mirror of
https://github.com/rtic-rs/rtic.git
synced 2024-12-26 11:59:33 +01:00
695 lines
28 KiB
HTML
695 lines
28 KiB
HTML
<!DOCTYPE HTML>
|
|
<html lang="en" class="light sidebar-visible" dir="ltr">
|
|
<head>
|
|
<!-- Book generated using mdBook -->
|
|
<meta charset="UTF-8">
|
|
<title>Resources - 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/cortex-m-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="resource-usage"><a class="header" href="#resource-usage">Resource usage</a></h1>
|
|
<p>The RTIC framework manages shared and task local resources allowing persistent data
|
|
storage and safe accesses without the use of <code>unsafe</code> code.</p>
|
|
<p>RTIC resources are visible only to functions declared within the <code>#[app]</code> module and the framework
|
|
gives the user complete control (on a per-task basis) over resource accessibility.</p>
|
|
<p>Declaration of system-wide resources is done by annotating <strong>two</strong> <code>struct</code>s within the <code>#[app]</code> module
|
|
with the attribute <code>#[local]</code> and <code>#[shared]</code>.
|
|
Each field in these structures corresponds to a different resource (identified by field name).
|
|
The difference between these two sets of resources will be covered below.</p>
|
|
<p>Each task must declare the resources it intends to access in its corresponding metadata attribute
|
|
using the <code>local</code> and <code>shared</code> arguments. Each argument takes a list of resource identifiers.
|
|
The listed resources are made available to the context under the <code>local</code> and <code>shared</code> fields of the
|
|
<code>Context</code> structure.</p>
|
|
<p>The <code>init</code> task returns the initial values for the system-wide (<code>#[shared]</code> and <code>#[local]</code>)
|
|
resources, and the set of initialized timers used by the application. The monotonic timers will be
|
|
further discussed in <a href="./monotonic.html">Monotonic & <code>spawn_{at/after}</code></a>.</p>
|
|
<h2 id="local-resources"><a class="header" href="#local-resources"><code>#[local]</code> resources</a></h2>
|
|
<p><code>#[local]</code> resources are locally accessible to a specific task, meaning that only that task can
|
|
access the resource and does so without locks or critical sections. This allows for the resources,
|
|
commonly drivers or large objects, to be initialized in <code>#[init]</code> and then be passed to a specific
|
|
task.</p>
|
|
<p>Thus, a task <code>#[local]</code> resource can only be accessed by one singular task.
|
|
Attempting to assign the same <code>#[local]</code> resource to more than one task is a compile-time error.</p>
|
|
<p>Types of <code>#[local]</code> resources must implement a <a href="https://doc.rust-lang.org/stable/core/marker/trait.Send.html"><code>Send</code></a> trait as they are being sent from <code>init</code>
|
|
to a target task, crossing a thread boundary.</p>
|
|
<p>The example application shown below contains two tasks where each task has access to its own
|
|
<code>#[local]</code> resource; the <code>idle</code> task has its own <code>#[local]</code> as well.</p>
|
|
<pre><pre class="playground"><code class="language-rust"><span class="boring">#![allow(unused)]
|
|
</span><span class="boring">fn main() {
|
|
</span>//! examples/locals.rs
|
|
|
|
#![deny(unsafe_code)]
|
|
#![deny(warnings)]
|
|
#![deny(missing_docs)]
|
|
#![deny(missing_docs)]
|
|
#![no_main]
|
|
#![no_std]
|
|
|
|
use panic_semihosting as _;
|
|
|
|
#[rtic::app(device = lm3s6965, dispatchers = [UART0, UART1])]
|
|
mod app {
|
|
use cortex_m_semihosting::{debug, hprintln};
|
|
|
|
#[shared]
|
|
struct Shared {}
|
|
|
|
#[local]
|
|
struct Local {
|
|
/// Local foo
|
|
local_to_foo: i64,
|
|
/// Local bar
|
|
local_to_bar: i64,
|
|
/// Local idle
|
|
local_to_idle: i64,
|
|
}
|
|
|
|
// `#[init]` cannot access locals from the `#[local]` struct as they are initialized here.
