cdirecomp — a Philips CD-i static recompiler

⚠️ Very early development

This project boots the real Philips CD-i system ROM as native code and can perform a very basic boot of a CD-i title — Hotel Mario reaches its title card. Gameplay is not yet reachable. Expect rough edges, missing features, incomplete hardware coverage, and breaking changes. This is a research project shared in the open, not a finished product — and it is a static recompiler, not an emulator.

cdirecomp is a static recompiler for the Philips CD-i. It lifts the console's Motorola 68000-family machine code (CPU: SCC68070) into portable C, then links that generated C against a hand-written runtime that re-creates the rest of the machine — the MCD212 video decoder, the CDIC / CIAP CD + XA-audio path, and the SLAVE / IKAT input controller — and runs the console's CD-RTOS / OS-9 operating system on top.

It shares the two-tier structure and spirit of the sibling projects nesrecomp, snesrecomp, segagenesisrecomp, and psxrecomp.

 

 

_{Real CD-RTOS player shell · Time/Date settings · the Philips Interactive Media bumper · and Hotel Mario reaching its title card — all running as native recompiled code.}

Philosophy: low-level, static, native-first

The guiding inspiration for cdirecomp is to be LLE (low-level emulation) and static / native-first:

• Low-level, not HLE. There is no hand-written OS-9 HLE layer. The whole CD-RTOS system ROM is recompiled and executed as native C. A game's TRAP #0 OS-9 system calls dispatch into the recompiled kernel, and kernel state lives in emulated RAM exactly as it does on hardware. Only the hardware chips are modeled by hand. (psxrecomp showed that stubbing the BIOS leads to silent failure; CD-i takes the opposite, faithful route.)
• Static, not interpreted. The 68000 code is translated ahead of time to C and compiled to a native binary. A clean-room interpreter is kept only as the correctness floor for RAM-resident / not-yet-statically-promoted code.

Why CD-i is unusual

The Genesis runs a bare-metal 68000 cartridge; CD-i does not. A CD-i title is a Green Book Mode-2 CD whose data track holds a CD-i/ISO-9660 file system. The program is a set of OS-9/68000 relocatable modules (sync word 0x4AFC) that CD-RTOS — a real-time OS based on Microware OS-9/68K — loads and relocates into RAM at run time, reaching the system through TRAP #0 system calls. So cdirecomp recompiles and executes the whole player system ROM first, then lets the game boot on top of it.

Current status

What works today:

• Boots the real CD-RTOS system ROM (user-supplied) to its interactive player shell — navigation, the Time/Date and storage settings UIs, media insert/eject, and persistence — running as native recompiled code.
• Very basic Hotel Mario boot. From the shell you can Play CD-I a user-supplied Hotel Mario (USA) disc; CD-RTOS loads the title, the Philips Interactive Media bumper plays with decoded XA audio, and the game reaches its title card with zero native dispatch misses.
• Real-time clock (RTC) on Windows. The runtime can seed the CD-i's DS1216 real-time clock from your Windows host clock once at startup (opt-in), and the player's on-screen Time & Date settings screen is functional.
• Working mouse control on Windows. The host mouse drives the CD-i pointer directly through the runtime's IKAT input model — including inside Hotel Mario, not just the shell.
• Clean-room device models for the MCD212 video pipeline (bitmap, CLUT, RGB555, DYUV, RL7/RL3, mosaic, transparency/matte compositing, cursor), the CDIC/CIAP CD + XA audio path, and IKAT input — rewritten from hardware documentation, with an optional local emulator used only as a black-box behavioral comparator during development.

What is not done yet:

• Gameplay is not reachable. Static native promotion of relocated game modules, and full-playthrough certification, are open work.
• Broader title compatibility beyond the current Hotel Mario bring-up.
• Unexercised I2C/MMU paths and additional exception cases remain platform backlog, driven by real applications as they are brought up.

See TODO.md, PLAN.md, and BIOS-CLOSEOUT.md for the detailed roadmap and the BIOS/player-shell milestone evidence.

What you must supply

cdirecomp ships no copyrighted material — no BIOS ROM, no disc images, and no game-derived generated code. To run anything you must provide, from your own legally dumped media:

• A CD-i player system ROM (e.g. a 512 KiB cdi490a.rom).
• A CD-i title as a raw Mode-2 .cue + .bin image.

Build

Toolchain: CMake + a C11 compiler + the SDL2 development package. Builds with Visual Studio 17 2022, and is also verified with MinGW gcc + Ninja.

# Recompiler (CdiRecomp) — 68000 frontend + CD-i disc/module inventory
cmake -S recompiler -B build/recompiler -G Ninja -DCMAKE_BUILD_TYPE=Release
cmake --build build/recompiler -j

# Recompile the CD-RTOS system ROM to C (emit generated BIOS)
build/recompiler/CdiRecompBios.exe bios/cdi490a.rom --emit

# Runtime (CdiRuntime) — hardware models + native/interpreted guest execution
cmake -S runner -B build/runner-release -G Ninja -DCMAKE_BUILD_TYPE=Release
cmake --build build/runner-release -j

Run

# Inventory a CD-i disc: tracks, volume descriptor, OS-9 modules
build/recompiler/CdiRecomp.exe "path/to/Game (Region).cue"

# Boot the user-supplied system ROM to the player shell
build/runner-release/CdiRuntime.exe bios/cdi490a.rom

# Boot with a Mode-2 disc mounted; click "Open" then "Play CD-I" in the shell
build/runner-release/CdiRuntime.exe bios/cdi490a.rom --disc "path/to/Game.cue"

Controls: the mouse moves the CD-i pointer (and clicks its buttons); arrows/WASD also move it; Enter/Space/Z is button 1; Backspace/X is button 2; F11 or Alt+Enter toggles fullscreen; Esc exits. A standard game controller maps D-pad/A/B. Dropping a .cue/.bin onto the window mounts media live.

Persistent player preferences

A normal run creates player.cfg in SDL's per-user preference folder (its path is printed at startup). Two opt-in preferences, both off by default:

[input]
capture_mouse = true          ; hide + capture the host cursor while focused

[rtc]
sync_host_on_startup = true   ; seed the CD-i clock from host time once at boot

capture_mouse maps relative host-mouse motion and the left/right buttons to the CD-i pointer and buttons 1/2; focus loss or Esc releases it immediately. sync_host_on_startup copies host-local time into the DS1216 only before the first guest instruction — it never continuously re-syncs. A normal run also maintains nvram.bin (the DS1216's battery-backed SRAM) beside player.cfg.

Provenance & third-party code

The 68000 frontend descends from the author's own segagenesisrecomp; the CD-i device models are clean-room rewrites from hardware specifications. No third-party emulator source is used in the recompiler or runtime. An optional CeDImu checkout may be used locally as a black-box behavioral oracle only — it is git-ignored and never committed, packaged, or required. See PROVENANCE.md and THIRD-PARTY-NOTICES.md (SDL2).

License

PolyForm Noncommercial License 1.0.0 — © 2026 Matthew Stan. This license covers the cdirecomp source only. It grants no rights to any Philips, Nintendo, or other third-party intellectual property; you must supply your own legally obtained system ROM and disc images.

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