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FPGA implementations are often implemented based on code or documentation from software emulation projects. An FPGA version of a PS2 has no guarantee of not imp

FPGA implementations are often implemented based on code or documentation from software emulation projects. An FPGA version of a PS2 has no guarantee of not implementing the same or similar bug.

crote 2y ago
The point here is that it is actually viable to reimplement such bugs without incurring significant performance penalties. A software emulator has to be able to execute a single PS2 instruction in the same amount of wall time as it'd take on the original hardware. With a regular multiplication that's fairly easy: x86 also has multiplication, so you can do a 1:1 translation and be fairly certain it's within your time budget. With a bugged multiplication you need to do a regular x86 multiplication, and wrap that in a few dozen other instructions to add the buggy behaviour to it. There's a pretty decent chance it's simply too expensive! When you're writing an FPGA emulator you are able to recreate the buggy multiplication directly in hardware. There's no additional wrapping needed, so (beyond figuring out intended behaviour) it's not any more costly than emulating a non-buggy multiplication. It's far easier to do a cycle-accurate emulation because you have direct control over the transistors!
- gamepsys 2y ago
  > There's a pretty decent chance it's simply too expensive! I doubt the 24 year old, 300Mhz RISC, 32MB Ram, PS2 instruction set is too expensive to do a cycle perfect replication.
  - trealira 2y ago
    Higan is a cycle-perfect SNES emulator, and it's very single-core CPU-intensive. This is what the FAQ [0] says: Full-speed emulation for the Super Famicom base unit requires an Intel Core 2 Duo (or AMD equivalent), full-speed for games with the SuperFX chip requires an Intel Ivy Bridge (or equivalent), full-speed for the wireframe animations in Mega Man X2 requires an even faster computer. Low-power CPUs like ARM chips, or Intel Atom and Celeron CPUS generally aren’t fast enough to emulate the Super Famicom with higan, although other emulated consoles may work. Work can't be split across cores (according to the FAQ) because that would compromise the accuracy of the timing. It may be that the PS2 has similar problems while being more powerful than the SNES. [0]: https://higan.readthedocs.io/en/v104b/faq/ https://higan.readthedocs.io/en/v104b/faq/
  - redox99 2y ago
    Idk about PS2, but N64 (a generation older, much slower) still doesn't have a cycle perfect emulator that runs in real time. Remember that you can't just perfectly emulate the CPU, you must also perfectly emulate the GPU, since they share the memory bus so one can slow the other.
    - rawbot 2y ago
      > since they share the memory bus so one can slow the other. You can look more into this in this video by Kaze Emanuar, famous N64 romhacker. https://www.youtube.com/watch?v=xwls5SpNn1s&t=427s https://www.youtube.com/watch?v=xwls5SpNn1s&t=427s
  - xcv123 2y ago
    You would probably need a terahertz CPU for cycle-accurate PS2 emulation. Cycle-accurate PS2 emulation means emulating the state of the CPU, GPU, other interacting processors, and their various interconnecting busses at clock cycle granularity and possibly at sub-cycle granularity if the processors are running asynchronously.
    - fobes 2y ago
      The IOP (PS1 processor used for I/O), SPU2 (sound processor), IPU (mpeg decoding), EE (main CPU), VU0, VU1, DMA controller and finally the GS (GPU) run asynchronously. It's naive for others to think perfect cycle accuracy for this machine might be possible with any hardware that exists today. PCSX2 is lucky to have VU1 on it's own thread. It still doesn't work perfectly IIRC, VU0 -> VU1 access is a little sketchy with it enabled.
  - anthk 2y ago
    You must be young. A PS2 can run a modernish Linux with WindowMaker and decode MP3's, maybe FLAC and Opus and some MP3+XVid/DivX videos. Not so far from a cycle accurate emulation of a low end Windows 98 era PC. A PS2 with Linux can comment on this page for instance. With TLS et all, if you use Dillo as the web browser as it uses MbedTLS. The TLS handshake might ast a few seconds but that's it. Try running that on a cycle accurate emulator without bringing an i7 to its knees. A similar PC would be a Pentium II-III at 450-500 MHZ with 64MB of RAM running Damn Small Linux or NetBSD with a small Window Maker setup. Bear in mind that you could run a non-accurate SNES emulation in that machine, with sound outputted at 8000 HZ and with no filters, enough for most common games such as Chrono Trigger and Super Mario World with lots of hacks fixing the imprecise timing under ZSNES.

