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Krill
Registered: Apr 2002
Posts: 2821 |
TIL: The instruction after SEI can be executed before a pending IRQ is handled
As described here: http://visual6502.org/wiki/index.php?title=6502_Timing_of_Inter..
I never knew this, after all those years, and thought i'd share this as a heads-up.
Thanks to Bubis for pointing it out to me! |
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ChristopherJam
Registered: Aug 2004
Posts: 1370 |
(actually scratch that "it may even" para from the end of my last comment, I didn't quite think that one through - if a CIA interrupt goes off during setup unacknowledged, the consequences are going be considerably worse than a single frame...) |
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Krill
Registered: Apr 2002
Posts: 2821 |
Quoting Oswaldthis is a religious argument This may be an academic discussion (unless you need the size, 4K and all), but it's certainly nothing to do with religion. Well, unless you are a cargo cultist. :) |
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Oswald
Registered: Apr 2002
Posts: 5017 |
"Either way all you are doing is adding extra bytes to your init code with zero improvements to reliability."
An IRQ may destroy A while you try to lda #$7f sta $dc0d. another irq from the other CIA may re-enable $dc0d. You may have interrupt sources from VICII too, fucking you up in all sorts of ways. (rewriting fffe/f after you've set them up for example).
"if there's a source you don't know about to disable, you're going to have bugs regardless of whether you SEI/CLI or not, as it's going to hit while your code isn't expecting it."
you may just forget about your super size effective irq setup and it will backfire when you least expect it. |
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Krill
Registered: Apr 2002
Posts: 2821 |
Now you're grasping at straws. |
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Oswald
Registered: Apr 2002
Posts: 5017 |
Quote: Now you're grasping at straws.
Now you're trolling. |
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Oswald
Registered: Apr 2002
Posts: 5017 |
anyhow I have real machine experience when I've been setting up raster irq without acking timer interrupt for ages, and then at a case it refused working, and I wondered how could I forget to set it up correctly. Since then I religiously ack it. |
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chatGPZ
Registered: Dec 2001
Posts: 11089 |
Quote:An IRQ may destroy A while you try to lda #$7f sta $dc0d
in that case you have much bigger problems than anything discussed here |
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Krill
Registered: Apr 2002
Posts: 2821 |
And we are discussing interrupt setup when run from a plain BASIC environment. So disabling CIA1 interrupts is enough, no SEI/CLI required. Period. :) |
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chatGPZ
Registered: Dec 2001
Posts: 11089 |
even in most other scenarios... eg in a trackmo you pretty much want to always do it at a very defined point to avoid glitches - and then you exactly know what happens anyway, and dont need sei/cli at all. you DO need them only when you do brute force AEG style linking =) |
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Frantic
Registered: Mar 2003
Posts: 1627 |
Okay. I'll always try to make sure to remember to use SEI/CLI then. |
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