[LispM-Hackers] Achieved some stuff

[John Morrison]

Hi;

Well, the PC SVGA/VGA architecture is well and truly hideous.

Having said that, I have definitely achieved linear frame buffer
access on my ATI Mach64 board by adhering to VESA VBE 2.0 protocols,
using the SVGA BIOS that came with the card, and *without* having to
write any SVGA board specific stuff.  

The achieved resolution was all the way up to 1280x1024, in 8 bit
color-indexed mode (256 colors).  This is enough to put the entire E3
screen on the display, at the price of having some extra margin.

I *think* that this should work for any SVGA card that supports the
"Linear" frame buffer access.  NO BOARD-SPECIFIC CODE.

Basically, I set up the video to the "right" mode, and then ask two
questions (one concerning the mode) and save the answers in low memory
buffers.  After I switch to protected mode, I grab the magical
physical memory address, and then start writing to the physical
memory.  Lo and behold, it worked.

It would have been impossible to do this without the serial output to
COM1 and saving the printouts to a file with minicom.  That seems to
work pretty well, too, and I think in all the hours I've used it, I've
only seen one anomalous either dropped or added character.  It seems
to be good enough to be useful.

-jm

-- 
==== John Morrison
==== MAK Technologies Inc.
==== 185 Alewife Brook Parkway, Cambridge, MA 02138
==== http://www.mak.com/
==== vox:617-876-8085 x115
==== fax:617-876-9208
==== jm@mak.com