Crate f3 [] [src]

A crate to play with the STM32F3DISCOVERY

(What? You don't have one? How come? They are awesome and cheap ($15 + shipping))

(No, I'm not associated to STM32. I just like this board in particular.)


  • High-level API over LEDs, sensors, timers, etc.

  • An iprint! family of macros that sink their output to the ITM (Instrumentation Trace Macrocell) so you send data to the host over the same USB cable that you are using to debug your device.

  • By default, panic!s also sink their messages to the ITM

  • An uprint! family of macros that send their messages through the Serial interface.

  • By default, an informative exception handler that tells you what went wrong.

  • By default, everything (LEDs, sensors, etc) is initialized before the user entry point, main. So everything Just Works out of the box.

  • Plenty of examples

Requirements and starter code

Today, you need these 6 things, one of them optional, but hopefully you won't need 3 of them in the future:

  • Nightly Rust compiler newer than 2016-10-05: rustup default nightly

  • Xargo version 0.1.13 or newer. (After rust-lang/rfcs#1133 gets accepted and implemented you won't need Xargo anymore)

  • A binary Cargo project that depends on this crate.

$ cargo new --bin foo && cd $_
$ edit Cargo.toml && tail -n2 $_
f3 = "0.1.0"
  • Optionally, you can also set profile.release.lto = true for even smaller binaries.
$ edit Cargo.toml && tail -n2 $_
lto = true
  • This .cargo/config in the root of your Cargo project. (If Cargo build scripts ever gain a feature to pass arbitrary arguments to the linker then you won't need this. Setting though always improves ergonomics)
$ cat .cargo/config
target = "thumbv7em-none-eabihf"

rustflags = [
  • And this starter code:
$ cat src/

extern crate f3;

#[export_name = "main"]
pub fn main() -> ! {
    // Your code goes here!

    loop {}

With all that in place, you can finally build the project using Xargo:

$ xargo build [--target thumbv7em-none-eabihf] [--release]

Check out my Copper book for instructions on how to Flash and Debug this program!

Also, check out my Discovery book for an introductory course in microcontrollers based on the STM32F3DISCOVERY.

Overriding default behaviors

Cargo features can be used to disable/override some default behaviors:

  • "default-exception-handler". If disabled, the default exception handler can be overridden using the _default_exception_handler symbol (extern "C" fn).

  • "default-init". If disabled, the pre-main initialization routine can be overridden via the _init symbol (fn).

  • "default-panic-fmt". If disabled, you can override the default behavior of panic! using the panic_fmt lang item (extern "C" fn) .

  • "interrupts". If disabled, interrupts can't be used (the handlers can't be "installed"/overriden). This saves some space in Flash memory.

  • "static-ram". If disabled, the RAM initialization routine is not executed and static mut variables can't be used. This saves some space in Flash memory and makes the boot process slightly faster.

Overriding the interrupt and exception handlers

By default, all the interrupts and exceptions are handled using the same "handler" (function). You can override this behavior exposing a "symbol" (extern "C" fn) in your crate. For example, the override the TIM7 interrupt handler, you would expose the _tim7 symbol:

#[export_name = "_tim7"]
pub extern "C" fn my_tim7_interrupt_handler() {
    // ..

For a list of these symbol, check the exception and interrupt modules. All the overridable symbols start with an underscore (_).


See the examples module.


pub extern crate stm32f30x_memory_map as peripheral;









Floating Point Unit (FPU)




ITM (Instrumentation Trace Macrocell)


L3GD20 - Gyroscope




LSM303DLHC - Accelerometer + Magnetometer


Serial Port communication


Temporal quantification



Puts the processor in Debug state. Debuggers can pick this up as a "breakpoint".


Macro for sending print!-formatted messages to the ITM (Instrumentation Trace Macrocell).


Macro for sending print!-formatted messages to the ITM, with a newline


Macro for sending print!-formatted messages over the Serial Port


Macro for sending print!-formatted messages over the Serial Port, with a newline



Three i16 integers packed in a struct