Tested on AMT host with working comconsole_pcidev setting and host with physical RS-232 com port:
console="comconsole" comconsole_speed="115200" comconsole_pcidev="0:22:3"
No change to working AMT host.
Real serial no longer explodes in BTX and emits useable errors:
Consoles: serial port BIOS drive C: is disk0 PXE version 2.1, real mode entry point @98d1:0106 BIOS 632kB/3134016kB available memory FreeBSD/x86 bootstrap loader, Revision 1.1 (Sat Dec 16 11:20:40 MST 2017 sbruno@lab) Loading /boot/defaults/loader.conf Cannot find specified pcidev Warning: bad definition on file /boot/loader.conf comconsole_pcidev="0:22:3"