[iyonix-support] Re: Pyjama effect - thoughts

Hi Richard

RJT wrote:

Another Pyjama photo (800k) at
http://www.4qd.org/temp/pj.jpeg

The contents of the screen memory when it happens are clearly semi-random.
But what's stopping the normal boot happening? I doubt that is the
graphics card. Has to be some problem in the ROM based boot system
accessing corrupted memory, does it not?
What actually happens is that the graphics card GPU makes a hash of its startup.. sometimes believing it is configured for AGP usage - which puts its pci select line on the same address as the cpu, or it comes up with unexpected results in its POR board reset register. This register captures various resistor pullup and pulldown settings on the graphics card as a result of reset, and this can frequently be seen to tell lies. As this reports to the software the hardware ram configuration etc in the card, it usually then results in an attempt to access non existant memory within the card - an almost guranteed hang. Earlier geforce2 cards were much better than later ones. It is rare in fx5200 cards, which is why I suggested you return under warranty. Other dependencies indicate power supply startup characteristics, slew rate, etc. There is no certain cure for it that I have so far identified, though all new machines go through an extensive burn in and test sequence to identify and eliminate those bad combinations.
Also, as the mobo consumes minimal power, if you have a monitor or other device that sources power back into the machine, it can hold the internal power lines at a level sufficiently high to defeat the poweron reset capabilities of the GPU. 

hope this turns on a light or two

john



OK John - I can return my machine under guarantee. But it's a general
problem. Others want a DIY solution.

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John Ballance        jwb@xxxxxxxxxx
Free Utilities? -> http://www.rosery.net
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