Geargrafx is a free, open-source emulator for NEC PC Engine, TurboGrafx-16, SuperGrafx and their CD-ROM systems. Its desktop application runs on Windows, macOS, Linux and FreeBSD; a separate Libretro core works inside RetroArch. It combines game playback with tools for inspecting the hardware that it emulates and controlling it through an MCP client.
Opening cartridges and discs
Users open a ROM or disc image, drop it onto the window, or pass its path on the command line. Geargrafx’s internal database identifies known games and selects matching hardware when the system options use Auto.
| Media | Input and firmware |
|---|---|
| HuCard | PC Engine and SuperGrafx ROMs run without external firmware. |
| CD-ROM | CUE track sets and CHD images require a System Card or Game Express BIOS. |
| LaserActive | MMI images require Japanese or US PAC firmware; some images specify an external System Card. |
The emulator also opens ZIP media and physical CD-ROMs. CUE audio tracks can use BIN, compatible WAV or Ogg Vorbis files; MP3 tracks do not work. For LaserActive, the media menu ejects the virtual disc, selects another side and inserts it again.
Saving and revisiting play
Save states capture the machine at a particular point. Users choose a slot with a preview or save to an explicit file. Loading the state returns the emulator to that point. Separate backup RAM controls save or import the game’s persistent data.
Rewind collects snapshots during play and moves backward through them at the chosen speed. Run-ahead instead executes extra speculative frames, displays their final picture and restores the underlying machine state. Users choose its frame count. Geargrafx disables rewind and run-ahead for LaserActive and active TurboLink sessions. Run-ahead also skips physical discs, debugging and fast-forward playback.
Controllers and shared sessions
Input settings map keyboard keys and gamepad controls for each player. Geargrafx offers standard pads, Avenue Pad 3, Avenue Pad 6 and a mouse. The three-button pad can choose its extra button’s function automatically from the game. Turbo controls repeatedly toggle buttons I and II at adjustable intervals.
Multi Tap supports up to five players. TurboLink connects two emulator instances through the same session number and local shared memory. Both instances must run on one computer. While that connection remains active, state loading also becomes unavailable.
Framing the picture
The desktop video menu changes integer scaling, window fitting, aspect ratio and visible scanlines. Color controls select RGB or composite output, palettes and a low-pass filter.
Geargrafx also reads programmable shader presets. A preset defines a sequence of GLSL passes that process the picture before the final pass reaches the display. Selecting a preset exposes its adjustable parameters as switches or sliders. The shader folder supplies presets when the application starts.
Sound and recordings
HES music ROMs play through the emulator’s sound system. Independent controls change master, PSG, CD-ROM and ADPCM volume; mute controls silence particular sources.
Screenshot commands save a frame as PNG. Video recording combines pictures that Geargrafx generates with sound in an AVI file, with scale, aspect ratio and quality controls. Stop finalizes the recording. Frames enter the file while emulation runs or steps forward. The separate VGM recorder starts and stops a music recording.
Codes and ROM patches
The Cheats dialog accepts address-and-value codes or imports a RetroArch CHT file. A code changes the value at a physical memory address. Users can remove codes or change their enabled state.
Optional softpatching applies a matching IPS patch beside the ROM when loading it. This changes the image that the emulator runs.
Inspecting the running machine
Debug mode shows CPU registers, instructions that its disassembler decodes and editable memory. Breakpoints stop execution at an address or on memory reads and writes. Step controls advance instructions, move over subroutine calls or run to an address.
Geargrafx loads symbol files to give addresses meaningful labels. Hardware viewers expose tiles, sprites, palettes, sound channels and CD-ROM subsystems. SuperGrafx inspection includes both video controllers. The trace logger records instructions and hardware events, while the profiler reports function calls and processor cycles.
Commands through MCP
The embedded MCP server lets compatible AI clients pause execution, inspect or change memory, control buttons and request screenshots. These commands act on the same machine state as the desktop debugger.
A client can launch Geargrafx through standard input and output, or connect to its HTTP server. Headless mode runs the tools without a graphical window. Multiple HTTP clients share control of one emulator instance.
