| <!DOCTYPE HTML> |
| <html lang="en" class="light sidebar-visible" dir="ltr"> |
| <head> |
| <!-- Book generated using mdBook --> |
| <meta charset="UTF-8"> |
| <title>Memory-mapped Registers - The Embedded Rust Book</title> |
| |
| |
| <!-- Custom HTML head --> |
| |
| <meta name="description" content=""> |
| <meta name="viewport" content="width=device-width, initial-scale=1"> |
| <meta name="theme-color" content="#ffffff"> |
| |
| <link rel="icon" href="../favicon-de23e50b.svg"> |
| <link rel="shortcut icon" href="../favicon-8114d1fc.png"> |
| <link rel="stylesheet" href="../css/variables-8adf115d.css"> |
| <link rel="stylesheet" href="../css/general-2459343d.css"> |
| <link rel="stylesheet" href="../css/chrome-ae938929.css"> |
| <link rel="stylesheet" href="../css/print-9e4910d8.css" media="print"> |
| |
| <!-- Fonts --> |
| <link rel="stylesheet" href="../fonts/fonts-9644e21d.css"> |
| |
| <!-- Highlight.js Stylesheets --> |
| <link rel="stylesheet" id="mdbook-highlight-css" href="../highlight-493f70e1.css"> |
| <link rel="stylesheet" id="mdbook-tomorrow-night-css" href="../tomorrow-night-4c0ae647.css"> |
| <link rel="stylesheet" id="mdbook-ayu-highlight-css" href="../ayu-highlight-3fdfc3ac.css"> |
| |
| <!-- Custom theme stylesheets --> |
| |
| |
| <!-- Provide site root and default themes to javascript --> |
| <script> |
| const path_to_root = "../"; |
| const default_light_theme = "light"; |
| const default_dark_theme = "navy"; |
| window.path_to_searchindex_js = "../searchindex-3d6e7a93.js"; |
| </script> |
| <!-- Start loading toc.js asap --> |
| <script src="../toc-f89f70b8.js"></script> |
| </head> |
| <body> |
| <div id="mdbook-help-container"> |
| <div id="mdbook-help-popup"> |
| <h2 class="mdbook-help-title">Keyboard shortcuts</h2> |
| <div> |
| <p>Press <kbd>←</kbd> or <kbd>→</kbd> to navigate between chapters</p> |
| <p>Press <kbd>S</kbd> or <kbd>/</kbd> to search in the book</p> |
| <p>Press <kbd>?</kbd> to show this help</p> |
| <p>Press <kbd>Esc</kbd> to hide this help</p> |
| </div> |
| </div> |
| </div> |
| <div id="mdbook-body-container"> |
| <!-- Work around some values being stored in localStorage wrapped in quotes --> |
| <script> |
| try { |
| let theme = localStorage.getItem('mdbook-theme'); |
| let sidebar = localStorage.getItem('mdbook-sidebar'); |
| |
| if (theme.startsWith('"') && theme.endsWith('"')) { |
| localStorage.setItem('mdbook-theme', theme.slice(1, theme.length - 1)); |
| } |
| |
| if (sidebar.startsWith('"') && sidebar.endsWith('"')) { |
| localStorage.setItem('mdbook-sidebar', sidebar.slice(1, sidebar.length - 1)); |
| } |
| } catch (e) { } |
| </script> |
| |
| <!-- Set the theme before any content is loaded, prevents flash --> |
| <script> |
| const default_theme = window.matchMedia("(prefers-color-scheme: dark)").matches ? default_dark_theme : default_light_theme; |
| let theme; |
| try { theme = localStorage.getItem('mdbook-theme'); } catch(e) { } |
| if (theme === null || theme === undefined) { theme = default_theme; } |
| const html = document.documentElement; |
| html.classList.remove('light') |
| html.classList.add(theme); |
| html.classList.add("js"); |
| </script> |
| |
| <input type="checkbox" id="mdbook-sidebar-toggle-anchor" class="hidden"> |
| |
| <!-- Hide / unhide sidebar before it is displayed --> |
| <script> |
| let sidebar = null; |
| const sidebar_toggle = document.getElementById("mdbook-sidebar-toggle-anchor"); |
| if (document.body.clientWidth >= 1080) { |
| try { sidebar = localStorage.getItem('mdbook-sidebar'); } catch(e) { } |
| sidebar = sidebar || 'visible'; |
| } else { |
| sidebar = 'hidden'; |
| sidebar_toggle.checked = false; |
| } |
| if (sidebar === 'visible') { |
| sidebar_toggle.checked = true; |
| } else { |
| html.classList.remove('sidebar-visible'); |
| } |
| </script> |
| |
| <nav id="mdbook-sidebar" class="sidebar" aria-label="Table of contents"> |
| <!-- populated by js --> |
| <mdbook-sidebar-scrollbox class="sidebar-scrollbox"></mdbook-sidebar-scrollbox> |
| <noscript> |
| <iframe class="sidebar-iframe-outer" src="../toc.html"></iframe> |
| </noscript> |
| <div id="mdbook-sidebar-resize-handle" class="sidebar-resize-handle"> |
| <div class="sidebar-resize-indicator"></div> |
