Egg of Time

A native PC port of Chrono Trigger for Nintendo DS, for Windows, Linux and macOS.

Egg of Time is not an emulator. It is a static recompilation: every function of the game's code is translated into C and compiled into a native program, with a small runtime standing in for the DS hardware. You get the DS version of the game running at native speed, with widescreen, high resolutions, high framerates, gamepad support and mods.

• This is an unofficial fan project, not affiliated with or endorsed by Square Enix or Nintendo. Chrono Trigger is a trademark of Square Enix.
• No copyrighted game data is distributed. You need your own copy of the game. Do not share the files made from it: rom/, extract/, game/ and the generated code in build/.
• AI assistance: this project was developed with Claude (Anthropic) through Claude Code. Claude did the reverse-engineering analysis and wrote the recompiler, the runtime and the documentation, under the direction of the repository owner.

1. Download the latest EggOfTime-<version>-windows-x64.zip from the Releases page.
2. Unzip it into a folder you can write to, such as Documents\Egg of Time. Avoid Program Files.
3. Start Egg of Time.exe and choose your ROM (a .nds file) when asked.
4. Wait for the first-start build. Egg of Time translates the game from your ROM into native code. This takes a few minutes and shows a progress bar. Later starts take about two seconds.

Where your files are. Everything stays in the Egg of Time folder:

1. Install Python 3 and a C compiler if you don't have them. The first-start build uses your system's python3 and cc (or clang / gcc):
   • Debian/Ubuntu: sudo apt install python3 build-essential
   • Fedora: sudo dnf install python3 gcc
   • Arch: sudo pacman -S python gcc
2. Download the latest EggOfTime-<version>-linux-x64.tar.gz from the Releases page and extract it: tar xzf EggOfTime-*-linux-x64.tar.gz.
3. Start Egg of Time in the extracted folder and choose your ROM, or pass it: "./Egg of Time" path/to/rom.nds.
4. Wait for the first-start build (about two minutes), as on Windows. Your files go in the same places, with /.

Egg of Time runs one version of the game only:

• Chrono Trigger, Nintendo DS, USA release (game code YQUE, English/French)
• SHA-1 11f9e8204e484eab42181b210c9f214584be75bf

The DS shows the game on two screens. Egg of Time shows it on one by default:

• The boot logos, title screen, Game Settings and name entry are laid out on a single screen. Any button starts the game from the title screen.
• New games use the game's own Classic battle mode, the one-screen layout of the original SNES game.
• The two-screen layouts are still there (F2): stacked, side by side, or swapped (F3).

• Widescreen: 16:9 by default, also 5:3, 21:9 or the window's own shape. You see more of the world while exploring and in battle, with nothing stretched. Menus and text boxes stay in the centred 4:3 area.
• Resolution: 1x (256×192) up to 11x (2816×2112), or Auto.
• Framerate: 30 to 144 fps or unlimited. Above 60 fps, scrolling is smoothed: the camera glides between the game's frames. The game itself still runs at 60, so timing, animation, sound and input are unchanged.
• Filters: Pixel, Sharp (default), Smooth, or LCD (the DS screen's pixel grid).
• Colour: the DS version's colours look washed out on a PC screen. The SNES settings (light, the default; moderate; strong) bring them closer to the SNES look. Original keeps the DS colours.
• Window: windowed, borderless (default) or fullscreen; V-Sync on or off.

• Cutscenes: put an MP4 video (H.264 or H.265, up to 4K) in mods\cutscenes\ to replace one of the anime cutscenes, for example op_ds.mp4 for the opening. The readme.txt there lists the file names.
• Music: put an audio file in mods\music\ to replace a music track, for example BGM_18.ogg for "Chrono Trigger". Use OGG, Opus, FLAC, MP3, WAV or M4A, looped with LOOPSTART/LOOPEND tags, or MSU-1 .pcm files. The readme.txt there lists every track with its Music Box title.
• Mods can be turned off in System Settings > Mods.

Open it with SELECT on the title menu or the Game Settings screen, or while the game is paused (START). Close it with B or SELECT. Changes apply immediately and are saved in eggoftime.ini.

