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Old 02-18-2006, 11:16 PM   #2
Disch
Senior Member
 
Join Date: Apr 2001
Posts: 4,387
Default Re: nes emulator with cpu core frequency settings?

Anyway. The short answer is: No, I don't know of any NES emus which allow you to change it.

The long answer of a reason why that might be the case:

For starters, it would be a lot of work (it wouldn't be as simple as changing a constant inside the emu -- there's a lot of timing sync stuff the emu has to keep track of, and most emus probably are built around the assumption of a fixed CPU:PPU clock ratio). Furthermore, it would probably only work for a handful of games.. and would break (or cause glitches in) many many many games.

Too many games rely on PPU/CPU syncronization. Upping the CPU clock speed would probably break many older games which don't take advantage of a PPU-based IRQ counter (MMC3, MMC5, and some mapper 90 IRQs are the only ones that would still work -- but most of those games would likely experience jitters right where the screen splits if you changed the CPU clock). Older games which split the screen in more than one place -- or that don't use Sprite-0 hit for timing would probably become unplayable. Some of them might even completely crash and burn. Extremely timing sensitive games such as Rad Racer and Battletoads would be pretty much unplayable (and in fact, I'm 99.999% sure Battletoads would crash and burn)

Although I suppose if you up the PPU clock rate so that it keeps the same sync ratio with the CPU -- that might work. You could just have the emu add a bunch of idle scanlines at the end of the frame before tripping an NMI. That way split screen effects and other PPU timing tricks won't be messed up -- but there will be more CPU time in the frame.

However upping the CPU clock rate (regardless of the method) would change the pitch of the music/sound effects (at least -- it would if the emu does it right). And could potentially break CPU-cycle based IRQ counters used by various mappers.

Metroid is one of the few games that would work without a hitch with an overclocked CPU since it never splits the screen (but again, the music/sound would be a higher pitch).
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