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| <section id="pwm-drivers"> |
| <h1>PWM Drivers<a class="headerlink" href="#pwm-drivers" title="Permalink to this heading"></a></h1> |
| <p>For the purposes of this driver, a PWM device is any device that |
| generates periodic output pulses of controlled frequency and pulse |
| width. Such a device might be used, for example, to perform |
| pulse-width modulated output or frequency/pulse-count modulated |
| output (such as might be needed to control a stepper motor).</p> |
| <p>The NuttX PWM driver is split into two parts:</p> |
| <ol class="arabic simple"> |
| <li><p>An “upper half”, generic driver that provides the common PWM |
| interface to application level code, and</p></li> |
| <li><p>A “lower half”, platform-specific driver that implements the |
| low-level timer controls to implement the PWM functionality.</p></li> |
| </ol> |
| <p>Files supporting PWM can be found in the following locations:</p> |
| <ul class="simple"> |
| <li><p><strong>Interface Definition</strong>. The header file for the NuttX PWM |
| driver reside at <code class="docutils literal notranslate"><span class="pre">include/nuttx/timers/pwm.h</span></code>. This header |
| file includes both the application level interface to the PWM |
| driver as well as the interface between the “upper half” and |
| “lower half” drivers. The PWM module uses a standard character |
| driver framework. However, since the PWM driver is a device |
| control interface and not a data transfer interface, the |
| majority of the functionality available to the application is |
| implemented in driver ioctl calls.</p></li> |
| <li><p><strong>“Upper Half” Driver</strong>. The generic, “upper half” PWM driver |
| resides at <code class="docutils literal notranslate"><span class="pre">drivers/timers/pwm.c</span></code>.</p></li> |
| <li><p><strong>“Lower Half” Drivers</strong>. Platform-specific PWM drivers reside |
| in <code class="docutils literal notranslate"><span class="pre">arch/<architecture>/src/<hardware></span></code> |
| directory for the specific processor <code class="docutils literal notranslate"><span class="pre"><architecture></span></code> and for |
| the specific <code class="docutils literal notranslate"><span class="pre"><chip></span></code> PWM peripheral devices.</p></li> |
| </ul> |
| <section id="application-level-interface"> |
| <h2>Application Level Interface<a class="headerlink" href="#application-level-interface" title="Permalink to this heading"></a></h2> |
| <p>The first necessary thing to be done in order to use the PWM driver in an |
| application is to include the header file for the NuttX timer driver. It contains |
| the Application Level Interface to the PWM driver. To do so, include:</p> |
| <div class="highlight-c notranslate"><div class="highlight"><pre><span></span><span class="cp">#include</span><span class="w"> </span><span class="cpf"><nuttx/timers/pwm.h></span> |
| </pre></div> |
| </div> |
| <p>PWM driver is registered as a POSIX character device file into <code class="docutils literal notranslate"><span class="pre">/dev</span></code> |
| namespace. It is necessary to open the device to get a file descriptor for |
| further operations.</p> |
| <p>The PWM is accessed only through <code class="docutils literal notranslate"><span class="pre">ioctl</span></code> interface, functions <code class="docutils literal notranslate"><span class="pre">read</span></code> |
| and <code class="docutils literal notranslate"><span class="pre">write</span></code> does not have any affect. Following <code class="docutils literal notranslate"><span class="pre">ioctl</span></code> commands are |
| available:</p> |
| <blockquote> |
| <div><ul class="simple"> |
