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   <section id="capture">
 <h1>Capture<a class="headerlink" href="#capture" title="Permalink to this heading"></a></h1>
 <p>The <strong>capture driver</strong> is a character device driver that allows capturing
 timer values on specific events. This is useful for tasks such as
 measuring the frequency, duty cycle, or pulse count of an input signal.</p>
 <p>This documentation is based on the STM32H7 timer capture driver.</p>
 <section id="usage">
 <h2>Usage<a class="headerlink" href="#usage" title="Permalink to this heading"></a></h2>
 <p>The capture driver is accessed via a device file (e.g., <code class="docutils literal notranslate"><span class="pre">/dev/capture0</span></code>).
 You can use standard file operations along with <code class="docutils literal notranslate"><span class="pre">ioctl()</span></code> calls to
 retrieve captured values or configure the driver.</p>
 <section id="supported-ioctl-commands">
 <h3>Supported <code class="docutils literal notranslate"><span class="pre">ioctl</span></code> Commands<a class="headerlink" href="#supported-ioctl-commands" title="Permalink to this heading"></a></h3>
 <dl class="c macro">
 <dt class="sig sig-object c" id="c.CAPIOC_DUTYCYCLE">
 <span class="sig-name descname"><span class="n"><span class="pre">CAPIOC_DUTYCYCLE</span></span></span><a class="headerlink" href="#c.CAPIOC_DUTYCYCLE" title="Permalink to this definition"></a><br /></dt>
 <dd><p>Get the PWM duty cycle from the capture unit.</p>
 <p><strong>Argument:</strong> <code class="docutils literal notranslate"><span class="pre">int8_t</span> <span class="pre">*</span></code> (pointer to duty cycle percentage).</p>
 </dd></dl>

 <dl class="c macro">
 <dt class="sig sig-object c" id="c.CAPIOC_FREQUENCE">
 <span class="sig-name descname"><span class="n"><span class="pre">CAPIOC_FREQUENCE</span></span></span><a class="headerlink" href="#c.CAPIOC_FREQUENCE" title="Permalink to this definition"></a><br /></dt>
 <dd><p>Get the pulse frequency from the capture unit.</p>
 <p><strong>Argument:</strong> <code class="docutils literal notranslate"><span class="pre">int32_t</span> <span class="pre">*</span></code> (pointer to frequency in Hz).</p>
 </dd></dl>

 <dl class="c macro">
 <dt class="sig sig-object c" id="c.CAPIOC_EDGES">
 <span class="sig-name descname"><span class="n"><span class="pre">CAPIOC_EDGES</span></span></span><a class="headerlink" href="#c.CAPIOC_EDGES" title="Permalink to this definition"></a><br /></dt>
 <dd><p>Get the number of PWM edges detected.</p>
 <p><strong>Argument:</strong> <code class="docutils literal notranslate"><span class="pre">int32_t</span> <span class="pre">*</span></code> (pointer to edge count).</p>
 </dd></dl>

 <dl class="c macro">
 <dt class="sig sig-object c" id="c.CAPIOC_ALL">
 <span class="sig-name descname"><span class="n"><span class="pre">CAPIOC_ALL</span></span></span><a class="headerlink" href="#c.CAPIOC_ALL" title="Permalink to this definition"></a><br /></dt>
 <dd><p>Get duty cycle, pulse frequency, and edge count in a single call.</p>
 <p><strong>Argument:</strong> <code class="docutils literal notranslate"><span class="pre">struct</span> <span class="pre">cap_all_s</span> <span class="pre">*</span></code> (structure containing all values).</p>
 </dd></dl>

 <dl class="c macro">
 <dt class="sig sig-object c" id="c.CAPIOC_PULSES">
 <span class="sig-name descname"><span class="n"><span class="pre">CAPIOC_PULSES</span></span></span><a class="headerlink" href="#c.CAPIOC_PULSES" title="Permalink to this definition"></a><br /></dt>
 <dd><p>Read the current pulse count value.</p>
 <p><strong>Argument:</strong> <code class="docutils literal notranslate"><span class="pre">int</span> <span class="pre">*</span></code> (pointer to pulse count).</p>
 </dd></dl>

