Comparing Embedded Rust (Embassy) and C (FreeRTOS) on STM32F446 Microcontroller

Introduction to the Comparison

This technical post details a comparison between two embedded development approaches: async Rust using Embassy and C using FreeRTOS. Both environments will be tested on an STM32F446 microcontroller, running applications that perform identical actions.

Evaluation Criteria

The primary metrics for judging the two implementations include interrupt latency, the overall program size, the amount of RAM consumed, and the perceived ease of programming. The goal is to provide a practical understanding of how RTOSes and async executors function in a real-world embedded context.

Application Design Principles

The applications developed for this comparison are designed to be portable across different chips and architectures, with the exception of hardware abstraction layer dependencies. They are straightforward implementations, tuned with standard options such as compiler optimizations, RTOS settings, and thread priorities to reflect typical development practices.

Testing Environment

Testing will be conducted on an STM32F446ZET6 microcontroller operating at 180MHz. An oscilloscope, specifically a Rigol DS1054Z, will be used for certain measurements, such as interrupt latency.

Understanding Async Rust

In Rust, an async function is syntactic sugar for a function that returns a future. A future is an object that can be polled, transforming into a state machine that resumes execution from where it last stopped. Futures are lazy, meaning they only execute when polled, and wakers are used to signal an executor when a future needs to be polled again.