[OpenBIOS] Problem with 256K BIOS build

Ronald G. Minnich rminnich at lanl.gov
Wed Feb 16 13:10:06 CET 2000


On Wed, 16 Feb 2000, Wallace I. Kroeker wrote:

> 
> I came across some documentation that claims that "32KB of BIOS expansion
> range from 0C0000H to 0C8000H is typically reserved for the video BIOS
> expansion ROM"  (source is M-Systems DiskOnChip 2000 data sheet).  If this
> is true then how do you fit the 256K bios in the system as we will need the
> range from C0000H all the way up to FFFFH and manage to avoid a collision
> with the video BIOS expansion ROM.

for 256K, you use the top of the 1M hole at 15M. For more, you use the
top of the 2M hole at 2^32-2^20. 

It appears that bioses run for a while in bigreal mode, then shift to real
mode when they boot the os, at which point they can't really access 256K
:-(

ron

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