| <li><p><a class="reference internal" href="#c.PWMIOC_SETCHARACTERISTICS" title="PWMIOC_SETCHARACTERISTICS"><code class="xref c c-macro docutils literal notranslate"><span class="pre">PWMIOC_SETCHARACTERISTICS</span></code></a></p></li> |
| <li><p><a class="reference internal" href="#c.PWMIOC_GETCHARACTERISTICS" title="PWMIOC_GETCHARACTERISTICS"><code class="xref c c-macro docutils literal notranslate"><span class="pre">PWMIOC_GETCHARACTERISTICS</span></code></a></p></li> |
| <li><p><a class="reference internal" href="#c.PWMIOC_START" title="PWMIOC_START"><code class="xref c c-macro docutils literal notranslate"><span class="pre">PWMIOC_START</span></code></a></p></li> |
| <li><p><code class="xref c c-macro docutils literal notranslate"><span class="pre">PWMIOC_STOP</span></code></p></li> |
| </ul> |
| </div></blockquote> |
| <dl class="c macro"> |
| <dt class="sig sig-object c" id="c.PWMIOC_SETCHARACTERISTICS"> |
| <span class="sig-name descname"><span class="n"><span class="pre">PWMIOC_SETCHARACTERISTICS</span></span></span><a class="headerlink" href="#c.PWMIOC_SETCHARACTERISTICS" title="Permalink to this definition"></a><br /></dt> |
| <dd></dd></dl> |
| |
| <p>The <code class="docutils literal notranslate"><span class="pre">PWMIOC_SETCHARACTERISTICS</span></code> command sets PWM characteristics such as |
| frequency, duty cycle, dead times and so on. These characteristics are |
| set through <code class="docutils literal notranslate"><span class="pre">pwm_info_s</span></code> structure.</p> |
| <dl class="c struct"> |
| <dt class="sig sig-object c" id="c.pwm_info_s"> |
| <span class="k"><span class="pre">struct</span></span><span class="w"> </span><span class="sig-name descname"><span class="n"><span class="pre">pwm_info_s</span></span></span><a class="headerlink" href="#c.pwm_info_s" title="Permalink to this definition"></a><br /></dt> |
| <dd></dd></dl> |
| |
| <div class="highlight-c notranslate"><div class="highlight"><pre><span></span><span class="k">struct</span><span class="w"> </span><span class="nc">pwm_info_s</span> |
| <span class="p">{</span> |
| <span class="w"> </span><span class="cm">/* Frequency of the pulse train */</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="cp">#ifdef CONFIG_PWM_MULTICHAN</span> |
| <span class="w"> </span><span class="cm">/* Per-channel output state */</span> |
| <span class="w"> </span><span class="k">struct</span><span class="w"> </span><span class="nc">pwm_chan_s</span><span class="w"> </span><span class="n">channels</span><span class="p">[</span><span class="n">CONFIG_PWM_NCHANNELS</span><span class="p">];</span> |
| <span class="cp">#else</span> |
| <span class="w"> </span><span class="cm">/* Duty of the pulse train, "1"-to-"0" duration.</span> |
| <span class="cm"> * Maximum: 65535/65536 (0x0000ffff)</span> |
| <span class="cm"> * Minimum: 1/65536 (0x00000001)</span> |
| <span class="cm"> */</span> |
| <span class="w"> </span><span class="n">ub16_t</span><span class="w"> </span><span class="n">duty</span><span class="p">;</span> |
| <span class="cp">#ifdef CONFIG_PWM_DEADTIME</span> |
| <span class="w"> </span><span class="cm">/* Dead time value for main output */</span> |
| <span class="w"> </span><span class="n">ub16_t</span><span class="w"> </span><span class="n">dead_time_a</span><span class="p">;</span> |
| <span class="w"> </span><span class="cm">/* Dead time value for complementary output */</span> |
| <span class="w"> </span><span class="n">ub16_t</span><span class="w"> </span><span class="n">dead_time_b</span><span class="p">;</span> |
| <span class="cp">#endif</span> |
| <span class="cp">#ifdef CONFIG_PWM_PULSECOUNT</span> |
| <span class="w"> </span><span class="cm">/* The number of pulse to generate. 0 means to</span> |
| <span class="cm"> * generate an indefinite number of pulses</span> |
| <span class="cm"> */</span> |
| <span class="w"> </span><span class="kt">uint32_t</span><span class="w"> </span><span class="n">count</span><span class="p">;</span> |
