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From:	"Rod Pemberton" <do_not_have AT nowhere DOT cmm>
Newsgroups:	comp.os.msdos.djgpp
Subject:	Re: DMA and paging
Date:	Mon, 24 Sep 2007 12:34:37 -0400
Organization:	Aioe.org NNTP Server
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References:	<46F7F665 DOT 1773 DOT 20651AE9 AT gerritvn DOT gpvno DOT co DOT za>
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"Gerrit van Niekerk" <gerritvn AT gpvno DOT co DOT za> wrote in message
news:46F7F665 DOT 1773 DOT 20651AE9 AT gerritvn DOT gpvno DOT co DOT za...
> The DJGPP FAQ (http://www.delorie.com/djgpp/v2faq/faq18_13.html) tells
> me to use XMS when a large DMA buffer is required, do some mapping
> tricks and use farptr functions to transfer between DJGPP memory and the
> DMA memory. My understanding is that paging is to blame for this
> complexity.
>
> My question: If paging is disabled by either configuring CWSDPMI with
> CWSPARAM or using CWSDPR0, will the physical to logical address
> mapping be 1:1? Can the physical address to program the DMA unit be
> simply computed by the data segment and offset?
>
>

?

> will the physical to logical address mapping be 1:1

To get non-paging 1:1 physical addressing, you could use PMODEDJ (i.e.,
PMODETSR.EXE).  Run stubedit.exe to change the DPMI host from CWSDPMI.EXE to
PMODETSR.EXE.

stubedit my_sample.exe dpmi=PMODETSR.EXE

Or, you can change the parameters interactively.  Stubedit will ask for
replacement values.  Stubedit will allow you to change the application's
stack space, RM transfer buffer, base filename, argv[0], and DPMI host.

stubedit my_sample.exe

I've used PMODEDJ to help find DPMI programming mistakes, and for one
situation where I don't want paging.


Rod Pemberton

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