| </div> |
| </nav> |
| |
| <div id="mdbook-page-wrapper" class="page-wrapper"> |
| |
| <div class="page"> |
| <div id="mdbook-menu-bar-hover-placeholder"></div> |
| <div id="mdbook-menu-bar" class="menu-bar sticky"> |
| <div class="left-buttons"> |
| <label id="mdbook-sidebar-toggle" class="icon-button" for="mdbook-sidebar-toggle-anchor" title="Toggle Table of Contents" aria-label="Toggle Table of Contents" aria-controls="mdbook-sidebar"> |
| <span class=fa-svg><svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 448 512"><!--! Font Awesome Free 6.2.0 by @fontawesome - https://fontawesome.com License - https://fontawesome.com/license/free (Icons: CC BY 4.0, Fonts: SIL OFL 1.1, Code: MIT License) Copyright 2022 Fonticons, Inc. --><path d="M0 96C0 78.3 14.3 64 32 64H416c17.7 0 32 14.3 32 32s-14.3 32-32 32H32C14.3 128 0 113.7 0 96zM0 256c0-17.7 14.3-32 32-32H416c17.7 0 32 14.3 32 32s-14.3 32-32 32H32c-17.7 0-32-14.3-32-32zM448 416c0 17.7-14.3 32-32 32H32c-17.7 0-32-14.3-32-32s14.3-32 32-32H416c17.7 0 32 14.3 32 32z"/></svg></span> |
| </label> |
| <button id="mdbook-theme-toggle" class="icon-button" type="button" title="Change theme" aria-label="Change theme" aria-haspopup="true" aria-expanded="false" aria-controls="mdbook-theme-list"> |
| <span class=fa-svg><svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 576 512"><!--! Font Awesome Free 6.2.0 by @fontawesome - https://fontawesome.com License - https://fontawesome.com/license/free (Icons: CC BY 4.0, Fonts: SIL OFL 1.1, Code: MIT License) Copyright 2022 Fonticons, Inc. --><path d="M371.3 367.1c27.3-3.9 51.9-19.4 67.2-42.9L600.2 74.1c12.6-19.5 9.4-45.3-7.6-61.2S549.7-4.4 531.1 9.6L294.4 187.2c-24 18-38.2 46.1-38.4 76.1L371.3 367.1zm-19.6 25.4l-116-104.4C175.9 290.3 128 339.6 128 400c0 3.9 .2 7.8 .6 11.6c1.8 17.5-10.2 36.4-27.8 36.4H96c-17.7 0-32 14.3-32 32s14.3 32 32 32H240c61.9 0 112-50.1 112-112c0-2.5-.1-5-.2-7.5z"/></svg></span> |
| </button> |
| <ul id="mdbook-theme-list" class="theme-popup" aria-label="Themes" role="menu"> |
| <li role="none"><button role="menuitem" class="theme" id="mdbook-theme-default_theme">Auto</button></li> |
| <li role="none"><button role="menuitem" class="theme" id="mdbook-theme-light">Light</button></li> |
| <li role="none"><button role="menuitem" class="theme" id="mdbook-theme-rust">Rust</button></li> |
| <li role="none"><button role="menuitem" class="theme" id="mdbook-theme-coal">Coal</button></li> |
| <li role="none"><button role="menuitem" class="theme" id="mdbook-theme-navy">Navy</button></li> |
| <li role="none"><button role="menuitem" class="theme" id="mdbook-theme-ayu">Ayu</button></li> |
| </ul> |
| <button id="mdbook-search-toggle" class="icon-button" type="button" title="Search (`/`)" aria-label="Toggle Searchbar" aria-expanded="false" aria-keyshortcuts="/ s" aria-controls="mdbook-searchbar"> |
| <span class=fa-svg><svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 512 512"><!--! Font Awesome Free 6.2.0 by @fontawesome - https://fontawesome.com License - https://fontawesome.com/license/free (Icons: CC BY 4.0, Fonts: SIL OFL 1.1, Code: MIT License) Copyright 2022 Fonticons, Inc. --><path d="M416 208c0 45.9-14.9 88.3-40 122.7L502.6 457.4c12.5 12.5 12.5 32.8 0 45.3s-32.8 12.5-45.3 0L330.7 376c-34.4 25.2-76.8 40-122.7 40C93.1 416 0 322.9 0 208S93.1 0 208 0S416 93.1 416 208zM208 352c79.5 0 144-64.5 144-144s-64.5-144-144-144S64 128.5 64 208s64.5 144 144 144z"/></svg></span> |
| </button> |
| </div> |
| |
| <h1 class="menu-title">The Embedded Rust Book</h1> |
| |
| <div class="right-buttons"> |
| <a href="../print.html" title="Print this book" aria-label="Print this book"> |
| <span class=fa-svg id="print-button"><svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 512 512"><!--! Font Awesome Free 6.2.0 by @fontawesome - https://fontawesome.com License - https://fontawesome.com/license/free (Icons: CC BY 4.0, Fonts: SIL OFL 1.1, Code: MIT License) Copyright 2022 Fonticons, Inc. --><path d="M128 0C92.7 0 64 28.7 64 64v96h64V64H354.7L384 93.3V160h64V93.3c0-17-6.7-33.3-18.7-45.3L400 18.7C388 6.7 371.7 0 354.7 0H128zM384 352v32 64H128V384 368 352H384zm64 32h32c17.7 0 32-14.3 32-32V256c0-35.3-28.7-64-64-64H64c-35.3 0-64 28.7-64 64v96c0 17.7 14.3 32 32 32H64v64c0 35.3 28.7 64 64 64H384c35.3 0 64-28.7 64-64V384zm-16-88c-13.3 0-24-10.7-24-24s10.7-24 24-24s24 10.7 24 24s-10.7 24-24 24z"/></svg></span> |
