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| <div class="section" id="tasks-and-priority-management"> |
| <h1>Tasks and Priority Management<a class="headerlink" href="#tasks-and-priority-management" title="Permalink to this headline">¶</a></h1> |
| <p><strong>Target Platform: Arduino M0 Pro</strong> (or legacy Arduino Zero or Zero Pro, |
| but not Arduino M0)</p> |
| <p>This lesson is designed to teach core OS concepts and strategies |
| encountered when building applications using Mynewt. Specifically, this |
| lesson will cover tasks, simple multitasking, and priority management |
| running on an Arduino M0 Pro.</p> |
| <div class="contents local topic" id="contents"> |
| <ul class="simple"> |
| <li><p><a class="reference internal" href="#prerequisites" id="id2">Prerequisites</a></p></li> |
| <li><p><a class="reference internal" href="#equipment" id="id3">Equipment</a></p></li> |
| <li><p><a class="reference internal" href="#build-your-application" id="id4">Build Your Application</a></p></li> |
| <li><p><a class="reference internal" href="#default-main-task" id="id5">Default Main Task</a></p></li> |
| <li><p><a class="reference internal" href="#create-a-new-task" id="id6">Create a New Task</a></p> |
| <ul> |
| <li><p><a class="reference internal" href="#task-stack" id="id7">Task Stack</a></p></li> |
| <li><p><a class="reference internal" href="#task-function" id="id8">Task Function</a></p></li> |
| <li><p><a class="reference internal" href="#task-priority" id="id9">Task Priority</a></p></li> |
| <li><p><a class="reference internal" href="#initialization" id="id10">Initialization</a></p></li> |
| </ul> |
| </li> |
| <li><p><a class="reference internal" href="#task-priority-preempting-and-context-switching" id="id11">Task Priority, Preempting, and Context Switching</a></p> |
| <ul> |
| <li><p><a class="reference internal" href="#priority-management-considerations" id="id12">Priority Management Considerations</a></p></li> |
| </ul> |
| </li> |
| </ul> |
| </div> |
| <div class="section" id="prerequisites"> |
| <h2><a class="toc-backref" href="#id2">Prerequisites</a><a class="headerlink" href="#prerequisites" title="Permalink to this headline">¶</a></h2> |
| <p>Before starting, you should read about Mynewt in the |
| <a class="reference internal" href="../../index.html"><span class="doc">Introduction</span></a> section and |
| complete the |
| <a class="reference internal" href="../../get_started/index.html"><span class="doc">QuickStart</span></a> |
| guide and the |
| <a class="reference internal" href="../blinky/arduino_zero.html"><span class="doc">Blinky</span></a> |
| tutorial. Furthermore, it may be helpful to take a peek at the <a class="reference internal" href="../../os/core_os/task/task.html"><span class="doc">task |
| documentation</span></a> for |
| additional insights.</p> |
| </div> |
| <div class="section" id="equipment"> |
| <h2><a class="toc-backref" href="#id3">Equipment</a><a class="headerlink" href="#equipment" title="Permalink to this headline">¶</a></h2> |
| <p>You will need the following equipment:</p> |
| <ul class="simple"> |
| <li><p>Arduino M0 Pro (or legacy Arduino Zero or Zero Pro, but not Arduino |
| M0)</p></li> |
| <li><p>Computer with Mynewt installed</p></li> |
| <li><p>USB to Micro USB Cable</p></li> |
| </ul> |
| </div> |
| <div class="section" id="build-your-application"> |
| <h2><a class="toc-backref" href="#id4">Build Your Application</a><a class="headerlink" href="#build-your-application" title="Permalink to this headline">¶</a></h2> |
| <p>To save time, we will simply modify the Blinky application. We’ll add |
| the Task Management code to the Blinky application. Follow the <a class="reference internal" href="../blinky/arduino_zero.html"><span class="doc">Arduino |
| Zero Blinky |
| tutorial</span></a> to |
| create a new project and build your bootloader and application. Finally, |
| build and load the application to your Arduino to verify that everything |
| is in order. Now let’s get started!</p> |
| </div> |
| <div class="section" id="default-main-task"> |
| <h2><a class="toc-backref" href="#id5">Default Main Task</a><a class="headerlink" href="#default-main-task" title="Permalink to this headline">¶</a></h2> |
| <p>During Mynewt system startup, Mynewt creates a default main task and |
| executes the application <code class="docutils literal notranslate"><span class="pre">main()</span></code> function in the context of this |