|
|
#[init]
|
|
fn init(_: init::Context) -> (Shared, Local, init::Monotonics) {
|
|
foo::spawn().unwrap();
|
|
bar::spawn().unwrap();
|
|
|
|
(
|
|
Shared {},
|
|
// initial values for the `#[local]` resources
|
|
Local {
|
|
local_to_foo: 0,
|
|
local_to_bar: 0,
|
|
local_to_idle: 0,
|
|
},
|
|
init::Monotonics(),
|
|
)
|
|
}
|
|
|
|
// `local_to_idle` can only be accessed from this context
|
|
#[idle(local = [local_to_idle])]
|
|
fn idle(cx: idle::Context) -> ! {
|
|
let local_to_idle = cx.local.local_to_idle;
|
|
*local_to_idle += 1;
|
|
|
|
hprintln!("idle: local_to_idle = {}", local_to_idle);
|
|
|
|
debug::exit(debug::EXIT_SUCCESS); // Exit QEMU simulator
|
|
|
|
// error: no `local_to_foo` field in `idle::LocalResources`
|
|
// _cx.local.local_to_foo += 1;
|
|
|
|
// error: no `local_to_bar` field in `idle::LocalResources`
|
|
// _cx.local.local_to_bar += 1;
|
|
|
|
loop {
|
|
cortex_m::asm::nop();
|
|
}
|
|
}
|
|
|
|
// `local_to_foo` can only be accessed from this context
|
|
#[task(local = [local_to_foo])]
|
|
fn foo(cx: foo::Context) {
|
|
let local_to_foo = cx.local.local_to_foo;
|
|
*local_to_foo += 1;
|
|
|
|
// error: no `local_to_bar` field in `foo::LocalResources`
|
|
// cx.local.local_to_bar += 1;
|
|
|
|
hprintln!("foo: local_to_foo = {}", local_to_foo);
|
|
}
|
|
|
|
// `local_to_bar` can only be accessed from this context
|
|
#[task(local = [local_to_bar])]
|
|
fn bar(cx: bar::Context) {
|
|
let local_to_bar = cx.local.local_to_bar;
|
|
*local_to_bar += 1;
|
|
|
|
// error: no `local_to_foo` field in `bar::LocalResources`
|
|
// cx.local.local_to_foo += 1;
|
|
|
|
hprintln!("bar: local_to_bar = {}", local_to_bar);
|
|
}
|
|
}
|
|
<span class="boring">}</span></code></pre></pre>
|
|
<p>Running the example:</p>
|
|
<pre><code class="language-console">$ cargo run --target thumbv7m-none-eabi --example locals
|
|
foo: local_to_foo = 1
|
|
bar: local_to_bar = 1
|
|
idle: local_to_idle = 1
|
|
</code></pre>
|
|
<p>Local resources in <code>#[init]</code> and <code>#[idle]</code> have <code>'static</code>
|
|
lifetimes. This is safe since both tasks are not re-entrant.</p>
|
|
<h3 id="task-local-initialized-resources"><a class="header" href="#task-local-initialized-resources">Task local initialized resources</a></h3>
|
|
<p>Local resources can also be specified directly in the resource claim like so:
|
|
<code>#[task(local = [my_var: TYPE = INITIAL_VALUE, ...])]</code>; this allows for creating locals which do no need to be
|
|
initialized in <code>#[init]</code>.</p>
|
|
<p>Types of <code>#[task(local = [..])]</code> resources have to be neither <a href="https://doc.rust-lang.org/stable/core/marker/trait.Send.html"><code>Send</code></a> nor <a href="https://doc.rust-lang.org/stable/core/marker/trait.Sync.html"><code>Sync</code></a> as they
|
|
are not crossing any thread boundary.</p>
|
|
<p>In the example below the different uses and lifetimes are shown:</p>
|
|
<pre><pre class="playground"><code class="language-rust"><span class="boring">#![allow(unused)]
|
|
</span><span class="boring">fn main() {
|
|
</span>//! examples/declared_locals.rs
|
|
|
|
#![deny(unsafe_code)]
|
|
#![deny(warnings)]
|
|
#![deny(missing_docs)]
|
|
#![no_main]
|
|
#![no_std]
|
|
|
|
use panic_semihosting as _;
|
|
|
|
#[rtic::app(device = lm3s6965, dispatchers = [UART0])]
|
|
mod app {
|
|
use cortex_m_semihosting::debug;
