End-to-End Analysis and Design of a Drone Flight Controller

Timing guarantees are crucial to embedded and cyber-physical applications that must bound the end-to-end delay between sensing, processing and actuation. For example, in a flight controller for a multirotor drone, the data from a gyro or inertial sensor must be gathered and processed to determine the attitude of the aircraft. Sensor data fusion is followed by control outputs that alter rotor speeds to adjust the drone’s flight. If the processing pipeline between sensor input and actuation is not bounded, the drone will lose control and possibly fail to maintain flight. This paper describes a composable pipe model for sensor data processing and actuation tasks. The pipe model is used to analyze two end-to-end semantics: 1) freshness and 2) reaction time. We provide a mathematical framework to derive feasible task periods and budgets that satisfy both schedulability and end-to-end timing requirements. We demonstrate the applicability of our design approach by using it to port the Cleanflight flight controller firmware to our in-house real-time operating system called Quest. Experiments show that Cleanflight ported to Quest is able to achieve end-to-end latencies within the predicted time bounds derived by analysis.