mirror of
https://github.com/rtic-rs/rtic.git
synced 2024-12-25 19:39:32 +01:00
258 lines
15 KiB
HTML
258 lines
15 KiB
HTML
<!DOCTYPE HTML>
|
|
<html lang="en" class="light sidebar-visible" dir="ltr">
|
|
<head>
|
|
<!-- Book generated using mdBook -->
|
|
<meta charset="UTF-8">
|
|
<title>Cortex-M architectures - Real-Time Interrupt-driven Concurrency</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.svg">
|
|
<link rel="shortcut icon" href="../favicon.png">
|
|
<link rel="stylesheet" href="../css/variables.css">
|
|
<link rel="stylesheet" href="../css/general.css">
|
|
<link rel="stylesheet" href="../css/chrome.css">
|
|
<link rel="stylesheet" href="../css/print.css" media="print">
|
|
|
|
<!-- Fonts -->
|
|
<link rel="stylesheet" href="../FontAwesome/css/font-awesome.css">
|
|
<link rel="stylesheet" href="../fonts/fonts.css">
|
|
|
|
<!-- Highlight.js Stylesheets -->
|
|
<link rel="stylesheet" href="../highlight.css">
|
|
<link rel="stylesheet" href="../tomorrow-night.css">
|
|
<link rel="stylesheet" href="../ayu-highlight.css">
|
|
|
|
<!-- Custom theme stylesheets -->
|
|
|
|
|
|
<!-- Provide site root to javascript -->
|
|
<script>
|
|
var path_to_root = "../";
|
|
var default_theme = window.matchMedia("(prefers-color-scheme: dark)").matches ? "navy" : "light";
|
|
</script>
|
|
<!-- Start loading toc.js asap -->
|
|
<script src="../toc.js"></script>
|
|
</head>
|
|
<body>
|
|
<div id="body-container">
|
|
<!-- Work around some values being stored in localStorage wrapped in quotes -->
|
|
<script>
|
|
try {
|
|
var theme = localStorage.getItem('mdbook-theme');
|
|
var 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>
|
|
var 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="sidebar-toggle-anchor" class="hidden">
|
|
|
|
<!-- Hide / unhide sidebar before it is displayed -->
|
|
<script>
|
|
var sidebar = null;
|
|
var sidebar_toggle = document.getElementById("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 = sidebar === 'visible';
|
|
html.classList.remove('sidebar-visible');
|
|
html.classList.add("sidebar-" + sidebar);
|
|
</script>
|
|
|
|
<nav id="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="sidebar-resize-handle" class="sidebar-resize-handle">
|
|
<div class="sidebar-resize-indicator"></div>
|
|
</div>
|
|
</nav>
|
|
|
|
<div id="page-wrapper" class="page-wrapper">
|
|
|
|
<div class="page">
|
|
<div id="menu-bar-hover-placeholder"></div>
|
|
<div id="menu-bar" class="menu-bar sticky">
|
|
<div class="left-buttons">
|
|
<label id="sidebar-toggle" class="icon-button" for="sidebar-toggle-anchor" title="Toggle Table of Contents" aria-label="Toggle Table of Contents" aria-controls="sidebar">
|
|
<i class="fa fa-bars"></i>
|
|
</label>
|
|
<button id="theme-toggle" class="icon-button" type="button" title="Change theme" aria-label="Change theme" aria-haspopup="true" aria-expanded="false" aria-controls="theme-list">
|
|
<i class="fa fa-paint-brush"></i>
|
|
</button>
|
|
<ul id="theme-list" class="theme-popup" aria-label="Themes" role="menu">
|
|
<li role="none"><button role="menuitem" class="theme" id="light">Light</button></li>
|
|
<li role="none"><button role="menuitem" class="theme" id="rust">Rust</button></li>
|
|
<li role="none"><button role="menuitem" class="theme" id="coal">Coal</button></li>
|
|
<li role="none"><button role="menuitem" class="theme" id="navy">Navy</button></li>
|
|
<li role="none"><button role="menuitem" class="theme" id="ayu">Ayu</button></li>
|
|
</ul>
|
|
<button id="search-toggle" class="icon-button" type="button" title="Search. (Shortkey: s)" aria-label="Toggle Searchbar" aria-expanded="false" aria-keyshortcuts="S" aria-controls="searchbar">
|
|
<i class="fa fa-search"></i>
|
|
</button>
|
|
</div>
|
|
|
|
<h1 class="menu-title">Real-Time Interrupt-driven Concurrency</h1>
|
|
|
|
<div class="right-buttons">
|
|
<a href="../print.html" title="Print this book" aria-label="Print this book">
|
|
<i id="print-button" class="fa fa-print"></i>
|
|
</a>
|
|
<a href="https://github.com/rtic-rs/rtic" title="Git repository" aria-label="Git repository">
|
|
<i id="git-repository-button" class="fa fa-github"></i>
|
|
</a>
|
|
|
|
</div>
|
|
</div>
|
|
|
|
<div id="search-wrapper" class="hidden">
|
|
<form id="searchbar-outer" class="searchbar-outer">
|
|