 <dl class="c macro">
 <dt class="sig sig-object c" id="c.CAPIOC_CLR_CNT">
 <span class="sig-name descname"><span class="n"><span class="pre">CAPIOC_CLR_CNT</span></span></span><a class="headerlink" href="#c.CAPIOC_CLR_CNT" title="Permalink to this definition"></a><br /></dt>
 <dd><p>Clear the pulse count value.</p>
 <p><strong>Argument:</strong> None.</p>
 </dd></dl>

 <dl class="c macro">
 <dt class="sig sig-object c" id="c.CAPIOC_FILTER">
 <span class="sig-name descname"><span class="n"><span class="pre">CAPIOC_FILTER</span></span></span><a class="headerlink" href="#c.CAPIOC_FILTER" title="Permalink to this definition"></a><br /></dt>
 <dd><p>Configure the glitch filter.</p>
 <p><strong>Argument:</strong> <code class="docutils literal notranslate"><span class="pre">uint32_t</span></code> (filter value in nanoseconds, <code class="docutils literal notranslate"><span class="pre">0</span></code> to disable).</p>
 </dd></dl>

 <dl class="c macro">
 <dt class="sig sig-object c" id="c.CAPIOC_HANDLER">
 <span class="sig-name descname"><span class="n"><span class="pre">CAPIOC_HANDLER</span></span></span><a class="headerlink" href="#c.CAPIOC_HANDLER" title="Permalink to this definition"></a><br /></dt>
 <dd><p>Set a user callback function for capture events.</p>
 <p><strong>Argument:</strong> <code class="docutils literal notranslate"><span class="pre">xcpt_t</span></code> (function pointer, <code class="docutils literal notranslate"><span class="pre">NULL</span></code> to disable).</p>
 </dd></dl>

 <dl class="c macro">
 <dt class="sig sig-object c" id="c.CAPIOC_ADD_WP">
 <span class="sig-name descname"><span class="n"><span class="pre">CAPIOC_ADD_WP</span></span></span><a class="headerlink" href="#c.CAPIOC_ADD_WP" title="Permalink to this definition"></a><br /></dt>
 <dd><p>Add a watchpoint to the capture unit.</p>
 <p><strong>Argument:</strong> <code class="docutils literal notranslate"><span class="pre">int</span></code> (value to watch for).</p>
 </dd></dl>

 </section>
 <section id="configuration">
 <h3>Configuration<a class="headerlink" href="#configuration" title="Permalink to this heading"></a></h3>
 <p>To enable the capture driver, enable the following configuration options:</p>
 <ul class="simple">
 <li><p><code class="docutils literal notranslate"><span class="pre">CONFIG_CAPTURE</span></code></p></li>
 <li><p><code class="docutils literal notranslate"><span class="pre">CONFIG_STM32H7_TIM4_CAP</span></code> (for STM32H7 Timer 4)</p></li>
 </ul>
 <p>The <code class="docutils literal notranslate"><span class="pre">CONFIG_CAPTURE</span></code> option enables the lower-half driver and registers
 the <code class="docutils literal notranslate"><span class="pre">/dev/capture</span></code> device.</p>
 <p>Without it, capture is still possible manually by including the appropriate
 header (e.g., <code class="docutils literal notranslate"><span class="pre">arch/arm/src/stm32h7/stm32_capture.h</span></code>) and performing a
 manual initialization.</p>
 </section>
 <section id="example">
 <h3>Example<a class="headerlink" href="#example" title="Permalink to this heading"></a></h3>
 <p>Here is a simple example of using the capture driver to read a signal’s
 frequency:</p>
 <div class="highlight-c notranslate"><div class="highlight"><pre><span></span><span class="cp">#include</span><span class="w"> </span><span class="cpf">&lt;stdio.h&gt;</span>
 <span class="cp">#include</span><span class="w"> </span><span class="cpf">&lt;fcntl.h&gt;</span>
 <span class="cp">#include</span><span class="w"> </span><span class="cpf">&lt;sys/ioctl.h&gt;</span>
 <span class="cp">#include</span><span class="w"> </span><span class="cpf">&lt;nuttx/timers/capture.h&gt;</span>

