Re: W98SE MCA Adapters

800x600 at 16 bpp (64K colors) at 60Hz:

Mode settings table completed: test machine setup, code changes, builds and
tests must follow. Since there is no explicit bits-per-pixel register
setting, one just wonders how the card finds out the effective pixel width.
The solution is very clever, it goes indirectly through certain registers,
far from being obvious. I calculated the values for a 16-bpp for the mode.

There are more mysteries. The basic design has been set up for a 4M card and
a palette color is a 24-bit color, though only 256 palette colors are
defined. When you go to Direct Color Mode, you have to init 128 palette
colors according to a defined scheme, where R=0 G=0 B=1-bit set. Get the
idea? A 16-bit direct color pixel goes possibly through an 8-bit palette
location, a byte at a time and the empty half of the palette buffers one
byte, then joines with the second byte in the other half to produce a
palette color. In this way, a palette entry is redefined each time for each
16-bit pixel. With 256 palette locations, that translates into processing
512 8-bit pixels to simulate 16-bit pixel processing. I suspect, that
doubles the Pixel Rate.

The Pixel Rate is allowed to reach "128.00 MHz in 1.00MHz increments" but
"the maximum PEL Frequency that should be programmed for the XGA-NI
Subsystem is 90MHz." Note, it says "should be" and not "must be"... Hmm, I
will certainly go beyond that to see if and how an XGA-2 could be toasted.

Video memory can be either 16-bit or 32-bit wide. There is no setting to
read out the amount of memory, you have to probe for it. That could mean,
the card is not hardwired for a certain memory size as long as it is below
4M.

The aperture (a window into video memory) - 64K, 1M or 4M has effect only
when the software exploits it. Real mode software (and W9x) works with a 64K
aperture, 1M or 4M are suitable only for protected mode operations.





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