249 lines
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<ol class="chapter"><li class="affix"><a href="../index.html">Introduction</a></li><li class="affix"><a href="../background/index.html">Background</a></li><li class="affix"><a href="../requirements/index.html">Requirements</a></li><li><a href="../hardware/index.html"><strong aria-hidden="true">1.</strong> Meet your hardware</a></li><li><a href="../setup/index.html"><strong aria-hidden="true">2.</strong> Development environment setup</a></li><li><ol class="section"><li><a href="../setup/LINUX.html"><strong aria-hidden="true">2.1.</strong> Linux</a></li><li><a href="../setup/WINDOWS.html"><strong aria-hidden="true">2.2.</strong> Windows</a></li><li><a href="../setup/MACOS.html"><strong aria-hidden="true">2.3.</strong> macOS</a></li><li><a href="../setup/VERIFY.html"><strong aria-hidden="true">2.4.</strong> Verify the installation</a></li></ol></li><li><a href="../getting-started/00.00.README.html"><strong aria-hidden="true">3.</strong> Getting started</a></li><li><ol class="section"><li><a href="../getting-started/01.00.BUILD.html"><strong aria-hidden="true">3.1.</strong> Building</a></li><li><a href="../getting-started/02.00.FLASH.html"><strong aria-hidden="true">3.2.</strong> Flashing</a></li><li><a href="../getting-started/03.00.DEBUG.html"><strong aria-hidden="true">3.3.</strong> Debugging</a></li><li><a href="../getting-started/04.00.SOLUTION.html"><strong aria-hidden="true">3.4.</strong> Solution</a></li></ol></li><li><a href="../hello-world/00.00.README.html"><strong aria-hidden="true">4.</strong> Hello world</a></li><li><ol class="section"><li><a href="../hello-world/01.00.SEMIHOSTING.html"><strong aria-hidden="true">4.1.</strong> Semihosting</a></li><li><a href="../hello-world/02.00.UART.html"><strong aria-hidden="true">4.2.</strong> Serial communication</a></li><li><ol class="section"><li><a href="../hello-world/02.01.NIX.html"><strong aria-hidden="true">4.2.1.</strong> *nix</a></li><li><a href="../hello-world/02.02.WINDOWS.html"><strong aria-hidden="true">4.2.2.</strong> Windows</a></li></ol></li><li><a href="../hello-world/03.00.LED.html"><strong aria-hidden="true">4.3.</strong> GPIO and LEDs</a></li><li><ol class="section"><li><a href="../hello-world/03.01.SOLUTION.html"><strong aria-hidden="true">4.3.1.</strong> Solution</a></li></ol></li></ol></li><li><a href="../choice/00.00.README.html"><strong aria-hidden="true">5.</strong> Choose Your Own Adventure</a></li><li><a href="../microbit/00.00.README.html"><strong aria-hidden="true">6.</strong> micro:bit HAL basics</a></li><li><ol class="section"><li><a href="../microbit/01.00.BUTTONS.html"><strong aria-hidden="true">6.1.</strong> Buttons</a></li><li><a href="../microbit/02.00.DELAY.html"><strong aria-hidden="true">6.2.</strong> Delays</a></li><li><a href="../microbit/03.00.DISPLAY.html"><strong aria-hidden="true">6.3.</strong> Display</a></li></ol></li><li><a href="../serial/00.00.README.html"><strong aria-hidden="true">7.</strong> Serial UART - Blocking</a></li><li><ol class="section"><li><a href="../serial/01.00.ECHO.html"><strong aria-hidden="true">7.1.</strong> Echo Server</a></li><li><ol class="section"><li><a href="../serial/01.01.THEORY.html"><strong aria-hidden="true">7.1.1.</strong> Theory</a></li><li><a href="../serial/01.02.ECHO.html"><strong aria-hidden="true">7.1.2.</strong> Solution</a></li></ol></li><li><a href="../serial/02.00.html"><strong aria-hidden="true">7.2.</strong> Exercises</a></li><li><ol class="section"><li><a href="../serial/02.01.html"><strong aria-hidden="true">7.2.1.</strong> Reverse echo</a></li><li><ol class="section"><li><a href="../serial/02.01.SOLUTION.html"><strong aria-hidden="true">7.2.1.1.</strong> Solution</a></li></ol></li><li><a href="../serial/02.02.html"><strong aria-hidden="true">7.2.2.</strong> Countdown</a></li><li><ol class="section"><li><a href="../serial/02.02.SOLUTION.html"><strong aria-hidden="true">7.2.2.1.</strong> Solution</a></li></ol></li><li><a href="../serial/02.04.html"><strong aria-hidden="true">7.2.3.</strong> Quiz</a></li><li><ol class="section"><li><a href="../serial/02.04.SOLUTION.html"><strong aria-hidden="true">7.2.3.1.</strong> Solution</a></li></ol></li></ol></li></ol></li><li><a href="../display/00.00.README.html"><strong aria-hidden="true">8.</strong> LED display</a></li><li><ol class="section"><li><a href="../display/01.00.THEORY.html"><strong aria-hidden="true">8.1.</strong> Theory</a></li><li><a href="../display/02.00.PROBLEM.html"><strong aria-hidden="true">8.2.</strong> Problem</a></li><li><ol class="section"><li><a href="../display/02.01.LAYOUT.html"><strong aria-hidden="true">8.2.1.</strong> Layout</a></li><li><a href="../display/02.02.DELAY.html" class="active"><strong aria-hidden="true">8.2.2.</strong> Delays</a></li><li><a href="../display/02.03.MULT.html"><strong aria-hidden="true">8.2.3.</strong> Multiplexing</a></li></ol></li><li><a href="../display/03.00.SOLUTION.html"><strong aria-hidden="true">8.3.</strong> Solution</a></li><li><ol class="section"><li><a href="../display/03.01.LAYOUT.html"><strong aria-hidden="true">8.3.1.</strong> Layout</a></li><li><a href="../display/03.02.MULT.html"><strong aria-hidden="true">8.3.2.</strong> Multiplexing</a></li><li><a href="../display/03.03.FULL.html"><strong aria-hidden="true">8.3.3.</strong> Full Solution</a></li></ol></li></ol></li><li><a href="../sensors/00.00.README.html"><strong aria-hidden="true">9.</strong> WIP - 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<main>
