Icarus Rev E - Firmware Bringup, Part 2

I’ve been slowly working away on the firmware for the Rev E of Icarus. I’m basically back to where I was with the Rev D version, written in C++. I should be able to start testing PIDs again soon!

About the Firmware

The firmware is written using Embassy, an async framework for embedded devices. Personally I think async-io on embedded just “makes sense” and I think it’s the future of embedded development and will probably be what pushes Rust past C++ for embedded.

The firmware is broken up into a few key tasks:

• RC input, for commands from the controller
• Sensors, for sensor fusion / state estimation
• Controls, PID control loops
• Telemetry, for sending data to a host machine for logging purposes

Each task interacts with queues (typically with just a size of 1 for the most recent data).

RC Input

The RC input is intended to be sent from a dedicated Gamepad RC stack. The data is received over UART using a bespoke protocol based on SBUS. I plan to use a new bus bus protocol in the future.

Sensors

Icarus has 3 onboard sensors: IMU, Magnetometer, and Barometer.

For now I’m only using the IMU for sensor fusion, but I’m planning on using the magnetometer in the future as well (The barometer is kind of a bonus).

The IMU data is passed through a AHRS algorithm to get orientation. The orientation is then passed to the controls task.

Controls

The control task takes the RC input and estimated state and feeds that into a PID controller for pitch and roll (yaw needs the magnetometer). The PID output is then mapped to PWM pins to drive the motors.

Telemetry

Used just for debugging, the telemetry task takes data like the state estimation and writes it over UART so I can log it.

Future Work

• PID tuning
• Updating the serial protocol used (I’m thinking about using OpenCyphal).