Re: problem reading VGA text fonts

Bender, Bernhard (br@elsa.de)
Tue, 19 Nov 96 15:50:21 -0500

Hi Harald,

>>>
I see 3 different types of font corruptions:

- some few ramdom pixels set (sometimes cleared) in the character glyph
- completely trashed glygh (random pattern)
- block of 16 characters/glyphs is "shifted", e.g. very often ASCII
0x30-0x3f (digits etc. up to '?') displays glyphs for ASCII 0x20-0x2f
so pressing '1' I see a '!'
since one character glyph is 32 bytes when saved/restored, the size
of such a "shifted" block is always 512 bytes. any idea about this
size?
<<<

Well, we have seen something very similar recently. I happend only rarely
during the boot procedure of the system BIOS on a very spacial (but
important :-) computer.

After very long search the problem was pinned down on accesses to the
BIOS ROM (the physical, not the shadowed image). These accesses cause
memory corruptions with ViRGE (and some other S3 chips).

Are you accessing the (physical) VGA BIOS ROM somewhere to detect the
type of board? Maybe the BIOS is not shadowed on the AXP machine?

Bernhard Bender

---
Group Manager Core Technology   ELSA Computer Graphics


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