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<a class="header" href="#delays" id="delays"><h2>Delays</h2></a>
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<blockquote>
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<p>Create a time delay.</p>
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</blockquote>
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<p>Another piece of information you will need is how to create a time delay before moving to the next row.
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we want the time spent switching LED lines on and off to be much shorter than the time spent waiting with LEDs on.</p>
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<a class="header" href="#for-loop" id="for-loop"><h3>For loop</h3></a>
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<p>A first attempt to implement the <code>delay</code> function
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without using any peripherals is to implement it as a <code>for</code> loop delay:</p>
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<pre><pre class="playpen"><code class="language-rust">
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# #![allow(unused_variables)]
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#fn main() {
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fn delay(ms: u16) {
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const K: u16 = 16_000; // 16MHz microprocessor, needs to be tweaked
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for _ in 0..(K*ms) {}
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}
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#}</code></pre></pre>
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<p>When compiled in release mode however, this is optimized away.
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To solve this we could explicitly add an operation inside the loop.
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The perfect candidate is the <a href="https://en.wikipedia.org/wiki/NOP">NOP</a>.</p>
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<pre><pre class="playpen"><code class="language-rust">
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# #![allow(unused_variables)]
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#fn main() {
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fn delay(ms: u16) {
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const K: u16 = 16_000; // 16MHz microprocessor, needs to be tweaked
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for _ in 0..(K*ms) {
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cortex_m::asm::nop();
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}
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}
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#}</code></pre></pre>
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<a class="header" href="#timers" id="timers"><h3>Timers</h3></a>
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<p>A better way of implementing delays is by using timers.
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A one-shot timer (also called one pulse mode) works like an alarm clock.
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You set it once with the amount of time you want, and then wait until it goes off.
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Fortuinately for us, HAL crates usually have already solved this for us.</p>
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<a class="header" href="#microbit" id="microbit"><h3>Microbit</h3></a>
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<p>The microbit has 3 timers, we will use the first: TIMER0.
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To use it, do the following:</p>
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<pre><pre class="playpen"><code class="language-rust">
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# #![allow(unused_variables)]
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#fn main() {
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if let Some(p) = microbit::Peripherals::take() {
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let mut delay = Delay::new(p.TIMER0);
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delay.delay_ms(1000_u32);
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}
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#}</code></pre></pre>
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