Re: Commodore joystick ports

From: Jim Brain (
Date: 2004-11-03 15:34:17

Marko Mäkelä wrote:

>You didn't mention one trick that Andreas Boose once told me: the double
>interrupt trick.  Set up two interrupts.  The first one would be served with
>some jitter, and the second one would be triggered while the first one is
>executing NOP instructions.  On the 6502, you'd have to get rid of the 0..1
>cycle jitter in the second interrupt because the shortest instructions take
>2 cycles, but on the AVR the first interrupt can be executing 1-cycle
>instructions, and the second interrupt will be cycle-exact.
This is a neat idea (I'll stuff it in my bag of tricks), but I'm not 
sure how to discern the 3 cycle jitter, as my first IRQ is the detection 
of the falling edge of the POT line.


Jim Brain, Brain Innovations                      
Dabbling in WWW, Embedded Systems, Old CBM computers, and Good Times!

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