rtic/examples/lock5_mutex.rs

//! examples/lock.rs

#![deny(unsafe_code)]
#![deny(warnings)]
#![no_main]
#![no_std]

use cortex_m_semihosting::{debug, hprintln};
use lm3s6965::Interrupt;
use panic_semihosting as _;
use rtic::Mutex;
use rtic_core::Exclusive;

#[rtic::app(device = lm3s6965)]
const APP: () = {
    struct Resources {
        #[init(0)]
        shared: u32,
    }

    #[init]
    fn init(_: init::Context) {
        rtic::pend(Interrupt::GPIOA);
    }

    // when omitted priority is assumed to be `1`
    #[task(binds = GPIOA, resources = [shared])]
    fn gpioa(c: gpioa::Context) {
        hprintln!("A").unwrap();

        // the lower priority task requires a critical section to access the data
        c.resources.shared.lock(|shared| {
            // data can only be modified within this critical section (closure)
            *shared += 1;

            // GPIOB will *not* run right now due to the critical section
            rtic::pend(Interrupt::GPIOB);

            hprintln!("B - shared = {}", *shared).unwrap();

            // GPIOC does not contend for `shared` so it's allowed to run now
            rtic::pend(Interrupt::GPIOC);
        });

        // critical section is over: GPIOB can now start

        hprintln!("E").unwrap();

        debug::exit(debug::EXIT_SUCCESS);
    }

    #[task(binds = GPIOB, priority = 2, resources = [shared])]
    fn gpiob(c: gpiob::Context) {
        static mut STATE: u32 = 28;
        c.resources.shared.lock(|shared| {
            *shared += 1;
            hprintln!("D - shared = {}", shared).unwrap();
        });
        advance(STATE, c.resources.shared);
    }

    #[task(binds = GPIOC, priority = 3, resources = [shared])]
    fn gpioc(c: gpioc::Context) {
        static mut STATE: u32 = 0;
        hprintln!("GPIOC(STATE = {})", *STATE).unwrap();
        *c.resources.shared += 2;
        let ex_shared = Exclusive::new(c.resources.shared);
        advance(STATE, ex_shared); // try swap order of (1)
        *c.resources.shared += 3; // and (2), will fail
        hprintln!("GPIOC(STATE = {})", *STATE).unwrap();
    }
};

// the second parameter is generic: it can be any type that implements the `Mutex` trait
fn advance(state: &mut u32, shared: impl Mutex<T = u32>) {
    *state += 1;

    let (old, new) = shared.lock(|shared: &mut u32| {
        let old = *shared;
        *shared += *state;
        (old, *shared)
    });

    hprintln!("shared: {} -> {}", old, new).unwrap();
}