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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"><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" class="active"><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.</st
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<h1 class="menu-title">Real-Time Interrupt-driven Concurrency</h1>
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<h1 id="the-magic-behind-monotonics"><a class="header" href="#the-magic-behind-monotonics">The magic behind Monotonics</a></h1>
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<p>Internally, all monotonics use a <a href="#the-timer-queue">Timer Queue</a>, which is a priority queue with entries describing the time at which their respective <code>Future</code>s should complete.</p>
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<h2 id="implementing-a-monotonic-timer-for-scheduling"><a class="header" href="#implementing-a-monotonic-timer-for-scheduling">Implementing a <code>Monotonic</code> timer for scheduling</a></h2>
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<p>The <a href="https://docs.rs/rtic-time/latest/rtic_time"><code>rtic-time</code></a> framework is flexible because it can use any timer which has compare-match and optionally supporting overflow interrupts for scheduling. The single requirement to make a timer usable with RTIC is implementing the <a href="https://docs.rs/rtic-time/latest/rtic_time/trait.Monotonic.html"><code>rtic-time::Monotonic</code></a> trait.</p>
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<p>For RTIC 2.0, we assume that the user has a time library, e.g. <a href="https://docs.rs/fugit/"><code>fugit</code></a>, as the basis for all time-based operations when implementing <a href="https://docs.rs/rtic-time/latest/rtic_time/trait.Monotonic.html"><code>Monotonic</code></a>. These libraries make it much easier to correctly implement the <a href="https://docs.rs/rtic-time/latest/rtic_time/trait.Monotonic.html"><code>Monotonic</code></a> trait, allowing the use of almost any timer in the system for scheduling.</p>
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<p>The trait documents the requirements for each method. There are reference implementations available in <a href="https://github.com/rtic-rs/rtic/tree/master/rtic-monotonics/"><code>rtic-monotonics</code></a> that can be used for inspriation.</p>
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<ul>
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<li><a href="https://github.com/rtic-rs/rtic/blob/master/rtic-monotonics/src/systick.rs"><code>Systick based</code></a>, runs at a fixed interrupt (tick) rate - with some overhead but simple and provides support for large time spans</li>
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<li><a href="https://github.com/rtic-rs/rtic/blob/master/rtic-monotonics/src/rp2040.rs"><code>RP2040 Timer</code></a>, a "proper" implementation with support for waiting for long periods without interrupts. Clearly demonstrates how to use the <a href="https://docs.rs/rtic-time/latest/rtic_time/struct.TimerQueue.html"><code>TimerQueue</code></a> to handle scheduling.</li>
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<li><a href="https://github.com/rtic-rs/rtic/blob/master/rtic-monotonics/src/nrf.rs"><code>nRF52 timers</code></a> implements monotonic & Timer Queue for the RTC and normal timers in nRF52's</li>
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<h2 id="contributing"><a class="header" href="#contributing">Contributing</a></h2>
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<p>Contributing new implementations of <code>Monotonic</code> can be done in multiple ways:</p>
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<ul>
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<li>Implement the trait behind a feature flag in <a href="https://github.com/rtic-rs/rtic/tree/master/rtic-monotonics/"><code>rtic-monotonics</code></a>, and create a PR for them to be included in the main RTIC repository. This way, the implementations of are in-tree, RTIC can guarantee their correctness, and can update them in the case of a new release.</li>
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<li>Implement the changes in an external repository. Doing so will not have them included in <a href="https://github.com/rtic-rs/rtic/tree/master/rtic-monotonics/"><code>rtic-monotonics</code></a>, but may make it easier to do so in the future.</li>
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</ul>
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<h2 id="the-timer-queue"><a class="header" href="#the-timer-queue">The timer queue</a></h2>
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<p>The timer queue is implemented as a list based priority queue, where list-nodes are statically allocated as part of the <code>Future</code> created when <code>await</code>-ing a Future created when waiting for the monotonic. Thus, the timer queue is infallible at run-time (its size and allocation are determined at compile time).</p>
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<p>Similarly the channels implementation, the timer-queue implementation relies on a global <em>Critical Section</em> (CS) for race protection. For the examples a CS implementation is provided by adding <code>--features test-critical-section</code> to the build options.</p>
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<script src="mermaid.min.js"></script>
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<script src="mermaid-init.js"></script>
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</body>
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