RE: Unexpected IRQ behaviour on a VIC-20

From: Baltissen, GJPAA (Ruud) <ruud.baltissen_at_apg.nl>
Date: Sat, 29 Jul 2017 07:37:22 +0000
Message-ID: <54F350D2C6501448A3EE14B7854C5FB560F0308B@WSV10441N3.office01.internalcorp.net>
Hallo Spiro,


> IRQroutine:  
> 	pla
> 	pla
> 	pla

I start my program from a cartridge ROM so the original IRQ routine is still effective. And that routine pushes A, X and Y on the stack before doing a "jmp ($0314)". I don't need them so I discarded them. The NMI doesn't push anything at all to stack before doing a "jmp ($0316)". 


> NMIroutine:  
> 	lda	#$33
> 	sta	IrqNmiCheck
> 
> 	sei				; disable interrupts
>
> Why do you want to disable the interrupts? 

I wanted to check various 6522 registers to see if the interrupt occurred or not AFTER the routine. I knew that not reading the correct register would cause another interrupt immediately. The idea was that SEI would stop that. But Marko explained why it wouldn't work. And, as I realized my self, it wouldn't work with a NMI at all.


> As said, it would be best if you could give a complete, but as small as possible, program code so we can see what you are doing, and tell us what you are expecting.

Not yet because I'm sure I will be accused of inventing the wheel twice again :)


Met vriendelijke groet / With kind regards, Ruud Baltissen

www.Baltissen.org



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Received on 2017-07-29 08:00:02

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