Learn a bit of embedded programming with Rust in a micro:bit v2
a project by aplanas
Updated 16 days ago. 1 hackers ♥️. 1 follower.

Description

micro:bit is a small single board computer with a ARM Cortex-M4 with the FPU extension, with a very constrain amount of memory and a bunch of sensors and leds.

The board is very well documented, with schematics and code for all the features available, so is an excellent platform for learning embedded programming.

Rust is a system programming language that can generate ARM code, and has crates (libraries) to access the micro:bit hardware. There is plenty documentation about how to make small programs that will run in the micro:bit.

Goals

Start learning about embedded programming in Rust, and maybe make some code to the small KS4036F Robot car from keyestudio.

Resources

Diary

Day 1

  • Start reading https://mb2.implrust.com/abstraction-layers.html
  • Prepare the dev environment (cross compiler, probe-rs)
  • Flash first code in the board (blinky led)
  • Checking differences between BSP and HAL
  • Compile and install a more complex example, with stack protection
  • Reading about the simplicity of xtask, as alias for workspace execution
  • Reading the CPP code of the official micro:bit libraries. They have a font!

Day 2

  • There are multiple BSP for the microbit. One is using async code for non-blocking operations
  • Download and study a bit the API for microbit-v2, the nRF official crate
  • Take a look of the KS4036F programming, seems that the communication is multiplexed via I2C
  • The motor speed can be selected via PWM (pulse with modulation): power it longer (high frequency), and it will increase the speed
  • Scrolling some text
  • Debug by printing! defmt is a crate that can be used with probe-rs to emit logs
  • Start reading input from the board: buttons
  • The logo can be touched and detected as a floating point value

Day 3

  • A bit confused how to read the float value from a pin
  • It is a typestate and I can only check islow / ishigh
  • Move a bit into the HAL layer
  • Ahh ... the floating is not about floating point value, is about driving or not (detecting) current
  • So there are 5 timers of 32 bits. What's the frequency, Kenneth? (1MHz, 16MHz)
  • Async in embedded Rust with Embassy!
  • Using Embassy is a bit of cheating, so park it for now
  • IRQs handlers for events triggered by devices
  • Seems that SPI is for fast devices, and I2C for slow ones, like the accelerometer
  • Start reading the rust-embedded book to see if concurrency should be done with interrupts

Day 4

  • Learning about RTT (real time transfer) for logs. Very nice interface
  • Specific drivers can be written from a generic trait that represent an abstract HAL
  • Thanks to the 2nd processor we can use gdb!
  • Seems that Tumbleweed's gdb can be used too, is it multiarch?
  • With gdb I can also print variables, and enter the core / hal code!
  • ... and trace the src and asm code. This is honestly cool.
  • Asm code can be directly injected via cortex_m::asm (to disable ints, for example)

I did not make my goal: work with the robot car, but this was really funny. I think that I found a new hobby topic, as there are more things that I want to learn about this, like for example the Embassy async framework.

Something that I want to explore in the weekends is how to put in the nfr and in the Embassy micro:bit BSP all the missing features that are present in the C++ reference implementation (like dim leds, touchpad integration)

Join this project

Looking for hackers with the skills:

rust microbit embedded

This project is part of:

Hack Week 25

Activity

  • 7 days ago: dmdiss liked this project.
  • 17 days ago: aplanas added keyword "embedded" to this project.
  • 17 days ago: aplanas added keyword "microbit" to this project.
  • 17 days ago: aplanas added keyword "rust" to this project.
  • 20 days ago: aplanas started this project.
  • 20 days ago: aplanas originated this project.


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