STM32F3 Discovery 🦀⚡

The LED Roulette example on the STM32F3 Discovery board, on steroids, written in Rust. An experiment to get started with embedded development in Rust, as well as testing the IDE based development and debugging experience in JetBrains CLion while using Rust RustRover.

This project covers:

• probe-rs flashing and defmt logging.
• Driving the user LEDs via a Timer interrupt.
• Querying the LSM303DLHC MEMS IMU via I²C (via lsm303dlhc-ng and lsm303dlhc-registers).
  • Observing the magnetometer's DRDY with an EXTI2_TSC interrupt.
  • Observing the accelerometer's I1DRDY1 with an EXTI4 interrupt.
• Querying the L3GD20 MEMS gyroscope via SPI (l3gd20-registers).
  • Observing the gyro's DRDY with an EXTI1 interrupt.
• Temperature readings of the sensors are queried at 1Hz as measured by a 1ms SysTick interrupt.
• Operating a USB CDC serial port for communication.
  • Uses serial-sensors-proto to serialize and byte-stuff the sensor readings and hands them over to serial-sensors for further shenanigans.

Led ring shenanigans:

• The accelerometer is used to have the downwards facing LED light up.
• The magnetometer is used to determine a heading. If the device is pointed away from north, the light wheel will turn in the appropriate direction. If the device faces north, the lights will flash.

Bin features

The sensors are set up to provide data at up to 400 Hz, which can make debugging complicated. To slow things down, enter slowpoke mode:

cargo run --features=slowpoke

Sensor orientation

The onboard LSM303DLHC's accelerometer sensor seems to be oriented in a left-handed coordinate system:

• X points forward (towards the USB connectors)
  • When pointing the USB ports downwards, the sensors reads a positive maximum on the X axis.
  • When pointing the opposite end downwards, the sensor reads a negative maximum on the X axis.
• Y points left
  • When pointing the left side downwards, the sensor reads a positive maximum on the Y axis.
• Z points down
  • When pointing the bottom side downwards, the sensor reads a positive maximum on the Z axis.

The magnetometer on the other hand - pun not intended - appears to use a right-handed coordinate system :

• X points backward (towards the LEDs)
  • When pointing the USB ports towards the earth's magnetic field vector, the sensors reads a negative maximum on the X axis.
  • When pointing the opposite end towards the vector, the sensor reads a positive maximum on the X axis.
• Y points right
  • When pointing the right side towards the vector, the sensor reads a positive maximum on the Y axis.
• Z points up
  • When pointing the top side towards the vector, the sensor reads a positive maximum on the Z axis.

Accelerometer	Magnetometer	Gyroscope

Flashing & Running

Easy.

DEFMT_LOG=info cargo run

Requirements

Target

This project uses the thumbv7em-none-eabihf target. Prepare it using:

rustup target add thumbv7em-none-eabihf

flip-link

Set up flip-link:

Adds zero-cost stack overflow protection to your embedded programs.

probe-rs

Set up probe-rs, and follow the setup instructions (e.g. the Linux udev rules).

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Troubleshooting

Outdated firmware

My STM32F3 Discovery had an outdated version of the ST-Link firmware, and probe-rs refused to work with it:

probe-rs failed to open the debug probe Error processing command: The firmware on the probe is outdated.

Go to ST-LINK, ST-LINK/V2, ST-LINK/V2-1, STLINK-V3 boards firmware upgrade and download the latest version. Unzip, run the application and follow the instructions.

java -jar STLinkUpgrade.jar

Invalid SRAM size definition

Error: The flashing procedure failed for 'target/thumbv7em-none-eabihf/debug/stm32f3disco-led-roulette'.

Caused by: 0: Failed to erase flash sector at address 0x08000000. 1: Something during the interaction with the core went wrong 2: A timeout occurred.

From this GitHub comment:

The problem is that the chip has 40KB of main SRAM, but the chip definition says 48KB, and we try to place the flash loader's stack at the end of that 48KB region.

I went the hard way and installed probe-rs from sources:

cargo install probe-rs-tools --git https://github.com/probe-rs/probe-rs --locked