Date: Tue, 26 Aug 2003 09:36:19 -0400
Message-Id: <200308261336.h7QDaJYS031854@envy.delorie.com>
From: DJ Delorie <dj AT delorie DOT com>
To: djgpp AT delorie DOT com
In-reply-to: <d2ad330a.0308260425.67eef84f@posting.google.com>
	(cbramix AT libero DOT it)
Subject: Re: DJGPP and old VGA feature
References:  <d2ad330a DOT 0308260425 DOT 67eef84f AT posting DOT google DOT com>
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> Long (long...) time ago I was using a very useful feature of DJGPP.
> I'm talking about the linear frame buffer emulation for video cards
> with bank switching function only.
> Now this feature has been removed and I thought it was caused by DPMI
> server (no functions available for doing that).
> But after reading the functions available in DPMI I got the impression
> it could be done, at least a small part.
> I think it would be interesting to add a new selector by default,
> maybe called _vga_ds, in addition to _dos_ds, _my_ds, etc.
> Or I could be simply wrong and this method can't be done right now.

You want near pointers, see <sys/nearptr.h>

The thing that made the old linear frame buffers work so well was that
we could trap the page accesses (page faults) and remap video memory
to "catch" them.  For today's cards, the best we can hope for is that
the card itself maps its memory into a linear frame buffer.