stm32-rs VS embassy

Developing code at the PAC, well, requires a PAC crate for the targeted controller. For the STM32 there exists a repo for all the supported PACs. These PACs are all generated using a command line tool called svd2rust. svd2rust grabs what is called an svd file and converts it into a PAC exposing API allowing access to peripheral registers. An SVD file is an Extensible Markup Language (XML) formatted file describing the hardware features of a device, listing all the peripherals and the registers associated with them. SVD files typically are released by microcontroller manufacturers.

In real world software, 99% of code is gluing preexisting lower-level functions together. In C/C++, the unsafe is implicit and needlessly covers everything. In Rust, the unsafe is only needed for the 1%.

You can safely implement a doubly-linked list in Rust, using unsafe, and that list can offer a safe interface so that the next higher level of code does not need to use unsafe. In fact, one doubly-linked list implementation that provides a safe interface is in the Rust standard library: https://doc.rust-lang.org/std/collections/struct.LinkedList.... . Most people do not rewrite std::list in C++ either.

Much of the Linux kernel really is the same: normal C code (maybe slightly more complicate than average userspace code, and definitely more carefully reviewed, but definitely not magic), that depends on extra carefully written lower level primitives that are _much_ more complicated internally than they appear from the outside (like the memory allocator, printk, RCU, etc.).

Rust is powerful enough to have libraries for register level access to micro-controllers (e.g. https://github.com/stm32-rs/stm32-rs), that encode moderately complex access rules safely in the type system (e.g. which specific set of bits is read-only or write-only, with which particular values (with nice human-readable names, even!), in which particular states of a state machine depending on other bits), all while allowing bypassing the restrictions with a simple unsafe keyword without even giving up on the nice API.

On the C/C++ side, I've used libopencm3, MBED, CMSIS, and everyone's favorite toy, Arduino. They're, in different ways, all much more mature and complete than anything Rust has today, but nothing comes even remotely close to Rust in terms of safety and long term potential.

Packages: Where would I start with e.g. running Ada on a stm32? Resources are just a bit tough to find, and there's only a single stm32 package on Alire (which was inspired by cargo). But Rust has easy to find PACs and HALs for everything in the family, plus an official guide to setting up a project, including HIL debugging and unit testing on qemu, that takes about 15 minutes.

> (I threw out all my C/C++ books about 15 years ago - oops!).

The future is here for STM32: https://github.com/stm32-rs/stm32-rs

Specifically these Rust register definitions are being auto-generated using SVD files published by the chip vendors (https://www.keil.com/pack/doc/CMSIS/SVD/html/index.html). For stm32 for example there are the auto-generated register definitions: https://github.com/stm32-rs/stm32-rs and then the HAL layers on top that try to build easy to use tools on top of the registers (e.g. an SPI or USART type with write and read functions). e.g. https://github.com/stm32-rs/stm32f4xx-hal for the stm32f4xx line

For STM32, check out the Peripheral Access Crates by the stm32-rs ream. For higher-level access, I wrote This HAL library for STM32. Works on most newer variants, and includes examples for specific peripherals, and simple applications.

Patches: https://github.com/stm32-rs/stm32-rs/tree/master/devices

thanks. looked that up. for the curious: https://embassy.dev/

Running the Embassy RP2040 USB CDC ACM serial example takes about 5 seconds on a Pico.

https://github.com/embassy-rs/embassy/blob/main/examples/rp/...

Async solves different problems, you can, for instance, have just a single-threaded CPU and still have a nice API if you have async-await. It might not be so cool at a higher level as Go's approach of channels and threads, but it's cool in embedded, read this:

https://github.com/embassy-rs/embassy?tab=readme-ov-file#rus...

"Rust's async/await allows for unprecedently easy and efficient multitasking in embedded systems. Tasks get transformed at compile time into state machines that get run cooperatively. It requires no dynamic memory allocation, and runs on a single stack, so no per-task stack size tuning is required. It obsoletes the need for a traditional RTOS with kernel context switching, and is faster and smaller than one!"

I'm just toying with Raspberry Pi Pico and it's pretty nice.

Go and Rust have different use cases, the async-await is nice at a low level.

I have not yet dipped by toes in the Rust waters, but reading about the embassy project is actually what piqued my curiosity about using C++ coroutines in embedded. Are you familiar with the project or have you found it lacking?

I think I get the basics (shoutout to the Rust Embedded Working Group!), and I've started looking for the stack I'd be using. I think Embassy is really amazing, as well as the work of the ESP team -- hats off.

> }

And this is how to do it using embassy, which is an async framework for embedded in rust:

https://github.com/embassy-rs/embassy/blob/main/examples/rp/...

> not good for embedded

embassy begs to differ

https://embassy.dev/

async/await is really just a syntax for building state machines in a way that resembles regular code. It's compiled down to the same code that you would write by hand anyway (early on it had some bloat in state size but I think it's all fixed now).

And embedded has a lot of state machines!

You can run multiple executors at different interrupt priority levels (with multiple tasks per executor), which allows tasks on the higher priority executor to interrupt other tasks. Here's an example https://github.com/embassy-rs/embassy/blob/main/examples/nrf...