PSXRecomp

Generic static recompiler framework for PlayStation 1: MIPS R3000A to C to native x64.

Background on the original prototype: I Built a PS1 Static Recompiler With No Prior Experience (and Claude Code)

What It Is

PSXRecomp translates PS1 MIPS binaries into C, then compiles that C as a native executable linked against a PS1 hardware runtime. The v4 architecture recompiles the real SCPH1001 BIOS and runs it as the kernel. There is no HLE BIOS layer, no stubs, and no general-purpose interpreter fallback for static code.

PSXRecomp is a framework. Game-specific projects live in their own repositories and link this one in as a git submodule to build a game binary. The active end-to-end targets are:

• TombaRecomp — Tomba!
• MegaManX6Recomp — Mega Man X6

New here? The fastest way in: docs/EXECUTION_MODEL.md (how a game actually runs — static / native-overlay / interpreter), then docs/ARCHITECTURE.md, docs/BUILDING.md, and CONTRIBUTING.md.

Philosophy — toward 100% static recompilation

The goal is simple and absolute: a PS1 game should run as native code, not be emulated. Every MIPS instruction the game executes should ideally have been translated to C and compiled ahead of time. No interpreter on the hot path, no HLE shims, no "good enough" approximation of the hardware — the recompiled BIOS is the kernel, and the recompiled game is the game.

PS1 games make that goal hard in one specific way: overlays. Games stream code off the disc into RAM at runtime and execute it, then overwrite it with the next overlay. That code does not exist in the executable at build time, so a pure ahead-of-time recompiler cannot see it. This is the frontier the project is working through, and it is why this is an alpha/beta: today a majority of a supported game runs as statically recompiled native code, but not yet 100%.

How we close the gap, without ever compromising correctness:

1. Static first. The main executable and the BIOS are fully recompiled ahead of time. This is the bulk of execution and it is always native.
2. Capture → compile → cache for overlays. As the game runs, overlays are captured the moment they load. Offline, each is recompiled to a native DLL keyed by its content, cached, and on later runs loaded and dispatched as native code before any fallback. Coverage grows as the game is played: every overlay someone reaches becomes native for everyone after.
3. Interpreter failover — only for code that isn't static yet. A small MIPS interpreter runs runtime-installed code (overlays/dirty RAM) that hasn't been captured-and-compiled. It is a safety net and a coverage feeder, never a substitute for recompiling static code, and never on the BIOS/main-EXE path.
4. Precision over recall. A piece of code we haven't compiled safely falls back to the interpreter and gets captured for next time — under-coverage self-heals. A piece we compile wrong would corrupt the machine, so the system biases hard toward correctness: native code is only dispatched when its source RAM is provably unchanged, and a registration is revoked the instant the RAM it was compiled from is overwritten.

Two honest bounds. The worst case is always performance, never correctness — anything not yet native simply runs interpreted, correctly.

Known corner case — genuinely self-modifying / per-load-relocated code. Some code is rewritten or relocated to different bytes on every load, so it is not static by definition and cannot be recompiled ahead of time into a single correct translation. This code remains interpreted — permanently, as far as the current design is concerned, and that is an accepted, correct outcome (the interpreter runs it faithfully; only speed is lost). It is a narrow corner, not a wall. We may someday aim to cover it — e.g. by detecting the relocation/patch pattern and baking it in at compile time (keyed by relocation parameters), or by compiling at load time — but we make no promise, and the project is fully correct without it.

The aspiration is 100% static coverage — every reachable instruction native, the interpreter idle. The capture-and-recompile loop converges toward it the more a game is played; this branch is where that machinery is being built.

