Date:	Thu, 6 Nov 1997 13:01:49 +0200 (IST)
From:	Eli Zaretskii <eliz AT is DOT elta DOT co DOT il>
To:	djgpp AT delorie DOT com
Subject:	Re: Taking over the keyboard interrupt
In-Reply-To:	<345f6e4c.1676365@news.demon.co.uk>
Message-ID:	<Pine.SUN.3.91.971106130115.4371B-100000@is>
MIME-Version:	1.0

On Tue, 4 Nov 1997, Sam. wrote:

> I have read the FAQ, I think it assumes you know what you're talking
> about to start with. What are IRET and STI instructions anyway? What
> context do they belong in?

Correct me if I'm wrong, but it seems that you have never written a
program for the x86 processors which handles interrupts.  If so, you
have a lot of catching up to do.  I don't think you should come close
to writing interrupt handlers without knowing how interrupts work on
the x86 processors, and that's a LOT of material.

> I know a bit of Z80 assembler, but this is
> really a huge leap to understanding 80386 protected mode and interrupt
> routines and locked memory and whatever else. There's far too much to
> learn, and I'd really rather dodge learning the entire DPMI spec until
> I have to.

You appear to mix here many issues that aren't directly related to
interrupt handling.  Both protected mode and DPMI have some effect on
interrupt handling, but IRET and STI are the basics, and if you don't
know what they are, there's no sense in getting into details of
protected mode and DPMI.

And yes, to write hardware interrupt handlers in DJGPP, you *will*
have to read the DPMI spec, at least those its parts which describe
how interrupts work in the DPMI environment.

> All the concepts in the FAQ and the Info seem to point to
> each other.

That is a known problem with most references.  Even the dictionaries
have the same problem.  They all assume some basic knowledge of the
subject matter.  A FAQ list is just that: a lits of questions that are
frequently asked.  You cannot expect it to describe everything.

If you have problems with specific concepts, check out the DJGPP
lexicon in http://www.delorie.com/djgpp/.

> Perhaps it's a stupid question, but is there a simple way
> to explain it?

Sorry, no simple way that is known to me, certainly not in a message
posted to a news group.  A good book about interrupt handling, TSRs
and related issues would be a good start.

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