| task. The main task priority defaults to 127 and can be configured with |
| the <code class="docutils literal notranslate"><span class="pre">OS_MAIN_TASK_PRIO</span></code> system configuration setting.</p> |
| <p>The blinky application only has the <code class="docutils literal notranslate"><span class="pre">main</span></code> task. The <code class="docutils literal notranslate"><span class="pre">main()</span></code> |
| function executes an infinite loop that toggles the led and sleeps for |
| one second.</p> |
| </div> |
| <div class="section" id="create-a-new-task"> |
| <h2><a class="toc-backref" href="#id6">Create a New Task</a><a class="headerlink" href="#create-a-new-task" title="Permalink to this headline">¶</a></h2> |
| <p>The purpose of this section is to give an introduction to the important |
| aspects of tasks and how to properly initialize them. First, let’s |
| define a second task called <code class="docutils literal notranslate"><span class="pre">work_task</span></code> in main.c (located in |
| apps/blinky/src):</p> |
| <div class="highlight-c notranslate"><div class="highlight"><pre><span></span><span class="k">struct</span><span class="w"> </span><span class="nc">os_task</span><span class="w"> </span><span class="n">work_task</span><span class="p">;</span> |
| </pre></div> |
| </div> |
| <p>A task is represented by the |
| <span class="xref std std-doc">os_task</span> |
| struct which will hold the task’s information (name, state, priority, |
| etc.). A task is made up of two main elements, a task function (also |
| known as a task handler) and a task stack.</p> |
| <p>Next, let’s take a look at what is required to initialize our new task.</p> |
| <div class="section" id="task-stack"> |
| <h3><a class="toc-backref" href="#id7">Task Stack</a><a class="headerlink" href="#task-stack" title="Permalink to this headline">¶</a></h3> |
| <p>The task stack is an array of type <code class="docutils literal notranslate"><span class="pre">os_stack_t</span></code> which holds the |
| program stack frames. Mynewt gives us the ability to set the stack size |
| for a task giving the application developer room to optimize memory |
| usage. Since we’re not short on memory, our <code class="docutils literal notranslate"><span class="pre">work_stack</span></code> is plenty |
| large for the purpose of this lesson. Notice that the elements in our |
| task stack are of type <code class="docutils literal notranslate"><span class="pre">os_stack_t</span></code> which are generally 32 bits, |
| making our entire stack 1024 Bytes.</p> |
| <div class="highlight-c notranslate"><div class="highlight"><pre><span></span><span class="cp">#define WORK_STACK_SIZE OS_STACK_ALIGN(256)</span> |
| </pre></div> |
| </div> |
| <p>Note: The <code class="docutils literal notranslate"><span class="pre">OS_STACK_ALIGN</span></code> macro is used to align the stack based on |
| the hardware architecture.</p> |
| </div> |
| <div class="section" id="task-function"> |
| <h3><a class="toc-backref" href="#id8">Task Function</a><a class="headerlink" href="#task-function" title="Permalink to this headline">¶</a></h3> |
| <p>A task function is essentially an infinite loop that waits for some |
| “event” to wake it up. In general, the task function is where the |
| majority of work is done by a task. Let’s write a task function for |
| <code class="docutils literal notranslate"><span class="pre">work_task</span></code> called <code class="docutils literal notranslate"><span class="pre">work_task_handler()</span></code>:</p> |
| <div class="highlight-c notranslate"><div class="highlight"><pre><span></span><span class="kt">void</span> |
| <span class="nf">work_task_handler</span><span class="p">(</span><span class="kt">void</span><span class="w"> </span><span class="o">*</span><span class="n">arg</span><span class="p">)</span> |
| <span class="p">{</span> |
| <span class="w"> </span><span class="k">struct</span><span class="w"> </span><span class="nc">os_task</span><span class="w"> </span><span class="o">*</span><span class="n">t</span><span class="p">;</span> |
| |
| <span class="w"> </span><span class="n">g_led_pin</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">LED_BLINK_PIN</span><span class="p">;</span> |
| <span class="w"> </span><span class="n">hal_gpio_init_out</span><span class="p">(</span><span class="n">g_led_pin</span><span class="p">,</span><span class="w"> </span><span class="mi">1</span><span class="p">);</span> |