| </a> |
| <a href="https://github.com/rust-embedded/book" title="Git repository" aria-label="Git repository"> |
| <span class=fa-svg><svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 496 512"><!--! Font Awesome Free 6.2.0 by @fontawesome - https://fontawesome.com License - https://fontawesome.com/license/free (Icons: CC BY 4.0, Fonts: SIL OFL 1.1, Code: MIT License) Copyright 2022 Fonticons, Inc. --><path d="M165.9 397.4c0 2-2.3 3.6-5.2 3.6-3.3.3-5.6-1.3-5.6-3.6 0-2 2.3-3.6 5.2-3.6 3-.3 5.6 1.3 5.6 3.6zm-31.1-4.5c-.7 2 1.3 4.3 4.3 4.9 2.6 1 5.6 0 6.2-2s-1.3-4.3-4.3-5.2c-2.6-.7-5.5.3-6.2 2.3zm44.2-1.7c-2.9.7-4.9 2.6-4.6 4.9.3 2 2.9 3.3 5.9 2.6 2.9-.7 4.9-2.6 4.6-4.6-.3-1.9-3-3.2-5.9-2.9zM244.8 8C106.1 8 0 113.3 0 252c0 110.9 69.8 205.8 169.5 239.2 12.8 2.3 17.3-5.6 17.3-12.1 0-6.2-.3-40.4-.3-61.4 0 0-70 15-84.7-29.8 0 0-11.4-29.1-27.8-36.6 0 0-22.9-15.7 1.6-15.4 0 0 24.9 2 38.6 25.8 21.9 38.6 58.6 27.5 72.9 20.9 2.3-16 8.8-27.1 16-33.7-55.9-6.2-112.3-14.3-112.3-110.5 0-27.5 7.6-41.3 23.6-58.9-2.6-6.5-11.1-33.3 2.6-67.9 20.9-6.5 69 27 69 27 20-5.6 41.5-8.5 62.8-8.5s42.8 2.9 62.8 8.5c0 0 48.1-33.6 69-27 13.7 34.7 5.2 61.4 2.6 67.9 16 17.7 25.8 31.5 25.8 58.9 0 96.5-58.9 104.2-114.8 110.5 9.2 7.9 17 22.9 17 46.4 0 33.7-.3 75.4-.3 83.6 0 6.5 4.6 14.4 17.3 12.1C428.2 457.8 496 362.9 496 252 496 113.3 383.5 8 244.8 8zM97.2 352.9c-1.3 1-1 3.3.7 5.2 1.6 1.6 3.9 2.3 5.2 1 1.3-1 1-3.3-.7-5.2-1.6-1.6-3.9-2.3-5.2-1zm-10.8-8.1c-.7 1.3.3 2.9 2.3 3.9 1.6 1 3.6.7 4.3-.7.7-1.3-.3-2.9-2.3-3.9-2-.6-3.6-.3-4.3.7zm32.4 35.6c-1.6 1.3-1 4.3 1.3 6.2 2.3 2.3 5.2 2.6 6.5 1 1.3-1.3.7-4.3-1.3-6.2-2.2-2.3-5.2-2.6-6.5-1zm-11.4-14.7c-1.6 1-1.6 3.6 0 5.9 1.6 2.3 4.3 3.3 5.6 2.3 1.6-1.3 1.6-3.9 0-6.2-1.4-2.3-4-3.3-5.6-2z"/></svg></span> |
| </a> |
| |
| </div> |
| </div> |
| |
| <div id="mdbook-search-wrapper" class="hidden"> |
| <form id="mdbook-searchbar-outer" class="searchbar-outer"> |
| <div class="search-wrapper"> |
| <input type="search" id="mdbook-searchbar" name="searchbar" placeholder="Search this book ..." aria-controls="mdbook-searchresults-outer" aria-describedby="searchresults-header"> |
| <div class="spinner-wrapper"> |
| <span class=fa-svg id="fa-spin"><svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 512 512"><!--! Font Awesome Free 6.2.0 by @fontawesome - https://fontawesome.com License - https://fontawesome.com/license/free (Icons: CC BY 4.0, Fonts: SIL OFL 1.1, Code: MIT License) Copyright 2022 Fonticons, Inc. --><path d="M304 48c0-26.5-21.5-48-48-48s-48 21.5-48 48s21.5 48 48 48s48-21.5 48-48zm0 416c0-26.5-21.5-48-48-48s-48 21.5-48 48s21.5 48 48 48s48-21.5 48-48zM48 304c26.5 0 48-21.5 48-48s-21.5-48-48-48s-48 21.5-48 48s21.5 48 48 48zm464-48c0-26.5-21.5-48-48-48s-48 21.5-48 48s21.5 48 48 48s48-21.5 48-48zM142.9 437c18.7-18.7 18.7-49.1 0-67.9s-49.1-18.7-67.9 0s-18.7 49.1 0 67.9s49.1 18.7 67.9 0zm0-294.2c18.7-18.7 18.7-49.1 0-67.9S93.7 56.2 75 75s-18.7 49.1 0 67.9s49.1 18.7 67.9 0zM369.1 437c18.7 18.7 49.1 18.7 67.9 0s18.7-49.1 0-67.9s-49.1-18.7-67.9 0s-18.7 49.1 0 67.9z"/></svg></span> |
| </div> |
| </div> |
| </form> |
| <div id="mdbook-searchresults-outer" class="searchresults-outer hidden"> |
| <div id="mdbook-searchresults-header" class="searchresults-header"></div> |
| <ul id="mdbook-searchresults"> |
| </ul> |
| </div> |
| </div> |
| |
| <!-- Apply ARIA attributes after the sidebar and the sidebar toggle button are added to the DOM --> |
| <script> |
| document.getElementById('mdbook-sidebar-toggle').setAttribute('aria-expanded', sidebar === 'visible'); |
| document.getElementById('mdbook-sidebar').setAttribute('aria-hidden', sidebar !== 'visible'); |
| Array.from(document.querySelectorAll('#mdbook-sidebar a')).forEach(function(link) { |
| link.setAttribute('tabIndex', sidebar === 'visible' ? 0 : -1); |
| }); |
| </script> |
| |
| <div id="mdbook-content" class="content"> |
| <main> |
| <h1 id="memory-mapped-registers"><a class="header" href="#memory-mapped-registers">Memory Mapped Registers</a></h1> |
