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261 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" class="active">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"><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 - Sensors and I²C</a></li><li><a href="../nb/00.00.README.html"><strong aria-hidden="true">10.</strong> WIP - Non-blocking</a></li><li><a href="../nb/00.00.README.html"><strong aria-hidden="true">11.</strong> WIP - Interrupts</a></li><li><a href="../rtfm/00.00.README.html"><strong aria-hidden="true">12.</strong> WIP - Real time</a></li><li><a href="../hal/00.00.README.html"><strong aria-hidden="true">13.</strong> WIP - Creating a HAL</a></li><li class="affix"><a href="../appendix/explore.html">Explore</a></li><li class="affix"><a href="../appendix/gdb.html">GDB cheatsheet</a></li><li class="affix"><a href="../appendix/troubleshooting.html">General troubleshooting</a></li></ol>
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<h1 class="menu-title">MicroRust</h1>
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<a class="header" href="#background" id="background"><h1>Background</h1></a>
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<a class="header" href="#what-is-a-microcontroller" id="what-is-a-microcontroller"><h2>What is a microcontroller?</h2></a>
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<p>A microcontroller is a <em>system</em> on a chip. Whereas your laptop is made up of several discrete
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components: a processor, RAM sticks, a hard drive, an ethernet port, etc.; a microcontroller has all
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those components built into a single "chip" or package. This makes it possible to build systems with
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minimal part count.</p>
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<a class="header" href="#what-can-you-do-with-a-microcontroller" id="what-can-you-do-with-a-microcontroller"><h2>What can you do with a microcontroller?</h2></a>
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<p>Lots of things! Microcontrollers are the central part of systems known as <em>embedded</em> systems. These
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systems are everywhere but you don't usually notice them. These systems control the brakes of your
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car, wash your clothes, print your documents, keep you warm, keep you cool, optimize the fuel
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consumption of your car, etc.</p>
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<p>The main trait of these systems is that they operate without user intervention even if they expose a
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user interface like a washing machine does; most of their operation is done on their own.</p>
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<p>The other common trait of these systems is that they <em>control</em> a process. And for that these systems
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usually have one or more sensors and one or more actuators. For example, an HVAC system has several
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sensors, thermometers and humidy sensors spread across some area, and several actuators as well,
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heating elements and fans connected to ducts.</p>
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<a class="header" href="#when-should-i-use-a-microcontroller" id="when-should-i-use-a-microcontroller"><h2>When should I use a microcontroller?</h2></a>
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<p>All these application I've mentioned, you can probably implement with a Raspberry Pi, a computer
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that runs Linux. Why should I bother with a microcontroller that operates without an OS? Sounds like
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it would be harder to develop a program.</p>
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<p>One main reason is cost. A microcontroller is much cheaper than a general purpose computer. Not only
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the microcontroller is cheaper; it also requires much less external electrical components to
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operate. This makes Printed Circuit Boards (PCB) smaller and cheaper to design and manufacture.</p>
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<p>Another big reason is power consumption. A microcontroller consumes orders of magnitude less power
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than a full blown processor. If your application will run on batteries that makes a huge difference.</p>
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<p>And last but not least: (hard) <em>real time</em> constraints. Some processes require their controllers to
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respond to some events within some time interval (e.g. a quadcopter/drone hit by a wind gust). If
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this <em>deadline</em> is not met, the process could end in catastrophic failure (e.g. the drone crashes to
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the ground). A general purpose computer running a general purpose OS has many services running in
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the background. This makes it hard to guarantee execution of a program within tight time constraints.</p>
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<a class="header" href="#when-should-i-not-use-a-microcontroller" id="when-should-i-not-use-a-microcontroller"><h2>When should I <em>not</em> use a microcontroller?</h2></a>
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<p>Where heavy computations are involved. To keep their power consumption low, microcontrollers have
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very limited computational resources available to them. For example, some microcontrollers don't
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even have hardware support for floating point operations. On those devices, performing a simple
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addition of single precision numbers can take hundreds of CPU cycles.</p>
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<a class="header" href="#development-on-the-microbit" id="development-on-the-microbit"><h2>Development on the micro:bit</h2></a>
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<p>The <a href="https://microbit.org/code/">micro:bit website</a> offers several very simple ways of programming a
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microbit, aimed at teaching school children how to program. This is a very good introduction to the
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world of microcontollers <strong>and</strong> programming, but falls short of teaching true embedded development.
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From there you would usually move to C to develop skills useful in industry, developing performant
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embedded software.</p>
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<a class="header" href="#why-use-rust-and-not-c" id="why-use-rust-and-not-c"><h2>Why use Rust and not C?</h2></a>
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<p>Hopefully I don't need to convince you here as you are probably familiar with the language
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differences between Rust and C. One point I do want to bring up is package management. C lacks an
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official, widely accepted package management solution whereas Rust has Cargo. This makes development
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<em>much</em> easier. And, IMO, easy package management encourages code reuse because libraries can be
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easily integrated into an application which is also a good thing as libraries get more "battle
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testing".</p>
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<a class="header" href="#why-should-i-not-use-rust" id="why-should-i-not-use-rust"><h2>Why should I not use Rust?</h2></a>
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<p>Or why should I prefer C over Rust?</p>
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<p>The C ecosystem is way more mature. Off the shelf solution for several problems already exist. If
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you need to control a time sensitive process, you can grab one of the existing commercial Real Time
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Operating Systems (RTOS) out there and solve your problem. There are no commercial, production-grade
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RTOSes in Rust yet so you would have to either create one yourself or try one of the ones that are
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in development. If you are looking to develop your skills to find a job, it is currently unlikely
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that a company doing embedded software development will be using Rust, and so your time would be
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better spent learning normal embedded development using C.</p>
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