|
|
|
|
|
|
by ZirconiumX
2312 days ago
|
|
|
There are three killers here: self-modifying code, synchronisation, and parallelism, all of which are major headaches for a JIT. The PS3 does not have self-modifying PPC code (SCEI forbade it), which means the PPE blob can be compiled ahead-of-time (RPCS3 converts it into LLVM). The SPE data can self-modify, however, but (to my knowledge) does not require extensive synchronisation, therefore each SPE core can be put on a thread. The PS2 code has fairly extensive use of self-modifying code; Naughty Dog in particular will frequently load parts of the executable in and out of memory on both the PS2 main processor (the EE) and the PS1 processor (the IOP), and rely on the synchronisation between these two separate processors to be fairly tight. Trying to make the EE and IOP separate threads running simultaneously breaks this synchronisation, so the EE and IOP have to run on the same thread. Additionally, the PS2 has two vector units; VU0 is associated with the EE (it can be used as a floating-point SIMD unit in the EE instruction stream) and VU1 is associated with the GS [the PS2's GPU, the Graphics Synthesizer] Interface (GIF) (it can directly output primitives to the GS). This means that VU0 needs to run on the same thread that the EE runs on (because there is instruction stream interlocking), and VU1 needs relatively tight synchronisation to the GS (it is feasible to put it on its own thread, but games can be quite picky with timings) |
|
|
Sony did manage to ship a PS2 emulator that ran on the second-generation PS3 though (1st generation PS3 had actual PS2 hardware inside, but the second generation was software-only emulation if I recall correctly?). Besides knowing exactly about every hardware detail, any idea how they pulled that off on hardware that was much weaker relative to a PS2, compared to a modern PC?