<input type="search" id="searchbar" name="searchbar" placeholder="Search this book ..." aria-controls="searchresults-outer" aria-describedby="searchresults-header">
|
|
</form>
|
|
<div id="searchresults-outer" class="searchresults-outer hidden">
|
|
<div id="searchresults-header" class="searchresults-header"></div>
|
|
<ul id="searchresults">
|
|
</ul>
|
|
</div>
|
|
</div>
|
|
|
|
<!-- Apply ARIA attributes after the sidebar and the sidebar toggle button are added to the DOM -->
|
|
<script>
|
|
document.getElementById('sidebar-toggle').setAttribute('aria-expanded', sidebar === 'visible');
|
|
document.getElementById('sidebar').setAttribute('aria-hidden', sidebar !== 'visible');
|
|
Array.from(document.querySelectorAll('#sidebar a')).forEach(function(link) {
|
|
link.setAttribute('tabIndex', sidebar === 'visible' ? 0 : -1);
|
|
});
|
|
</script>
|
|
|
|
<div id="content" class="content">
|
|
<main>
|
|
<h1 id="target-architecture"><a class="header" href="#target-architecture">Target Architecture</a></h1>
|
|
<p>While RTIC can currently target all Cortex-m devices there are some key architecture differences that
|
|
users should be aware of. Namely, the absence of Base Priority Mask Register (<code>BASEPRI</code>) which lends
|
|
itself exceptionally well to the hardware priority ceiling support used in RTIC, in the ARMv6-M and
|
|
ARMv8-M-base architectures, which forces RTIC to use source masking instead. For each implementation
|
|
of lock and a detailed commentary of pros and cons, see the implementation of
|
|
<a href="https://github.com/rtic-rs/rtic/blob/master/src/export.rs">lock in src/export.rs</a>.</p>
|
|
<p>These differences influence how critical sections are realized, but functionality should be the same
|
|
except that ARMv6-M/ARMv8-M-base cannot have tasks with shared resources bound to exception
|
|
handlers, as these cannot be masked in hardware.</p>
|
|
<p>Table 1 below shows a list of Cortex-m processors and which type of critical section they employ.</p>
|
|
<h4 id="table-1-critical-section-implementation-by-processor-architecture"><a class="header" href="#table-1-critical-section-implementation-by-processor-architecture"><em>Table 1: Critical Section Implementation by Processor Architecture</em></a></h4>
|
|
<div class="table-wrapper"><table><thead><tr><th style="text-align: left">Processor</th><th style="text-align: center">Architecture</th><th style="text-align: center">Priority Ceiling</th><th style="text-align: center">Source Masking</th></tr></thead><tbody>
|
|
<tr><td style="text-align: left">Cortex-M0</td><td style="text-align: center">ARMv6-M</td><td style="text-align: center"></td><td style="text-align: center">✓</td></tr>
|
|
<tr><td style="text-align: left">Cortex-M0+</td><td style="text-align: center">ARMv6-M</td><td style="text-align: center"></td><td style="text-align: center">✓</td></tr>
|
|
<tr><td style="text-align: left">Cortex-M3</td><td style="text-align: center">ARMv7-M</td><td style="text-align: center">✓</td><td style="text-align: center"></td></tr>
|
|
<tr><td style="text-align: left">Cortex-M4</td><td style="text-align: center">ARMv7-M</td><td style="text-align: center">✓</td><td style="text-align: center"></td></tr>
|
|
<tr><td style="text-align: left">Cortex-M7</td><td style="text-align: center">ARMv7-M</td><td style="text-align: center">✓</td><td style="text-align: center"></td></tr>
|
|
<tr><td style="text-align: left">Cortex-M23</td><td style="text-align: center">ARMv8-M-base</td><td style="text-align: center"></td><td style="text-align: center">✓</td></tr>
|
|
<tr><td style="text-align: left">Cortex-M33</td><td style="text-align: center">ARMv8-M-main</td><td style="text-align: center">✓</td><td style="text-align: center"></td></tr>
|
|
</tbody></table>
|
|
</div>
|
|
<h2 id="priority-ceiling"><a class="header" href="#priority-ceiling">Priority Ceiling</a></h2>
|
|
<p>This is covered by the <a href="../by-example/resources.html">Resources</a> page of this book.</p>
|
|
<h2 id="source-masking"><a class="header" href="#source-masking">Source Masking</a></h2>
|
|
<p>Without a <code>BASEPRI</code> register which allows for directly setting a priority ceiling in the Nested
|
|
Vectored Interrupt Controller (NVIC), RTIC must instead rely on disabling (masking) interrupts.
