Log inRegister an accountBrowse CSDbHelp & documentationFacts & StatisticsThe forumsAvailable RSS-feeds on CSDbSupport CSDb Commodore 64 Scene Database
 Welcome to our latest new user ATOO ! (Registered 2017-11-21) 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 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. :)
2017-11-10 11:22
Groepaz

Registered: Dec 2001
Posts: 8275
64er mag had some example for this.... it was slooooooooooow =)
2017-11-10 11:24
MagerValp

Registered: Dec 2001
Posts: 891
It's also possible to press restore while running, and to use SD2IEC. If you set yourself up for failure, don't be surprised when you fail :)
2017-11-10 11:30
Oswald

Registered: Apr 2002
Posts: 4126
Quote: 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.

relying on things that are not under your control is usually a bad idea. (machine is in an after reset state). this is much more of a cargo cult, than using SEI/CLI.
2017-11-10 11:55
Bitbreaker

Registered: Oct 2002
Posts: 430
After all, why bother about those few wasted bytes, where's the highly optimized demo parts? :-D How can this behaviour finally be misused? By having the upcoming instruction of the SEI on a register being read or not?
2017-11-10 13:30
Krill

Registered: Apr 2002
Posts: 902
Since the succeeding opcode is merely fetched, and not executed, then the pipeline flushed and the interrupt handled, then the opcode re-fetched and finally executed...
I can only imagine some arcane anti-cracking/debugging/reverse-engineering setup there, nothing demo-worthy.
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
chesser/Nigaz
www.gb64.com
Seven
Ziggy72
r242
iAN CooG/HVSC
DonChaos
Wiklund/Fairlight
Groepaz
Guests online: 53
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 Pro Memoria 4  (9.3)
10 KAOS 64  (9.3)
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 Graphicians
1 Jok  (10)
2 JonEgg  (9.8)
3 Mirage  (9.8)
4 Archmage  (9.7)
5 Veto  (9.7)

Home - Disclaimer
Copyright © No Name 2001-2017
Page generated in: 0.97 sec.