[OpenBIOS] Video (particularly 440GX)

David Christensen dchrist at home.com
Tue Feb 22 08:19:05 CET 2000


The problem with this idea is that the video BIOS, while included in the
flash device, is probably compressed and won't be easy to identify.  Many
BIOS implementations need to use compression to fit all of the necessary
code into the flash part.  The code at the reset vector is uncompressed so
that the system can start booting.  Once RAM is available the BIOS can
uncompress initialization code for things like PnP and PCI and execute them
out of RAM.  Since this code isn't used at runtime it can easily be
discarded.  Near the end of POST the final runtime BIOS is shadowed into
F000:0000h and the system will boot an OS.  Option ROMs like video and SCSI,
graphic splash screens, multi-language support, etc. will almost always be
compressed.

Dave

-----Original Message-----
From: owner-openbios at elvis.informatik.uni-freiburg.de
[mailto:owner-openbios at elvis.informatik.uni-freiburg.de]On Behalf Of
Marcus Gossner
Sent: Tuesday, February 22, 2000 4:54 AM
To: 'openbios at freiburg.linux.de'
Subject: RE: [OpenBIOS] Video (particularly 440GX)


>
>> so, i gather that this dedicated pci bus connects to the graphics
chipset.
>> and since it appears as another pci device, it must implement the pci
>> configuration space, and thus it has an expansion ROM base address
>> register which we can determine if a BIOS exist or not. If it has one,
>> then it is likely that the initialization of the graphics chip is done by
>> the this BIOS instead of the system BIOS.
>
>Unfortunately it may not be that simple on motherboards with integrated
>graphics. There is only one NVRAM chip. This NVRAM is owned by the PIIX4E
>bridge. I am not sure how they would do the expansion ROM base address for
>the AGP stuff.
>
>But it is certainly worth a look.

If there is only one NVRAM the Video BIOS must be included
in the system BIOS.

Maybe you can do the following:
- start with your original BIOS
- copy the Video BIOS to a file (it starts at 0xC0000)
- include the file into your BIOS
- move the Video BIOS to 0xC0000
- start it

I think that should work.

Marcus
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