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From:	Charles Sandmann <sandmann AT clio DOT rice DOT edu>
Newsgroups:	comp.os.msdos.djgpp
Subject:	Re: Linear frame buffer idea and questions
Date:	Tue, 31 Oct 1995 08:11:47 CST
Organization:	Rice University, Houston, Texas
Lines:	16
References:	<473o51$7lm AT sarin DOT cs DOT pdx DOT edu>
Reply-To:	sandmann AT clio DOT rice DOT edu
Nntp-Posting-Host:	clio.rice.edu
To:	djgpp AT sun DOT soe DOT clarkson DOT edu
Dj-Gateway:	from newsgroup comp.os.msdos.djgpp

> Ok, I've seen many posts to this group and others about using the MMU to
> create a linear frame buffer.  Most people seem to think that it is
> possible to do using DPMI 1.0.  However, I have yet to see ANYONE post
> any sort of a suggestion as to HOW.  Well, I've done a little research

This is because there is only one DPMI 1.0 provider out there, and noone
wants to write code which requires 386MAX V7 to run.  Also, all new video
cards are 32+ bit and live on VLB or PCI busses which give access to true
linear memory without banking.  Still, if you want to play with emulating
the DJGPP V1.x video driver behavior:

What you do is use the uncommitted page feature to force page faults,
then handle them with the extended exception handler call which also
provides CR2 (to give the address of the fault).  In the fault you can
do the video calls and change which pages are committed/uncommitted.
This will be somewhat slow, however.

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