| <span class="cp">#endif</span> |
| <span class="w"> </span><span class="cm">/* Channel polarity */</span> |
| <span class="w"> </span><span class="kt">uint8_t</span><span class="w"> </span><span class="n">cpol</span><span class="p">;</span> |
| <span class="w"> </span><span class="cm">/* Disabled channel polarity */</span> |
| <span class="w"> </span><span class="kt">uint8_t</span><span class="w"> </span><span class="n">dcpol</span><span class="p">;</span> |
| <span class="cp">#endif </span><span class="cm">/* CONFIG_PWM_MULTICHAN */</span> |
| <span class="w"> </span><span class="cm">/* User provided argument to be used in the lower half */</span> |
| <span class="w"> </span><span class="n">FAR</span><span class="w"> </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> |
| </pre></div> |
| </div> |
| <p>Structure <code class="docutils literal notranslate"><span class="pre">pwm_chan_s</span></code> holds the representation of one PWM channel |
| if multiple channels are used ( <code class="docutils literal notranslate"><span class="pre">CONFIG_PWM_MULTICHAN</span></code> is set).</p> |
| <dl class="c struct"> |
| <dt class="sig sig-object c" id="c.pwm_chan_s"> |
| <span class="k"><span class="pre">struct</span></span><span class="w"> </span><span class="sig-name descname"><span class="n"><span class="pre">pwm_chan_s</span></span></span><a class="headerlink" href="#c.pwm_chan_s" title="Permalink to this definition"></a><br /></dt> |
| <dd></dd></dl> |
| |
| <div class="highlight-c notranslate"><div class="highlight"><pre><span></span><span class="k">struct</span><span class="w"> </span><span class="nc">pwm_chan_s</span> |
| <span class="p">{</span> |
| <span class="w"> </span><span class="cm">/* Duty of the pulse train, "1"-to-"0" duration.</span> |
| <span class="cm"> * Maximum: 65535/65536 (0x0000ffff)</span> |
| <span class="cm"> * Minimum: 1/65536 (0x00000001)</span> |
| <span class="cm"> */</span> |
| <span class="w"> </span><span class="n">ub16_t</span><span class="w"> </span><span class="n">duty</span><span class="p">;</span> |
| <span class="cp">#ifdef CONFIG_PWM_OVERWRITE</span> |
| <span class="w"> </span><span class="cm">/* Channel overwrite */</span> |
| <span class="w"> </span><span class="kt">bool</span><span class="w"> </span><span class="n">ch_outp_ovrwr</span><span class="p">;</span> |
| <span class="w"> </span><span class="cm">/* Channel overwrite value */</span> |
| <span class="w"> </span><span class="kt">bool</span><span class="w"> </span><span class="n">ch_outp_ovrwr_val</span><span class="p">;</span> |
| <span class="cp">#endif</span> |
| <span class="cp">#ifdef CONFIG_PWM_DEADTIME</span> |
| <span class="w"> </span><span class="cm">/* Dead time value for main output */</span> |
| <span class="w"> </span><span class="n">ub16_t</span><span class="w"> </span><span class="n">dead_time_a</span><span class="p">;</span> |
| <span class="w"> </span><span class="cm">/* Dead time value for complementary output */</span> |
| <span class="w"> </span><span class="n">ub16_t</span><span class="w"> </span><span class="n">dead_time_b</span><span class="p">;</span> |
| <span class="cp">#endif</span> |
| <span class="w"> </span><span class="cm">/* Channel polarity */</span> |
| <span class="w"> </span><span class="kt">uint8_t</span><span class="w"> </span><span class="n">cpol</span><span class="p">;</span> |
| <span class="w"> </span><span class="cm">/* Disabled channel polarity */</span> |
| <span class="w"> </span><span class="kt">uint8_t</span><span class="w"> </span><span class="n">dcpol</span><span class="p">;</span> |
| <span class="w"> </span><span class="cm">/* Channel number */</span> |
| <span class="w"> </span><span class="kt">int8_t</span><span class="w"> </span><span class="n">channel</span><span class="p">;</span> |
