Re: problem reading VGA text fonts

Bender, Bernhard (br@elsa.de)
Wed, 20 Nov 96 9:37:39 -0500

Hi,

>>>
now the interesting question is: how can we read the BIOS (esp. on AXP)
without currupting video memory ?
<<<

Basically, you can't :-(

One possible solution may be to save all of the VGA memory before reading
the ROM, and restore it afterwards.

The reading of the BIOS ROM itself causes corruption of memory contents,
no matter how you do it. You can read fast or slow, byte of Dwords, no
change.

On Wintel machines, there is not problem, as PCI spec requires the VGA
BIOS to be copied to RAM before execution. The BIOS emulation on the AXP
machine will do the same, but does not keep the copy after it is done (at
least I guess so).

>>>
thanks a lot for this big hint (why didn't I ask earlier? :-(
<<<

If you had asked me two weeks ago, I wouldn't have known, we only found
our very recently, after looking for the reason of the problem for about
4 months, together with engineer at a large computer manufacturer... So
that wasn't really easy, an I only found out the ROM access by
coincidence.

As for what S3 chips may be affected: The ViRGE for sure, maybe the
TrioV+ also. There is no mention in S3's stepping info about this.

Bernhard Bender

---
Group Manager Core Technology   ELSA Computer Graphics

ELSA GmbH Email: br@elsa.de Sonnenweg 11 Fax : +49 (2405) 450 100 D-52 070 Aachen, Germany WWW : http://www.elsa.de

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