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From: acmfiu@serss0.fiu.edu (ACMFIU)
Newsgroups: comp.sys.apple2
Subject: heartbeat interrupts
Message-ID: <2037@kluge.fiu.edu>
Date: 18 Jan 91 04:49:58 GMT
Sender: news@kluge.fiu.edu
Organization: Florida International University, Miami
Lines: 102

Awhile back I posted a message concerning HeartBeat interrupts. I wanted to,
when a key was pressed, pause my program and, if oa-period was pressed,
terminate the program. Thanks to Tim Meekins and Jawaid Bazyar for their
responses. I have come up with the following code, although their remains to
be one bug.

int
main (void)
{
	char *kybdvector;
	<blah>

	EMStartup (blah);
	kybdvector = GetVector (kybdIntHnd);
	SetVector (kybdIntHnd, check_key);

	<blah>

	bye ();
}

void
bye (void)
{
	SetVector (kybdIntHnd, kybdvector);
	EMShutDown ();
	Close (0);		/* close all files */
	exit (1);
}

asm void
check_key (void)
{
		rep	#$30			/* just to make sure */
		php
		phb
		phk
		plb
		jsl	incbusyflag

		lda	$e0c000
		bpl	end
		cmp	#"."
		bne	wait
		lda	$<wherever oa status is>
		cmp	#<is oa key pressed>
		bne	wait

		pha				/* space for result */
		pushlong #bye
		_SchAddTask
		pla				/* i KNOW it worked */
		bra	end

	wait	pha
		pushlong #pause
		_SchAddTask
		pla

	end	plb
		plp
		jsl	decbusyflag
		rtl
}

asm void
pause (void)
{
		lda	$e0c000
	wait	lda	$e0c010
		bpl	wait
		lda	$e0c000
		rtl
}

What I basically do is startup the Event Manager which automatically makes
keyboard interrupts available (ala IntSource) and then I modify the interrupt
handler that the Event Manger uses for the keyboard interrupts to my own.
When I run my program, pressing any key appropriately causes the program to
pause, then I press the key again and it resumes execution. The problem comes
with oa-period. When I press it, the program ends and I'm back in the shell.
however, when I run it again, NO key I press does anything. It's like the
keyboard interrupts were disabled. If I press "AAAAAAAAAAAAAAA", they will
appear on the command line AFTER the program is finished executing.

My question is, how in the world do keyboard interrupts get disabled from
the above code (the above code is not 100% correct but you should get the 
idea). Since I get the keyboard interrupt vector used by the Event Manager
and restore it before I EMShutDown(), how does it get corrupted?

I also used the above code without the Event Manager. Using the Misc Tool
Set you can do it via:
	IntSource (kybdEnable);
	kybdvector = GetVector (kybdIntHnd);
	SetVector (kybdIntHnd, check_key);
	<foo>
	SetVector (kybdIntHnd, kybdvector);
	exit (0);

Any ideas?

albert