| <span class="p">};</span> |
| </pre></div> |
| </div> |
| <p>Apart from duty cycle and frequency, the <code class="docutils literal notranslate"><span class="pre">ioctl</span></code> command allows to |
| set many other PWM characteristics. These functionalities might not be |
| supported by all PWM controllers and user should always refer to target |
| documentation in this case.</p> |
| <p>If <code class="docutils literal notranslate"><span class="pre">CONFIG_PWM_OVERWRITE</span></code> is set and <code class="docutils literal notranslate"><span class="pre">ch_outp_ovrwr</span></code> is true, it is |
| possible to overwrite channel output with value set in <code class="docutils literal notranslate"><span class="pre">ch_outp_ovrwr_val</span></code>. |
| Configuration option <code class="docutils literal notranslate"><span class="pre">CONFIG_PWM_DEADTIME</span></code> and fields <code class="docutils literal notranslate"><span class="pre">dead_time_a</span></code> |
| and <code class="docutils literal notranslate"><span class="pre">dead_time_b</span></code> provides an option to set dead time between complementary |
| outputs. This instructs the driver to automatically insert output activation |
| delay for complementary PWM outputs and is useful for H-bridge motor control |
| for example.</p> |
| <p>User may also set default channel polarity <code class="docutils literal notranslate"><span class="pre">cpol</span></code> and disabled channel |
| polarity <code class="docutils literal notranslate"><span class="pre">dcpol</span></code>. If set to zero, default controller values (or values |
| determined in the configuration) are used. Following defines can be used |
| to set the polarities:</p> |
| <div class="highlight-c notranslate"><div class="highlight"><pre><span></span><span class="cm">/* Not defined, the default output state is arch dependent */</span> |
| <span class="cp">#define PWM_CPOL_NDEF 0</span> |
| <span class="cm">/* Logical zero */</span> |
| <span class="cp">#define PWM_CPOL_LOW 1</span> |
| <span class="cm">/* Logical one */</span> |
| <span class="cp">#define PWM_CPOL_HIGH 2</span> |
| |
| <span class="cm">/* Not defined, the default output state is arch dependent */</span> |
| <span class="cp">#define PWM_DCPOL_NDEF 0</span> |
| <span class="w"> </span><span class="cm">/* Logical zero */</span> |
| <span class="cp">#define PWM_DCPOL_LOW 1</span> |
| <span class="w"> </span><span class="cm">/* Logical one */</span> |
| <span class="cp">#define PWM_DCPOL_HIGH 2</span> |
| </pre></div> |
| </div> |
| <dl class="c macro"> |
| <dt class="sig sig-object c" id="c.PWMIOC_GETCHARACTERISTICS"> |
| <span class="sig-name descname"><span class="n"><span class="pre">PWMIOC_GETCHARACTERISTICS</span></span></span><a class="headerlink" href="#c.PWMIOC_GETCHARACTERISTICS" title="Permalink to this definition"></a><br /></dt> |
| <dd></dd></dl> |
| |
| <p>Command <code class="docutils literal notranslate"><span class="pre">PWMIOC_GETCHARACTERISTICS</span></code> operates the same way as |
| <code class="docutils literal notranslate"><span class="pre">PWMIOC_SETCHARACTERISTICS</span></code> but it obtains currently set values |
| instead of setting them.</p> |
| <dl class="c macro"> |
| <dt class="sig sig-object c" id="c.PWMIOC_START"> |
| <span class="sig-name descname"><span class="n"><span class="pre">PWMIOC_START</span></span></span><a class="headerlink" href="#c.PWMIOC_START" title="Permalink to this definition"></a><br /></dt> |
| <dd></dd></dl> |
| |
| <p>The <code class="docutils literal notranslate"><span class="pre">PWMIOC_START</span></code> command starts the pulsed output. Characteristics |
| of PWM channels should be set before this operation.</p> |
| <dl class="c macro"> |
| <dt class="sig sig-object c" id="c.PWMIOC_STOPS"> |