|
|
|
|
#[shared]
|
|
struct Shared {}
|
|
|
|
#[local]
|
|
struct Local {}
|
|
|
|
#[init(local = [a: u32 = 0])]
|
|
fn init(cx: init::Context) -> (Shared, Local, init::Monotonics) {
|
|
// Locals in `#[init]` have 'static lifetime
|
|
let _a: &'static mut u32 = cx.local.a;
|
|
|
|
debug::exit(debug::EXIT_SUCCESS); // Exit QEMU simulator
|
|
|
|
(Shared {}, Local {}, init::Monotonics())
|
|
}
|
|
|
|
#[idle(local = [a: u32 = 0])]
|
|
fn idle(cx: idle::Context) -> ! {
|
|
// Locals in `#[idle]` have 'static lifetime
|
|
let _a: &'static mut u32 = cx.local.a;
|
|
|
|
loop {}
|
|
}
|
|
|
|
#[task(local = [a: u32 = 0])]
|
|
fn foo(cx: foo::Context) {
|
|
// Locals in `#[task]`s have a local lifetime
|
|
let _a: &mut u32 = cx.local.a;
|
|
|
|
// error: explicit lifetime required in the type of `cx`
|
|
// let _a: &'static mut u32 = cx.local.a;
|
|
}
|
|
}
|
|
<span class="boring">}</span></code></pre></pre>
|
|
<!-- ``` console
|
|
$ cargo run --target thumbv7m-none-eabi --example declared_locals
|
|
|
|
``` -->
|
|
<h2 id="shared-resources-and-lock"><a class="header" href="#shared-resources-and-lock"><code>#[shared]</code> resources and <code>lock</code></a></h2>
|
|
<p>Critical sections are required to access <code>#[shared]</code> resources in a data race-free manner and to
|
|
achieve this the <code>shared</code> field of the passed <code>Context</code> implements the <a href="../../../api/rtic/trait.Mutex.html"><code>Mutex</code></a> trait for each
|
|
shared resource accessible to the task. This trait has only one method, <a href="../../../api/rtic/trait.Mutex.html#method.lock"><code>lock</code></a>, which runs its
|
|
closure argument in a critical section.</p>
|
|
<p>The critical section created by the <code>lock</code> API is based on dynamic priorities: it temporarily
|
|
raises the dynamic priority of the context to a <em>ceiling</em> priority that prevents other tasks from
|
|
preempting the critical section. This synchronization protocol is known as the
|
|
<a href="https://en.wikipedia.org/wiki/Priority_ceiling_protocol">Immediate Ceiling Priority Protocol (ICPP)</a>, and complies with
|
|
<a href="https://en.wikipedia.org/wiki/Stack_Resource_Policy">Stack Resource Policy (SRP)</a> based scheduling of RTIC.</p>
|
|
<p>In the example below we have three interrupt handlers with priorities ranging from one to three.
|
|
The two handlers with the lower priorities contend for a <code>shared</code> resource and need to succeed in locking the
|
|
resource in order to access its data. The highest priority handler, which does not access the <code>shared</code>
|
|
resource, is free to preempt a critical section created by the lowest priority handler.</p>
|
|
<pre><pre class="playground"><code class="language-rust"><span class="boring">#![allow(unused)]
|
|
</span><span class="boring">fn main() {
|
|
</span>//! examples/lock.rs
|
|
|
|
#![deny(unsafe_code)]
|
|
#![deny(warnings)]
|
|
#![deny(missing_docs)]
|
|
#![no_main]
|
|
#![no_std]
|
|
|
|
use panic_semihosting as _;
|
|
|
|
#[rtic::app(device = lm3s6965, dispatchers = [GPIOA, GPIOB, GPIOC])]
|
|
mod app {
|
|
use cortex_m_semihosting::{debug, hprintln};
|
|
|
|
#[shared]
|
|
struct Shared {
|
|
shared: u32,
|
|
}
|
|
|
|
#[local]
|
|
struct Local {}
|
|
|
|
#[init]
|
|
fn init(_: init::Context) -> (Shared, Local, init::Monotonics) {
|
|
