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| <div class="section" id="scheduler"> |
| <h1>Scheduler<a class="headerlink" href="#scheduler" title="Permalink to this headline">¶</a></h1> |
| <p>Scheduler’s job is to maintain the list of tasks and decide which one |
| should be running next.</p> |
| <div class="section" id="description"> |
| <h2>Description<a class="headerlink" href="#description" title="Permalink to this headline">¶</a></h2> |
| <p>Task states can be <em>running</em>, <em>ready to run</em> or <em>sleeping</em>.</p> |
| <p>When task is <em>running</em>, CPU is executing in that task’s context. The |
| program counter (PC) is pointing to instructions task wants to execute |
| and stack pointer (SP) is pointing to task’s stack.</p> |
| <p>Task which is <em>ready to run</em> wants to get on the CPU to do its work.</p> |
| <p>Task which is <em>sleeping</em> has no more work to do. It’s waiting for |
| someone else to wake it up.</p> |
| <p>Scheduler algorithm is simple: from among the tasks which are ready to |
| run, pick the the one with highest priority (lowest numeric value in |
| task’s <code class="xref c c-member docutils literal notranslate"><span class="pre">t_prio</span></code> field), and make its state <em>running</em>.</p> |
| <p>Tasks which are either <em>running</em> or <em>ready to run</em> are kept in linked |
| list <code class="docutils literal notranslate"><span class="pre">g_os_run_list</span></code>. This list is ordered by priority.</p> |
| <p>Tasks which are <em>sleeping</em> are kept in linked list <code class="docutils literal notranslate"><span class="pre">g_os_sleep_list</span></code>.</p> |
| <p>Scheduler has a CPU architecture specific component; this code is |
| responsible for swapping in the task which should be <em>running</em>. This |
| process is called context switch. During context switching the state of |
| the CPU (e.g. registers) for the currently <em>running</em> task is stored and |
| the new task is swapped in.</p> |
| </div> |
| <div class="section" id="api"> |
| <h2>API<a class="headerlink" href="#api" title="Permalink to this headline">¶</a></h2> |
| <dl class="c function"> |
| <dt id="c.os_sched_get_current_task"> |
| <span class="target" id="group___o_s_sched_1gae76543413dbb2abc71c8236da4e93cfb"></span><em class="property"><span class="pre">struct</span></em> <a class="reference internal" href="../task/task.html#c.os_task" title="os_task"><span class="pre">os_task</span></a> <span class="pre">*</span><code class="sig-name descname"><span class="pre">os_sched_get_current_task</span></code><span class="sig-paren">(</span><span class="pre">void</span><span class="sig-paren">)</span><a class="headerlink" href="#c.os_sched_get_current_task" title="Permalink to this definition">¶</a><br /></dt> |
| <dd><p>Returns the currently running task. </p> |
| <p>Note that this task may or may not be the highest priority task ready to run.</p> |
| <p><dl class="simple"> |
| <dt><strong>Return</strong></dt><dd><p>The currently running task. </p> |
| </dd> |
| </dl> |
| </p> |
| </dd></dl> |
| |
| <dl class="c function"> |
| <dt id="c.os_sched_set_current_task"> |
| <span class="target" id="group___o_s_sched_1gaf61f1ee217e2f1169f1cb4f34df57a10"></span><span class="pre">void</span> <code class="sig-name descname"><span class="pre">os_sched_set_current_task</span></code><span class="sig-paren">(</span><em class="property"><span class="pre">struct</span></em> <a class="reference internal" href="../task/task.html#c.os_task" title="os_task"><span class="pre">os_task</span></a><span class="pre">*</span><span class="sig-paren">)</span><a class="headerlink" href="#c.os_sched_set_current_task" title="Permalink to this definition">¶</a><br /></dt> |
| <dd></dd></dl> |
| |
| <dl class="c function"> |
| <dt id="c.os_sched_next_task"> |
| <span class="target" id="group___o_s_sched_1ga5bb9ddd317310d64f1f85c868ffab923"></span><em class="property"><span class="pre">struct</span></em> <a class="reference internal" href="../task/task.html#c.os_task" title="os_task"><span class="pre">os_task</span></a> <span class="pre">*</span><code class="sig-name descname"><span class="pre">os_sched_next_task</span></code><span class="sig-paren">(</span><span class="pre">void</span><span class="sig-paren">)</span><a class="headerlink" href="#c.os_sched_next_task" title="Permalink to this definition">¶</a><br /></dt> |
| <dd></dd></dl> |
| |
| <dl class="c function"> |
| <dt id="c.os_sched"> |
| <span class="target" id="group___o_s_sched_1gabf7d98a6bb6558a60d1f471736d29ba7"></span><span class="pre">void</span> <code class="sig-name descname"><span class="pre">os_sched</span></code><span class="sig-paren">(</span><em class="property"><span class="pre">struct</span></em> <a class="reference internal" href="../task/task.html#c.os_task" title="os_task"><span class="pre">os_task</span></a><span class="pre">*</span><span class="sig-paren">)</span><a class="headerlink" href="#c.os_sched" title="Permalink to this definition">¶</a><br /></dt> |
| <dd><p>Performs context switch if needed. </p> |
| <p>If next_t is set, that task will be made running. If next_t is NULL, highest priority ready to run is swapped in. This function can be called when new tasks were made ready to run or if the current task is moved to sleeping state.</p> |
| <p>This function will call the architecture specific routine to swap in the new task.</p> |
| <p><div class="highlight-none notranslate"><div class="highlight"><pre><span></span>// example |
| os_error_t |
| os_mutex_release(struct os_mutex *mu) |
| { |
| ... |
| OS_EXIT_CRITICAL(sr); |
| |
| // Re-schedule if needed |
| if (resched) { |
| os_sched(rdy); |
| } |
| |
| return OS_OK; |
| |
| } |
| </pre></div> |
| </div> |
| <dl class="simple"> |
| <dt><strong>Return</strong></dt><dd><p>n/a</p> |
| </dd> |
| <dt><strong>Note</strong></dt><dd><p>Interrupts must be disabled when calling this.</p> |
| </dd> |
| <dt><strong>Parameters</strong></dt><dd><ul class="breatheparameterlist simple"> |
| <li><p><code class="docutils literal notranslate"><span class="pre">next_t</span></code>: Pointer to task which must run next (optional)</p></li> |
| </ul> |
| </dd> |
| </dl> |
| </p> |
| </dd></dl> |
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