Using Rust in an Embedded Project: A Simple Example

I’ve written a few posts on using Rust for embedded projects:

• Rust Sysroots for Easier Embedded Projects
• Using Rust 1.8 Stable for Building Embedded Firmware
• Generating Rust Bindings for Embedded Libraries
• Embedded Rust Right Now!

I think they gave a decent overview of a couple of tricky parts, but as always, the devil is in the details. To help with all the gritty details, I’ve written up a more complete example.

Overview

In order to actually run this example, you’ll need an STM32L1 Discovery Board. I don’t expect many readers to have this exact board, but it should be relatively easy to port to other targets/boards, and I thought a complete example would be useful as a point of comparison. This is basically just STM’s GPIO_IOToggle example but with the core inner loop replaced with some Rust code.

Essentially what I did was:

• Started with STM’s GPIO_IOToggle example
• Added a Makefile to build the example
• Setup the Cargo configuration necessary to target a Cortex-M3 in .cargo/config
• Added rules to the Makefile to build a Rust sysroot containing a valid libcore
• Used bindgen to wrap the STM32 HAL libraries for use in Rust
• Replaced the core inner loop in main.c of the GPIO_IOToggle example with Rust code
• Added rules to the Makefile to build the Rust code and link the resulting static library into the final binary

Running My Example

To run my example:

Grab a Rust nightly

• Install multirust from here if you haven’t already
• Run multirust update nightly

Make a directory to work in

mkdir embedded_rust_experiment
cd embedded_rust_experiment
multirust override nightly

Clone my embedded Rust example

git clone https://github.com/jvranish/rust-embedded-example.git

Clone Rust src into sibling directory

We need to clone the Rust repo:

git clone [email protected]:rust-lang/rust.git

And then we need to check out the commit that matches the version of our compiler. To find the commit for our current compiler you can do this:

$ rustc -vV
rustc 1.11.0-nightly (ad7fe6521 2016-06-23)
binary: rustc
commit-hash: ad7fe6521b8a59d84102113ad660edb21de2cba6
commit-date: 2016-06-23
host: x86_64-apple-darwin
release: 1.11.0-nightly

And then check out that specific commit:

cd rust
git checkout 8903c21d618fd25dca61d9bb668c5299d21feac9
cd ..

Your commit-hash will almost certainly be different than what I have here. Don’t just copy what I have :)

Download ARM gcc from here and put it into a sibling directory. In my case, I put it in ../tools/gcc-arm-none-eabi-5_3-2016q1/

Get STM32 Cube for L1 line

Get the Cube HAL from here and put it into sibling directory. In my case, I put it in ../STM32Cube_FW_L1_V1.5.0/

Install openocd

Install my favorite debugger toolchain. On macOS, if you have Homebrew installed, you can just do this:

brew install openocd

Run example

Open up Makefile in embedded_rust_experiment and make sure the variables: GCC_ARM_PATH, STM32_CUBE_PATH and RUST_SRC_PATH are set to sensible values.

Then to run the example:

• In one console, run openocd.

cd rust-embedded-example
make openocd

• In another console, build and debug.

cd rust-embedded-example
make debug

When the gdb prompt shows up, you should be able to press c and enter. Then you should see blinking lights on your discovery board. That’s it!