[atari7800] Re: DMA TIMING

> > FWIW, MESS doesn't work according to spec, it reads all three palette
bits
> in 320B mode not just the high bit.
>
> Whoops.  Let me verify that with the CC2, then I can fix vidhrdw/a7800.c

I just had an AH-HH! moment about this.  MARIA has two 800 bit line RAMs, so
each 160H pixel has 5 bits as a color LUT index.  The 320H modes don't
change how the line RAM is written to, just how it is read.  Which,
unfortunately, means there are only 2.5 bits per 320H pixel, or max 8 colors
per pixel with one bit shared between the two half pixels.

It's unfortunate that the MARIA designers didn't have enough transistors for
320x5 (or even 320x6) bit line RAMs, but there is a little bit of genius in
how they did manage to squeeze the 320H modes out of the 160H line RAM.  I
also wonder whether this means there are a couple more 160H modes hidden in
there.

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