Message-ID:	<365693BC.6B54EC5C@jps.net>
Date:	Sat, 21 Nov 1998 02:19:40 -0800
From:	Willy Lee <willy2 AT jps DOT net>
Organization:	WombatSoft
X-Mailer:	Mozilla 4.04 [en] (Win95; I)
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Newsgroups:	comp.os.msdos.djgpp
Subject:	TSRs with DJGPP?
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To:	djgpp AT delorie DOT com
DJ-Gateway:	from newsgroup comp.os.msdos.djgpp
Reply-To:	djgpp AT delorie DOT com

Hi,

I've been trying to write a little keyboard-translation TSR today and
was looking in the FAQ; there's quite a bit there about interrupt
handling which has been very useful but I couldn't find very much about
installing an interrupt handler as a TSR. Has anyone any pointers or
tutorials dealing with this topic?

I saw the DPMI functions for staying resident as a protected-mode
service provider to other DPMI clients, but I want to stay resident to
hook hardware interrupts while at the DOS command prompt, so that won't
work.

I guess I need to install a real-mode interrupt handler, and actually
place the handler code in conventional memory (by allocating a DOS block
and copying the code there). And I'm guessing that the real-mode handler
code can use segment:offset addressing, since it will only be called in
real mode. Now when I terminate and stay resident (using DOS function
Int21h, 31h), my allocated DOS blocks will stay in memory. So the
interrupt vectors will point to the right code. I could even write a
real-mode callback, since the protected-mode memory would never get
released, since the app never really exited as far as the DPMI host
knows...can this be right??

Wait a second! Does __dpmi_set_real_mode_interrupt_vector set the vector
only in the current IDT, or does it set the entry in the real-mode IVT
at 0000:0000? The DPMI spec isn't clear to me on this question. It seems
to me that the TSR would need the vector set in the real-mode IVT.

My head is starting to buzz and it's getting pretty late for me to
think, so I'll quit here for the night and await any answers you might
have.

P.S. please cc: me any replies, I suspect that my ISP has a tendency to
have newsgroup posts go missing occasionally.

Thanks,
=wl

-- 
Willy Lee uses some form of Emacs      http://www.jps.net/willy2
ICQ-UIN: 7570905             "People hardly ever make use of the
freedom which they have, for example, freedom of thought; instead
they demand freedom of speech as a compensation." -- S.K.

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