Editing PS2 Emulation

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All emulators use built-in stripped developement version of PS2 BIOS with disabled debug functions that can affect some games. This is done because some games print debug info on screen when found that are run on dev bios. Bios between ps2_emu, and ps2_gxemu/ps2_netemu are different. Ps2_emu BIOS is able to run only on ps2emu version of emulator due to RDRAM check.
All emulators use built-in stripped developement version of PS2 BIOS with disabled debug functions that can affect some games. This is done because some games print debug info on screen when found that are run on dev bios. Bios between ps2_emu, and ps2_gxemu/ps2_netemu are different. Ps2_emu BIOS is able to run only on ps2emu version of emulator due to RDRAM check.


PS3 models without Emotion Engine unit use "SPE-compatible SIMD graphics-rounding mode for VMX/Altivec Instructions" for FPU, and VU0 emulated floats calculations. This is set on emulator init by HV call 97 with param 1. VU1 actually run at SPE core so no compatibility mode need (or can) to be set. SPE compatible mode for PPE mean that rounding mode is set as round to zero, denormals are treated as zero, and there are no infinities or NaNs. So theoretically what PS2 FPU/VU was originally. Although SPE and PPE SPE compatibility mode is still inaccurate comparing to PS2, because Sony decided to cut off 2 guard bits from calculations on PS2. Probably because there was no need for round and sticky bits (no Nan/Inf, one round mode, etc.). Additionally float divide algorithm is custom and not fully understood up to this day. Good example here are TriAce games, or Castlevania COD where SPE calculation is wrong by 1 bit making games unplayable without patch. This are PS2 math algo specific inaccuracies in FPU/VU implementation that are not present on any other hardware.
PS3 models without Emotion Engine unit use "SPE-compatible SIMD graphics-rounding mode for VMX/Altivec Instructions" for FPU, and VU0 emulated floats calculations. This is set on emulator init by HV call 97 with param 1. VU1 actually run at SPE core so no compatibility mode need (or can) to be set. SPE compatible mode for PPE mean that rounding mode is set as round to zero, denormals are treated as zero, and there are no infinities or NaNs. So theoretically what PS2 FPU/VU was originally. Although SPE and PPE SPE compatibility mode is still inaccurate comparing to PS2, because Sony decided to cut off 2 guard bits from calculations. Probably because there was no need for round and sticky bits (no Nan/Inf, one round mode, etc.). Additionally float divide algorithm is custom and not fully understood up to this day. Good example here are TriAce games, or Castlevania COD where SPE calculation is wrong by 1 bit making games unplayable without patch. This are PS2 math algo specific inaccuracies in FPU/VU implementation that are not present on any other hardware.


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