ct-recomp

Static recompiler for Chrono Trigger (SNES, US 1.0) 65816 code to C, plus a C runtime. The recompiler and runtime are game-agnostic; everything specific to Chrono Trigger lives in game/ct/.

Planned features after boot (MSU-1, achievements, save states, widescreen and more) are listed in ROADMAP.md.

Progress

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69.4% recompiled: 1414 of 2036 known functions are compiled to C.

• Native at runtime: 97.6% of the instructions in a 1500-frame boot run as compiled C (the rest run in the interpreter).
• Milestones: 3 of 7 closed.

Updated by tools/progress.py with every push; details in game/ct/PROGRESS.md.

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Layout

• recomp/ — the translator (Python): decoder with static M/X tracking, C emitter.
• runtime/ — CPU, bus, cycle model, interpreter, frame scheduler; the vendored PPU/DMA/APU core lives in third_party/snes/.
• frontend/ — SDL2 frontend; tools/ct_boot.c — headless boot probe.
• test/ — engine tests; they run on a synthetic ROM generated at build time.
• game/ct/ — everything specific to Chrono Trigger: game.toml (ROM identity), funcs.toml / unresolved.toml (symbols), extern hooks, game tools, the ROM-dependent tests, and PROGRESS.md.

Build

Requirements: CMake 3.20+, a C11 compiler, Python 3.11+, SDL2 (optional, for ct_sdl).

Engine only (no ROM needed; what CI runs):

cmake -S . -B build && cmake --build build -j && ctest --test-dir build -LE rom

With the game. Supply your own headerless US 1.0 ROM; it is checked against game/ct/game.toml at configure time:

export CT_ROM=/path/to/chrono_trigger.sfc   # headerless, 4 MB
cmake -S . -B build && cmake --build build -j && ctest --test-dir build

This builds game/ct (generated C goes to build/game/ct/out/) and two programs at the top of build/. For investigations, a Debug tree builds in about 30 seconds (runtime at -Og, generated code at -O1, see CT_GEN_OPT): cmake -S . -B build-dbg -DCMAKE_BUILD_TYPE=Debug. The build uses ccache when it is installed.

build/ct_sdl                           # play: window, audio, keyboard/controller
mkdir -p shots && build/ct_boot --frames 1500 --dump shots   # headless: PNGs of what changed

ct_sdl keys: arrows, Z=B, X=A, A=Y, S=X, Q=L, W=R, Enter=Start, Right Shift=Select; a game controller works too. Ctrl+Q or closing the window quits. ct_sdl --record FILE saves your pad input as a script; ct_boot --script FILE --frames N replays it exactly (N is on its last line), and ct_sdl --script FILE plays it back in the window. A reset F line in a script presses the reset button as frame F begins. ct_boot also takes --input F1-F2:BUTTONS to script the pad, --wav FILE for audio, --hash-log FILE for per-frame state hashes (tools/lockstep.py compares native and interpreted runs with them), and --needed-hw FILE to report where emulation stops.

Reference comparison: tools/ref_compare.py --probe build/ct_boot --mesen PATH --rom $CT_ROM --frames N [--script FILE] runs the same input in Mesen 2 (used as a tool, headless under xvfb-run, with a private settings folder) and reports the first frame where WRAM or the picture differs, with the differing WRAM ranges. tools/trace_diff.py --probe build/ct_boot --mesen PATH --rom $CT_ROM --from F --to G [--script FILE] runs both untraced up to frame F and compares every instruction of frames F-G (address, clock, X, Y), reporting the first difference; about a minute for a window 12,000 frames in. tools/tas_convert.py MOVIE OUT turns a TASVideos BizHawk .bk2 or lsnes .lsmv movie (from power-on) into an input script for both, resets included. Replays of a new game into Leene Square and into the first battle are in game/ct/test/replay/.

The ROM is never committed, and CI never sees it.

Symbol names partly derived from dscotton/ct_disassembly (public domain) and ChronoRET.

License

This code is MIT-licensed (see LICENSE). The Chrono Trigger ROM and its assets are not included and remain the property of their copyright holders — you must supply your own legally obtained ROM via $CT_ROM. Symbol names are credited to dscotton/ct_disassembly (public domain) and ChronoRET. See THIRD_PARTY.md for vendored/adapted third-party code.