| =============== |
| Audio Subsystem |
| =============== |
| |
| This page discusses the audio subsystem support for NuttX which is only built if |
| ``CONFIG_AUDIO`` is defined in the NuttX configuration file. |
| |
| Files in nuttx/audio |
| ==================== |
| |
| 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. |
| |
| * ``audio.c`` - 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. |
| * ``pcm_decode.c`` - Routines to decode PCM / WAV type data. |
| |
| Portions of the audio system interface have application interfaces. Those |
| portions reside in the ``nuttx/libc/audio`` directory where the will be built for |
| access by both OS driver logic and user application logic. Those relevant |
| files in ``nuttx/libc/audio`` include: |
| |
| * ``buffer.c`` - 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). |
| |
| Related Header Files |
| ==================== |
| |
| ``include/nuttx/audio/audio.h`` - Top level include file defining the audio interface |
| ``include/nuttx/audio/vs1053.h`` - Specific driver initialization prototypes |
| |
| Configuration Settings |
| ====================== |
| |
| General Audio Settings |
| ---------------------- |
| |
| * ``CONFIG_AUDIO`` |
| Enables overall support for audio subsystem |
| * ``CONFIG_AUDIO_MULTI_SESSION`` |
| Enables support for the audio subsystem to track multiple open sessions |
| with lower-level audio devices. |
| * ``CONFIG_AUDIO_LARGE_BUFFERS`` |
| 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. |
| * ``CONFIG_AUDIO_NUM_BUFFERS`` |
| Sets the number of audio buffers to use for audio operations. If the |
| configuration has set ``CONFIG_AUDIO_DRIVER_SPECIFIC_BUFFERS``, and an audio |
| device does not support the operation, then this becomes the default number |
| of buffers to use. |
| * ``CONFIG_AUDIO_BUFFER_SIZE`` |
| Sets the size of the audio buffers to use for audio operations. If the |
| configuration has set ``CONFIG_AUDIO_DRIVER_SPECIFIC_BUFFERS``, and an audio |
| device does not support the operation, then this becomes the default size |
| of buffers to use. |
| * ``CONFIG_AUDIO_DRIVER_SPECIFIC_BUFFERS`` |
| 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. |
| * ``CONFIG_AUDIO_CUSTOM_DEV_PATH`` |
| Specifies that all audio devices should be registered in the filesystem at |
| a location other than the standard ``/dev/audio`` directory. |
| * ``CONFIG_AUDIO_DEV_ROOT`` |
| Specifies that all audio devices should be registered in the ``/dev`` 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 ``/dev`` must be opened and tested if they provide audio support. |
| Available only if ``CONFIG_AUDIO_CUSTOM_DEV_PATH`` is selected. |
| * ``CONFIG_AUDIO_DEV_PATH`` |
| Specifies a custom directory where audio devices will be registered. |
| Available if ``CONFIG_AUDIO_CUSTOM_DEV_PATH`` is selected and ``CONFIG_AUDIO_DEV_ROOT`` |
| is not selected. |
| |
| Audio Format Support Selections |
| ------------------------------- |
| |
| * ``CONFIG_AUDIO_FORMAT_AC3`` |
| Specifies that AC3 support should be enabled if available by a lower-half driver. |
| * ``CONFIG_AUDIO_FORMAT_DTS`` |
| Specifies that DTS support should be enabled if available by a lower-half driver. |
| * ``CONFIG_AUDIO_FORMAT_PCM`` |
| Specifies that PCM support should be enabled if available by a lower-half driver. |
| * ``CONFIG_AUDIO_FORMAT_MP3`` |
| Specifies that MP3 support should be enabled if available by a lower-half driver. |
| * ``CONFIG_AUDIO_FORMAT_MIDI`` |
| Specifies that MIDI support should be enabled if available by a lower-half driver. |
| * ``CONFIG_AUDIO_FORMAT_WMA`` |
| Specifies that WMA support should be enabled if available by a lower-half driver. |
| * ``CONFIG_AUDIO_FORMAT_OGG_VORBIS`` |
| Specifies that Ogg Vorbis support should be enabled if available by a lower-half driver. |
| |
| Audio feature exclusion Selections |
| ---------------------------------- |
| |
| * ``CONFIG_AUDIO_EXCLUDE_VOLUME`` |
| 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. |
| * ``CONFIG_AUDIO_EXCLUDE_BALANCE`` |
| 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. |
| * ``CONFIG_AUDIO_EXCLUDE_TONE`` |
| Disables support for setting bass and treble. |
| * ``CONFIG_AUDIO_EXCLUDE_PAUSE_RESUME`` |
| Disables support in all libraries and drivers for pausing and resuming playback. |
| * ``CONFIG_AUDIO_EXCLUDE_STOP`` |
| 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). |
| |
| Related Subdirectories |
| ====================== |
| |
| * ``drivers/audio`` - Contains the lower-level device specific drivers. |
| * ``apps/system/nxplayer`` - User-mode audio subsystem interface library. |
