Path: utzoo!attcan!uunet!mcsun!cernvax!rbt
From: rbt@cernvax.UUCP (roberto divia)
Newsgroups: comp.sys.m68k
Subject: Re: Interrupt Handling
Message-ID: <1143@cernvax.UUCP>
Date: 21 Nov 89 09:08:58 GMT
References: <DLEROY.89Nov17093930@x102a.harris-atd.com>
Reply-To: rbt@cernvax.UUCP (roberto divia)
Distribution: comp.sys.m68k
Organization: CERN European Laboratory for Particle Physics, CH-1211 Geneva, Switzerland
Lines: 49

In article <DLEROY.89Nov17093930@x102a.harris-atd.com> dleroy@x102a.harris-atd.com (leroy david 01354) writes:
>I'm new to writing exception handling routines for the 68000 and have
>run into severel problems. [...]
> [...] When I add processing in the main loop
>however, the interrupts seem to occur about 3 or 4 times and then the
>processor seems to be off in the weeds somewhere.

Easy and quick solution: the interrupt service routine should INCREMENT an
interrupt counter and RTE, e.g.:

IntE	ADDQ.L	#1,IntCtr	! Interrupt service routine: IntCtr must be
	RTE			! "imported" from C

static int IntCtr = 0;		! This must be exported to ASM
...
    << enable interrupts >>;
    for (;;) {
	while (IntCtr != 0) {
	    << serve the interrupt request >>;
	    IntCtr--;
	}
	<< other things >>;
    }

You might have more then one interrupt counter. This will work fine if the
interrupt doesn't require short response time. If interrupts are generated
very fast and you don't mind loosing some of them, another method is the
following:

IntE	MOVE.L	#1,IntFlg	! Interrupt service routine: IntFlg must be
	RTE			! "imported" from C

static int IntFlg = 0;		! This must be exported to ASM
...
    << enable interrupts >>;
    for (;;) {
	if (IntFlg != 0) {
	    << serve the interrupt request >>;
	    IntFlg = 0;
	}
	<< other things >>;
    }
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