FPGA implementations are often implemented based on code or documentation from software emulation projects. An FPGA version of a PS2 has no guarantee of not implementing the same or similar bug.

crote 2y ago

The point here is that it is actually viable to reimplement such bugs without incurring significant performance penalties. A software emulator has to be able to execute a single PS2 instruction in the same amount of wall time as it'd take on the original hardware. With a regular multiplication that's fairly easy: x86 also has multiplication, so you can do a 1:1 translation and be fairly certain it's within your time budget. With a bugged multiplication you need to do a regular x86 multiplication, and wrap that in a few dozen other instructions to add the buggy behaviour to it. There's a pretty decent chance it's simply too expensive! When you're writing an FPGA emulator you are able to recreate the buggy multiplication directly in hardware. There's no additional wrapping needed, so (beyond figuring out intended behaviour) it's not any more costly than emulating a non-buggy multiplication. It's far easier to do a cycle-accurate emulation because you have direct control over the transistors!

gamepsys 2y ago
> There's a pretty decent chance it's simply too expensive! I doubt the 24 year old, 300Mhz RISC, 32MB Ram, PS2 instruction set is too expensive to do a cycle perfect replication.
- trealira 2y ago
  Higan is a cycle-perfect SNES emulator, and it's very single-core CPU-intensive. This is what the FAQ [0] says: Full-speed emulation for the Super Famicom base unit requires an Intel Core 2 Duo (or AMD equivalent), full-speed for games with the SuperFX chip requires an Intel Ivy Bridge (or equivalent), full-speed for the wireframe animations in Mega Man X2 requires an even faster computer. Low-power CPUs like ARM chips, or Intel Atom and Celeron CPUS generally aren’t fast enough to emulate the Super Famicom with higan, although other emulated consoles may work. Work can't be split across cores (according to the FAQ) because that would compromise the accuracy of the timing. It may be that the PS2 has similar problems while being more powerful than the SNES. [0]: https://higan.readthedocs.io/en/v104b/faq/ https://higan.readthedocs.io/en/v104b/faq/
- redox99 2y ago
  Idk about PS2, but N64 (a generation older, much slower) still doesn't have a cycle perfect emulator that runs in real time. Remember that you can't just perfectly emulate the CPU, you must also perfectly emulate the GPU, since they share the memory bus so one can slow the other.
  - rawbot 2y ago
    > since they share the memory bus so one can slow the other. You can look more into this in this video by Kaze Emanuar, famous N64 romhacker. https://www.youtube.com/watch?v=xwls5SpNn1s&t=427s https://www.youtube.com/watch?v=xwls5SpNn1s&t=427s
- xcv123 2y ago
  You would probably need a terahertz CPU for cycle-accurate PS2 emulation. Cycle-accurate PS2 emulation means emulating the state of the CPU, GPU, other interacting processors, and their various interconnecting busses at clock cycle granularity and possibly at sub-cycle granularity if the processors are running asynchronously.
  - fobes 2y ago
    The IOP (PS1 processor used for I/O), SPU2 (sound processor), IPU (mpeg decoding), EE (main CPU), VU0, VU1, DMA controller and finally the GS (GPU) run asynchronously. It's naive for others to think perfect cycle accuracy for this machine might be possible with any hardware that exists today. PCSX2 is lucky to have VU1 on it's own thread. It still doesn't work perfectly IIRC, VU0 -> VU1 access is a little sketchy with it enabled.
- anthk 2y ago
  You must be young. A PS2 can run a modernish Linux with WindowMaker and decode MP3's, maybe FLAC and Opus and some MP3+XVid/DivX videos. Not so far from a cycle accurate emulation of a low end Windows 98 era PC. A PS2 with Linux can comment on this page for instance. With TLS et all, if you use Dillo as the web browser as it uses MbedTLS. The TLS handshake might ast a few seconds but that's it. Try running that on a cycle accurate emulator without bringing an i7 to its knees. A similar PC would be a Pentium II-III at 450-500 MHZ with 64MB of RAM running Damn Small Linux or NetBSD with a small Window Maker setup. Bear in mind that you could run a non-accurate SNES emulation in that machine, with sound outputted at 8000 HZ and with no filters, enough for most common games such as Chrono Trigger and Super Mario World with lots of hacks fixing the imprecise timing under ZSNES.