| <p>Embedded systems can only get so far by executing normal Rust code and moving data around in RAM. If we want to get any information into or out of our system (be that blinking an LED, detecting a button press or communicating with an off-chip peripheral on some sort of bus) we’re going to have to dip into the world of Peripherals and their ‘memory mapped registers’.</p> |
| <p>You may well find that the code you need to access the peripherals in your micro-controller has already been written, at one of the following levels:</p> |
| <p align="center"> |
| <img title="Common crates" src="../assets/crates.png"> |
| </p> |
| |
| <ul> |
| <li>Micro-architecture Crate - This sort of crate handles any useful routines common to the processor core your microcontroller is using, as well as any peripherals that are common to all micro-controllers that use that particular type of processor core. For example the <a href="https://crates.io/crates/cortex-m">cortex-m</a> crate gives you functions to enable and disable interrupts, which are the same for all Cortex-M based micro-controllers. It also gives you access to the ‘SysTick’ peripheral included with all Cortex-M based micro-controllers.</li> |
| <li>Peripheral Access Crate (PAC) - This sort of crate is a thin wrapper over the various memory-wrapper registers defined for your particular part-number of micro-controller you are using. For example, <a href="https://crates.io/crates/tm4c123x">tm4c123x</a> for the Texas Instruments Tiva-C TM4C123 series, or <a href="https://crates.io/crates/stm32f30x">stm32f30x</a> for the ST-Micro STM32F30x series. Here, you’ll be interacting with the registers directly, following each peripheral’s operating instructions given in your micro-controller’s Technical Reference Manual.</li> |
| <li>HAL Crate - These crates offer a more user-friendly API for your particular processor, often by implementing some common traits defined in <a href="https://crates.io/crates/embedded-hal">embedded-hal</a>. For example, this crate might offer a <code>Serial</code> struct, with a constructor that takes an appropriate set of GPIO pins and a baud rate, and offers some sort of <code>write_byte</code> function for sending data. See the chapter on <a href="../portability/index.html">Portability</a> for more information on <a href="https://crates.io/crates/embedded-hal">embedded-hal</a>.</li> |
| <li>Board Crate - These crates go one step further than a HAL Crate by pre-configuring various peripherals and GPIO pins to suit the specific developer kit or board you are using, such as <a href="https://crates.io/crates/stm32f3-discovery">stm32f3-discovery</a> for the STM32F3DISCOVERY board.</li> |
| </ul> |
| <h2 id="board-crate"><a class="header" href="#board-crate">Board Crate</a></h2> |
| <p>A board crate is the perfect starting point, if you’re new to embedded Rust. They nicely abstract the HW details that might be overwhelming when starting studying this subject, and makes standard tasks easy, like turning a LED on or off. The functionality it exposes varies a lot between boards. Since this book aims at staying hardware agnostic, the board crates won’t be covered by this book.</p> |
| <p>If you want to experiment with the STM32F3DISCOVERY board, it is highly recommended to take a look at the <a href="https://crates.io/crates/stm32f3-discovery">stm32f3-discovery</a> board crate, which provides functionality to blink the board LEDs, access its compass, bluetooth and more. The <a href="https://rust-embedded.github.io/discovery/">Discovery</a> book offers a great introduction to the use of a board crate.</p> |
| <p>But if you’re working on a system that doesn’t yet have dedicated board crate, or you need functionality not provided by existing crates, read on as we start from the bottom, with the micro-architecture crates.</p> |
| <h2 id="micro-architecture-crate"><a class="header" href="#micro-architecture-crate">Micro-architecture crate</a></h2> |
| <p>Let’s look at the SysTick peripheral that’s common to all Cortex-M based micro-controllers. We can find a pretty low-level API in the <a href="https://crates.io/crates/cortex-m">cortex-m</a> crate, and we can use it like this:</p> |
| <pre><code class="language-rust ignore">#![no_std] |
| #![no_main] |
| use cortex_m::peripheral::{syst, Peripherals}; |
| use cortex_m_rt::entry; |
