Geartowns MCP Server

Geartowns

Geartowns is a very accurate, cross-platform Fujitsu FM Towns emulator written in C++ that runs on Windows, macOS, Linux, BSD and RetroArch, with an embedded MCP server for AI debugging and development.

This is an open source project with its ongoing development made possible thanks to the support by these awesome backers. If you find it useful, please consider sponsoring.

Don't hesitate to report bugs or ask for new features by opening an issue.

Downloads

Platform Architecture Download Link

Windows Desktop x64 Geartowns-1.0.6-desktop-windows-x64.zip

Desktop ARM64 Geartowns-1.0.6-desktop-windows-arm64.zip

macOS Homebrew brew install --cask drhelius/geardome/geartowns

Desktop Apple Silicon Geartowns-1.0.6-desktop-macos-arm64.zip

Desktop Intel Geartowns-1.0.6-desktop-macos-intel.zip

Linux Ubuntu PPA drhelius/ppa-geardome

Fedora RPM drhelius/rpm-geardome

Desktop Ubuntu 26.04 x64 Geartowns-1.0.6-desktop-ubuntu26.04-x64.zip

Desktop Ubuntu 26.04 ARM64 Geartowns-1.0.6-desktop-ubuntu26.04-arm64.zip

Desktop Ubuntu 24.04 x64 Geartowns-1.0.6-desktop-ubuntu24.04-x64.zip

Desktop Ubuntu 24.04 ARM64 Geartowns-1.0.6-desktop-ubuntu24.04-arm64.zip

MCPB All platforms MCP Readme

RetroArch All platforms Libretro core documentation

Dev Builds All platforms GitHub Actions

Notes:

• Windows: May need Visual C++ Redistributable and OpenGL Compatibility Pack
• Homebrew: If Homebrew asks you to trust the third-party tap, run brew trust --tap drhelius/geardome
• Linux: May need libsdl3

Features

• Very accurate 80386 core that passes test386 and SingleStepTests/80386.
• FM Towns (Model 1/2), 1F/2F, 10F/20F, FM Towns II CX, UX, UG, HG, HR, UR, ME, MA, MX and MF/Fresh, and FM Towns Marty emulation.
• CD-ROM drive emulation with cue/bin, iso and chd images, m3u disc playlists and disc swapping, with optional compressed images (zip).
• Physical CD-ROM discs on Windows, macOS and Linux.
• Floppy disk emulation with two drives supporting d77, d88, hdm, xdf, img and HxC mfm images, m3u playlists, write protection and optional persistence of disk changes.
• SCSI hard disks on IDs 0-6 with raw and chd images, blank disk creation and Towns OS installation.
• IC memory card slot with raw card images, the JEIDA 4 banked windows, blank card creation and booting from the card.
• Save states with 5 slots and rewind support.
• Run-ahead support to reduce input latency.
• Video recording to AVI and screenshots.
• VGM recorder for the YM3438 and RF5C68 sound chips.
• Internal database for automatic media detection and hardware selection if Auto options are selected.
• Supported platforms (standalone): Windows, Linux, BSD and macOS.
• Supported platforms (libretro): Windows, Linux, macOS, Raspberry Pi, Android, iOS, tvOS, webOS, PlayStation 3, Nintendo GameCube, Nintendo WiiU, Nintendo Switch, Emscripten, Classic Mini systems (NES, SNES, C64, ...), OpenDingux, RetroFW and QNX.
• Full debugger:
• Just-in-time disassembler, code navigation, call stack, debug symbols and automatic labels.
• Execute, data, I/O and interrupt breakpoints.
• Memory editor, trace logger and profiler.
• i386 registers, descriptor tables and paging inspectors.
• Viewers for CRTC, palettes, framebuffers, sprites, YM3438, RF5C68, CD-ROM, floppy controller and disks, SCSI controller and disks, interrupts, timers, DMA, RTC, keyboard and game ports.
• MCP server for AI-assisted debugging with Claude Code, Codex and similar, exposing tools for execution control, memory inspection, hardware status, rewind and more.
• Windows, Linux and macOS *Portable Mode*.
• Programmable Shader Chain.
• Media loading from the command line by adding the CD-ROM, floppy, hard disk or IC memory card image path as an argument.
• Media loading using drag & drop.
• Support for modern game controllers through gamecontrollerdb.txt file located in the same directory as the application binary.

