GUI2C (proof of concept)

GUI2C is a compact binary protocol for driving small display modules from microcontroller-based Eurorack modules.

This repository is now the protocol/specification repository. Firmware and C implementation code live in separate repos:

• ../gui2c_client_library_rp2350_rp2040: Pico-SDK C client library
• ../gui2c_server_ili9488: Pico-SDK ILI9488 display-server firmware
• ../gui2c_demo_client: Pico-SDK demo client firmware

Protocol Model

GUI2C defines an application-level client/server relationship:

• a GUI2C display server offers display services
• a GUI2C client reserves and updates a display view
• current packets are binary, little-endian command frames
• current object IDs are client-managed, with object ID 0 reserved by the server

For the first I2C implementation, the electrical/bus roles are:

• GUI2C client: I2C controller
• GUI2C display server: I2C target

This keeps one controller per I2C bus. Future multi-view displays can expose multiple physical I2C ports, one per client/controller, and map each port to a virtual view internally.

Documents

• docs/protocol.md: packet format, command IDs, payload layouts and object semantics
• docs/architecture.md: repository split, I2C roles, sessions/views roadmap

Current Protocol Scope

The current protocol draft covers:

• PING
• HELLO_STRING
• DESTROY_ALL_OBJECTS
• text objects
• rectangle objects
• line objects
• bar objects
• ring objects
• waveform objects

Planned protocol work includes explicit capability discovery, view reservation, session IDs, present/update semantics, timeouts and release/reset behavior.