| use panic_halt as _; |
| |
| #[entry] |
| fn main() -> ! { |
| let peripherals = Peripherals::take().unwrap(); |
| let mut systick = peripherals.SYST; |
| systick.set_clock_source(syst::SystClkSource::Core); |
| systick.set_reload(1_000); |
| systick.clear_current(); |
| systick.enable_counter(); |
| while !systick.has_wrapped() { |
| // Loop |
| } |
| |
| loop {} |
| }</code></pre> |
| <p>The functions on the <code>SYST</code> struct map pretty closely to the functionality defined by the ARM Technical Reference Manual for this peripheral. There’s nothing in this API about ‘delaying for X milliseconds’ - we have to crudely implement that ourselves using a <code>while</code> loop. Note that we can’t access our <code>SYST</code> struct until we have called <code>Peripherals::take()</code> - this is a special routine that guarantees that there is only one <code>SYST</code> structure in our entire program. For more on that, see the <a href="../peripherals/index.html">Peripherals</a> section.</p> |
| <h2 id="using-a-peripheral-access-crate-pac"><a class="header" href="#using-a-peripheral-access-crate-pac">Using a Peripheral Access Crate (PAC)</a></h2> |
| <p>We won’t get very far with our embedded software development if we restrict ourselves to only the basic peripherals included with every Cortex-M. At some point, we’re going to need to write some code that’s specific to the particular micro-controller we’re using. In this example, let’s assume we have an Texas Instruments TM4C123 - a middling 80MHz Cortex-M4 with 256 KiB of Flash. We’re going to pull in the <a href="https://crates.io/crates/tm4c123x">tm4c123x</a> crate to make use of this chip.</p> |
| <pre><code class="language-rust ignore">#![no_std] |
| #![no_main] |
| |
| use panic_halt as _; // panic handler |
| |
| use cortex_m_rt::entry; |
| use tm4c123x; |
| |
| #[entry] |
| pub fn init() -> (Delay, Leds) { |
| let cp = cortex_m::Peripherals::take().unwrap(); |
| let p = tm4c123x::Peripherals::take().unwrap(); |
| |
| let pwm = p.PWM0; |
| pwm.ctl.write(|w| w.globalsync0().clear_bit()); |
| // Mode = 1 => Count up/down mode |
| pwm._2_ctl.write(|w| w.enable().set_bit().mode().set_bit()); |
| pwm._2_gena.write(|w| w.actcmpau().zero().actcmpad().one()); |
| // 528 cycles (264 up and down) = 4 loops per video line (2112 cycles) |
| pwm._2_load.write(|w| unsafe { w.load().bits(263) }); |
| pwm._2_cmpa.write(|w| unsafe { w.compa().bits(64) }); |
| pwm.enable.write(|w| w.pwm4en().set_bit()); |
| } |
| </code></pre> |
| <p>We’ve accessed the <code>PWM0</code> peripheral in exactly the same way as we accessed the <code>SYST</code> peripheral earlier, except we called <code>tm4c123x::Peripherals::take()</code>. As this crate was auto-generated using <a href="https://crates.io/crates/svd2rust">svd2rust</a>, the access functions for our register fields take a closure, rather than a numeric argument. While this looks like a lot of code, the Rust compiler can use it to perform a bunch of checks for us, but then generate machine-code which is pretty close to hand-written assembler! Where the auto-generated code isn’t able to determine that all possible arguments to a particular accessor function are valid (for example, if the SVD defines the register as 32-bit but doesn’t say if some of those 32-bit values have a special meaning), then the function is marked as <code>unsafe</code>. We can see this in the example above when setting the <code>load</code> and <code>compa</code> sub-fields using the <code>bits()</code> function.</p> |
| <h3 id="reading"><a class="header" href="#reading">Reading</a></h3> |
| <p>The <code>read()</code> function returns an object which gives read-only access to the various sub-fields within this register, as defined by the manufacturer’s SVD file for this chip. You can find all the functions available on special <code>R</code> return type for this particular register, in this particular peripheral, on this particular chip, in the <a href="https://docs.rs/tm4c123x/0.7.0/tm4c123x/pwm0/ctl/struct.R.html">tm4c123x documentation</a>.</p> |
| <pre><code class="language-rust ignore">if pwm.ctl.read().globalsync0().is_set() { |
| // Do a thing |
| }</code></pre> |
