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SubjectRe: Possible critical VIA vt82c686a chip bug
Vojtech Pavlik <> writes:

> Hi!
> I've found a bug in my VIA SuperSouth (vt82c686a) chip (ISA bridge
> revision 0x12, silicon rev CD) on my FIC VA-503A rev 1.2:
> When there is heavy disk activity (several tars running concurrently on
> UDMA66 drive, or tar'ing from one UDMA66 drive to another over two
> channels), the system time, namely gettimeofday() goes crazy - now and
> then it advances the time about 1:20 for a fraction of a second and then
> changes back to normal time.
> This causes X to blank the screen when it should not,

Really strange, I'm getting exactly the same problem on a machine
with the same chipset...

This is an athlon 750 machine, with scsi and ide a disk...
I've tryed to see where the problem was comming from for age
( the problem is what you describe and it happen after some time
(1 to 24 hour, it depend) and often while or after heavy I/O...
the only fix is to reboot the machine. )


> Now I'd like to know if I have a faulty chip, faulty motherboard or
> whether this problem exists in more chips as well.

I've changed my motherboard thinking it was a default of it.
it is not.

> If anyone owning a motherboard with the vt82c686a chip (VIA with UDMA66
> and audio), could test this, I'd appreciate that.

I've this kind of motherboard without audio.

> Attached is a patch that makes the problems go away by reprogramming the
> chip in the problematic case.

I'll try it ASAP, then do a feedback.

-- Yoann
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