| <span class="sig-name descname"><span class="n"><span class="pre">PWMIOC_STOPS</span></span></span><a class="headerlink" href="#c.PWMIOC_STOPS" title="Permalink to this definition"></a><br /></dt> |
| <dd></dd></dl> |
| |
| <p>The <code class="docutils literal notranslate"><span class="pre">PWMIOC_STOPS</span></code> command stops the pulsed output.</p> |
| <dl class="c macro"> |
| <dt class="sig sig-object c" id="c.PWMIOC_FAULTS_FETCH_AND_CLEAR"> |
| <span class="sig-name descname"><span class="n"><span class="pre">PWMIOC_FAULTS_FETCH_AND_CLEAR</span></span></span><a class="headerlink" href="#c.PWMIOC_FAULTS_FETCH_AND_CLEAR" title="Permalink to this definition"></a><br /></dt> |
| <dd></dd></dl> |
| |
| <p>The <code class="docutils literal notranslate"><span class="pre">PWMIOC_FAULTS_FETCH_AND_CLEAR</span></code> command clears fault inputs. Some |
| faults can be latched (remain active even if the source is not active |
| anymore) and have to be cleared from the software. This provides an option |
| to clear faults from the application and re-enable PWM output. It can be |
| also used to fetch the current faults.</p> |
| <p>The call takes a pointer to <code class="docutils literal notranslate"><span class="pre">unsigned</span> <span class="pre">long</span></code> variable as an argument, a |
| bitmask defining which faults are to be cleared. The driver clears these |
| faults and fills the argument with the active faults prior to this clear. |
| Having the argument variable equal to zero will result in no faults cleared |
| but the user will get the currently active faults. If NULL is passed as |
| an argument, then all currently set faults are cleared and fetch is not |
| performed.</p> |
| <p>This may not be supported by all drivers.</p> |
| <section id="application-example"> |
| <h3>Application Example<a class="headerlink" href="#application-example" title="Permalink to this heading"></a></h3> |
| <p>An example application can be found in <code class="docutils literal notranslate"><span class="pre">nuttx-apps</span></code> repository under the |
| path <code class="docutils literal notranslate"><span class="pre">examples/pwm</span></code>.</p> |
| <div class="highlight-bash notranslate"><div class="highlight"><pre><span></span>nsh><span class="w"> </span>pwm |
| </pre></div> |
| </div> |
| </section> |
| </section> |
| <section id="configuration"> |
| <h2>Configuration<a class="headerlink" href="#configuration" title="Permalink to this heading"></a></h2> |
| <p>This section describes common PWM configuration in <code class="docutils literal notranslate"><span class="pre">Kconfig</span></code>. The reader |
| should refer to target documentation for target specific configuration.</p> |
| <p>PWM is enabled by <code class="docutils literal notranslate"><span class="pre">CONFIG_PWM</span></code> configuration option. Option |
| <code class="docutils literal notranslate"><span class="pre">CONFIG_PWM_MULTICHAN</span></code> selects support for multiple channels for one PWM |
| instance. If multiple channels are used, configuration option |
| <code class="docutils literal notranslate"><span class="pre">CONFIG_PWM_NCHANNELS</span></code> defines the maximum number of channels per instance. |
| Each timer/controller may support fewer output channels than this value.</p> |
| <p>Generation of pin overwrite is enabled by <code class="docutils literal notranslate"><span class="pre">CONFIG_PWM_OVERWRITE</span></code> option. |
| This supports generation of a pin overwrite with 0 or 1 without the need to |
| wait for an end of cycle.</p> |
| <p>The <code class="docutils literal notranslate"><span class="pre">CONFIG_PWM_DEADTIME</span></code> option brings the possibility to introduce |
| dead time values between complementary PWM outputs.</p> |
| </section> |
| </section> |
| |
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