foo::spawn().unwrap();
|
|
|
|
(Shared { shared: 0 }, Local {}, init::Monotonics())
|
|
}
|
|
|
|
// when omitted priority is assumed to be `1`
|
|
#[task(shared = [shared])]
|
|
fn foo(mut c: foo::Context) {
|
|
hprintln!("A");
|
|
|
|
// the lower priority task requires a critical section to access the data
|
|
c.shared.shared.lock(|shared| {
|
|
// data can only be modified within this critical section (closure)
|
|
*shared += 1;
|
|
|
|
// bar will *not* run right now due to the critical section
|
|
bar::spawn().unwrap();
|
|
|
|
hprintln!("B - shared = {}", *shared);
|
|
|
|
// baz does not contend for `shared` so it's allowed to run now
|
|
baz::spawn().unwrap();
|
|
});
|
|
|
|
// critical section is over: bar can now start
|
|
|
|
hprintln!("E");
|
|
|
|
debug::exit(debug::EXIT_SUCCESS); // Exit QEMU simulator
|
|
}
|
|
|
|
#[task(priority = 2, shared = [shared])]
|
|
fn bar(mut c: bar::Context) {
|
|
// the higher priority task does still need a critical section
|
|
let shared = c.shared.shared.lock(|shared| {
|
|
*shared += 1;
|
|
|
|
*shared
|
|
});
|
|
|
|
hprintln!("D - shared = {}", shared);
|
|
}
|
|
|
|
#[task(priority = 3)]
|
|
fn baz(_: baz::Context) {
|
|
hprintln!("C");
|
|
}
|
|
}
|
|
<span class="boring">}</span></code></pre></pre>
|
|
<pre><code class="language-console">$ cargo run --target thumbv7m-none-eabi --example lock
|
|
A
|
|
B - shared = 1
|
|
C
|
|
D - shared = 2
|
|
E
|
|
</code></pre>
|
|
<p>Types of <code>#[shared]</code> resources have to be <a href="https://doc.rust-lang.org/stable/core/marker/trait.Send.html"><code>Send</code></a>.</p>
|
|
<h2 id="multi-lock"><a class="header" href="#multi-lock">Multi-lock</a></h2>
|
|
<p>As an extension to <code>lock</code>, and to reduce rightward drift, locks can be taken as tuples. The
|
|
following examples show this in use:</p>
|
|
<pre><pre class="playground"><code class="language-rust"><span class="boring">#![allow(unused)]
|
|
</span><span class="boring">fn main() {
|
|
</span>//! examples/mutlilock.rs
|
|
|
|
#![deny(unsafe_code)]
|
|
#![deny(warnings)]
|
|
#![deny(missing_docs)]
|
|
#![no_main]
|
|
#![no_std]
|
|
|
|
use panic_semihosting as _;
|
|
|
|
#[rtic::app(device = lm3s6965, dispatchers = [GPIOA])]
|
|
mod app {
|
|
use cortex_m_semihosting::{debug, hprintln};
|
|
|
|
#[shared]
|
|
struct Shared {
|
|
shared1: u32,
|
|
shared2: u32,
|
|
shared3: u32,
|
|
}
|
|
|
|
#[local]
|
|
struct Local {}
|
|
|
|
#[init]
|
|
fn init(_: init::Context) -> (Shared, Local, init::Monotonics) {
|
|
locks::spawn().unwrap();
|
|
|
|
(
|
|
Shared {
|
|
shared1: 0,
|
|
shared2: 0,
|
|
shared3: 0,
|
|
},
|
|
Local {},
|
|
init::Monotonics(),
|
|
)
|
|
}
|
|
|
|
// when omitted priority is assumed to be `1`
|
|
#[task(shared = [shared1, shared2, shared3])]
|
|
fn locks(c: locks::Context) {
|
|
let s1 = c.shared.shared1;
|
|
let s2 = c.shared.shared2;
|
|
let s3 = c.shared.shared3;
|
|
|
|
(s1, s2, s3).lock(|s1, s2, s3| {
|
|
*s1 += 1;
|
|
*s2 += 1;
|
|
*s3 += 1;
|
|
|
|
hprintln!("Multiple locks, s1: {}, s2: {}, s3: {}", *s1, *s2, *s3);
|
|
});
|
|
|
|
debug::exit(debug::EXIT_SUCCESS); // Exit QEMU simulator
|
|
}
|
|
}
|
|
<span class="boring">}</span></code></pre></pre>
|
|
<pre><code class="language-console">$ cargo run --target thumbv7m-none-eabi --example multilock
|
|
Multiple locks, s1: 1, s2: 1, s3: 1
|
|
</code></pre>
|
|
