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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="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)</code>, where <code>Shared</code> and <code>Local</code> are resource structures defined by the user.</p>
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<p>The <code>init</code> task executes after system reset, [after an optionally defined <code>pre-init</code> code section]<sup class="footnote-reference"><a href="#pre-init">1</a></sup> and an always occurring internal RTIC 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 <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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<div class="footnote-definition" id="pre-init"><sup class="footnote-definition-label">1</sup>
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<p><a href="https://docs.rs/cortex-m-rt/latest/cortex_m_rt/attr.pre_init.html">https://docs.rs/cortex-m-rt/latest/cortex_m_rt/attr.pre_init.html</a></p>
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</div>
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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> variable with <code>'static</code> lifetime. 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><code class="language-rust noplayground">//! examples/init.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, 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) {
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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 section
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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 {})
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}
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}</code></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 xtask qemu --verbose --example init
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</code></pre>
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<pre><code class="language-console">init
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</code></pre>
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