 <span class="kt">int</span><span class="w"> </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="kt">int</span><span class="w"> </span><span class="n">fd</span><span class="p">;</span>
 <span class="w">  </span><span class="kt">uint32_t</span><span class="w"> </span><span class="n">frequency</span><span class="p">;</span>

 <span class="w">  </span><span class="n">fd</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">open</span><span class="p">(</span><span class="s">&quot;/dev/capture0&quot;</span><span class="p">,</span><span class="w"> </span><span class="n">O_RDONLY</span><span class="p">);</span>
 <span class="w">  </span><span class="k">if</span><span class="w"> </span><span class="p">(</span><span class="n">fd</span><span class="w"> </span><span class="o">&lt;</span><span class="w"> </span><span class="mi">0</span><span class="p">)</span>
 <span class="w">    </span><span class="p">{</span>
 <span class="w">      </span><span class="n">perror</span><span class="p">(</span><span class="s">&quot;Failed to open capture device&quot;</span><span class="p">);</span>
 <span class="w">      </span><span class="k">return</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="k">if</span><span class="w"> </span><span class="p">(</span><span class="n">ioctl</span><span class="p">(</span><span class="n">fd</span><span class="p">,</span><span class="w"> </span><span class="n">CAPIOC_FREQUENCE</span><span class="p">,</span><span class="w"> </span><span class="p">(</span><span class="kt">unsigned</span><span class="w"> </span><span class="kt">long</span><span class="p">)</span><span class="o">&amp;</span><span class="n">frequency</span><span class="p">)</span><span class="w"> </span><span class="o">&lt;</span><span class="w"> </span><span class="mi">0</span><span class="p">)</span>
 <span class="w">    </span><span class="p">{</span>
 <span class="w">      </span><span class="n">perror</span><span class="p">(</span><span class="s">&quot;Failed to get frequency&quot;</span><span class="p">);</span>
 <span class="w">      </span><span class="n">close</span><span class="p">(</span><span class="n">fd</span><span class="p">);</span>
 <span class="w">      </span><span class="k">return</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">printf</span><span class="p">(</span><span class="s">&quot;Frequency: %u Hz</span><span class="se">\n</span><span class="s">&quot;</span><span class="p">,</span><span class="w"> </span><span class="n">frequency</span><span class="p">);</span>

 <span class="w">  </span><span class="n">close</span><span class="p">(</span><span class="n">fd</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>
 </section>
 <section id="notes">
 <h3>Notes<a class="headerlink" href="#notes" title="Permalink to this heading"></a></h3>
 <ul class="simple">
 <li><p>The actual set of supported <code class="docutils literal notranslate"><span class="pre">ioctl</span></code> commands may vary depending on
 the hardware and driver implementation.</p></li>
 <li><p>The <code class="docutils literal notranslate"><span class="pre">CAPIOC_FREQUENCE</span></code> macro name is preserved for compatibility,
 even though “frequency” is the correct English spelling.</p></li>
 <li><p>Always check return values from <code class="docutils literal notranslate"><span class="pre">ioctl()</span></code> calls for error handling.</p></li>
 <li><p><strong>Important:</strong> In debug builds of NuttX, calling an unsupported
 <code class="docutils literal notranslate"><span class="pre">ioctl</span></code> command will trigger a <code class="docutils literal notranslate"><span class="pre">DEBUGASSERT</span></code> in the driver,
 which will halt or crash the system.</p></li>
 </ul>
 </section>
 </section>
 </section>


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