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From: braner@batcomputer.tn.cornell.edu (braner)
Newsgroups: comp.sys.atari.st
Subject: Re: Vertical Blank Interrupts
Message-ID: <451@batcomputer.tn.cornell.edu>
Date: Wed, 18-Mar-87 22:36:07 EST
Article-I.D.: batcompu.451
Posted: Wed Mar 18 22:36:07 1987
Date-Received: Sat, 21-Mar-87 04:22:42 EST
References: <741@eneevax.UUCP>
Reply-To: braner@batcomputer.UUCP (braner)
Distribution: world
Organization: Theory Center, Cornell University, Ithaca NY
Lines: 12
Summary: Avoid new VB interrupts reentering the handler

[]

You must avoid reentering your VBI routine upon every VBI (71 times a second
with a monochrome monitor)!  (That's why it crashes...)  (I learned it the
hard way...)

I solved it like this:  the first time your VBI routine is called, it sets
a flag, which is cleared at the end of the routine.  At the beginning of
the routine it checks the flag, and if it is set it knows that it is a
recursive interrupt and it simply returns, doing nothing.

- Moshe Braner