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bsnes-emu / bsnes

bsnes is a Super Nintendo (SNES) emulator focused on performance, features, and ease of use.
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[Accurate and fast PPU issue] Kishin Douji Zenki - Tenchi Meidou (Japan) - blackscreen [bsnes v110] #216

Closed Max833 closed 3 years ago

Max833 commented 3 years ago

https://archive.is/Mz9Vc

Start the game and you get a blackscreen.

Near:

Okay, I added a workaround fix.

//Kishin Douji Zenki - Tenchi Meidou requires bus hold delays on CPU I/O reads.
//smp_mem_access_times requires no bus hold delays on APU RAM reads.
if((address & 0xfffc) == 0x00f4) {  //0x00f4 - 0x00f7
  wait(address, 1);
  uint8 data = readRAM(address);
  if((address & 0xfff0) == 0x00f0) data = readIO(address);
  wait(address, 1);
  return data;
} else {
  wait(address, 0);
  uint8 data = readRAM(address);
  if((address & 0xfff0) == 0x00f0) data = readIO(address);
  return data;
}

The second argument to wait is "half cycles", eg only take 12 clocks instead of 24 clocks (exact amount is based on the TEST >register settings, but in 100% of cases, it's always 12/24.) So what's actually happening here is that SMP reads from internal functionality (eg timers and RAM) is different than SMP >reads from the shared CPU I/O ports. I'm simulating this with the above address check, because short of someone sending me an SNES modified to use a single >crystal oscillator used by both the SNES CPU and SMP, I can't really write more exacting tests to get the exact values here. This is definitely one of the most extreme edge cases so far in SNES emulation.

https://github.com/bsnes-emu/bsnes/commit/454b90be240ae5d06eb55665b6e23674e356552f