From owner-freebsd-hackers  Tue May 25  8:49:51 1999
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Date: Tue, 25 May 1999 16:49:54 +0100
From: Roger Hardiman <roger@cs.strath.ac.uk>
Organization: Strathclyde University
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To: Thomas David Rivers <rivers@dignus.com>
Cc: hackers@FreeBSD.ORG
Subject: Re: How to find the PCI chipset type inside a driver
References: <199905251337.JAA05274@lakes.dignus.com>
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David,

>  Just out of curiosity - every now-and-then, when watching TV with my
> bt848 - the machine will lock up hard..

Lockups are a possibility with older motherboards where the PCI bus gets
overloaded, or on some older SIS, VIA and OPTi motherboards where they
did not implement the PCI spec properly when it comes to bus mastering.
(the broken SiS/VIA chipsets toggle the PCI control lines incorrectly)

Obviously Brooktree decided that SIS and VIA chipsets were sufficiently
broken to add extra compatibility hardware into the Bt878 and Bt879.

The Bt848 has the MYSTERY_BIT (see the source), which is not defined in
the
datasheets, but Brooktree told us to set it! It enables the Bt848's
430FX
compatibilty mode and a small performance hit.

So, your lockups could be due to either a PCI bus saturation or
due to an old chipset.
To avoid saturation, grab smaller image sizes. That worked for me on my
very old VIA chipset embedded systems. Max grab size of 320x256 is
stable.

You may get better results from changing your BIOS PCI settings.
Try turning OFF some of the PCI speedups, like combined writes.
This seemed to help one person's stability.


Ayway, I still want the driver to determine the motherboard PCI bus
chipset
for itself.

Bye
Roger


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