Date:	Wed, 8 Oct 1997 13:26:16 +0200 (IST)
From:	Eli Zaretskii <eliz AT is DOT elta DOT co DOT il>
To:	"Gurunandan R. Bhat" <grbhat AT unigoa DOT ernet DOT in>
cc:	djgpp AT delorie DOT com
Subject:	Re: three .externs whose purpose and origin I know not
In-Reply-To:	<Pine.LNX.3.91.971007175832.2426A-100000@aditya.unigoa.ernet.in>
Message-ID:	<Pine.SUN.3.91.971008131753.28780C-100000@is>
MIME-Version:	1.0

On Tue, 7 Oct 1997, Gurunandan R. Bhat wrote:

> > (the usual DS selector is made
> > invalid when a signal, such as SIGINT, is pending, while the alias
> > selector is *always* valid, and should therefore be used by interrupt
> > handlers).
> > 
> 
> Very important advice. Shouldn't this be documented 
> somewhere?. If it isn't already that is.

A *lot* of things about hardware interrupts should be documented, because 
it's so much of a black art.  The question is (a) where? and (b) how do 
you get people to read that, instead of posting the same questions all 
over again.

There should be a tutorial on writing interrupt handlers.  Martynas 
Kunigelis once wrote a draft of such a thing (see the pointer in the 
FAQ); I'd imagine that this is documented there somewhere.  I'd love to 
see some continuation to that effort, it seems to me that there are quite 
a few people here that have first-hand experience with this.

Barring that, anybody who wants to futz with hardware interrupts, needs to
take a very good lookat the few handlers built into DJGPP (the keyboard
handler for generating SIGINT on ^C and the timer handler for profiling). 
If they do, they will see the DS alias used all over the place. 

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