Brian Degenhardt
bbda693a7f
Reported on an Xbox One controller: every control on the pad binds except the triggers, which do nothing at the "press a button" prompt. The binding model is keyed on Android keycodes, and most pads — an Xbox controller among them — report their triggers ONLY as analog axes, never as KEYCODE_BUTTON_L2/R2. The capture path already bridges motion to key for the HAT and for stick deflection; triggers were simply never added, and since that path consumes the motion event the press vanished without a trace. Pads whose triggers do send key events were unaffected, which is why this only surfaced now. A pulled trigger now stands in for the keycode a key-emitting pad would send, so it is an ordinary button to everything downstream: bindable to any PS2 control, stealable by another row, assignable as a hotkey or a macro, usable as a combo member. Gameplay resolves that same keycode back through the binding table, so what the capture records is what gets honoured — the two now share one axis resolver rather than each knowing its own list. That makes trigger-bound hotkeys and macros reachable from the Hotkeys and Pad tabs, so the gameplay side has to be able to fire them, or binding one would be a dead end. Both act on the press and the release, which lets a trigger drive the hold-type hotkeys (fast-forward, pressure modifier, gyro hold) that a stick edge cannot. Second fix, same area: the right trigger has a per-device fallback axis for pads that report it on AXIS_RZ, and the left had none. A pad Android has no vendor key layout for passes raw HID through, putting the triggers on plain Z and RZ — so on those devices the right trigger worked and the LEFT ONE WAS READ BY NOTHING, dead in gameplay rather than merely unbindable. Both sides now take the fallback, gated on a 0..1 range so a stick axis (-1..1) can never be mistaken for a trigger.
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