I have a completely DIY embedded board on my bench and need a clean, production-ready firmware image that focuses on solid, well-tested communication protocols. The hardware is custom, so there is no vendor SDK or reference code to lean on—everything starts from a bare-metal bring-up. What has to work • Core serial links (UART, SPI, I²C) plus a higher-level protocol of your choice (e.g. CAN, USB CDC or simple TCP/IP over an external PHY) so the board can stream data to an external host and accept configuration commands. • Interrupt-driven, non-blocking code written in modern C or C++, with clear HAL separation so that I can port it later if the MCU changes. • Simple CLI or register map so I can verify functions over a terminal. Deliverables • Fully commented source, a reproducible build (Makefile or CMake), and the compiled binary/hex. • Pin-level hardware init sheet and a short README that explains toolchain setup, flash procedure, and how to exercise each protocol. • A basic Python script or similar that demonstrates packet exchange and echoes board status—this doubles as the acceptance test. Acceptance criteria The firmware compiles without warnings, flashes and boots on first power-up, and passes the scripted communication test in under three seconds. Clean, well-structured commits are a must; single dump commits will be rejected. If you are comfortable starting from a schematic and oscilloscope traces instead of vendor examples, this should be a straightforward yet interesting project. Let me know the toolchain you prefer so we can align before the first milestone.