| |
| <span class="w"> </span><span class="k">while</span><span class="w"> </span><span class="p">(</span><span class="mi">1</span><span class="p">)</span><span class="w"> </span><span class="p">{</span> |
| <span class="w"> </span><span class="n">t</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">os_sched_get_current_task</span><span class="p">();</span> |
| <span class="w"> </span><span class="n">assert</span><span class="p">(</span><span class="n">t</span><span class="o">-></span><span class="n">t_func</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="n">work_task_handler</span><span class="p">);</span> |
| <span class="w"> </span><span class="cm">/* Do work... */</span> |
| <span class="w"> </span><span class="p">}</span> |
| <span class="p">}</span> |
| </pre></div> |
| </div> |
| <p>The task function is called when the task is initially put into the |
| <em>running</em> state by the scheduler. We use an infinite loop to ensure that |
| the task function never returns. Our assertion that the current task’s |
| handler is the same as our task handler is for illustration purposes |
| only and does not need to be in most task functions.</p> |
| </div> |
| <div class="section" id="task-priority"> |
| <h3><a class="toc-backref" href="#id9">Task Priority</a><a class="headerlink" href="#task-priority" title="Permalink to this headline">¶</a></h3> |
| <p>As a preemptive, multitasking RTOS, Mynewt decides which tasks to run |
| based on which has a higher priority; the highest priority being 0 and |
| the lowest 255. Thus, before initializing our task, we must choose a |
| priority defined as a macro variable.</p> |
| <p>Let’s set the priority of <code class="docutils literal notranslate"><span class="pre">work_task</span></code> to 0, because everyone knows |
| that work is more important than blinking.</p> |
| <div class="highlight-c notranslate"><div class="highlight"><pre><span></span><span class="cp">#define WORK_TASK_PRIO (0)</span> |
| </pre></div> |
| </div> |
| </div> |
| <div class="section" id="initialization"> |
| <h3><a class="toc-backref" href="#id10">Initialization</a><a class="headerlink" href="#initialization" title="Permalink to this headline">¶</a></h3> |
| <p>To initialize a new task we use <code class="docutils literal notranslate"><span class="pre">os_task_init()</span></code> |
| which takes a number of arguments including our new task function, |
| stack, and priority.</p> |
| <p>Add the <code class="docutils literal notranslate"><span class="pre">init_tasks()</span></code> function to initialize <code class="docutils literal notranslate"><span class="pre">work_task</span></code> to keep |
| our main function clean.</p> |
| <div class="highlight-c notranslate"><div class="highlight"><pre><span></span><span class="kt">int</span> |
| <span class="nf">init_tasks</span><span class="p">(</span><span class="kt">void</span><span class="p">)</span> |
| <span class="p">{</span> |
| <span class="w"> </span><span class="cm">/* … */</span> |
| <span class="w"> </span><span class="n">os_stack_t</span><span class="w"> </span><span class="o">*</span><span class="n">work_stack</span><span class="p">;</span> |
| <span class="w"> </span><span class="n">work_stack</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">malloc</span><span class="p">(</span><span class="k">sizeof</span><span class="p">(</span><span class="n">os_stack_t</span><span class="p">)</span><span class="o">*</span><span class="n">WORK_STACK_SIZE</span><span class="p">);</span> |
| |
| <span class="w"> </span><span class="n">assert</span><span class="p">(</span><span class="n">work_stack</span><span class="p">);</span> |
| <span class="w"> </span><span class="n">os_task_init</span><span class="p">(</span><span class="o">&</span><span class="n">work_task</span><span class="p">,</span><span class="w"> </span><span class="s">"work"</span><span class="p">,</span><span class="w"> </span><span class="n">work_task_handler</span><span class="p">,</span><span class="w"> </span><span class="nb">NULL</span><span class="p">,</span> |
| <span class="w"> </span><span class="n">WORK_TASK_PRIO</span><span class="p">,</span><span class="w"> </span><span class="n">OS_WAIT_FOREVER</span><span class="p">,</span><span class="w"> </span><span class="n">work_stack</span><span class="p">,</span> |
