static const unsigned char flags[NOPT] = {
 	RBX_DUAL,
 	RBX_SERIAL,
@@ -71,6 +71,7 @@
 	RBX_NOINTR,
 	RBX_PAUSE,
 	RBX_QUIET,
+	RBX_RTERM,
 	RBX_DFLTROOT,
 	RBX_SINGLE,
 	RBX_VERBOSE
@@ -83,6 +84,7 @@
 static struct dsk dsk;
 static char kname[1024];
 static int comspeed = SIOSPD;
+static const char resettermcmd[] = SIORST;
 static struct bootinfo bootinfo;
 
 static vm_offset_t	high_heap_base;
@@ -472,8 +474,13 @@
 			ioctrl = OPT_CHECK(RBX_DUAL) ? (IO_SERIAL|IO_KEYBOARD) :
 			    OPT_CHECK(RBX_SERIAL) ? IO_SERIAL : IO_KEYBOARD;
 			if (ioctrl & IO_SERIAL) {
-				if (sio_init(115200 / comspeed) != 0)
+				if (sio_init(115200 / comspeed) != 0) {
 					ioctrl &= ~IO_SERIAL;
+				} else if (OPT_CHECK(RBX_RTERM)) {
+					for (i = 0; resettermcmd[i]; i++)
+						sio_putc(resettermcmd[i]);
+					sio_flush();
+				}
 			}
 		} else {
 			for (q = arg--; *q && *q != '('; q++);
Index: stand/i386/zfsboot/Makefile
===================================================================
--- stand/i386/zfsboot/Makefile
+++ stand/i386/zfsboot/Makefile
@@ -25,6 +25,7 @@
 	-DSIOPRT=${BOOT_COMCONSOLE_PORT} \
 	-DSIOFMT=${B2SIOFMT} \
 	-DSIOSPD=${BOOT_COMCONSOLE_SPEED} \
+	-DSIORST=\"${BOOT_COMCONSOLE_RESET_TERM_CMD}\" \
 	-I${LDRSRC} \
 	-I${BOOTSRC}/i386/common \
 	-I${BOOTSRC}/i386/libi386 \
Index: stand/i386/zfsboot/zfsboot.c
===================================================================
--- stand/i386/zfsboot/zfsboot.c
+++ stand/i386/zfsboot/zfsboot.c
@@ -53,7 +53,7 @@
 #include "libzfs.h"
 
 #define	ARGS			0x900
-#define	NOPT			14
+#define	NOPT			15
 #define	NDEV			3
 
 #define	BIOS_NUMDRIVES		0x475
@@ -67,7 +67,7 @@
 
 extern uint32_t _end;
 
-static const char optstr[NOPT] = "DhaCcdgmnpqrsv"; /* Also 'P', 'S' */
+static const char optstr[NOPT] = "DhaCcdgmnpqRrsv"; /* Also 'P', 'S' */
 static const unsigned char flags[NOPT] = {
     RBX_DUAL,
     RBX_SERIAL,
@@ -80,6 +80,7 @@
     RBX_NOINTR,
     RBX_PAUSE,
     RBX_QUIET,
+    RBX_RTERM,
     RBX_DFLTROOT,
     RBX_SINGLE,
     RBX_VERBOSE
@@ -111,6 +112,7 @@
 static char cmddup[512];
 static char kname[1024];
 static int comspeed = SIOSPD;
+static const char resettermcmd[] = SIORST;
 static struct bootinfo bootinfo;
 static uint32_t bootdev;
 static struct zfs_boot_args zfsargs;
@@ -610,8 +612,13 @@
 			ioctrl = OPT_CHECK(RBX_DUAL) ? (IO_SERIAL|IO_KEYBOARD) :
 			    OPT_CHECK(RBX_SERIAL) ? IO_SERIAL : IO_KEYBOARD;
 			if (ioctrl & IO_SERIAL) {
-				if (sio_init(115200 / comspeed) != 0)
+				if (sio_init(115200 / comspeed) != 0) {
 					ioctrl &= ~IO_SERIAL;
+				} else if (OPT_CHECK(RBX_RTERM)) {
+					for (i = 0; resettermcmd[i]; i++)
+						sio_putc(resettermcmd[i]);
+					sio_flush();
+				}
 			}
 		} if (c == '?') {
 			printf("\n");