Firmware Architecture

The GB-Link firmware turns an RP2040 into a USB-to-Game Boy Link Cable adapter, bridging retro hardware to modern web clients.

Project history#

The firmware originated from the Celio Firmware (CelioLink project) for Pokémon Generation III online functionality. It merged with the GB-Link project, which added Tetris online, multiboot, Game Boy Printer emulation, and Advance Wars support.

The GB-Link fork and Celio-Link share the same core codebase and releases but are maintained separately.

Supported modes#

Software stack#

• MCU: Raspberry Pi RP2040 (dual-core Arm Cortex-M0+)
• RTOS: Zephyr 3.7.99
• Host communication: WebUSB command endpoint
• Link layer: RP2040 PIO for Game Boy bit-level protocol

Zephyr provides most low-level abstractions. The only MCU-specific implementation is in /src/layers/linkLayer_.c, which handles the low-level bit-layer of the link protocol. The remaining firmware is largely MCU-agnostic.

Repository structure#

GBLink-Firmware/
├── src/              # Application source
├── boards/           # Board definitions
├── dts/bindings/     # Device tree bindings
├── scripts/          # Build and permission scripts
├── tests/host/       # Host-side tests
├── prj.conf          # Zephyr project config
├── west.yml          # West manifest
└── CMakeLists.txt    # Build configuration

Web frontends#

You are free to use whichever web frontend you prefer:

• launcher.gblink.io — Launcher for all subprojects
• celi0.link — GBA-focused frontend (Pokémon Gen 3)

License#

GPL-3.0 — see the firmware repository.