| <h3 id="writing"><a class="header" href="#writing">Writing</a></h3> |
| <p>The <code>write()</code> function takes a closure with a single argument. Typically we call this <code>w</code>. This argument then gives read-write access to the various sub-fields within this register, as defined by the manufacturer’s SVD file for this chip. Again, you can find all the functions available on the ‘w’ for this particular register, in this particular peripheral, on this particular chip, in the <a href="https://docs.rs/tm4c123x/0.7.0/tm4c123x/pwm0/ctl/struct.W.html">tm4c123x documentation</a>. Note that all of the sub-fields that we do not set will be set to a default value for us - any existing content in the register will be lost.</p> |
| <pre><code class="language-rust ignore">pwm.ctl.write(|w| w.globalsync0().clear_bit());</code></pre> |
| <h3 id="modifying"><a class="header" href="#modifying">Modifying</a></h3> |
| <p>If we wish to change only one particular sub-field in this register and leave the other sub-fields unchanged, we can use the <code>modify</code> function. This function takes a closure with two arguments - one for reading and one for writing. Typically we call these <code>r</code> and <code>w</code> respectively. The <code>r</code> argument can be used to inspect the current contents of the register, and the <code>w</code> argument can be used to modify the register contents.</p> |
| <pre><code class="language-rust ignore">pwm.ctl.modify(|r, w| w.globalsync0().clear_bit());</code></pre> |
| <p>The <code>modify</code> function really shows the power of closures here. In C, we’d have to read into some temporary value, modify the correct bits and then write the value back. This means there’s considerable scope for error:</p> |
| <pre><code class="language-C">uint32_t temp = pwm0.ctl.read(); |
| temp |= PWM0_CTL_GLOBALSYNC0; |
| pwm0.ctl.write(temp); |
| uint32_t temp2 = pwm0.enable.read(); |
| temp2 |= PWM0_ENABLE_PWM4EN; |
| pwm0.enable.write(temp); // Uh oh! Wrong variable! |
| </code></pre> |
| <h2 id="using-a-hal-crate"><a class="header" href="#using-a-hal-crate">Using a HAL crate</a></h2> |
| <p>The HAL crate for a chip typically works by implementing a custom Trait for the raw structures exposed by the PAC. Often this trait will define a function called <code>constrain()</code> for single peripherals or <code>split()</code> for things like GPIO ports with multiple pins. This function will consume the underlying raw peripheral structure and return a new object with a higher-level API. This API may also do things like have the Serial port <code>new</code> function require a borrow on some <code>Clock</code> structure, which can only be generated by calling the function which configures the PLLs and sets up all the clock frequencies. In this way, it is statically impossible to create a Serial port object without first having configured the clock rates, or for the Serial port object to misconvert the baud rate into clock ticks. Some crates even define special traits for the states each GPIO pin can be in, requiring the user to put a pin into the correct state (say, by selecting the appropriate Alternate Function Mode) before passing the pin into Peripheral. All with no run-time cost!</p> |
| <p>Let’s see an example:</p> |
| <pre><code class="language-rust ignore">#![no_std] |
| #![no_main] |
| |
| use panic_halt as _; // panic handler |
| |
| use cortex_m_rt::entry; |
| use tm4c123x_hal as hal; |
| use tm4c123x_hal::prelude::*; |
| use tm4c123x_hal::serial::{NewlineMode, Serial}; |
| use tm4c123x_hal::sysctl; |
| |
| #[entry] |
| fn main() -> ! { |
| let p = hal::Peripherals::take().unwrap(); |
| let cp = hal::CorePeripherals::take().unwrap(); |
| |
| // Wrap up the SYSCTL struct into an object with a higher-layer API |
| let mut sc = p.SYSCTL.constrain(); |
| // Pick our oscillation settings |
| sc.clock_setup.oscillator = sysctl::Oscillator::Main( |
| sysctl::CrystalFrequency::_16mhz, |
| sysctl::SystemClock::UsePll(sysctl::PllOutputFrequency::_80_00mhz), |
| ); |
| // Configure the PLL with those settings |
| let clocks = sc.clock_setup.freeze(); |
| |
| // Wrap up the GPIO_PORTA struct into an object with a higher-layer API. |
| // Note it needs to borrow `sc.power_control` so it can power up the GPIO |
