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<ol class="chapter"><li class="chapter-item expanded affix "><a href="../preface.html">Preface</a></li><li class="chapter-item expanded affix "><li class="spacer"></li><li class="chapter-item expanded "><a href="../starting_a_project.html"><strong aria-hidden="true">1.</strong> Starting a new project</a></li><li class="chapter-item expanded "><a href="../by-example.html"><strong aria-hidden="true">2.</strong> RTIC by example</a></li><li><ol class="section"><li class="chapter-item expanded "><a href="../by-example/app.html" class="active"><strong aria-hidden="true">2.1.</strong> The app</a></li><li class="chapter-item expanded "><a href="../by-example/hardware_tasks.html"><strong aria-hidden="true">2.2.</strong> Hardware tasks</a></li><li class="chapter-item expanded "><a href="../by-example/software_tasks.html"><strong aria-hidden="true">2.3.</strong> Software tasks & spawn</a></li><li class="chapter-item expanded "><a href="../by-example/resources.html"><strong aria-hidden="true">2.4.</strong> Resources</a></li><li class="chapter-item expanded "><a href="../by-example/app_init.html"><strong aria-hidden="true">2.5.</strong> The init task</a></li><li class="chapter-item expanded "><a href="../by-example/app_idle.html"><strong aria-hidden="true">2.6.</strong> The idle task</a></li><li class="chapter-item expanded "><a href="../by-example/channel.html"><strong aria-hidden="true">2.7.</strong> Channel based communication</a></li><li class="chapter-item expanded "><a href="../by-example/delay.html"><strong aria-hidden="true">2.8.</strong> Delay and Timeout using Monotonics</a></li><li class="chapter-item expanded "><a href="../by-example/app_minimal.html"><strong aria-hidden="true">2.9.</strong> The minimal app</a></li><li class="chapter-item expanded "><a href="../by-example/tips/index.html"><strong aria-hidden="true">2.10.</strong> Tips & Tricks</a></li><li><ol class="section"><li class="chapter-item expanded "><a href="../by-example/tips/destructureing.html"><strong aria-hidden="true">2.10.1.</strong> Resource de-structure-ing</a></li><li class="chapter-item expanded "><a href="../by-example/tips/indirection.html"><strong aria-hidden="true">2.10.2.</strong> Avoid copies when message passing</a></li><li class="chapter-item expanded "><a href="../by-example/tips/static_lifetimes.html"><strong aria-hidden="true">2.10.3.</strong> 'static super-powers</a></li><li class="chapter-item expanded "><a href="../by-example/tips/view_code.html"><strong aria-hidden="true">2.10.4.</strong> Inspecting generated code</a></li></ol></li></ol></li><li class="chapter-item expanded "><a href="../monotonic_impl.html"><strong aria-hidden="true">3.</strong> Monotonics & the Timer Queue</a></li><li class="chapter-item expanded "><a href="../rtic_vs.html"><strong aria-hidden="true">4.</strong> RTIC vs. the world</a></li><li class="chapter-item expanded "><a href="../rtic_and_embassy.html"><strong aria-hidden="true">5.</strong> RTIC and Embassy</a></li><li class="chapter-item expanded "><a href="../awesome_rtic.html"><strong aria-hidden="true">6.</strong> Awesome RTIC examples</a></li><li class="chapter-item expanded affix "><li class="spacer"></li><li class="chapter-item expanded "><a href="../migration_v1_v2.html"><strong aria-hidden="true">7.</strong> Migrating from v1.0.x to v2.0.0</a></li><li><ol class="section"><li class="chapter-item expanded "><a href="../migration_v1_v2/monotonics.html"><strong aria-hidden="true">7.1.</strong> Migrating to rtic-monotonics</a></li><li class="chapter-item expanded "><a href="../migration_v1_v2/async_tasks.html"><strong aria-hidden="true">7.2.</strong> Software tasks must now be async</a></li><li class="chapter-item expanded "><a href="../migration_v1_v2/rtic-sync.html"><strong aria-hidden="true">7.3.</strong> Using and understanding rtic-sync</a></li><li class="chapter-item expanded "><a href="../migration_v1_v2/complete_example.html"><strong aria-hidden="true">7.4.</strong> A code example on migration</a></li></ol></li><li class="chapter-item expanded "><li class="spacer"></li><li class="chapter-item expanded "><a href="../internals.html"><strong aria-hidden="true">8.</strong> Under the hood</a></li><li><ol class="section"><li class="chapter-item expanded "><a href="../internals/targets.html"><strong aria-hidden="true">8.1.</strong> Cortex-M architectures</a></li></ol></li></ol>
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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="the-app-attribute-and-an-rtic-application"><a class="header" href="#the-app-attribute-and-an-rtic-application">The <code>#[app]</code> attribute and an RTIC application</a></h1>
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<h2 id="requirements-on-the-app-attribute"><a class="header" href="#requirements-on-the-app-attribute">Requirements on the <code>app</code> attribute</a></h2>
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<p>All RTIC applications use the <a href="../../../api/rtic_macros/attr.app.html"><code>app</code></a> attribute (<code>#[app(..)]</code>). This attribute only applies to a <code>mod</code>-item containing the RTIC application.</p>
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<p>The <code>app</code> attribute has a mandatory <code>device</code> argument that takes a <em>path</em> as a value. This must be a full path pointing to a <em>peripheral access crate</em> (PAC) generated using <a href="https://crates.io/crates/svd2rust"><code>svd2rust</code></a> <strong>v0.14.x</strong> or newer.</p>
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<p>The <code>app</code> attribute will expand into a suitable entry point and thus replaces the use of the <a href="https://docs.rs/cortex-m-rt-macros/latest/cortex_m_rt_macros/attr.entry.html"><code>cortex_m_rt::entry</code></a> attribute.</p>
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<h2 id="structure-and-zero-cost-concurrency"><a class="header" href="#structure-and-zero-cost-concurrency">Structure and zero-cost concurrency</a></h2>
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<p>An RTIC <code>app</code> is an executable system model for single-core applications, declaring a set of <code>local</code> and <code>shared</code> resources operated on by a set of <code>init</code>, <code>idle</code>, <em>hardware</em> and <em>software</em> tasks.</p>
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<ul>
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<li><code>init</code> runs before any other task, and returns the <code>local</code> and <code>shared</code> resources.</li>
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<li>Tasks (both hardware and software) run preemptively based on their associated static priority.</li>
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<li>Hardware tasks are bound to underlying hardware interrupts.</li>
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<li>Software tasks are schedulied by an set of asynchronous executors, one for each software task priority.</li>
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<li><code>idle</code> has the lowest priority, and can be used for background work, and/or to put the system to sleep until it is woken by some event.</li>
