Brian DegenhardtandClaude Opus 4.8
5cbcadaa1e
The ios/pr-ready merge (04ea993e99) introduced two independent
regressions in the shared core:
1. DEV9/AdapterUtils.cpp included Apple-only <TargetConditionals.h>
unconditionally under __POSIX__, so every non-Apple POSIX target
(Linux, Android, FreeBSD) failed to compile. Guard the include with
__APPLE__; TARGET_OS_IPHONE is only consulted to keep iOS out of the
BSD-socket block, and on non-Apple it correctly evaluates to 0.
2. SPU2::RegisterNEONBackend() is called from spu2.cpp on every arm64
target (guarded by __aarch64__ / _M_ARM64), but spu2_neon.cpp was
only added to the build for Android/iOS -- so desktop arm64
(macOS/Linux/Windows) failed to link with an undefined symbol.
Compile spu2_neon.cpp on all ARCH_ARM64 targets. The NEON reverb
backend stays opt-in (SPU2/NeonReverbSIMD, default off).
While wiring it up for desktop:
- Drop the unused spu2_neon_mixer/_reverb_ex/_dcfilter includes from
spu2_neon.cpp. They hold helpers for a mixer.cpp/ReaVerb.cpp
integration that hasn't happened, and use the MSVC-only
__forceinline keyword unguarded (breaks clang). The TU only needs
the reverb FIR plus the SVE2 hook.
- Guard spu2_optimize.h's x86-only <xmmintrin.h>/_mm_prefetch off
MSVC-on-ARM64 (falls back to the no-op prefetch).
Verified locally: clean Release build + link on Linux arm64
(RegisterNEONBackend now defined in the binary).
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
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
- ✅ PS1 games (IOP mode) run at full speed — e.g. Gran Turismo 2 is fully playable
- ✅ 3D games run (if crash try disabling MTVU)
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