#9 GXE64 support

[jmk@plan9.att.com jmk@plan9.att.com]

the ATT21C498 is the production version of the ATT20C498 according to the
datasheet.

my suspicion is that aux/vga is not switching over to 2x8-bit mode for the
higher clock rates when it can, we've never played with any resolution
requiring a clock between 80MHz and 135MHz.

please post your parameters.

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From:	jeremy@sour.sw.oz.au (Jeremy Fitzhardinge)
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Subject: #9 GXE64 support
To:	9fans@cse.psu.edu (Graverobbers from Outer Space!)
Date:	Mon, 7 Aug 1995 06:05:09 -0400
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Hi all,

I've been successfully using the PC demo disks on my system with
a #9 GXE64 card in 1024x768x8 mode.  I calculated some new parameters
for use with X under Linux which make better use of my hardware,
and came up with a 1184x888@67Hz mode (100MHz dot clock), and a
1152x864 mode (at both 80MHz and 90MHz dot clocks).

These all worked well under XFree86, producing solid clear images.
I tried using the same parameters in /lib/vgadb, but only the
1152x864 w/ 80MHz dot clock worked properly.  The others had flickery
pixels, with 1 pixel-wide vertical lines disappearing altogether;
in other words it looked like something was being overclocked, and
it appears to happen at dot clocks somewhere between 80 and 90 MHz

vgadb's entry for the GXE64 lists the RAMDAC as being an att21x498-135.
However, my card has a att20c498-135 RAMDAC and aux/vga doesn't
seem to explicitly support this chip (isn't accepted in vgadb,
and strings doesn't show any mention in aux/vga itself).

I assume they are quite similar, but is there some slight difference
between them which needs to be handled differently with dot clocks
over, say, 80MHz? The 1152x864 w/ 80MHz dot clock is OK, but only
refreshes at 57Hz, so it's a bit too flickery for long-term use.

Thanks,
	J