bmdhacks
fc5ca4aca4
_vuCalculateEATAN's eatanconst[] is a hand-transcription of the atan
coefficients microVU keeps in mVU_Globals (microVU_Misc.h). Eight of the
nine round-trip to those globals bit for bit, and so do all five of the
sinconsts[] added alongside them. One did not:
T3 printed: -0.139085337519646
in tree: -0.13085337519646 <- the 9 after "0.13" is gone
Origin: 857ab07f1c (refractionpcsx2, 2021-09-06, "VUInt: Fix macro
flags and implement EFU ops correctly"), the commit that first gave the
interpreter a real EFU model -- before it, _vuEATAN was a one-line
atan() call behind a DevCon.Warning. The typo was there in that
function's first revision and has stood since; b0d1d4ff44 ("VU Int:
Clang formatting", six days later) reflowed the neighbouring lines but
left the literal untouched. It is upstream code, still present upstream
as of this tree's last sync, and several accuracy passes over VUops.cpp
have gone past it. T3 itself has been 0xBE0E6C63 in microVU since
04fba659014e (2009).
Silicon decides it. Interpreter values through the test harness against
the ps2autotests EFU capture, before and after:
EATAN of fs.z console before ulp after ulp
1.0 3f490fda 3f490fdb 1 3f490fdb 1
1.99999988 3f8db70b 3f8db72c 33 3f8db70c 1
2.0 3f8db70b 3f8db72c 33 3f8db70c 1
3.0 3f9fe0ba 3f9fe2d7 541 3f9fe0bb 1
1.5707964 3f807f4c 3f807f4e 2 3f807f4c 0
3.1415927 3fa19dc4 3fa1a070 684 3fa19dc5 1
4.712389 3fae4be7 3fae591e 3383 3fae4be9 2
Across all 208 EFU cases, 17 interpreter values move, every one of them
closer to the console and none away; the recompiler's values are
untouched, as a control. The error grows as the reduced argument to the
seventh power, which is why it vanishes at Fs = 1.0 (where the reduction
gives exactly 0) and is worst at CVF_3PI_OVER2. EATAN(0) is the cleanest
signature: the interpreter returned 0xBC06DF00 = -0.0082362, which is
the coefficient delta itself.
EATAN CVF_PI_OVER2 now reproduces silicon exactly, so its bad_interp
flag and kEfuBadInterp go with it.
Verified both directions: the old source against the new expectations
fails with "new divergence from silicon", the new source against the old
expectations fails with "now MATCHES silicon", and together the suite is
1551/1551.
That measurement also refutes the reason vu1_efu_console_conformance_
tests.cpp gave for these rows -- double-vs-single precision drift "a few
ULP" wide from the interpreter's pow(). It was never that; the remaining
gap is hundreds of ULP and sits on the recompiler side. Comment
corrected rather than left to mislead the next reader.
Idea by pstef.
ARMSX2 — Native ARM64 JIT Fork of PCSX2
ARMSX2 is a free and open-source PlayStation 2 (PS2) emulator based on PCSX2. Its purpose is to emulate the PS2's hardware, using a combination of MIPS CPU Interpreters, Recompilers and a Virtual Machine which manages hardware states and PS2 system memory. This allows you to play PS2 games on your phone, PC, or gaming handheld, with many additional features and benefits.
Thank You
The ARMSX2 team is eternally indebted to the PCSX2 project it is based on. We are so fortunate to build on their 20 years of hardcore development.
About This Fork
The upstream PCSX2 project ships an ARM64 interpreter build for ARM, but its high-performance JIT recompilers (EE, IOP, VU0, VU1, and vtlb fast memory) are x86-64 only.
This fork exists to close that gap. The goal is to preserve the correctness features of 20 years of PCSX2 development, while generating the fastest native ARM performance possible.
Current status:
- ✅ EE (Emotion Engine) recompiler — integer, float, MMI, COP0/COP1/COP2, branches, load/store
- ✅ IOP (I/O Processor / R3000A) recompiler — full integer, load/store, branches, coprocessors
- ✅ VU (Vector Unit) recompiler — microVU skeleton + Upper FMAC vector ISA complete; Lower ISA and runtime complete
- ✅ vtlb fast memory
- ✅ Native ARM64 binary builds and boots the PS2 BIOS
- ✅ 2D games are already playable
- ✅ 3D games run
Why LLMs / AI Were Used
A word on methodology:
The x86-64 JIT code in upstream ARMSX2 is already proven correct — it has run thousands of PS2 titles for years. The challenge in this port is not emulator design or JIT theory; it is mechanical translation of a large, well-understood x86-64 assembly codebase into equivalent ARM64 assembly (via VIXL) while preserving the exact same register-allocation contracts, block lifecycle, and recompiler semantics.
Large language models (LLMs) were used as an accelerant for this translation work — pattern-matching x86 JIT boilerplate to ARM64 equivalents, scaffolding emit routines, and keeping the porting velocity high. The JIT logic (block compiler, dispatcher, analysis passes, flag pipelines, clamping rules, Tri-Ace hacks, etc.) is taken directly from the upstream x86 implementation and validated against it. Nothing was hallucinated from scratch.
In other words: the hard engineering was done by the PCSX2 team over two decades. The hard typing — translating ~50k lines of x86 emitter code into ARM64 — is what AI helped compress.
System Requirements
ARMSX2 targets ARM64 across desktop (macOS, Windows, Linux) and mobile (Android, iOS/iPadOS), all from the single shared core. Our setup documentation page contains additional details on software and hardware requirements.
Please note that a BIOS dump from a legitimately-owned PS2 console is required to use the emulator. For more information, visit this page.
Building
Check out our github actions for the latest build recipe