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<main>
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<h1 id="software-tasks--spawn"><a class="header" href="#software-tasks--spawn">Software tasks & spawn</a></h1>
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<p>The RTIC concept of a software task shares a lot with that of <a href="./hardware_tasks.html">hardware tasks</a>
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with the core difference that a software task is not explicitly bound to a specific
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interrupt vector, but rather bound to a “dispatcher” interrupt vector running
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at the intended priority of the software task (see below).</p>
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<p>Thus, software tasks are tasks which are not <em>directly</em> bound to an interrupt vector.</p>
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<p>The <code>#[task]</code> attributes used on a function determine if it is
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software tasks, specifically the absence of a <code>binds = InterruptName</code>
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argument to the attribute definition.</p>
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<p>The static method <code>task_name::spawn()</code> spawns (schedules) a software
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task by registering it with a specific dispatcher. If there are no
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higher priority tasks available to the scheduler (which serves a set
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of dispatchers), the task will start executing directly.</p>
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<p>All software tasks at the same priority level share an interrupt handler bound to their dispatcher.
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What differentiates software and hardware tasks is the usage of either a dispatcher or a bound interrupt vector.</p>
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<p>The interrupt vectors used as dispatchers cannot be used by hardware tasks.</p>
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<p>Availability of a set of “free” (not in use by hardware tasks) and usable interrupt vectors allows the framework
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to dispatch software tasks via dedicated interrupt handlers.</p>
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<p>This set of dispatchers, <code>dispatchers = [FreeInterrupt1, FreeInterrupt2, ...]</code> is an
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argument to the <code>#[app]</code> attribute.</p>
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<p>Each interrupt vector acting as dispatcher gets assigned to a unique priority level meaning that
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the list of dispatchers needs to cover all priority levels used by software tasks.</p>
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<p>Example: The <code>dispatchers =</code> argument needs to have at least 3 entries for an application using
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three different priorities for software tasks.</p>
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<p>The framework will give a compilation error if there are not enough dispatchers provided.</p>
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<p>See the following example:</p>
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<pre><pre class="playground"><code class="language-rust"><span class="boring">#![allow(unused)]
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</span><span class="boring">fn main() {
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</span>//! examples/spawn.rs
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#![deny(unsafe_code)]
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#![deny(warnings)]
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#![deny(missing_docs)]
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#![no_main]
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#![no_std]
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use panic_semihosting as _;
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#[rtic::app(device = lm3s6965, dispatchers = [SSI0])]
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mod app {
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use cortex_m_semihosting::{debug, hprintln};
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#[shared]
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struct Shared {}
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#[local]
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struct Local {}
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#[init]
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fn init(_: init::Context) -> (Shared, Local, init::Monotonics) {
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hprintln!("init");
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foo::spawn().unwrap();
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(Shared {}, Local {}, init::Monotonics())
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}
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#[task]
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fn foo(_: foo::Context) {
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hprintln!("foo");
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debug::exit(debug::EXIT_SUCCESS); // Exit QEMU simulator
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}
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}
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<span class="boring">}</span></code></pre></pre>
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<pre><code class="language-console">$ cargo run --target thumbv7m-none-eabi --example spawn
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init
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foo
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</code></pre>
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