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<h1 class="menu-title">Real-Time Interrupt-driven Concurrency</h1>
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<h1 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></h1>
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<p>The framework is flexible because it can use any timer which has compare-match and optionally
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supporting overflow interrupts for scheduling.
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The single requirement to make a timer usable with RTIC is implementing the
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<a href="https://docs.rs/rtic-monotonic/"><code>rtic_monotonic::Monotonic</code></a> trait.</p>
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<p>Implementing time counting that supports large time spans is generally <strong>difficult</strong>, in RTIC 0.5
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implementing time handling was a common problem.
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Moreover, the relation between time and timers used for scheduling was difficult to understand.</p>
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<p>For RTIC 1.0 we instead assume the user has a time library, e.g. <a href="https://docs.rs/fugit/"><code>fugit</code></a> or <a href="https://docs.rs/embedded_time/"><code>embedded_time</code></a>,
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as the basis for all time-based operations when implementing <code>Monotonic</code>.
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These libraries make it much easier to correctly implement the <code>Monotonic</code> trait, allowing the use of
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almost any timer in the system for scheduling.</p>
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<p>The trait documents the requirements for each method,
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and for inspiration here is a list of <code>Monotonic</code> implementations:</p>
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<ul>
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<li><a href="https://github.com/kalkyl/f411-rtic/blob/a696fce7d6d19fda2356c37642c4d53547982cca/src/mono.rs"><code>STM32F411 series</code></a>, implemented for the 32-bit timers</li>
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<li><a href="https://github.com/kalkyl/nrf-play/blob/47f4410d4e39374c18ff58dc17c25159085fb526/src/mono.rs"><code>Nordic nRF52 series Timer</code></a>, implemented for the 32-bit timers</li>
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<li><a href="https://gist.github.com/korken89/fe94a475726414dd1bce031c76adc3dd"><code>Nordic nRF52 series RTC</code></a>, implemented for the RTCs</li>
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<li><a href="https://github.com/rtic-rs/systick-monotonic"><code>Systick based</code></a>, runs at a fixed interrupt (tick) rate - with some overhead but simple and with support for large time spans</li>
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<li><a href="https://github.com/rtic-rs/dwt-systick-monotonic"><code>DWT and Systick based</code></a>, a more efficient (tickless) implementation - requires both <code>SysTick</code> and <code>DWT</code>, supports both high resolution and large time spans</li>
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</ul>
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<p>If you know of more implementations feel free to add them to this list.</p>
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