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| <li class="toctree-l2 current"><a class="current reference internal" href="#">Audio Subsystem</a><ul> |
| <li class="toctree-l3"><a class="reference internal" href="#files-in-nuttx-audio">Files in nuttx/audio</a></li> |
| <li class="toctree-l3"><a class="reference internal" href="#related-header-files">Related Header Files</a></li> |
| <li class="toctree-l3"><a class="reference internal" href="#configuration-settings">Configuration Settings</a><ul> |
| <li class="toctree-l4"><a class="reference internal" href="#general-audio-settings">General Audio Settings</a></li> |
| <li class="toctree-l4"><a class="reference internal" href="#audio-format-support-selections">Audio Format Support Selections</a></li> |
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| <section id="audio-subsystem"> |
| <h1>Audio Subsystem<a class="headerlink" href="#audio-subsystem" title="Permalink to this heading"></a></h1> |
| <p>This page discusses the audio subsystem support for NuttX which is only built if |
| <code class="docutils literal notranslate"><span class="pre">CONFIG_AUDIO</span></code> is defined in the NuttX configuration file.</p> |
| <section id="files-in-nuttx-audio"> |
| <h2>Files in nuttx/audio<a class="headerlink" href="#files-in-nuttx-audio" title="Permalink to this heading"></a></h2> |
| <p>This directory holds the NuttX audio subsystem upper-half. The upper-half provides |
| a common interface for applications to interface with and also defines a bind |
| layer for specific lower-half audio device drivers.</p> |
| <ul class="simple"> |
| <li><p><code class="docutils literal notranslate"><span class="pre">audio.c</span></code> - The upper-half driver that binds to a lower-half driver from the |
| drivers/audio subdirectory. For each attached audio device, there |
| will be an instance of this upper-half driver bound to the |
| instance of the lower half driver context.</p></li> |
| <li><p><code class="docutils literal notranslate"><span class="pre">pcm_decode.c</span></code> - Routines to decode PCM / WAV type data.</p></li> |
| </ul> |
| <p>Portions of the audio system interface have application interfaces. Those |
| portions reside in the <code class="docutils literal notranslate"><span class="pre">nuttx/libc/audio</span></code> directory where the will be built for |
| access by both OS driver logic and user application logic. Those relevant |
| files in <code class="docutils literal notranslate"><span class="pre">nuttx/libc/audio</span></code> include:</p> |
| <ul class="simple"> |
| <li><p><code class="docutils literal notranslate"><span class="pre">buffer.c</span></code> - Routines to manage creattion and destruction of audio pipeline buffers |
| (apb) used in the audio subsystem. Audio pipeline buffers are passed |
| between user applications and the audio drivers to deliver audio |
| content for playback (or possibly recording in the future).</p></li> |
| </ul> |
| </section> |
| <section id="related-header-files"> |
| <h2>Related Header Files<a class="headerlink" href="#related-header-files" title="Permalink to this heading"></a></h2> |
| <p><code class="docutils literal notranslate"><span class="pre">include/nuttx/audio/audio.h</span></code> - Top level include file defining the audio interface |
| <code class="docutils literal notranslate"><span class="pre">include/nuttx/audio/vs1053.h</span></code> - Specific driver initialization prototypes</p> |
| </section> |
| <section id="configuration-settings"> |
| <h2>Configuration Settings<a class="headerlink" href="#configuration-settings" title="Permalink to this heading"></a></h2> |
| <section id="general-audio-settings"> |
| <h3>General Audio Settings<a class="headerlink" href="#general-audio-settings" title="Permalink to this heading"></a></h3> |
| <ul class="simple"> |
| <li><p><code class="docutils literal notranslate"><span class="pre">CONFIG_AUDIO</span></code> |
| Enables overall support for audio subsystem</p></li> |
| <li><p><code class="docutils literal notranslate"><span class="pre">CONFIG_AUDIO_MULTI_SESSION</span></code> |
| Enables support for the audio subsystem to track multiple open sessions |
| with lower-level audio devices.</p></li> |
| <li><p><code class="docutils literal notranslate"><span class="pre">CONFIG_AUDIO_LARGE_BUFFERS</span></code> |
| Specifies that buffer size variables should be 32-bit vs. the normal 16-bit |
| size. This allows buffers to be larger than 64K bytes on systems with |
| an abundance of RAM.</p></li> |
| <li><p><code class="docutils literal notranslate"><span class="pre">CONFIG_AUDIO_NUM_BUFFERS</span></code> |
| Sets the number of audio buffers to use for audio operations. If the |
| configuration has set <code class="docutils literal notranslate"><span class="pre">CONFIG_AUDIO_DRIVER_SPECIFIC_BUFFERS</span></code>, and an audio |
| device does not support the operation, then this becomes the default number |
| of buffers to use.</p></li> |
| <li><p><code class="docutils literal notranslate"><span class="pre">CONFIG_AUDIO_BUFFER_SIZE</span></code> |
| Sets the size of the audio buffers to use for audio operations. If the |
| configuration has set <code class="docutils literal notranslate"><span class="pre">CONFIG_AUDIO_DRIVER_SPECIFIC_BUFFERS</span></code>, and an audio |
| device does not support the operation, then this becomes the default size |
| of buffers to use.</p></li> |
| <li><p><code class="docutils literal notranslate"><span class="pre">CONFIG_AUDIO_DRIVER_SPECIFIC_BUFFERS</span></code> |
| Enables support for lower-level audio drivers to specify the number and size |
