From:	Tero Parvinen <tero AT mnar DOT tky DOT hut DOT fi>
Newsgroups:	comp.os.msdos.djgpp
Subject:	Mapping DOS mem. as near
Date:	Thu, 14 Nov 1996 16:34:03 +0200
Organization:	Helsinki University of Technology
Lines:	24
Distribution:	inet
Message-ID:	<328B2DDB.16DDC2BA@mnar.tky.hut.fi>
NNTP-Posting-Host:	mnar.tky.hut.fi
Mime-Version:	1.0
To:	djgpp AT delorie DOT com
DJ-Gateway:	from newsgroup comp.os.msdos.djgpp

I was wondering if it is possible to map a piece of conventional memory
into the djgpp data selector area. I'm trying to program a DMA routine
which would work by first allocating DOS memory and finding a block of
page aligned memory and then adding __djgpp_conventional_base to the
address and returning this. Then you could use the returned pointer to
write stuff there, and the actual DMA transfer routine would first
subtract __djgpp_conventional_base from the pointer passed to it and
then perform the transfer based on the original DOS address.

Is this possible with __djgpp_map_physical_memory or do I need to
__djgpp_nearptr_enable? Just curious because I think this technique is
used in MikMod as well and there's no mention of any mapping like this.
The little test I ran came (of course) up with an error after I added
the conventional base like described and tried to put stuff into the
buffer without any additional mappings...

Does __djgpp_conventional_base make any sense before calling
__djgpp_nearptr_enable? What would be the best way to cope with this?

Thanks,
--
Tero Parvinen
Tero DOT Parvinen AT hut DOT fi
http://www.niksula.cs.hut.fi/~tparvine

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