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Mail Archives: djgpp/1999/03/03/01:43:51

Date: Wed, 3 Mar 1999 08:40:55 +0200 (IST)
From: Eli Zaretskii <eliz AT is DOT elta DOT co DOT il>
X-Sender: eliz AT is
To: "John S. Fine" <johnfine AT erols DOT com>
cc: djgpp AT delorie DOT com
Subject: Re: HELP! Assembly language dual mode interrupt handler for djgpp program
In-Reply-To: <36DC2727.34F0@erols.com>
Message-ID: <Pine.SUN.3.91.990303084023.7979G-100000@is>
MIME-Version: 1.0
Reply-To: djgpp AT delorie DOT com

On Tue, 2 Mar 1999, John S. Fine wrote:

> If you run
> CWSDPMI without EMM386, then CWSDPMI is responsible for things that
> otherwise EMM386 would handle.

Only a small part of them, actually.  CWSDPMI is not a replacement for
memory manager.  For example, when no memory manager is present,
CWSDPMI grabs all the extended memory to itself, even if the client
doesn't ned that much.

> I think you are saying that CWSDPMI,
> then uses true real mode for DOS calls, rather than using V86 mode.

Yes.

> I think using true real mode is a bad design for many reasons

You didn't expect a 20K program written by an engineer on his free
time to include a memory manager and a V86 monitor, did you?

Real mode may be ``bad design'' (I don't think so, personally), but it
has significant advantages: it is simple, well-documented, and it
works on any machine.  In contrast, the list of conflicts for any
memory manager, even the best ones, goes for many pages.

>   If CWSDPMI really uses real mode that way, and I was seting up a
> system to service 20Hz interrupts in djgpp, I think I would make
> sure QEMM or EMM386 or something was loaded first.

Not necessary a good idea, I'm afraid.  Certain versions of EMM386,
for example, are known to slow down interrupt processing significantly
(see section 18.11 of the FAQ).

>   One of my projects runs mainly in V86 mode on a 50Mhz 486.  All
> interrupts are in pmode and it often sevices interrupts well over
> 20Khz for sustained periods.

Interesting.

What system configuration was that?  Did you use MS-DOS and standard
memory managers to get to V86, or some custom software as well?

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