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From: Charles Sandmann <sandmann AT clio DOT rice DOT edu>
Newsgroups: comp.os.msdos.djgpp
Subject: Re: __djgpp_ds_alias - Why?
Date: Tue, 14 Nov 1995 09:11:52 CST
Organization: Rice University, Houston, Texas
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> 1.  What is its purpose?

The hardware interrupt to exception algorithm in V2 twiddles with the 
limits on DS to re-schedule hardware interrupt signals to a time when
they can be handled in an appropriate manner.  But some uses of DS must
not trigger exceptions, especially inside a DPMI host.  Very complicated,
send me email if you want ugly details.

> 2.  Why is it different from ds?

It should be identical in all cases except when we want to cause the 
executing program to raise a signal.

> 3.  Why does it seem to be required in the handlers for some interrupts
> (timer) but not others (keyboard)?

If you see a seeming inconsistency, send me a note, it may be an oversight.