From:	"Andrej Brodnik (Andy)" <Andrej DOT Brodnik AT sm DOT luth DOT se>
Newsgroups:	comp.os.msdos.djgpp
Subject:	__dpmi_physical_address_mapping
Date:	Fri, 11 Oct 1996 18:09:05 +0200
Organization:	Lulea University
Lines:	29
Message-ID:	<325E7121.167EB0E7@sm.luth.se>
NNTP-Posting-Host:	my21.sm.luth.se
Mime-Version:	1.0
To:	djgpp AT delorie DOT com
DJ-Gateway:	from newsgroup comp.os.msdos.djgpp

We are building a PC board which occupies 256kB of
address space. It'l be put somewhere above 1M and inside
24-bit address space. Now, the SW will be running under
(for testing purposes -- yeap it's a research) DOS. We are
using djgpp C compiler and we think to use procedure
__dpmi_physical_address_mapping to access the board. I have 
a couple of questions answers on which I'd appreciate a lot.

1) Does somebody has a piece of code using the above procedure?
If yes, can we get it? (not the whole programme, only the piece
which uses the procedure.

2) How "expensive" is to access the memory this way? How many
instructions?

3) How complicated is to put the whole programme (we are under DOS)
in the protected mode at the beginning and then (is possible) access
the memory directly? What does such an attempt mean from the point
of view of (re)coding of the existing programme (we are using gcc
now).

Thanx in advance a lot for your answers!

Andrej


PS: If you have an answer on one, few or all questions, please
do not hesitate to send it/them. I will appreciate all of
them greatly.

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