Audio Library Parent topic: Audio Library

snd_pcm_channel_status_t

PCM channel status structure

Synopsis:

typedef struct snd_pcm_channel_status
{
    int32_t                 channel;
    int32_t                 mode;
    int32_t                 status;
    uint32_t                scount;
    struct timeval          stime;
    uint64_t                ust_stime;
    int32_t                 frag;
    int32_t                 count;
    int32_t                 free;
    int32_t                 underrun;
    int32_t                 overrun;
    int32_t                 overrange;
    uint32_t                subbuffered;
    snd_pcm_status_data_t   status_data;
    struct timeval          stop_time;
    uint8_t                 hw_device;
    uint8_t                 reserved[111];  /* must be filled with zero */
} snd_pcm_channel_status_t;

Description:

The snd_pcm_channel_status_t structure describes the status of a PCM channel. The members include:

channel
The channel direction; one of SND_PCM_CHANNEL_PLAYBACK or SND_PCM_CHANNEL_CAPTURE.
mode
The transfer mode: SND_PCM_MODE_BLOCK. (SND_PCM_MODE_STREAM is deprecated.)
status
The channel status. Valid values are:
  • SND_PCM_STATUS_NOTREADY — the driver isn't prepared for any operation. After a successful call to snd_pcm_channel_params(), the state is changed to SND_PCM_STATUS_READY.
  • SND_PCM_STATUS_READY — the driver is ready for operation. You can mmap() the audio buffer only in this state, but the samples still can't be transferred. After a successful call to snd_pcm_channel_prepare(), snd_pcm_capture_prepare(), snd_pcm_playback_prepare(), or snd_pcm_plugin_prepare(), the state is changed to SND_PCM_STATUS_PREPARED.
  • SND_PCM_STATUS_PREPARED — the driver is prepared for operation. The samples may be transferred in this state.
  • SND_PCM_STATUS_RUNNING — the driver is actively transferring data through the hardware. The samples may be transferred in this state.
  • SND_PCM_STATUS_UNDERRUN — the playback channel is in an underrun state. The driver completely drained the buffers before new data was ready to be played. You must reprepare the channel before continuing, by calling snd_pcm_channel_prepare(), snd_pcm_playback_prepare(), or snd_pcm_plugin_prepare(). See the wave.c example in the appendix.
  • SND_PCM_STATUS_OVERRUN — the capture channel is in an overrun state. The driver has processed the incoming data faster than it's coming in; the channel is stalled. You must reprepare the channel before continuing, by calling snd_pcm_channel_prepare(), snd_pcm_capture_prepare(), or snd_pcm_plugin_prepare(). See the waverec.c example in the appendix.
  • SND_PCM_STATUS_PAUSED — the playback is paused (not supported by QSA).
scount
The number of bytes processed since the playback/capture last started. This value wraps around to 0 when it passes the value of SND_PCM_BOUNDARY, and is reset when you prepare the channel.
stime
The playback/capture start time, in the format used by gettimeofday() (see the QNX Neutrino C Library Reference).

This member is valid only when the time flags is active in the snd_pcm_channel_params_t structure.

ust_stime
The playback/capture start time, in UST format. This member is valid only when the ust_time flags is active in the snd_pcm_channel_params_t structure.
frag
The current fragment number (available only in the block mode).
count
The number of bytes in the queue/buffer; see the note below.
free
The number of bytes in the queue that are still free; see the note below.
underrun
The number of playback underruns since the last status.
overrun
The number of capture overruns since the last status.
overrange
The number of ADC capture overrange detections since the last status.
subbuffered
The number of bytes subbuffered in the plugin interface.
status_data
Additional data relevant to a particular value for status.
stop_time
The time at which the last sample was played or recorded in the most recent case where the channel stopped for any reason.
hw_device
Which device, from the audio_manager_device_t enumerated type, is currently being used. It might not be available, in which case, it's set to AUDIO_DEVICE_COUNT.
Note:
  • The count and free members aren't used if the mmap plugin is used. To disable the mmap plugin, call snd_pcm_plugin_set_disable().
  • The stop_time and stime members hold valid data only if there's data present in the channel; they aren't necessarily valid as soon as the channel goes to a SND_PCM_STATUS_RUNNING state, but they're guaranteed to be valid as soon as scount indicates that some data has been processed.

Classification:

QNX Neutrino

Parent topic: Audio Library