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<h1 class="menu-title">Real-Time Interrupt-driven Concurrency</h1>
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<main>
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<h1 id="hardware-tasks"><a class="header" href="#hardware-tasks">Hardware tasks</a></h1>
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<p>At its core RTIC is using a hardware interrupt controller (<a href="https://developer.arm.com/documentation/100166/0001/Nested-Vectored-Interrupt-Controller/NVIC-functional-description/NVIC-interrupts">ARM NVIC on cortex-m</a>) to schedule and start execution of tasks. All tasks except <code>pre-init</code> (a hidden "task"), <code>#[init]</code> and <code>#[idle]</code> run as interrupt handlers.</p>
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<p>To bind a task to an interrupt, use the <code>#[task]</code> attribute argument <code>binds = InterruptName</code>. This task then becomes the interrupt handler for this hardware interrupt vector.</p>
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<p>All tasks bound to an explicit interrupt are called <em>hardware tasks</em> since they start execution in reaction to a hardware event.</p>
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<p>Specifying a non-existing interrupt name will cause a compilation error. The interrupt names are commonly defined by <a href="https://docs.rust-embedded.org/book/start/registers.html">PAC or HAL</a> crates.</p>
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<p>Any available interrupt vector should work. Specific devices may bind specific interrupt priorities to specific interrupt vectors outside user code control. See for example the <a href="https://github.com/rtic-rs/rtic/issues/434">nRF “softdevice”</a>.</p>
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<p>Beware of using interrupt vectors that are used internally by hardware features; RTIC is unaware of such hardware specific details.</p>
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<h2 id="example"><a class="header" href="#example">Example</a></h2>
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<p>The example below demonstrates the use of the <code>#[task(binds = InterruptName)]</code> attribute to declare a hardware task bound to an interrupt handler.</p>
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<pre><code class="language-rust noplayground">//! examples/hardware.rs
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#![no_main]
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#![no_std]
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#![deny(warnings)]
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#![deny(unsafe_code)]
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#![deny(missing_docs)]
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use panic_semihosting as _;
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#[rtic::app(device = lm3s6965)]
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mod app {
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use cortex_m_semihosting::{debug, hprintln};
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use lm3s6965::Interrupt;
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#[shared]
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struct Shared {}
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#[local]
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struct Local {}
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#[init]
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fn init(_: init::Context) -> (Shared, Local) {
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// Pends the UART0 interrupt but its handler won't run until *after*
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// `init` returns because interrupts are disabled
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rtic::pend(Interrupt::UART0); // equivalent to NVIC::pend
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hprintln!("init");
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(Shared {}, Local {})
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}
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#[idle]
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fn idle(_: idle::Context) -> ! {
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// interrupts are enabled again; the `UART0` handler runs at this point
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hprintln!("idle");
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// Some backends provide a manual way of pending an
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// interrupt.
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rtic::pend(Interrupt::UART0);
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loop {
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cortex_m::asm::nop();
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debug::exit(debug::EXIT_SUCCESS); // Exit QEMU simulator
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}
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}
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#[task(binds = UART0, local = [times: u32 = 0])]
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fn uart0(cx: uart0::Context) {
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// Safe access to local `static mut` variable
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*cx.local.times += 1;
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hprintln!(
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"UART0 called {} time{}",
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*cx.local.times,
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if *cx.local.times > 1 { "s" } else { "" }
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);
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}
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}</code></pre>
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<pre><code class="language-console">$ cargo xtask qemu --verbose --example hardware
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</code></pre>
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<pre><code class="language-console">init
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UART0 called 1 time
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idle
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UART0 called 2 times
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</code></pre>
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