Xref:	news2.mv.net comp.os.msdos.djgpp:1329
From:	jtsilla AT ccs DOT neu DOT edu (James Tsillas)
Newsgroups:	comp.os.msdos.djgpp
Subject:	In stalling protected mode ISR
Date:	22 Feb 1996 17:50:08 GMT
Organization:	Northeastern University
Lines:	39
Distribution:	world
Message-ID:	<JTSILLA.96Feb22125008@everest.ccs.neu.edu>
NNTP-Posting-Host:	everest.ccs.neu.edu
To:	djgpp AT delorie DOT com
DJ-Gateway:	from newsgroup comp.os.msdos.djgpp

Dear DJGPP'ers,

I am writing a program which needs to intercept keyboard interrupts. I'd
like this program to work under all DPMI servers (even Windows based). I
suspect I need to chain the existing interrupt handler with my new
p-mode handler.

After some research I found a technique where I can allocate a real mode
callback and set it to my handler function. This should work but I can
see no way to chain the handlers such that the system handler also gets
to run.

I see there is a dpmi function to get the existing handler and I can see
how to set the handler to my callback. Is there a way that I can have my
callback switch back to real mode and call the system ISR?

The ISR is for the keyboard interrupt and is supposed to catch all
keyevents to maintain an in-memory keymap. My application can then poll
the keymap at any given time to check if a given key is pressed.

I can probably simulate the function by having some sort of non-blocking
getchar() in an event loop. But I am curious to see if I can get it to
work via the ISR.

thanks for your kind help,
-Jim.

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