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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 "><a href="../by-example.html"><strong aria-hidden="true">1.</strong> RTIC by example</a></li><li><ol class="section"><li class="chapter-item expanded "><a href="../by-example/app.html"><strong aria-hidden="true">1.1.</strong> The app</a></li><li class="chapter-item expanded "><a href="../by-example/resources.html"><strong aria-hidden="true">1.2.</strong> Resources</a></li><li class="chapter-item expanded "><a href="../by-example/app_init.html" class="active"><strong aria-hidden="true">1.3.</strong> The init task</a></li><li class="chapter-item expanded "><a href="../by-example/app_idle.html"><strong aria-hidden="true">1.4.</strong> The idle task</a></li><li class="chapter-item expanded "><a href="../by-example/app_task.html"><strong aria-hidden="true">1.5.</strong> Defining tasks</a></li><li><ol class="section"><li class="chapter-item expanded "><a href="../by-example/hardware_tasks.html"><strong aria-hidden="true">1.5.1.</strong> Hardware tasks</a></li><li class="chapter-item expanded "><a href="../by-example/software_tasks.html"><strong aria-hidden="true">1.5.2.</strong> Software tasks & spawn</a></li><li class="chapter-item expanded "><a href="../by-example/message_passing.html"><strong aria-hidden="true">1.5.3.</strong> Message passing & capacity</a></li><li class="chapter-item expanded "><a href="../by-example/app_priorities.html"><strong aria-hidden="true">1.5.4.</strong> Task priorities</a></li><li class="chapter-item expanded "><a href="../by-example/monotonic.html"><strong aria-hidden="true">1.5.5.</strong> Monotonic & spawn_{at/after}</a></li></ol></li><li class="chapter-item expanded "><a href="../by-example/starting_a_project.html"><strong aria-hidden="true">1.6.</strong> Starting a new project</a></li><li class="chapter-item expanded "><a href="../by-example/app_minimal.html"><strong aria-hidden="true">1.7.</strong> The minimal app</a></li><li class="chapter-item expanded "><a href="../by-example/tips.html"><strong aria-hidden="true">1.8.</strong> Tips & Tricks</a></li><li><ol class="section"><li class="chapter-item expanded "><a href="../by-example/tips_monotonic_impl.html"><strong aria-hidden="true">1.8.1.</strong> Implementing Monotonic</a></li><li class="chapter-item expanded "><a href="../by-example/tips_destructureing.html"><strong aria-hidden="true">1.8.2.</strong> Resource de-structure-ing</a></li><li class="chapter-item expanded "><a href="../by-example/tips_indirection.html"><strong aria-hidden="true">1.8.3.</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">1.8.4.</strong> 'static super-powers</a></li><li class="chapter-item expanded "><a href="../by-example/tips_view_code.html"><strong aria-hidden="true">1.8.5.</strong> Inspecting generated code</a></li><li class="chapter-item expanded "><a href="../by-example/tips_from_ram.html"><strong aria-hidden="true">1.8.6.</strong> Running tasks from RAM</a></li></ol></li></ol></li><li class="chapter-item expanded "><a href="../awesome_rtic.html"><strong aria-hidden="true">2.</strong> Awesome RTIC examples</a></li><li class="chapter-item expanded "><a href="../migration.html"><strong aria-hidden="true">3.</strong> Migration Guides</a></li><li><ol class="section"><li class="chapter-item expanded "><a href="../migration/migration_v5.html"><strong aria-hidden="true">3.1.</strong> v0.5.x to v1.0.x</a></li><li class="chapter-item expanded "><a href="../migration/migration_v4.html"><strong aria-hidden="true">3.2.</strong> v0.4.x to v0.5.x</a></li><li class="chapter-item expanded "><a href="../migration/migration_rtic.html"><strong aria-hidden="true">3.3.</strong> RTFM to RTIC</a></li></ol></li><li class="chapter-item expanded "><a href="../internals.html"><strong aria-hidden="true">4.</strong> Under the hood</a></li><li><ol class="section"><li class="chapter-item expanded "><a href="../internals/targets.html"><strong aria-hidden="true">4.1.</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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<h1 id="app-initialization-and-the-init-task"><a class="header" href="#app-initialization-and-the-init-task">App initialization and the <code>#[init]</code> task</a></h1>
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<p>An RTIC application requires an <code>init</code> task setting up the system. The corresponding <code>init</code> function must have the
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signature <code>fn(init::Context) -> (Shared, Local, init::Monotonics)</code>, where <code>Shared</code> and <code>Local</code> are resource
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structures defined by the user.</p>
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<p>The <code>init</code> task executes after system reset, <a href="https://docs.rs/cortex-m-rt/latest/cortex_m_rt/attr.pre_init.html">after an optionally defined <code>pre-init</code> code section</a> and an always occurring internal RTIC
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initialization.</p>
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<p>The <code>init</code> and optional <code>pre-init</code> tasks runs <em>with interrupts disabled</em> and have exclusive access to Cortex-M (the
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<code>bare_metal::CriticalSection</code> token is available as <code>cs</code>).</p>
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<p>Device specific peripherals are available through the <code>core</code> and <code>device</code> fields of <code>init::Context</code>.</p>
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<h2 id="example"><a class="header" href="#example">Example</a></h2>
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<p>The example below shows the types of the <code>core</code>, <code>device</code> and <code>cs</code> fields, and showcases the use of a <code>local</code>
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variable with <code>'static</code> lifetime.
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Such variables can be delegated from the <code>init</code> task to other tasks of the RTIC application.</p>
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<p>The <code>device</code> field is only available when the <code>peripherals</code> argument is set to the default value <code>true</code>.
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In the rare case you want to implement an ultra-slim application you can explicitly set <code>peripherals</code> to <code>false</code>.</p>
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<pre><pre class="playground"><code class="language-rust"><span class="boring">#![allow(unused)]
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</span><span class="boring">fn main() {
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</span>//! examples/init.rs
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#![deny(unsafe_code)]
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#![deny(warnings)]
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#![deny(missing_docs)]
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#![no_main]
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#![no_std]
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use panic_semihosting as _;
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#[rtic::app(device = lm3s6965, peripherals = true)]
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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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#[init(local = [x: u32 = 0])]
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fn init(cx: init::Context) -> (Shared, Local, init::Monotonics) {
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// Cortex-M peripherals
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let _core: cortex_m::Peripherals = cx.core;
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// Device specific peripherals
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let _device: lm3s6965::Peripherals = cx.device;
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// Locals in `init` have 'static lifetime
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let _x: &'static mut u32 = cx.local.x;
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// Access to the critical section token,
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// to indicate that this is a critical seciton
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let _cs_token: bare_metal::CriticalSection = cx.cs;
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hprintln!("init");
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debug::exit(debug::EXIT_SUCCESS); // Exit QEMU simulator
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(Shared {}, Local {}, init::Monotonics())
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}
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}
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<span class="boring">}</span></code></pre></pre>
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<p>Running the example will print <code>init</code> to the console and then exit the QEMU process.</p>
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<pre><code class="language-console">$ cargo run --target thumbv7m-none-eabi --example init
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init
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</code></pre>
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