Re: XGA208 with 832x624 Released

Praytell, now that you've figured out how to handle the shutdown to
DOS, why did the original W9x driver need MODE: CO80 or whatever to
prompt the display to work?

MODE CO80 selects an 80-lines color text mode, in doing so it changes to the
VGA mode, i.e. there is a reset involved. This was needed because the
original driver was leaving the card in an undefined state. There is a
defined procedure in the techref on how to leave an XGA mode and prepare the
card for VGA. When the card is ready to VGA, a VGA mode must be still
selected. This procedure was called from several parts in the M$ driver, it
was not at all clear WTF was in charge for the transition from XGA to VGA.
One part set the text mode, another parts did not.

I did not trace the calls, but this procedure must have been performed
twice: the first time, at disabling the driver (XGA to VGA, correct), and
the second time before system exit (XGA to VGA performed in VGA mode,
imagine this!). The M$ driver also lacked the palette portion in the
XGA-to-VGA procedure code.

The M$ driver hooks the system exit and this made me suspicous, so I
compared it with the other samples (ATI, Cirrus, S3). Then I removed the
system exit hook, and it worked. I re-enabled it but left there only the
procedure call to erase the display buffer. I will test further, I want to
completely eliminate the system exit hook

If the XGA display buffer is not erased on switching from XGA to VGA,
"flashes of random data" occur on mode switching. The techref advises to
clear the first 256 KB for going to VGA, but apparently it is cleaner when
the complete video memory is erased. This is done now.

BTW, it is easily possible to move the default to the 132-column mode
instead of the usual 80 columns text mode. The techref describes also a
procedure how to achieve it when the XGA BIOS lacks the 132-column mode
call. Moreover, I could attempt to detect the monitor ID without the BIOS
call (there is a techref procedure) to deny modes not suitable for the IBM
9515 monitor.

The new 960x720 mode @85 Hz looks very good on a 17" monitor.





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