<h2 id="only-shared---access"><a class="header" href="#only-shared---access">Only shared (<code>&-</code>) access</a></h2>
|
|
<p>By default, the framework assumes that all tasks require exclusive access (<code>&mut-</code>) to resources,
|
|
but it is possible to specify that a task only requires shared access (<code>&-</code>) to a resource using the
|
|
<code>&resource_name</code> syntax in the <code>shared</code> list.</p>
|
|
<p>The advantage of specifying shared access (<code>&-</code>) to a resource is that no locks are required to
|
|
access the resource even if the resource is contended by more than one task running at different
|
|
priorities. The downside is that the task only gets a shared reference (<code>&-</code>) to the resource,
|
|
limiting the operations it can perform on it, but where a shared reference is enough this approach
|
|
reduces the number of required locks. In addition to simple immutable data, this shared access can
|
|
be useful where the resource type safely implements interior mutability, with appropriate locking
|
|
or atomic operations of its own.</p>
|
|
<p>Note that in this release of RTIC it is not possible to request both exclusive access (<code>&mut-</code>)
|
|
and shared access (<code>&-</code>) to the <em>same</em> resource from different tasks. Attempting to do so will
|
|
result in a compile error.</p>
|
|
<p>In the example below a key (e.g. a cryptographic key) is loaded (or created) at runtime and then
|
|
used from two tasks that run at different priorities without any kind of lock.</p>
|
|
<pre><pre class="playground"><code class="language-rust"><span class="boring">#![allow(unused)]
|
|
</span><span class="boring">fn main() {
|
|
</span>//! examples/only-shared-access.rs
|
|
|
|
#![deny(unsafe_code)]
|
|
#![deny(warnings)]
|
|
#![deny(missing_docs)]
|
|
#![no_main]
|
|
#![no_std]
|
|
|
|
use panic_semihosting as _;
|
|
|
|
#[rtic::app(device = lm3s6965, dispatchers = [UART0, UART1])]
|
|
mod app {
|
|
use cortex_m_semihosting::{debug, hprintln};
|
|
|
|
#[shared]
|
|
struct Shared {
|
|
key: u32,
|
|
}
|
|
|
|
#[local]
|
|
struct Local {}
|
|
|
|
#[init]
|
|
fn init(_: init::Context) -> (Shared, Local, init::Monotonics) {
|
|
foo::spawn().unwrap();
|
|
bar::spawn().unwrap();
|
|
|
|
(Shared { key: 0xdeadbeef }, Local {}, init::Monotonics())
|
|
}
|
|
|
|
#[task(shared = [&key])]
|
|
fn foo(cx: foo::Context) {
|
|
let key: &u32 = cx.shared.key;
|
|
hprintln!("foo(key = {:#x})", key);
|
|
|
|
debug::exit(debug::EXIT_SUCCESS); // Exit QEMU simulator
|
|
}
|
|
|
|
#[task(priority = 2, shared = [&key])]
|
|
fn bar(cx: bar::Context) {
|
|
hprintln!("bar(key = {:#x})", cx.shared.key);
|
|
}
|
|
}
|
|
<span class="boring">}</span></code></pre></pre>
|
|
<pre><code class="language-console">$ cargo run --target thumbv7m-none-eabi --example only-shared-access
|
|
bar(key = 0xdeadbeef)
|
|
foo(key = 0xdeadbeef)
|
|
</code></pre>
|
|
<h2 id="lock-free-resource-access-of-shared-resources"><a class="header" href="#lock-free-resource-access-of-shared-resources">Lock-free resource access of shared resources</a></h2>
|
|
<p>A critical section is <em>not</em> required to access a <code>#[shared]</code> resource that's only accessed by tasks
|
|
running at the <em>same</em> priority. In this case, you can opt out of the <code>lock</code> API by adding the
|
|
