From: sjm AT miles DOT miles DOT com (scott mark)
Subject: SVGA and GO32 v2.0
To: djgpp AT sun DOT soe DOT clarkson DOT edu (DJGPP Mailing List)
Date: Mon, 15 Mar 93 16:03:50 EST
Reply-To: se01!sjm AT gator DOT rn DOT com

John Horigan wrote:
> 
> How about support for VGA chips that can map video memory into a
> contiguous 1meg block? My WD 90C31 will put the video buffer into
> any 1meg block in the first 16meg and I think that many other VGA
> chips have this option too. Thanks for the great work!

I like this idea, but lets be more general about the solution.

[also, I think that the whole idea is that video memory is already
mapped into a contiguous block, but that's another story]

For example, the ATI Ultra Pro Local-Bus version, which is the
standard video card for several of the Gateway computers, has
a 2 meg block, that can map anywhere into the first 128 meg, and I
believe that the chip can support 4 meg without modification.

I think that if we have to pick a fixed amount of video memory to
support, we should go for AT LEAST 8 Meg, and possibly 16 Meg.


But is it necessary to support a fixed amount of video memory?

Currently, the video RAM is mapped in three locations:

	0xD000:0000	is 1 Meg of r/w video memory
	0xD010:0000	is 1 Meg of read only video memory
	0xD020:0000	is 1 Meg of write only video memory


But I don't see why it is necessary that the video memory be mapped into
a fixed location.

Why not include a call into the graphics library that returns a pointer
to the start of video memory?

You could tell it what type of memory you want (r/w, read, or write) and
how much video memory you want, etc, etc.

Or you could extend it to have the driver figure out for you if you should
be using r/w (because the card is in a flat mode or else cannot support
different read and write page selection) or if you should be using separate
read and write regions because the card is NOT in flat mode, but DOES support
separate read and write page selection.

Anyway, I think that video memories are becoming larger and larger, and I'd
like to be able to use a flat accessing scheme for all of them.


Scott Mark
se01!sjm AT gator DOT rn DOT com