From mboxrd@z Thu Jan  1 00:00:00 1970
To: 9fans@cse.psu.edu
Subject: Re: [9fans] More Mach64 Problems
From: "Russ Cox" <rsc@plan9.bell-labs.com>
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Message-Id: <20011119171514.3FF3D1998A@mail.cse.psu.edu>
Date: Mon, 19 Nov 2001 12:15:11 -0500
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The problem is in fact the memory timings, but it's ever so difficult
to figure out the exact bits without sitting there at the machine.
(It's basically trial and error, which is much harder when it takes a
day or two to do a round trip.)

There's some code in /sys/src/cmd/aux/vga/mach64xx.c that handles
sniffing the card and trying to get the timings set right, but it
appears to fail on some cards, including apparently yours.
If you're game, I can tell you how to tweak the registers and
you can sit there poking bits until it works, but it's really an
open-ended process: sometimes you get it, sometimes you don't.
It will help a lot if you have graphics working on this system in
some other operating system that lets you poke at the VGA card,
to read out a working register dump.  Such systems include Windows 9x,
Linux, and FreeBSD but not Windows NT or 2000.

I tried to help someone via email with this Mach 64 problem a month
ago and it just didn't work, even with working register dumps to
compare against.

In the case of the person with the similar S3 problem, that was more
easily fixed because the S3 chipset handles most of those calculations
for you.  We just had to add the card type to the driver.

Russ