Gearsystem is a very accurate, cross-platform Sega Master System / Game Gear / SG-1000 emulator written in C++ that runs on Windows, macOS, Linux, BSD and RetroArch, with an embedded MCP server for debugging and tooling.

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.

Notes:

• Windows: May need Visual C++ Redistributable and OpenGL Compatibility Pack
• Linux: May need libsdl3

• Sega Mark III
• Sega Master System
• Sega Game Gear
• Sega Game 1000 (SG-1000)
• Othello Multivision

• Accurate Z80 core, including undocumented opcodes and behaviors like R and MEMPTR registers.
• Supported cartridges: ROM, ROM + RAM, SEGA, Codemasters, Korean, MSX + Nemesis, Janggun, SG-1000, and many Korean multi-carts.
• Automatic region detection: NTSC-JAP, NTSC-USA, PAL-EUR.
• Accurate VDP emulation, including timing and VDP specifics for SMS, SMS2, GG, and TMS9918 modes.
• Support for YM2413 (OPLL) FM sound chip.
• Light Phaser and Paddle Control support.
• Internal database for ROM detection.
• Battery powered RAM save support.
• Save states with preview.
• Compressed ROM support (ZIP).
• Game Genie and Pro Action Replay cheat support.
• VGM recorder.
• Supported platforms (standalone): Windows, Linux, BSD and macOS.
• Supported platforms (libretro): Windows, Linux, macOS, Raspberry Pi, Android, iOS, tvOS, PlayStation Vita, PlayStation 3, Nintendo 3DS, Nintendo GameCube, Nintendo Wii, Nintendo WiiU, Nintendo Switch, Emscripten, Classic Mini systems (NES, SNES, C64, ...), OpenDingux, RetroFW and QNX.
• Full debugger with just-in-time disassembler, CPU breakpoints, memory access breakpoints, code navigation (goto address, JP JR and CALL double clicking), debug symbols, automatic labels, memory editor, trace logger, IO inspector and VRAM viewer including tiles, sprites, backgrounds and palettes.
• MCP server for AI-assisted debugging with GitHub Copilot, Claude, ChatGPT and similar, exposing tools for execution control, memory inspection, hardware status, and more.
• Windows and Linux Portable Mode.
• ROM loading from the command line by adding the ROM path as an argument.
• ROM loading using drag & drop.
• Support for modern game controllers through gamecontrollerdb.txt file located in the same directory as the application binary.

• BIOS: Gearsystem can run with or without a BIOS. You can optionally load a BIOS and enable it. It's possible to run the title included in the BIOS by setting Media Slot to None in the Emulator menu. This emulates a machine without any media plugged in.
• Overscan: For a precise representation of the original image, select Overscan Top+Bottom and Aspect Ratio Standard (4:3 DAR) in the Video menu. Game Gear will ignore any overscan settings.
• Mouse Cursor: Automatically hides when hovering over the main output window or when Main Menu is disabled.
• Portable Mode: Create an empty file named portable.ini in the same directory as the application binary to enable portable mode.

• Docking Windows: In debug mode, you can dock windows together by pressing SHIFT and dragging a window onto another.
• Multi-viewport: In Windows or macOS, you can enable "multi-viewport" in the debug menu. You must restart the emulator for the change to take effect. Once enabled, you can drag debugger windows outside the main window.
• Debug Symbols: The emulator automatically tries to load a symbol file when loading a ROM (.sym, .noi). For example, for path_to_rom_file.sms it tries to load path_to_rom_file.sym. You can also load a symbol file using the GUI or the CLI. It supports sjasmplus/Pasmo (EQU), SDCC/NoICE (.noi), wla-dx and vasm/generic file formats.

gearsystem [options] [rom_file] [symbol_file]

Arguments:
  [rom_file]               ROM file: accepts ROMs (.sms, .gg, .sg, .mv) or ZIP (.zip)
  [symbol_file]            Optional symbol file for debugging

Options:
  -f, --fullscreen         Start in fullscreen mode
  -w, --windowed           Start in windowed mode with menu visible
      --mcp-stdio          Auto-start MCP server with stdio transport
      --mcp-http           Auto-start MCP server with HTTP transport
      --mcp-http-port N    HTTP port for MCP server (default: 7777)
  -v, --version            Display version information
  -h, --help               Display this help message

Gearsystem includes a Model Context Protocol (MCP) server that enables AI-assisted debugging through AI agents like GitHub Copilot, Claude, ChatGPT and similar. The server provides tools for execution control, memory inspection, breakpoints, disassembly, hardware status, and more.

For complete setup instructions and tool documentation, see MCP_README.md.

• Install Microsoft Visual Studio Community 2022 or later.
• Open the Gearsystem Visual Studio solution platforms/windows/Gearsystem.sln and build.

• Install Xcode and run xcode-select --install in the terminal for the compiler to be available on the command line.
• Run these commands to generate a Mac app bundle:

brew install sdl3
cd platforms/macos
make dist

• Ubuntu / Debian / Raspberry Pi (Raspbian):

If you are using Ubuntu 25.04 or later, you can install SDL3 directly. Use the following commands to build:

sudo apt install build-essential libsdl3-dev libgtk-3-dev
cd platforms/linux
make

For older Ubuntu versions (22.04, 24.04), you need to build SDL3 from source first. Use the following commands to build both SDL3 and Gearsystem:

sudo apt install build-essential cmake libgtk-3-dev
git clone --depth 1 --branch release-3.4.x https://github.com/libsdl-org/SDL.git /tmp/SDL3
cmake -S /tmp/SDL3 -B /tmp/SDL3/build -DCMAKE_INSTALL_PREFIX=/usr -DSDL_TESTS=OFF -DSDL_EXAMPLES=OFF
cmake --build /tmp/SDL3/build -j$(nproc)
sudo cmake --install /tmp/SDL3/build
cd platforms/linux
make

• Fedora:

sudo dnf install @development-tools gcc-c++ SDL3-devel gtk3-devel
cd platforms/linux
make

• Arch Linux:

sudo pacman -S base-devel sdl3 gtk3
cd platforms/linux
make

• FreeBSD:

su root -c "pkg install -y git gmake pkgconf SDL3 lang/gcc gtk3"
cd platforms/bsd
gmake

• NetBSD:

su root -c "pkgin install gmake pkgconf SDL3 lang/gcc gtk3"
cd platforms/bsd
gmake

• Ubuntu / Debian / Raspberry Pi (Raspbian):

sudo apt install build-essential
cd platforms/libretro
make

• Fedora:

sudo dnf install @development-tools gcc-c++
cd platforms/libretro
make

Zexall Z80 instruction exerciser (from SMS Power!)

Gearsystem passes all tests in Zexall, including undocumented instructions and behaviors.

SMS VDP Test (from SMS Power!)

Thank you to all the people who have already contributed to Gearsystem!

Gearsystem is licensed under the GNU General Public License v3.0 License, see LICENSE for more information.