Tips

Basic Usage

• Firmware: Geartowns requires the FM Towns system ROMs to run. Use Emulator → Firmware... to choose the folder that holds them, with one subfolder or MAME zip per set. See BIOS_README.md for the sets each model needs, where to put them and their checksums.
• Machine: Machine → Model, CPU Speed and Main RAM default to Auto, which picks:
• The model, CPU speed and RAM that the game database names for the game.
• The FM Towns II HG for 1.44 MB floppy disks.
• The FM Towns (Model 1/2) for other content.
• CD-ROM Images: Geartowns supports chd, zipped and unzipped cue/bin and iso images, and m3u playlists for multi-disc games. CUE audio tracks can use raw BIN, compatible WAV (44100 Hz, 16-bit, stereo) or Ogg Vorbis files. Change discs from Drives → CD-ROM.
• Floppy Images: Insert floppy disks from Drives → Floppies, or load them from the command line. Supported images are d77, d88, hdm, xdf, img and mfm, also inside zip files, and m3u playlists.
• Portable Mode: Run with --portable, or create an empty file named portable.ini in the same directory as the application binary. On macOS, place the file next to the .app bundle.

Hard Disks

Up to seven SCSI hard disks can be attached, on IDs 0-6:

• 1F/2F and later: built-in SCSI interface.
• FM Towns (Model 1/2): a SCSI card is fitted while a disk is attached.
• FM Towns Marty: no SCSI.

Image Formats

• Raw images (hdd, h0-h6, and hdm over 8 MB): 512-byte sectors. Smaller hdm images are floppies.
• MAME hard disk `chd`: read-only. At the first write, Geartowns makes a raw working copy in the Save Files folder and uses it from then on.

Attaching Disks

• Desktop: use Drives → Hard Disks, drag & drop or the command line. With drag & drop and the command line, the extension picks the ID:
• h0-h6: that SCSI ID.
• hdd and hdm over 8 MB: the first free ID.
• Libretro: load the image as content, alone or in an m3u playlist with the CD. Changes go to a working copy in the save directory and the original is never written.
• Running machine: attaching or detaching a disk takes effect at the next reset.

Disk Writes and Save States

• Writes are saved a few seconds after the machine stops writing.
• Save states, rewind and run-ahead hold no disk data. Loading one undoes the disk writes made since then (the last 32 MB of them per disk), and warns when it can't.

Installing Games

With Formatted checked, New Blank Disk... makes a disk partitioned and formatted like Towns OS does, with one empty drive per 127 MB (up to ten). Games booted from their CD can install to it. It holds no system and doesn't boot.

Installing Towns OS

1. Create a disk with New Blank Disk... and Formatted unchecked.
2. Boot the Towns OS V2.1 CD and run HD Install from the Tools folder of TownsMENU V2.1.
3. Eject the CD and reset.

Towns OS V2.1 needs 4 MB of RAM to start from a hard disk. Main RAM on Auto gives at least that while a disk is attached.

Booting From the Hard Disk

• A bootable CD boots before the disk.
• To boot the disk with a CD inserted, pick it in Geartowns → Reset and Boot From. This holds the system ROM's boot keys (H and the SCSI ID) through the reset.
• The Model 1/2 and Marty ROMs don't read these keys.

Drive Letters

Towns OS keeps hard disk drive letters in the model's CMOS, not on the disk, and only uses the partitions that have one.

• Assign Drive Letters on (Drives → Hard Disks, the default): each reset gives the free letters from D: to the partitions of an attached disk that have none. Letters already set are kept. This lets a disk installed on another model or emulator boot.
• Assign Drive Letters off: assign the letters yourself in Towns OS:

1. Boot the Towns OS V2.1 CD.
2. Open Settings → Drive Configuration.
3. Click the disk's SCSI ID, then Add Drive and Execute.
4. Eject the CD and reset.

IC Memory Card

Every model has one slot for a battery-backed SRAM card. Towns OS uses the card as a drive.

Images

• Raw images (icm): the card's bytes, a whole number of KB up to 64 MB. The file is the card: writes are saved a few seconds after the machine