| // peripheral automatically. |
| let mut porta = p.GPIO_PORTA.split(&sc.power_control); |
| |
| // Activate the UART. |
| let uart = Serial::uart0( |
| p.UART0, |
| // The transmit pin |
| porta |
| .pa1 |
| .into_af_push_pull::<hal::gpio::AF1>(&mut porta.control), |
| // The receive pin |
| porta |
| .pa0 |
| .into_af_push_pull::<hal::gpio::AF1>(&mut porta.control), |
| // No RTS or CTS required |
| (), |
| (), |
| // The baud rate |
| 115200_u32.bps(), |
| // Output handling |
| NewlineMode::SwapLFtoCRLF, |
| // We need the clock rates to calculate the baud rate divisors |
| &clocks, |
| // We need this to power up the UART peripheral |
| &sc.power_control, |
| ); |
| |
| loop { |
| writeln!(uart, "Hello, World!\r\n").unwrap(); |
| } |
| }</code></pre> |
| |
| </main> |
| |
| <nav class="nav-wrapper" aria-label="Page navigation"> |
| <!-- Mobile navigation buttons --> |
| <a rel="prev" href="../start/hardware.html" class="mobile-nav-chapters previous" title="Previous chapter" aria-label="Previous chapter" aria-keyshortcuts="Left"> |
| <span class=fa-svg><svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 320 512"><!--! Font Awesome Free 6.2.0 by @fontawesome - https://fontawesome.com License - https://fontawesome.com/license/free (Icons: CC BY 4.0, Fonts: SIL OFL 1.1, Code: MIT License) Copyright 2022 Fonticons, Inc. --><path d="M41.4 233.4c-12.5 12.5-12.5 32.8 0 45.3l160 160c12.5 12.5 32.8 12.5 45.3 0s12.5-32.8 0-45.3L109.3 256 246.6 118.6c12.5-12.5 12.5-32.8 0-45.3s-32.8-12.5-45.3 0l-160 160z"/></svg></span> |
| </a> |
| |
| <a rel="next prefetch" href="../start/semihosting.html" class="mobile-nav-chapters next" title="Next chapter" aria-label="Next chapter" aria-keyshortcuts="Right"> |
| <span class=fa-svg><svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 320 512"><!--! Font Awesome Free 6.2.0 by @fontawesome - https://fontawesome.com License - https://fontawesome.com/license/free (Icons: CC BY 4.0, Fonts: SIL OFL 1.1, Code: MIT License) Copyright 2022 Fonticons, Inc. --><path d="M278.6 233.4c12.5 12.5 12.5 32.8 0 45.3l-160 160c-12.5 12.5-32.8 12.5-45.3 0s-12.5-32.8 0-45.3L210.7 256 73.4 118.6c-12.5-12.5-12.5-32.8 0-45.3s32.8-12.5 45.3 0l160 160z"/></svg></span> |
| </a> |
| |
| <div style="clear: both"></div> |
| </nav> |
| </div> |
| </div> |
| |
| <nav class="nav-wide-wrapper" aria-label="Page navigation"> |
| <a rel="prev" href="../start/hardware.html" class="nav-chapters previous" title="Previous chapter" aria-label="Previous chapter" aria-keyshortcuts="Left"> |
| <span class=fa-svg><svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 320 512"><!--! Font Awesome Free 6.2.0 by @fontawesome - https://fontawesome.com License - https://fontawesome.com/license/free (Icons: CC BY 4.0, Fonts: SIL OFL 1.1, Code: MIT License) Copyright 2022 Fonticons, Inc. --><path d="M41.4 233.4c-12.5 12.5-12.5 32.8 0 45.3l160 160c12.5 12.5 32.8 12.5 45.3 0s12.5-32.8 0-45.3L109.3 256 246.6 118.6c12.5-12.5 12.5-32.8 0-45.3s-32.8-12.5-45.3 0l-160 160z"/></svg></span> |
| </a> |
| |
| <a rel="next prefetch" href="../start/semihosting.html" class="nav-chapters next" title="Next chapter" aria-label="Next chapter" aria-keyshortcuts="Right"> |
| <span class=fa-svg><svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 320 512"><!--! Font Awesome Free 6.2.0 by @fontawesome - https://fontawesome.com License - https://fontawesome.com/license/free (Icons: CC BY 4.0, Fonts: SIL OFL 1.1, Code: MIT License) Copyright 2022 Fonticons, Inc. --><path d="M278.6 233.4c12.5 12.5 12.5 32.8 0 45.3l-160 160c-12.5 12.5-32.8 12.5-45.3 0s-12.5-32.8 0-45.3L210.7 256 73.4 118.6c-12.5-12.5-12.5-32.8 0-45.3s32.8-12.5 45.3 0l160 160z"/></svg></span> |
| </a> |
| </nav> |
| |
| </div> |
| |
| <template id=fa-eye><span class=fa-svg><svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 576 512"><!--! Font Awesome Free 6.2.0 by @fontawesome - https://fontawesome.com License - https://fontawesome.com/license/free (Icons: CC BY 4.0, Fonts: SIL OFL 1.1, Code: MIT License) Copyright 2022 Fonticons, Inc. --><path d="M288 32c-80.8 0-145.5 36.8-192.6 80.6C48.6 156 17.3 208 2.5 243.7c-3.3 7.9-3.3 16.7 0 24.6C17.3 304 48.6 356 95.4 399.4C142.5 443.2 207.2 480 288 480s145.5-36.8 192.6-80.6c46.8-43.5 78.1-95.4 93-131.1c3.3-7.9 3.3-16.7 0-24.6c-14.9-35.7-46.2-87.7-93-131.1C433.5 68.8 368.8 32 288 32zM432 256c0 79.5-64.5 144-144 144s-144-64.5-144-144s64.5-144 144-144s144 64.5 144 144zM288 192c0 35.3-28.7 64-64 64c-11.5 0-22.3-3-31.6-8.4c-.2 2.8-.4 5.5-.4 8.4c0 53 43 96 96 96s96-43 96-96s-43-96-96-96c-2.8 0-5.6 .1-8.4 .4c5.3 9.3 8.4 20.1 8.4 31.6z"/></svg></span></template> |
