GDT selectors

[Stephen Hocking]

	Hello all,
Sorry for not posting to comp.unix.microport, or what ever it is now, we
dont have it in Oz.

I'm in the process of writing a device driver that wishes to talk to the EGA
screen memory. It's a graphics driver to simply (at the moment) draw coloured
lines. I've been able to do all this from user space, but one needs to do
endless outbs in order to change colour, which is an agonisingly slow ioctl
on /dev/mem under Uport. (V/AT 2.3).

I've got to find a valid value for a char * to point to the base of video
memory. Most of the driver is in place, all in C (to be converted to assembler
later) with the code that worked OK in user space. The problem is finding that 
blasted memory location. I suspect one has to go through the gdt via mapin()
on VIDEO2SEL, but this has yet to give much joy. Are you out there,
John Plocher or Jim Sully? I'd love an answer on this, it's driving me nuts.

I anticipate that the end result will fly. Most of the code comes from
David Lewis and the July 1988 Microsystems Journal. At this stage, all the 
driver will end up being is a place for ioctls that ask for lines to be
drawn, or blockfills to be done.

If there is enough interest, I'll summarise to the net. If anybody is
interested, we also have a driver for a DT2801 ADC board.

	Cheers,
	Stephen

#include <std witty disclaimer>

	Stephen Hocking 	ACSnet shocking at physiol.oz
				UUCP ...!uunet!munnari!physiol!shocking