<code>#[lock_free]</code> field-level attribute to the resource declaration (see example below). Note that
|
|
this is merely a convenience to reduce needless resource locking code, because even if the
|
|
<code>lock</code> API is used, at runtime the framework will <strong>not</strong> produce a critical section due to how
|
|
the underlying resource-ceiling preemption works.</p>
|
|
<p>Also worth noting: using <code>#[lock_free]</code> on resources shared by
|
|
tasks running at different priorities will result in a <em>compile-time</em> error -- not using the <code>lock</code>
|
|
API would be a data race in that case.</p>
|
|
<pre><pre class="playground"><code class="language-rust"><span class="boring">#![allow(unused)]
|
|
</span><span class="boring">fn main() {
|
|
</span>//! examples/lock-free.rs
|
|
|
|
#![deny(unsafe_code)]
|
|
#![deny(warnings)]
|
|
#![deny(missing_docs)]
|
|
#![no_main]
|
|
#![no_std]
|
|
|
|
use panic_semihosting as _;
|
|
|
|
#[rtic::app(device = lm3s6965, dispatchers = [GPIOA])]
|
|
mod app {
|
|
use cortex_m_semihosting::{debug, hprintln};
|
|
|
|
#[shared]
|
|
struct Shared {
|
|
#[lock_free] // <- lock-free shared resource
|
|
counter: u64,
|
|
}
|
|
|
|
#[local]
|
|
struct Local {}
|
|
|
|
#[init]
|
|
fn init(_: init::Context) -> (Shared, Local, init::Monotonics) {
|
|
foo::spawn().unwrap();
|
|
|
|
(Shared { counter: 0 }, Local {}, init::Monotonics())
|
|
}
|
|
|
|
#[task(shared = [counter])] // <- same priority
|
|
fn foo(c: foo::Context) {
|
|
bar::spawn().unwrap();
|
|
|
|
*c.shared.counter += 1; // <- no lock API required
|
|
let counter = *c.shared.counter;
|
|
hprintln!(" foo = {}", counter);
|
|
}
|
|
|
|
#[task(shared = [counter])] // <- same priority
|
|
fn bar(c: bar::Context) {
|
|
foo::spawn().unwrap();
|
|
|
|
*c.shared.counter += 1; // <- no lock API required
|
|
let counter = *c.shared.counter;
|
|
hprintln!(" bar = {}", counter);
|
|
|
|
debug::exit(debug::EXIT_SUCCESS); // Exit QEMU simulator
|
|
}
|
|
}
|
|
<span class="boring">}</span></code></pre></pre>
|
|
<pre><code class="language-console">$ cargo run --target thumbv7m-none-eabi --example lock-free
|
|
foo = 1
|
|
bar = 2
|
|
</code></pre>
|
|
|
|
</main>
|
|
|
|
<nav class="nav-wrapper" aria-label="Page navigation">
|
|
<!-- Mobile navigation buttons -->
|
|
<a rel="prev" href="../by-example/app.html" class="mobile-nav-chapters previous" title="Previous chapter" aria-label="Previous chapter" aria-keyshortcuts="Left">
|
|
<i class="fa fa-angle-left"></i>
|
|
</a>
|
|
|
|
<a rel="next prefetch" href="../by-example/app_init.html" class="mobile-nav-chapters next" title="Next chapter" aria-label="Next chapter" aria-keyshortcuts="Right">
|
|
<i class="fa fa-angle-right"></i>
|
|
</a>
|
|
|
|
<div style="clear: both"></div>
|
|
</nav>
|
|
</div>
|
|
</div>
|
|
|
|
<nav class="nav-wide-wrapper" aria-label="Page navigation">
|
|
<a rel="prev" href="../by-example/app.html" class="nav-chapters previous" title="Previous chapter" aria-label="Previous chapter" aria-keyshortcuts="Left">
|
|
<i class="fa fa-angle-left"></i>
|
|
</a>
|
|
|
|
<a rel="next prefetch" href="../by-example/app_init.html" class="nav-chapters next" title="Next chapter" aria-label="Next chapter" aria-keyshortcuts="Right">
|
|
<i class="fa fa-angle-right"></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 -->
|
|
|
|
|
|
</div>
|
|
</body>
|
|
</html>
|