| <template id=fa-eye-slash><span class=fa-svg><svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 640 512"><!--! Font Awesome Free 6.2.0 by @fontawesome - https://fontawesome.com License - https://fontawesome.com/license/free (Icons: CC BY 4.0, Fonts: SIL OFL 1.1, Code: MIT License) Copyright 2022 Fonticons, Inc. --><path d="M38.8 5.1C28.4-3.1 13.3-1.2 5.1 9.2S-1.2 34.7 9.2 42.9l592 464c10.4 8.2 25.5 6.3 33.7-4.1s6.3-25.5-4.1-33.7L525.6 386.7c39.6-40.6 66.4-86.1 79.9-118.4c3.3-7.9 3.3-16.7 0-24.6c-14.9-35.7-46.2-87.7-93-131.1C465.5 68.8 400.8 32 320 32c-68.2 0-125 26.3-169.3 60.8L38.8 5.1zM223.1 149.5C248.6 126.2 282.7 112 320 112c79.5 0 144 64.5 144 144c0 24.9-6.3 48.3-17.4 68.7L408 294.5c5.2-11.8 8-24.8 8-38.5c0-53-43-96-96-96c-2.8 0-5.6 .1-8.4 .4c5.3 9.3 8.4 20.1 8.4 31.6c0 10.2-2.4 19.8-6.6 28.3l-90.3-70.8zm223.1 298L373 389.9c-16.4 6.5-34.3 10.1-53 10.1c-79.5 0-144-64.5-144-144c0-6.9 .5-13.6 1.4-20.2L83.1 161.5C60.3 191.2 44 220.8 34.5 243.7c-3.3 7.9-3.3 16.7 0 24.6c14.9 35.7 46.2 87.7 93 131.1C174.5 443.2 239.2 480 320 480c47.8 0 89.9-12.9 126.2-32.5z"/></svg></span></template> |
| <template id=fa-copy><span class=fa-svg><svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 512 512"><!--! Font Awesome Free 6.2.0 by @fontawesome - https://fontawesome.com License - https://fontawesome.com/license/free (Icons: CC BY 4.0, Fonts: SIL OFL 1.1, Code: MIT License) Copyright 2022 Fonticons, Inc. --><path d="M502.6 70.63l-61.25-61.25C435.4 3.371 427.2 0 418.7 0H255.1c-35.35 0-64 28.66-64 64l.0195 256C192 355.4 220.7 384 256 384h192c35.2 0 64-28.8 64-64V93.25C512 84.77 508.6 76.63 502.6 70.63zM464 320c0 8.836-7.164 16-16 16H255.1c-8.838 0-16-7.164-16-16L239.1 64.13c0-8.836 7.164-16 16-16h128L384 96c0 17.67 14.33 32 32 32h47.1V320zM272 448c0 8.836-7.164 16-16 16H63.1c-8.838 0-16-7.164-16-16L47.98 192.1c0-8.836 7.164-16 16-16H160V128H63.99c-35.35 0-64 28.65-64 64l.0098 256C.002 483.3 28.66 512 64 512h192c35.2 0 64-28.8 64-64v-32h-47.1L272 448z"/></svg></span></template> |
| <template id=fa-play><span class=fa-svg><svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 384 512"><!--! Font Awesome Free 6.2.0 by @fontawesome - https://fontawesome.com License - https://fontawesome.com/license/free (Icons: CC BY 4.0, Fonts: SIL OFL 1.1, Code: MIT License) Copyright 2022 Fonticons, Inc. --><path d="M73 39c-14.8-9.1-33.4-9.4-48.5-.9S0 62.6 0 80V432c0 17.4 9.4 33.4 24.5 41.9s33.7 8.1 48.5-.9L361 297c14.3-8.7 23-24.2 23-41s-8.7-32.2-23-41L73 39z"/></svg></span></template> |
| <template id=fa-clock-rotate-left><span class=fa-svg><svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 512 512"><!--! Font Awesome Free 6.2.0 by @fontawesome - https://fontawesome.com License - https://fontawesome.com/license/free (Icons: CC BY 4.0, Fonts: SIL OFL 1.1, Code: MIT License) Copyright 2022 Fonticons, Inc. --><path d="M75 75L41 41C25.9 25.9 0 36.6 0 57.9V168c0 13.3 10.7 24 24 24H134.1c21.4 0 32.1-25.9 17-41l-30.8-30.8C155 85.5 203 64 256 64c106 0 192 86 192 192s-86 192-192 192c-40.8 0-78.6-12.7-109.7-34.4c-14.5-10.1-34.4-6.6-44.6 7.9s-6.6 34.4 7.9 44.6C151.2 495 201.7 512 256 512c141.4 0 256-114.6 256-256S397.4 0 256 0C185.3 0 121.3 28.7 75 75zm181 53c-13.3 0-24 10.7-24 24V256c0 6.4 2.5 12.5 7 17l72 72c9.4 9.4 24.6 9.4 33.9 0s9.4-24.6 0-33.9l-65-65V152c0-13.3-10.7-24-24-24z"/></svg></span></template> |
| |
| |
| |
| <script> |
| window.playground_copyable = true; |
| </script> |
| |
| |
| <script src="../elasticlunr-ef4e11c1.min.js"></script> |
| <script src="../mark-09e88c2c.min.js"></script> |
| <script src="../searcher-c2a407aa.js"></script> |
| |
| <script src="../clipboard-1626706a.min.js"></script> |
| <script src="../highlight-abc7f01d.js"></script> |
| <script src="../book-a0b12cfe.js"></script> |
| |
| <!-- Custom JS scripts --> |
| |
| |
| |
| </div> |
| </body> |
| </html> |
