Module cortex_m::peripheral

Expand description

Core peripherals

API

To use (most of) the peripheral API first you must get an instance of the peripheral. All the core peripherals are modeled as singletons (there can only ever be, at most, one instance of any one of them at any given point in time) and the only way to get an instance of them is through the Peripherals::take method.

extern crate cortex_m;

use cortex_m::peripheral::Peripherals;

fn main() {
    let mut peripherals = Peripherals::take().unwrap();
    peripherals.DWT.enable_cycle_counter();
}

This method can only be successfully called once – this is why the method returns an Option. Subsequent calls to the method will result in a None value being returned.

extern crate cortex_m;

use cortex_m::peripheral::Peripherals;

fn main() {
    let ok = Peripherals::take().unwrap();
    let panics = Peripherals::take().unwrap();
}

A part of the peripheral API doesn’t require access to a peripheral instance. This part of the API is provided as static methods on the peripheral types. One example is the DWT::get_cycle_count method.

extern crate cortex_m;

use cortex_m::peripheral::{DWT, Peripherals};

fn main() {
    {
        let mut peripherals = Peripherals::take().unwrap();
        peripherals.DWT.enable_cycle_counter();
    } // all the peripheral singletons are destroyed here

    // but this method can be called without a DWT instance
    let cyccnt = DWT::get_cycle_count();
}

The singleton property can be unsafely bypassed using the ptr static method which is available on all the peripheral types. This method is a useful building block for implementing safe higher level abstractions.

extern crate cortex_m;

use cortex_m::peripheral::{DWT, Peripherals};

fn main() {
    {
        let mut peripherals = Peripherals::take().unwrap();
        peripherals.DWT.enable_cycle_counter();
    } // all the peripheral singletons are destroyed here

    // actually safe because this is an atomic read with no side effects
    let cyccnt = unsafe { (*DWT::ptr()).cyccnt.read() };
}