NES PAL timing vs NSTC timing and in general

Discuss emulation of the Nintendo Entertainment System and Famicom.

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Coldberg
Posts: 34
Joined: Fri Jul 18, 2008 9:12 am

NES PAL timing vs NSTC timing and in general

Post by Coldberg » Sat Dec 24, 2011 4:25 pm

i did some calculations it seems NTSC has a perfect 3:1 ratio of ppu cycles to cpu cycles but PAL has 3.20481928~~ is that correct ?
And how does that play out in synchronisation in making a cycle perfect emulator (like on nstc i'd run 1 cpu cycle and 3 ppu cycles but what about pal ? run 1 cpu cycle 3 ppu and then insert one ppu cycle for every 4 passes? sounds kind of a pain)
And how different ntsc/pal is actually ? cpu/apu/ppu what considerations should i take when coding say a nstc version then adapting it to pal?

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miker00lz
Posts: 235
Joined: Thu Sep 23, 2010 7:28 pm

Re: NES PAL timing vs NSTC timing and in general

Post by miker00lz » Sat Dec 24, 2011 4:35 pm

Coldberg wrote:i did some calculations it seems NTSC has a perfect 3:1 ratio of ppu cycles to cpu cycles but PAL has 3.20481928~~ is that correct ?
And how does that play out in synchronisation in making a cycle perfect emulator (like on nstc i'd run 1 cpu cycle and 3 ppu cycles but what about pal ? run 1 cpu cycle 3 ppu and then insert one ppu cycle for every 4 passes? sounds kind of a pain)
And how different ntsc/pal is actually ? cpu/apu/ppu what considerations should i take when coding say a nstc version then adapting it to pal?
every 5 passes, add a PPU cycle. i don't see what is such a pain there. if the PPU tick modulo 5 is 0, do an extra tick......... it's no different than how you execute an extra CPU cycle on the NTSC version every third scanline.

NTSC CPU = master clock / 12
NTSC PPU = master clock / 4

PAL CPU = master clock / 16
PAL PPU = master clock / 5

http://wiki.nesdev.com/w/index.php/Clock_rate

there's a lot of info on the wiki. you should look at it.

Coldberg
Posts: 34
Joined: Fri Jul 18, 2008 9:12 am

Post by Coldberg » Sat Dec 24, 2011 4:41 pm

thanks :)
i tried looking at it but got a bit comfused

johannesmutlu
Posts: 26
Joined: Fri Mar 11, 2011 2:22 pm

Post by johannesmutlu » Wed Dec 28, 2011 9:41 am

no doubt that the timing between the pal and ntsc nes systems are different,wich explaines wich some pal,ntsc games,do,nt work on each other,even not with a clunky convertor,like the pirate version of superdonkeykong2(wich i run on the powerpak),it works on a ntsc nes,but not on a pal nes,all i get is a black screen, wich really pisses me off.
it,s so sad that some pal,ntsc games require crucial timing to work properly, aaarrrggg!!!

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