Status

Current milestone as of 2026-05-18:

Subsystem	State
BIOS recompilation (SCPH1001.BIN)	Boots and hands off to Tomba
Game EXE recompilation	Tomba title, OPTIONS, NEW GAME, save/load, and gameplay reached
CD-ROM / MDEC / XA	Tomba FMVs stream and play at the game's 15 fps cadence
Memory cards	Tomba save and load verified
SIO0 controllers	Digital pad polling plus DualShock config replies used by Tomba
GPU	Functional for BIOS boot, FMVs, menus, and first gameplay area
Interrupts, COP0, timers	Working for current Tomba path
Dirty-RAM support	BIOS/game RAM-installed dispatch paths handled
Controller input	Keyboard plus SDL/XInput-style controller mapping via input.ini

Known follow-up work:

• The recent Tomba visual burn-down fixed the BIOS PS logo, title/menu glyph seams, dialog/pause panel seams, terrain shading, and shaded textured branch rendering observed in the first area.
• SPU coverage is partial; reverb, noise, sweep, and accurate SPU IRQ behavior are not complete.
• The historical Windows "Not Responding" hang is mitigated but should stay on the watch list until longer in-game soak tests are clean.
• Neither game is fully validated end to end yet. Tomba has considerably more coverage; Mega Man X6 is playable (stages, controller, and memory-card save/load all work). Full playthroughs of both are still unverified.

For the current game milestone, build and run the sibling TombaRecomp project:

cd ../TombaRecomp
cmake --build build -j16
./build/psx-runtime.exe --game game.toml

Running this repository's runtime without --game is still useful for BIOS-only memory card management.

Release Package

The framework release package is BIOS-only:

1. Download PSXRecomp-v*-windows-x64.zip from Releases.
2. Extract it and run PSXRecomp.exe.
3. Select your legally obtained SCPH1001.BIN BIOS when prompted.

The package does not include a PS1 BIOS, game disc image, generated game code, or save data. The selected BIOS path is saved next to the executable as bios.cfg; delete that file to pick a different BIOS later.

Game-specific recomp projects, including TombaRecomp, use the same runtime picker contract but also prompt for a legally obtained game disc image.

Setup

Builds natively on Windows (MSVC/MinGW), macOS (Apple Silicon & Intel), and Linux. The BIOS thread scheduler uses host fibers — Win32 Fibers on Windows, ucontext on POSIX (runtime/src/psx_fiber.c) — so the recompiled BIOS's cooperative thread switching (the CD-boot handoff in particular) behaves the same on every platform.

Requirements at a glance (full details, dependency table, and per-platform prerequisites in docs/BUILDING.md):

• A C/C++ toolchain: MSVC or MinGW/MSYS2 (Windows), Apple Clang (macOS), Clang/GCC (Linux). CMake 3.20+; on macOS/Linux also ninja and pkg-config.
• SDL2 (system / bundled). RmlUi and FreeType come in as git submodules — clone with --recurse-submodules.
• A legally obtained SCPH1001.BIN BIOS dump. Not included.
• For game projects, a legally obtained game disc/EXE dump. Not included.

Build the framework (recompiler tool + BIOS-only runtime):

git clone --recurse-submodules https://github.com/mstan/psxrecomp.git && cd psxrecomp

cmake -S recompiler -B recompiler/build -G Ninja -DCMAKE_BUILD_TYPE=Release && cmake --build recompiler/build
cmake -S runtime    -B runtime/build    -G Ninja -DCMAKE_BUILD_TYPE=Release && cmake --build runtime/build --target psx-runtime

On Windows swap -G Ninja for your generator if you prefer (e.g. -G "Unix Makefiles"); always keep an explicit -DCMAKE_BUILD_TYPE so the generated C is optimized. Game projects generate their own generated/<serial>_*.c files and link this runtime through CMake — see docs/BUILDING.md.

Keyboard Map

PSX button	Keyboard
D-Pad Up / Down / Left / Right	Arrow keys
Cross	X
Square	Z
Circle	S
Triangle	A
L1 / R1	Q / W
L2 / R2	E / R
L3 / R3 (stick clicks)	T / Y
Start	Enter
Select	Right Shift
Turbo	Tab (hold)
Fullscreen	F11 / Alt+Enter / Cmd+F

Controller Map

Xbox-style controller defaults are enabled when a controller is connected:

PSX button	Xbox controller
D-Pad Up / Down / Left / Right	D-pad or left stick
Cross	A
Circle	B
Square	X
Triangle	Y
L1 / R1	LB / RB
L2 / R2	LT / RT
L3 / R3	Left / right stick click
Start	Menu
Select	View / Back

Release builds create/use input.ini next to the executable. Edit that file to change controller device index, deadzone, or button mapping.