| <span class="w"> </span><span class="n">WORK_STACK_SIZE</span><span class="p">);</span> |
| |
| <span class="w"> </span><span class="k">return</span><span class="w"> </span><span class="mi">0</span><span class="p">;</span> |
| <span class="p">}</span> |
| </pre></div> |
| </div> |
| <p>Add the call to <code class="docutils literal notranslate"><span class="pre">init_tasks()</span></code> in <code class="docutils literal notranslate"><span class="pre">main()</span></code> before the <code class="docutils literal notranslate"><span class="pre">while</span></code> |
| loop:</p> |
| <div class="highlight-c notranslate"><div class="highlight"><pre><span></span><span class="kt">int</span> |
| <span class="nf">main</span><span class="p">(</span><span class="kt">int</span><span class="w"> </span><span class="n">argc</span><span class="p">,</span><span class="w"> </span><span class="kt">char</span><span class="w"> </span><span class="o">**</span><span class="n">argv</span><span class="p">)</span> |
| <span class="p">{</span> |
| |
| <span class="w"> </span><span class="p">...</span> |
| |
| <span class="w"> </span><span class="cm">/* Initialize the work task */</span> |
| <span class="w"> </span><span class="n">init_tasks</span><span class="p">();</span> |
| |
| <span class="w"> </span><span class="k">while</span><span class="w"> </span><span class="p">(</span><span class="mi">1</span><span class="p">)</span><span class="w"> </span><span class="p">{</span> |
| <span class="w"> </span><span class="p">...</span> |
| <span class="w"> </span><span class="p">}</span> |
| <span class="p">}</span> |
| </pre></div> |
| </div> |
| <p>And that’s it! Now run your application using the newt run command.</p> |
| <div class="highlight-console notranslate"><div class="highlight"><pre><span></span><span class="gp">$ </span>newt<span class="w"> </span>run<span class="w"> </span>arduino_blinky<span class="w"> </span><span class="m">0</span>.0.0 |
| </pre></div> |
| </div> |
| <p>When GDB appears press C then Enter to continue and … <em>wait, why |
| doesn’t our LED blink anymore?</em></p> |
| <div class="section" id="review"> |
| <h4>Review<a class="headerlink" href="#review" title="Permalink to this headline">¶</a></h4> |
| <p>Before we run our new app, let’s review what we need in |
| order to create a task. This is a general case for a new task called |
| mytask:</p> |
| <p><strong>1)</strong> Define a new task, task stack, and priority:</p> |
| <div class="highlight-c notranslate"><div class="highlight"><pre><span></span><span class="cm">/* My Task */</span> |
| <span class="k">struct</span><span class="w"> </span><span class="nc">os_task</span><span class="w"> </span><span class="n">mytask</span> |
| <span class="cm">/* My Task Stack */</span> |
| <span class="cp">#define MYTASK_STACK_SIZE OS_STACK_ALIGN(256)</span> |
| <span class="n">os_stack_t</span><span class="w"> </span><span class="n">mytask_stack</span><span class="p">[</span><span class="n">MYTASK_STACK_SIZE</span><span class="p">];</span> |
| <span class="cm">/* My Task Priority */</span> |
| <span class="cp">#define MYTASK_PRIO (0)</span> |
| </pre></div> |
| </div> |
| <p><strong>2)</strong> Define task function:</p> |
| <div class="highlight-c notranslate"><div class="highlight"><pre><span></span><span class="kt">void</span> |
| <span class="nf">mytask_handler</span><span class="p">(</span><span class="kt">void</span><span class="w"> </span><span class="o">*</span><span class="n">arg</span><span class="p">)</span> |
| <span class="p">{</span> |
| <span class="w"> </span><span class="k">while</span><span class="w"> </span><span class="p">(</span><span class="mi">1</span><span class="p">)</span><span class="w"> </span><span class="p">{</span> |
| <span class="w"> </span><span class="cm">/* ... */</span> |
| <span class="w"> </span><span class="p">}</span> |
| <span class="p">}</span> |
| </pre></div> |
| </div> |
| <p><strong>3)</strong> Initialize the task:</p> |
| <div class="highlight-c notranslate"><div class="highlight"><pre><span></span><span class="n">os_task_init</span><span class="p">(</span><span class="o">&</span><span class="n">mytask</span><span class="p">,</span><span class="w"> </span><span class="s">"mytask"</span><span class="p">,</span><span class="w"> </span><span class="n">mytask_handler</span><span class="p">,</span><span class="w"> </span><span class="nb">NULL</span><span class="p">,</span> |
