Re: Unexpected IRQ behaviour on a VIC-20

From: Marko Mäkelä <>
Date: Sat, 29 Jul 2017 11:37:47 +0300
Message-ID: <20170729083747.s4s4zwzanac2jr5m@hp>
Hi Ruud,

>I wanted to check various 6522 registers to see if the interrupt 
>occurred or not AFTER the routine.

The obvious solution would be to communicate via shared memory. For 
example, set up a circular buffer for the latest interrupt events, and a 
"cursor" variable to point to the latest event. Or just increment a 
counter. The main program could poll the counter to determine if an 
interrupt occurred.

My understanding is that the Atari 8-bit computers use a concept of 
"shadow registers" in RAM to allow cleaner access to the chips from 
BASIC. I do not know if this covers other chips than the video chip(s).


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Received on 2017-07-29 09:00:01

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