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</ul>
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<p>At compile time the task/resource model is analyzed under the Stack Resource Policy (SRP) and executable code generated with the following outstanding properties:</p>
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<ul>
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<li>Guaranteed race-free resource access and deadlock-free execution on a single-shared stack.</li>
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<li>Hardware task scheduling is performed directly by the hardware.</li>
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<li>Software task scheduling is performed by auto generated async executors tailored to the application.</li>
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</ul>
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<p>Overall, the generated code infers no additional overhead in comparison to a hand-written implementation, thus in Rust terms RTIC offers a zero-cost abstraction to concurrency.</p>
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<h2 id="priority"><a class="header" href="#priority">Priority</a></h2>
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<p>Priorities in RTIC are specified using the <code>priority = N</code> (where N is a positive number) argument passed to the <code>#[task]</code> attribute. All <code>#[task]</code>s can have a priority. If the priority of a task is not specified, it is set to the default value of 0.</p>
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<p>Priorities in RTIC follow a higher value = more important scheme. For examples, a task with priority 2 will preempt a task with priority 1.</p>
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<h2 id="an-rtic-application-example"><a class="header" href="#an-rtic-application-example">An RTIC application example</a></h2>
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<p>To give a taste of RTIC, the following example contains commonly used features.
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In the following sections we will go through each feature in detail.</p>
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<pre><code class="language-rust noplayground">//! examples/common.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, dispatchers = [UART0, UART1])]
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mod app {
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use cortex_m_semihosting::{debug, hprintln};
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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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local_to_foo: i64,
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local_to_bar: i64,
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local_to_idle: i64,
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}
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// `#[init]` cannot access locals from the `#[local]` struct as they are initialized here.
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#[init]
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fn init(_: init::Context) -> (Shared, Local) {
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foo::spawn().unwrap();
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bar::spawn().unwrap();
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(
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Shared {},
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// initial values for the `#[local]` resources
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Local {
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local_to_foo: 0,
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local_to_bar: 0,
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local_to_idle: 0,
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},
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)
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}
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// `local_to_idle` can only be accessed from this context
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#[idle(local = [local_to_idle])]
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fn idle(cx: idle::Context) -> ! {
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let local_to_idle = cx.local.local_to_idle;
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*local_to_idle += 1;
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hprintln!("idle: local_to_idle = {}", local_to_idle);
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debug::exit(debug::EXIT_SUCCESS); // Exit QEMU simulator
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// error: no `local_to_foo` field in `idle::LocalResources`
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// _cx.local.local_to_foo += 1;
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// error: no `local_to_bar` field in `idle::LocalResources`
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// _cx.local.local_to_bar += 1;
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loop {
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cortex_m::asm::nop();
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}
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}
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// `local_to_foo` can only be accessed from this context
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#[task(local = [local_to_foo], priority = 1)]
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async fn foo(cx: foo::Context) {
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let local_to_foo = cx.local.local_to_foo;
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*local_to_foo += 1;
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// error: no `local_to_bar` field in `foo::LocalResources`
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// cx.local.local_to_bar += 1;
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hprintln!("foo: local_to_foo = {}", local_to_foo);
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}
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// `local_to_bar` can only be accessed from this context
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#[task(local = [local_to_bar], priority = 1)]
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async fn bar(cx: bar::Context) {
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let local_to_bar = cx.local.local_to_bar;
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*local_to_bar += 1;
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// error: no `local_to_foo` field in `bar::LocalResources`
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// cx.local.local_to_foo += 1;
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hprintln!("bar: local_to_bar = {}", local_to_bar);
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}
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}</code></pre>
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