| <span class="w"> </span><span class="n">MYTASK_PRIO</span><span class="p">,</span><span class="w"> </span><span class="n">OS_WAIT_FOREVER</span><span class="p">,</span><span class="w"> </span><span class="n">mytask_stack</span><span class="p">,</span> |
| <span class="w"> </span><span class="n">MYTASK_STACK_SIZE</span><span class="p">);</span> |
| </pre></div> |
| </div> |
| </div> |
| </div> |
| </div> |
| <div class="section" id="task-priority-preempting-and-context-switching"> |
| <h2><a class="toc-backref" href="#id11">Task Priority, Preempting, and Context Switching</a><a class="headerlink" href="#task-priority-preempting-and-context-switching" title="Permalink to this headline">¶</a></h2> |
| <p>A preemptive RTOS is one in which a higher priority task that is <em>ready |
| to run</em> will preempt (i.e. take the place of) the lower priority task |
| which is <em>running</em>. When a lower priority task is preempted by a higher |
| priority task, the lower priority task’s context data (stack pointer, |
| registers, etc.) is saved and the new task is switched in.</p> |
| <p>In our example, <code class="docutils literal notranslate"><span class="pre">work_task</span></code> (priority 0) has a higher priority than |
| the <code class="docutils literal notranslate"><span class="pre">main</span></code> task (priority 127). Since <code class="docutils literal notranslate"><span class="pre">work_task</span></code> is never put into |
| a <em>sleep</em> state, it holds the processor focus on its context.</p> |
| <p>Let’s give <code class="docutils literal notranslate"><span class="pre">work_task</span></code> a delay and some simulated work to keep it |
| busy. The delay is measured in os ticks and the actual number of ticks |
| per second is dependent on the board. We multiply <code class="docutils literal notranslate"><span class="pre">OS_TICKS_PER_SEC</span></code>, |
| which is defined in the MCU, by the number of seconds we wish to delay.</p> |
| <div class="highlight-c notranslate"><div class="highlight"><pre><span></span><span class="kt">void</span> |
| <span class="nf">work_task_handler</span><span class="p">(</span><span class="kt">void</span><span class="w"> </span><span class="o">*</span><span class="n">arg</span><span class="p">)</span> |
| <span class="p">{</span> |
| <span class="w"> </span><span class="k">struct</span><span class="w"> </span><span class="nc">os_task</span><span class="w"> </span><span class="o">*</span><span class="n">t</span><span class="p">;</span> |
| |
| <span class="w"> </span><span class="n">g_led_pin</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">LED_BLINK_PIN</span><span class="p">;</span> |
| <span class="w"> </span><span class="n">hal_gpio_init_out</span><span class="p">(</span><span class="n">g_led_pin</span><span class="p">,</span><span class="w"> </span><span class="mi">1</span><span class="p">);</span> |
| |
| <span class="w"> </span><span class="k">while</span><span class="w"> </span><span class="p">(</span><span class="mi">1</span><span class="p">)</span><span class="w"> </span><span class="p">{</span> |
| <span class="w"> </span><span class="n">t</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">os_sched_get_current_t</span><span class="o">:</span><span class="n">ask</span><span class="p">();</span> |
| <span class="w"> </span><span class="n">assert</span><span class="p">(</span><span class="n">t</span><span class="o">-></span><span class="n">t_func</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="n">work_task_handler</span><span class="p">);</span> |
| <span class="w"> </span><span class="cm">/* Do work... */</span> |
| <span class="w"> </span><span class="kt">int</span><span class="w"> </span><span class="n">i</span><span class="p">;</span> |
| <span class="w"> </span><span class="k">for</span><span class="p">(</span><span class="n">i</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="mi">0</span><span class="p">;</span><span class="w"> </span><span class="n">i</span><span class="w"> </span><span class="o"><</span><span class="w"> </span><span class="mi">1000000</span><span class="p">;</span><span class="w"> </span><span class="o">++</span><span class="n">i</span><span class="p">)</span><span class="w"> </span><span class="p">{</span> |
| <span class="w"> </span><span class="cm">/* Simulate doing a noticeable amount of work */</span> |
