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BIOS(4) Device Drivers Manual (i386) BIOS(4)

bios
a driver for PC Firmware, aka BIOS

bios0 at mainbus0 flags 0x0000
apm0 at bios0 flags 0x0000
pcibios0 at bios0 flags 0x0000

OpenBSD provides support for PC firmware, aka BIOS and some of its functions, currently: APM subsystem, BIOS32 extensions, PCI BIOS subsystem.

The bios driver also identifies BIOS type (such as "AT/286+", which is almost always used in modern machines) and BIOS image date stamp, which is, presumably, the day the BIOS image was compiled by vendor and could be used as a crude BIOS version identification. The bios driver also scans the ISA memory hole at 640K-1M for optional ROM images and reserves the space from being used by various ISA devices, for example pcic(4).

Flags is a bit mask, each bit of which specifies which functions of the driver to disable.

0x0001
BIOS32 attachment.

Do not probe or attach to BIOS32 extensions. BIOS32 is one of the interfaces to the PCI BIOS configuration tables.

0x0002
PCI BIOS attachment.

Do not probe or attach the pcibios(4) device, which performs certain PCI configuration tasks.

0x0004
Do not perform the scan for ROM images in the ISA memory hole (0xc0000 - 0xf0000 physical addresses).
0x0008
SMBIOS attachment.

Do not probe or attach to SMBIOS. SMBIOS provides greater detail about system hardware configuration and is required to attach ipmi(4) on most systems.

apm(4), intro(4), pcibios(4), pcmcia(4)

The bios driver appeared in OpenBSD 2.2.

On some machines optional ROM images do not pass checksum check, but it's considered better to reserve space for those anyway, choosing lesser evil from many.
May 31, 2007 OpenBSD-current