| of buffers that should be allocated for best performance while interacting |
| with that driver.</p></li> |
| <li><p><code class="docutils literal notranslate"><span class="pre">CONFIG_AUDIO_CUSTOM_DEV_PATH</span></code> |
| Specifies that all audio devices should be registered in the filesystem at |
| a location other than the standard <code class="docutils literal notranslate"><span class="pre">/dev/audio</span></code> directory.</p></li> |
| <li><p><code class="docutils literal notranslate"><span class="pre">CONFIG_AUDIO_DEV_ROOT</span></code> |
| Specifies that all audio devices should be registered in the <code class="docutils literal notranslate"><span class="pre">/dev</span></code> directory. |
| Saves a tiny bit of code and RAM space since an additional directory isn’t needed, |
| but at the expense of execution speed when searching for audio devices since all |
| entries in <code class="docutils literal notranslate"><span class="pre">/dev</span></code> must be opened and tested if they provide audio support. |
| Available only if <code class="docutils literal notranslate"><span class="pre">CONFIG_AUDIO_CUSTOM_DEV_PATH</span></code> is selected.</p></li> |
| <li><p><code class="docutils literal notranslate"><span class="pre">CONFIG_AUDIO_DEV_PATH</span></code> |
| Specifies a custom directory where audio devices will be registered. |
| Available if <code class="docutils literal notranslate"><span class="pre">CONFIG_AUDIO_CUSTOM_DEV_PATH</span></code> is selected and <code class="docutils literal notranslate"><span class="pre">CONFIG_AUDIO_DEV_ROOT</span></code> |
| is not selected.</p></li> |
| </ul> |
| </section> |
| <section id="audio-format-support-selections"> |
| <h3>Audio Format Support Selections<a class="headerlink" href="#audio-format-support-selections" title="Permalink to this heading"></a></h3> |
| <ul class="simple"> |
| <li><p><code class="docutils literal notranslate"><span class="pre">CONFIG_AUDIO_FORMAT_AC3</span></code> |
| Specifies that AC3 support should be enabled if available by a lower-half driver.</p></li> |
| <li><p><code class="docutils literal notranslate"><span class="pre">CONFIG_AUDIO_FORMAT_DTS</span></code> |
| Specifies that DTS support should be enabled if available by a lower-half driver.</p></li> |
| <li><p><code class="docutils literal notranslate"><span class="pre">CONFIG_AUDIO_FORMAT_PCM</span></code> |
| Specifies that PCM support should be enabled if available by a lower-half driver.</p></li> |
| <li><p><code class="docutils literal notranslate"><span class="pre">CONFIG_AUDIO_FORMAT_MP3</span></code> |
| Specifies that MP3 support should be enabled if available by a lower-half driver.</p></li> |
| <li><p><code class="docutils literal notranslate"><span class="pre">CONFIG_AUDIO_FORMAT_MIDI</span></code> |
| Specifies that MIDI support should be enabled if available by a lower-half driver.</p></li> |
| <li><p><code class="docutils literal notranslate"><span class="pre">CONFIG_AUDIO_FORMAT_WMA</span></code> |
| Specifies that WMA support should be enabled if available by a lower-half driver.</p></li> |
| <li><p><code class="docutils literal notranslate"><span class="pre">CONFIG_AUDIO_FORMAT_OGG_VORBIS</span></code> |
| Specifies that Ogg Vorbis support should be enabled if available by a lower-half driver.</p></li> |
| </ul> |
| </section> |
| <section id="audio-feature-exclusion-selections"> |
| <h3>Audio feature exclusion Selections<a class="headerlink" href="#audio-feature-exclusion-selections" title="Permalink to this heading"></a></h3> |
| <ul class="simple"> |
| <li><p><code class="docutils literal notranslate"><span class="pre">CONFIG_AUDIO_EXCLUDE_VOLUME</span></code> |
| Disables support in all libraries and drivers for setting the playback volume. In |
| this case, the device volume will depend on the default level defined by the |
| lower-level driver, typically via a config setting.</p></li> |
| <li><p><code class="docutils literal notranslate"><span class="pre">CONFIG_AUDIO_EXCLUDE_BALANCE</span></code> |
| Disables support in all libraries and drivers for setting the playback balance. |
| Also, the volume support must not be excluded for balance to work or make sense.</p></li> |
| <li><p><code class="docutils literal notranslate"><span class="pre">CONFIG_AUDIO_EXCLUDE_TONE</span></code> |
| Disables support for setting bass and treble.</p></li> |
| <li><p><code class="docutils literal notranslate"><span class="pre">CONFIG_AUDIO_EXCLUDE_PAUSE_RESUME</span></code> |
| Disables support in all libraries and drivers for pausing and resuming playback.</p></li> |
| <li><p><code class="docutils literal notranslate"><span class="pre">CONFIG_AUDIO_EXCLUDE_STOP</span></code> |
| Disables support in all libraries and drivers for stopping an audio playback |
| once it has started. Typically selected if only short notification audio sounds |
| are needed (vs. media playing type applications).</p></li> |
| </ul> |
| </section> |
| </section> |
| <section id="related-subdirectories"> |
| <h2>Related Subdirectories<a class="headerlink" href="#related-subdirectories" title="Permalink to this heading"></a></h2> |
| <ul class="simple"> |
| <li><p><code class="docutils literal notranslate"><span class="pre">drivers/audio</span></code> - Contains the lower-level device specific drivers.</p></li> |
| <li><p><code class="docutils literal notranslate"><span class="pre">apps/system/nxplayer</span></code> - User-mode audio subsystem interface library.</p></li> |
| </ul> |
| </section> |
| </section> |
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