| <span class="w"> </span><span class="n">hal_gpio_write</span><span class="p">(</span><span class="n">g_led_pin</span><span class="p">,</span><span class="w"> </span><span class="mi">1</span><span class="p">);</span> |
| <span class="w"> </span><span class="p">}</span> |
| <span class="w"> </span><span class="n">os_time_delay</span><span class="p">(</span><span class="mi">3</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="n">OS_TICKS_PER_SEC</span><span class="p">);</span> |
| <span class="w"> </span><span class="p">}</span> |
| <span class="p">}</span> |
| </pre></div> |
| </div> |
| <p>In order to notice the LED changing, modify the time delay in |
| <code class="docutils literal notranslate"><span class="pre">main()</span></code> to blink at a higher frequency.</p> |
| <div class="highlight-c notranslate"><div class="highlight"><pre><span></span><span class="n">os_time_delay</span><span class="p">(</span><span class="n">OS_TICKS_PER_SEC</span><span class="o">/</span><span class="mi">10</span><span class="p">);</span> |
| </pre></div> |
| </div> |
| <p>Before we run the app, let’s predict the behavior. With the newest |
| additions to <code class="docutils literal notranslate"><span class="pre">work_task_handler()</span></code>, our first action will be to sleep |
| for three seconds. This allows the <code class="docutils literal notranslate"><span class="pre">main</span></code> task, running <code class="docutils literal notranslate"><span class="pre">main()</span></code>, to |
| take over the CPU and blink to its heart’s content. After three seconds, |
| <code class="docutils literal notranslate"><span class="pre">work_task</span></code> will wake up and be made <em>ready to run</em>. This causes it to |
| preempt the <code class="docutils literal notranslate"><span class="pre">main</span></code> task. The LED will then remain lit for a short |
| period while <code class="docutils literal notranslate"><span class="pre">work_task</span></code> loops, then blink again for another three |
| seconds while <code class="docutils literal notranslate"><span class="pre">work_task</span></code> sleeps.</p> |
| <p>You should see that our prediction was correct!</p> |
| <div class="section" id="priority-management-considerations"> |
| <h3><a class="toc-backref" href="#id12">Priority Management Considerations</a><a class="headerlink" href="#priority-management-considerations" title="Permalink to this headline">¶</a></h3> |
| <p>When projects grow in scope, from blinking LEDs into more sophisticated |
| applications, the number of tasks needed increases alongside complexity. |
| It remains important, then, that each of our tasks is capable of doing |
| its work within a reasonable amount of time.</p> |
| <p>Some tasks, such as the Shell task, execute quickly and require almost |
| instantaneous response. Therefore, the Shell task should be given a high |
| priority. On the other hand, tasks which may be communicating over a |
| network, or processing data, should be given a low priority in order to |
| not hog the CPU.</p> |
| <p>The diagram below shows the different scheduling patterns we would |
| expect when we set the <code class="docutils literal notranslate"><span class="pre">work_task</span></code> priority higher and lower than the |
| <code class="docutils literal notranslate"><span class="pre">main</span></code> task priority.</p> |
| <div class="figure align-default" id="id1"> |
| <img alt="Task Scheduling" src="../../_images/task_lesson.png" /> |
| <p class="caption"><span class="caption-text">Task Scheduling</span><a class="headerlink" href="#id1" title="Permalink to this image">¶</a></p> |
| </div> |
| <p>In the second case where the <code class="docutils literal notranslate"><span class="pre">main</span></code> task has a higher priority, |
| <code class="docutils literal notranslate"><span class="pre">work_task</span></code> runs and executes “work” when the <code class="docutils literal notranslate"><span class="pre">main</span></code> task sleeps, |
| saving us idle time compared to the first case.</p> |
| <p><strong>Note:</strong> Defining the same priority for two tasks fires an assert in |
| <code class="docutils literal notranslate"><span class="pre">os_task_init()</span></code> and must be avoided. Priority 127 is reserved for main |
| task, 255 for idle task.</p> |
| </div> |
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