|
|
Consider Figure 1 below, showing two tasks A and B where A has higher priority but shares a resource
|
|
with B.</p>
|
|
<h4 id="figure-1-shared-resources-and-source-masking"><a class="header" href="#figure-1-shared-resources-and-source-masking"><em>Figure 1: Shared Resources and Source Masking</em></a></h4>
|
|
<pre><code class="language-text"> ┌────────────────────────────────────────────────────────────────┐
|
|
│ │
|
|
│ │
|
|
3 │ Pending Preempts │
|
|
2 │ ↑- - -A- - - - -↓A─────────► │
|
|
1 │ B───────────────────► - - - - B────────► │
|
|
0 │Idle┌─────► Resumes ┌────────► │
|
|
├────┴────────────────────────────────────────────┴──────────────┤
|
|
│ │
|
|
└────────────────────────────────────────────────────────────────┴──► Time
|
|
t1 t2 t3 t4
|
|
</code></pre>
|
|
<p>At time <em>t1</em>, task B locks the shared resource by selectively disabling (using the NVIC) all other
|
|
tasks which have a priority equal to or less than any task which shares resources with B. In effect
|
|
this creates a virtual priority ceiling, mirroring the <code>BASEPRI</code> approach. Task A is one such task that shares resources with
|
|
task B. At time <em>t2</em>, task A is either spawned by task B or becomes pending through an interrupt
|
|
condition, but does not yet preempt task B even though its priority is greater. This is because the
|
|
NVIC is preventing it from starting due to task A being disabled. At time <em>t3</em>, task B
|
|
releases the lock by re-enabling the tasks in the NVIC. Because task A was pending and has a higher
|
|
priority than task B, it immediately preempts task B and is free to use the shared resource without
|
|
risk of data race conditions. At time <em>t4</em>, task A completes and returns the execution context to B.</p>
|
|
<p>Since source masking relies on use of the NVIC, core exception sources such as HardFault, SVCall,
|
|
PendSV, and SysTick cannot share data with other tasks.</p>
|
|
|
|
</main>
|
|
|
|
<nav class="nav-wrapper" aria-label="Page navigation">
|
|
<!-- Mobile navigation buttons -->
|
|
<a rel="prev" href="../internals.html" class="mobile-nav-chapters previous" title="Previous chapter" aria-label="Previous chapter" aria-keyshortcuts="Left">
|
|
<i class="fa fa-angle-left"></i>
|
|
</a>
|
|
|
|
|
|
<div style="clear: both"></div>
|
|
</nav>
|
|
</div>
|
|
</div>
|
|
|
|
<nav class="nav-wide-wrapper" aria-label="Page navigation">
|
|
<a rel="prev" href="../internals.html" class="nav-chapters previous" title="Previous chapter" aria-label="Previous chapter" aria-keyshortcuts="Left">
|
|
<i class="fa fa-angle-left"></i>
|
|
</a>
|
|
|
|
</nav>
|
|
|
|
</div>
|
|
|
|
|
|
|
|
|
|
<script>
|
|
window.playground_copyable = true;
|
|
</script>
|
|
|
|
|
|
<script src="../elasticlunr.min.js"></script>
|
|
<script src="../mark.min.js"></script>
|
|
<script src="../searcher.js"></script>
|
|
|
|
<script src="../clipboard.min.js"></script>
|
|
<script src="../highlight.js"></script>
|
|
<script src="../book.js"></script>
|
|
|
|
<!-- Custom JS scripts -->
|
|
<script src="../mermaid.min.js"></script>
|
|
<script src="../mermaid-init.js"></script>
|
|
|
|
|
|
</div>
|
|
</body>
|
|
</html>
|