snd_pcm_channel

Block until buffered data is fully consumed and then stop the stream (playback) or stop the stream immediately but preserve the buffered data (capture)

Synopsis:

#include <sys/asoundlib.h>

int snd_pcm_channel_drain( snd_pcm_t *pcm,
                           int channel );

Arguments:

pcm: The handle for the PCM device, which you must have opened by calling snd_pcm_open_name(), snd_pcm_open(), or snd_pcm_open_preferred().
channel: The channel; SND_PCM_CHANNEL_CAPTURE or SND_PCM_CHANNEL_PLAYBACK.

Library:

libasound.so

Use the -l asound option with qcc to link against this library.

Description:

For playback, the snd_pcm_channel_drain() function blocks until buffered data is fully consumed by the hardware and the stream is stopped.

For capture, it stops the stream immediately but preserves the buffered data so that clients can continue to read it until it is fully consumed.

If you use this call to process playback data, there are two considerations:

Since this call is a blocking call, if the channel is in the SND_PCM_STATUS_SUSPENDED state, an error occurs if you call this function.
If this function is called while in the SND_PCM_STATUS_PAUSED state, playback automatically resumes and the call blocks until the data is fully consumed and the stream is stopped. If there is not enough buffered data to start the stream, silence is appended to the buffer to meet the minimum buffering that is required to resume the stream. If there is an error resuming the stream, the buffered data is discarded and the stream is stopped.

If the operation is successful (zero is returned), the channel's state is changed to SND_PCM_STATUS_READY, and the channel is stopped.

Note: This function isn't plugin-aware. It functions exactly the same way as snd_pcm_plugin_drain(). Make sure that you don't mix and match plugin- and nonplugin-aware functions in your application, or you may get undefined behavior and misleading results.

Returns:

EOK on success, a negative errno upon failure. The errno values are available in the errno.h file.

Errors:

-EAGAIN: The state was SND_PCM_STATUS_SUSPENDED while trying to call this function. This error is also returned if the state was SND_PCM_STATUS_PAUSED, but resuming the playback failed.
-EBADFD: The connection to io-audio is no longer valid (i.e., the connection was closed).
-EINTR: The operation was interrupted because of a system signal (such as a timer) or an error was returned asynchronously.
-EINVAL: The state of pcm is invalid, an invalid channel was provided as input, or an invalid state change occurred. You can call snd_pcm_channel_status() to check if the state change was invalid.
-EIO: An invalid channel was specified, or the data wasn't all drained.

Classification:

QNX Neutrino

Safety:
Cancellation point	No
Interrupt handler	No
Signal handler	Yes
Thread	Read the Caveats

Caveats:

This function is not thread safe if pcm (snd_pcm_t) is used across multiple threads.