F5 saves and F7 loads. There is one slot, rom\CT.state, next to your in-game saves. States keep working after updates and move between Windows and Linux.

Gamepads work out of the box. The DS face buttons map by position: A is the right button, B the bottom one.

• Playable from the start: tested through the opening, the Millennial Fair, the first time warp, battles and Game Over. Sound, music and cutscenes work.
• Windows (clang) and Linux (gcc) are tested. macOS compiles but is untested.
• Not implemented: Wi-Fi, the microphone, and the DS 3D engine (no 3D has been seen in the tested parts).

The release contains a runtime (the DS hardware, written for this project) and a toolkit, but none of the game. On the first start:

1. ds-decomp extracts the game's code from your ROM.
2. The recompiler (tools/recomp/) translates each of the game's ~9,000 ARM and Thumb functions into one C function.
3. clang compiles them into the game library, game\eggoftime_game.dll, which the runtime loads.

The runtime provides what the code expects from a DS:

• both 2D graphics engines;
• the sound driver, reimplemented so the game's own music and sound data play;
• threads, interrupts, saves, touch and the clock.

The game's anime cutscenes play through its own recompiled decoder.

DESIGN.md explains the architecture and the problems solved along the way.

For development, or to play on Linux and macOS.

• CMake 3.25 or newer, and Ninja.
• A C11 compiler: clang (llvm-mingw on Windows) or gcc.
• Python 3 with Capstone (pip install capstone).
• SDL3:
  • Windows: the SDL3 development zip.
  • macOS: brew install sdl3.
  • Linux: your distro's package if it has one. Otherwise CMake builds SDL 3.4.18 from source; install the X11/Wayland and ALSA/PulseAudio development packages first.
• FFmpeg (libavformat, libavcodec, libavutil, libswscale, libswresample), for movie and music mods:
  • Windows: a shared build such as ffmpeg-n8.1-latest-win64-lgpl-shared-8.1.zip from BtbN/FFmpeg-Builds. The build copies its DLLs next to the executable.
  • macOS: brew install ffmpeg.
  • Linux (Debian/Ubuntu): libavformat-dev libavcodec-dev libswscale-dev libswresample-dev.
• ds-decomp (dsd) v0.12.1, in tools/dsd/ or on your PATH.

1. Add your ROM as rom/CT.nds (see Your ROM).

2. Extract it. This creates extract/, which the recompiler reads. It holds game data: it stays on your machine, never commit it.

   dsd rom extract --rom rom/CT.nds --output-path extract

3. Build. The build generates the C code from extract/ and config/ (the dsd analysis, included in this repository), then compiles it. The first build takes a few minutes.

   • Linux / macOS: scripts/build.sh (output in build/).

   • Windows (llvm-mingw, SDL3 zip, FFmpeg build):

     cmake -S . -B build -G Ninja -DCMAKE_C_COMPILER=clang "-DCMAKE_PREFIX_PATH=<SDL3>/x86_64-w64-mingw32;<FFmpeg>"
     cmake --build build

4. Run. Copy your ROM to build/rom/CT.nds. Then run Egg of Time (Egg of Time.exe on Windows) from build/. You can also pass a ROM path: "Egg of Time" path/to/rom.nds. Saves go next to the ROM.

• -DEGG_SINGLE_SCREEN=OFF keeps the DS's two-screen presentation and defaults, for devices with two screens.
• -DEGG_RUNTIME_ONLY=ON builds only the runtime, without the game, which needs no ROM. CI and the release use it.

Pushing a v* tag runs .github/workflows/release.yml. It builds the runtime for Windows and Linux, packages each with the toolkit (scripts/package.py) and publishes the Windows zip and the Linux tar.gz. The packager refuses ROMs, extracted files and generated code.

• ds-decomp and dsd-ghidra by AetiasHax, for the analysis the recompiler builds on.
• SDL3, FFmpeg (LGPL, linked dynamically), minicoro (bundled in runtime/third_party/, under its own license), Capstone, and llvm-mingw and Python in the Windows release.
• Hardware details from GBATEK.
• The LCD filter is based on the lcd3x shader by Gigaherz (public domain).