The #[app] attribute and an RTIC application

Requirements on the app attribute

All RTIC applications use the app attribute (#[app(..)]). This attribute only applies to a mod-item containing the RTIC application. The app attribute has a mandatory device argument that takes a path as a value. This must be a full path pointing to a peripheral access crate (PAC) generated using svd2rust v0.14.x or newer.

The app attribute will expand into a suitable entry point and thus replaces the use of the cortex_m_rt::entry attribute.

An RTIC application example

To give a flavour of RTIC, the following example contains commonly used features. In the following sections we will go through each feature in detail.


#![allow(unused)]
fn main() {
//! examples/common.rs

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

use panic_semihosting as _;

#[rtic::app(device = lm3s6965, dispatchers = [SSI0, QEI0])]
mod app {
    use cortex_m_semihosting::{debug, hprintln};
    use systick_monotonic::*; // Implements the `Monotonic` trait

    // A monotonic timer to enable scheduling in RTIC
    #[monotonic(binds = SysTick, default = true)]
    type MyMono = Systick<100>; // 100 Hz / 10 ms granularity

    // Resources shared between tasks
    #[shared]
    struct Shared {
        s1: u32,
        s2: i32,
    }

    // Local resources to specific tasks (cannot be shared)
    #[local]
    struct Local {
        l1: u8,
        l2: i8,
    }

    #[init]
    fn init(cx: init::Context) -> (Shared, Local, init::Monotonics) {
        let systick = cx.core.SYST;

        // Initialize the monotonic (SysTick rate in QEMU is 12 MHz)
        let mono = Systick::new(systick, 12_000_000);

        // Spawn the task `foo` directly after `init` finishes
        foo::spawn().unwrap();

        // Spawn the task `bar` 1 second after `init` finishes, this is enabled
        // by the `#[monotonic(..)]` above
        bar::spawn_after(1.secs()).unwrap();

        debug::exit(debug::EXIT_SUCCESS); // Exit QEMU simulator

        (
            // Initialization of shared resources
            Shared { s1: 0, s2: 1 },
            // Initialization of task local resources
            Local { l1: 2, l2: 3 },
            // Move the monotonic timer to the RTIC run-time, this enables
            // scheduling
            init::Monotonics(mono),
        )
    }

    // Background task, runs whenever no other tasks are running
    #[idle]
    fn idle(_: idle::Context) -> ! {
        loop {
            continue;
        }
    }

    // Software task, not bound to a hardware interrupt.
    // This task takes the task local resource `l1`
    // The resources `s1` and `s2` are shared between all other tasks.
    #[task(shared = [s1, s2], local = [l1])]
    fn foo(_: foo::Context) {
        // This task is only spawned once in `init`, hence this task will run
        // only once

        hprintln!("foo").ok();
    }

    // Software task, also not bound to a hardware interrupt
    // This task takes the task local resource `l2`
    // The resources `s1` and `s2` are shared between all other tasks.
    #[task(shared = [s1, s2], local = [l2])]
    fn bar(_: bar::Context) {
        hprintln!("bar").ok();

        // Run `bar` once per second
        bar::spawn_after(1.secs()).unwrap();
    }

    // Hardware task, bound to a hardware interrupt
    // The resources `s1` and `s2` are shared between all other tasks.
    #[task(binds = UART0, priority = 3, shared = [s1, s2])]
    fn uart0_interrupt(_: uart0_interrupt::Context) {
        // This task is bound to the interrupt `UART0` and will run
        // whenever the interrupt fires

        // Note that RTIC does NOT clear the interrupt flag, this is up to the
        // user

        hprintln!("UART0 interrupt!").ok();
    }
}
}