Log inRegister an accountBrowse CSDbHelp & documentationFacts & StatisticsThe forumsAvailable RSS-feeds on CSDbSupport CSDb Commodore 64 Scene Database
You are not logged in 
CSDb User Forums


Forums > C64 Coding > TIL: The instruction after SEI can be executed before a pending IRQ is handled
2017-11-07 16:56
Krill

Registered: Apr 2002
Posts: 902
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!
 
... 89 posts hidden. Click here to view all posts....
 
2017-11-09 15:43
TWW

Registered: Jul 2009
Posts: 409
Ground the fucker ^^
2017-11-09 16:18
MagerValp

Registered: Dec 2001
Posts: 891
For reference, here's a bog standard raster IRQ setup that'll work every time if run from basic:
	lda #$7f
	sta $dc0d

	lda #$35
	sta $01

	lda #$1b
	sta $d011
	lda #$fa
	sta $d012

	lda #<irq
	sta $fffe
	lda #>irq
	sta $ffff

	lda #1
	sta $d019
	sta $d01a
NB: Clearing pending IRQs with $d019 is not strictly necessary if you run from a freshly reset machine (the kernal writes $0f to $d019 on reset), but if something else ran before and exited to the basic prompt there may be an unacknowledged raster IRQ pending.
2017-11-09 16:27
Krill

Registered: Apr 2002
Posts: 902
Quoting MagerValp
but if something else ran before and exited to the basic prompt there may be an unacknowledged raster IRQ pending.
Hmm, if whatever ran before left unacknowledged interrupts behind, wouldn't they trigger time and again without ever being acknowledged, so the BASIC prompt would never be reached and IRQs be handled in an endless loop? :)
2017-11-09 16:44
MagerValp

Registered: Dec 2001
Posts: 891
No, they're still masked by a zero value in $d01a. Hmm, I wonder if the soft reset before the ready prompt clears it... Just checked, and afaict, nope.
2017-11-09 16:48
iAN CooG

Registered: May 2002
Posts: 1751
" if run from basic "
and what about if it's not? Why even assuming it? It's not better to be safe and put ALSO sei/cli, and clearing $D019 too in any case?
2017-11-09 16:51
MagerValp

Registered: Dec 2001
Posts: 891
Clearing $d019 is necessary, and testing a bit more it seems like it's necessary even on a freshly reset machine. SEI/CLI is still useless though, and only creates the problem of having to clear $dc0d.
2017-11-09 19:01
Stone

Registered: Oct 2006
Posts: 118
Quoting iAN CooG
" if run from basic "
and what about if it's not?
Then you either know about the calling context and set things up accordingly, OR you know nothing, in which case initial setup is the responsibility of the caller.
2017-11-10 08:56
ChristopherJam

Registered: Aug 2004
Posts: 682
Quoting MagerValp
For reference, here's a bog standard raster IRQ setup that'll work every time if run from basic.


…and if you also zero $d01a at the start of the routine, it should then behave itself if your predecessor left a raster interrupt installed :)
2017-11-10 11:16
MagerValp

Registered: Dec 2001
Posts: 891
Quote: Quoting MagerValp
For reference, here's a bog standard raster IRQ setup that'll work every time if run from basic.


…and if you also zero $d01a at the start of the routine, it should then behave itself if your predecessor left a raster interrupt installed :)


You wouldn't even be able to load stuff from disk with a raster IRQ running, so I don't think it's necessary for account for that.
2017-11-10 11:20
Krill

Registered: Apr 2002
Posts: 902
You can load fine from disk using KERNAL routines, with a raster IRQ running. You just need to do it right. And it loads even slower, of course. :)
Previous - 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 - Next
RefreshSubscribe to this thread:

You need to be logged in to post in the forum.

Search the forum:
Search   for   in  
All times are CET.
Search CSDb
Advanced
Users Online
Alakran_64
Psycho Stick/Napalm,..
Guests online: 37
Top Demos
1 Uncensored  (9.7)
2 Edge of Disgrace  (9.7)
3 Coma Light 13  (9.6)
4 The Shores of Reflec..  (9.6)
5 Lunatico  (9.6)
6 Comaland 100%  (9.5)
7 Incoherent Nightmare  (9.5)
8 Wonderland XII  (9.5)
9 Comaland  (9.5)
10 Wonderland XIII  (9.5)
Top onefile Demos
1 Pandemoniac Part 2 o..  (9.6)
2 FMX Music Demo  (9.6)
3 Daah, Those Acid Pil..  (9.5)
4 Dawnfall V1.1  (9.5)
5 Synthesis  (9.5)
6 Dawnfall  (9.4)
7 Treu Love [reu]  (9.4)
8 Field Sort  (9.4)
9 KAOS 64  (9.3)
10 One-Der  (9.2)
Top Groups
1 Oxyron  (9.4)
2 Booze Design  (9.4)
3 Censor Design  (9.3)
4 Crest  (9.3)
5 The Judges  (9.3)
Top NTSC-Fixers
1 Horizon  (9.9)
2 Pudwerx  (9.6)
3 Stormbringer  (9.6)
4 Fungus  (9.6)
5 Moloch  (9.3)

Home - Disclaimer
Copyright © No Name 2001-2017
Page generated in: 0.285 sec.