On Thu, Jan 28, 1999 at 10:55:39AM -0600, Paul Victor Novarese wrote:
> Could someone explain this "noisy" cache/RAM? That sounds like it may be
> the problem.
As I recall, someone reported a similar symptom to what you're
reporting: i.e. a "noisy" video signal. One possible cause that was
advanced on the mailing list was that Mersenne's heavy usage of the
FPU or cache might be generating enough interference to cause the
problem.
> More facts for you detectives out there:
>
> 1) This is a Dell Optiplex. All three models (slimline, desktop,
> midtower) exhibit this behavior.
They probably all share the same motherboard design.
> 4) The distributed.net client does not cause this behavior. My
> understanding is that it does not use either FPU or cache.
That's certainly not true. Distributed.net's program _does_ use
memory (and hence, the cache). It may use it _less_ than mersenne,
but less is not "does not use". That difference could conceivably be
enough to cause the behavior you're seeing. Depending on which core
you're using, Distributed.net might use MMX (which use the FPU
registers, but perhaps not the FPU itself) or solely integer
instructions.
Do you see the same behavior in all video modes? If you switch to
text mode (DOS mode), do you still see it? Could you take a picture
of the interference or try to describe it?
I'm very curious about this...
Here's some speculation: since you're not reporting screen corruption
(just picture instability), I'll speculate that the corruption is
occurring either between the frame buffer memory (VRAM) and the
RAMDAC, or in the analog video signal after it leaves the RAMDAC. The
second makes the most sense, since that's an analog signal and is more
susceptible to interference than the digital signals from the VRAM.
The question in my mind is how the CPU can generate a strong enough
signal to interfere with the video signal...
-andy
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