Architecture

The recompiler emits C functions and dispatch tables for BIOS and game code. The runtime loads the BIOS/game assets into emulated PS1 memory, links the generated C as native code, and simulates hardware through MMIO handlers for GPU, DMA, timers, CD-ROM, MDEC, SIO0, memory cards, SPU, GTE, and interrupt delivery. The recompiled SCPH1001.BIN is the low-level (LLE) kernel and the correctness oracle; an optional HLE tier lays instant boot-skip and a few BIOS services on top, always falling through to the recompiled BIOS.

Code that can't be seen ahead of time (disc-streamed overlays) is captured and compiled to native code the first time it appears (static → gcc → tcc backend), with a small interpreter as the correctness fallback until it is. Full story in docs/EXECUTION_MODEL.md; component-level detail in docs/ARCHITECTURE.md.

See CONTRIBUTING.md and CLAUDE.md for the development rules, and docs/internal/ for the phased plans and deep design notes (PLAN.md, FAITHFUL_TIMING_PLAN.md, …).

Disc Speed

Per-game disc_speed in game.toml [runtime] compresses CD-ROM timing:

Value	Effect
"1x"	Authentic PSX timing. Default for all games.
"2x" / "4x"	2× / 4× faster reads and seeks.
"instant"	Minimum-floor delays. Known to hang some games during early initialization; root cause not yet identified. Use "4x" instead until resolved.

FMV playback is always protected: the CD-ROM layer reverts to 1× whenever XA audio streaming is active, regardless of disc_speed. The speed switch fires only after the BIOS has handed off to the game EXE — boot and the license screen always run at authentic 1×.

Help make your game faster — just by playing it

Why isn't the game already at full speed everywhere? Most of a game's code is converted ("recompiled") into a fast native program ahead of time. But PlayStation games don't keep all of their code on screen at once — they stream extra chunks of code off the disc as you reach new areas (these chunks are called overlays). We can't convert a chunk we've never seen, and the only way to see it is for someone to actually visit that area. Until then, that area's code runs in a slower compatibility mode.

You can help, just by playing. While you play, the game quietly notices which areas are still running in the slow mode, takes a snapshot of them, and converts them to fast native code in the background — often within a minute, while you keep playing. The more places you visit, the faster the game gets. This happens automatically; you don't have to do anything.

Your discoveries persist for you. They are saved in a file written next to the game called overlay_captures.json, and your local cache is rebuilt from it automatically — areas you have visited stay fast on every later session.

Please do not post overlay_captures.json publicly. The file contains verbatim snapshots of the game's code read from your disc, which is copyrighted material — keep it on your own machine, alongside your disc image. A metadata-only contribution format (addresses and checksums, no game code) is planned so discoveries can be shared safely in the future.

Contributing

Contributions are welcome — AI-assisted or not — as long as they're reviewed, tested, and keep the core game-agnostic. A few things hold this project together: the faithful recompiled BIOS is the baseline and oracle, generated code is never hand-edited (fix the recompiler and regenerate), and a change proves itself against the Beetle oracle / on screen rather than by assertion. Game-specific work lives in the game repos, which pin an exact framework commit as a submodule.

Read CONTRIBUTING.md before opening a PR — it covers the core rules, how to verify a change, the regression checklist across the known games, and how a framework fix reaches a game through its pin. Bugs and build problems go to GitHub issues (include gcc -v / OS / generator for build failures); design discussion happens in the R.A.I.D. Discord (invite below).

License

PolyForm Noncommercial 1.0.0. See LICENSE.

The PSX BIOS and game disc images remain copyrighted by their respective owners. This project distributes no BIOS images, no disc images, and no game assets — those are always supplied by the user from their own collection. Release executables (and per-game overlay caches) contain statically recompiled (machine-translated) builds of the original code, the same distribution model used by other static recompilation projects such as N64: Recompiled.

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_{R.A.I.D. — Retro AI Development · a Discord for AI-assisted retro reverse-engineering, decomp & recomp}