snd_pcm_channel_status()

Get current PCM runtime status

Synopsis:

#include <sys/asoundlib.h>

int snd_pcm_channel_status( 
                  snd_pcm_t * handle, 
                  snd_pcm_channel_status_t * status );

The snd_pcm_channel_status() function fills the status structure with data about the PCM channel runtime status selected by handle. The channel member specifies the direction. Other members are read-only.

typedef struct snd_pcm_channel_status
{
    int32_t         channel;        /* channel information */
    int32_t         mode;           /* transfer mode */
    int32_t         status;         /* channel status-SND_PCM_STATUS_XXXX */
    uint32_t        scount;         /* number of bytes processed from playback/capture start */
    struct timeval  stime;          /* time when playback/capture was started */
    uint64_t        ust_stime;      /* UST time when playback/capture was started */
    int32_t         frag;           /* current fragment */
    int32_t         count;          /* number of bytes in queue/buffer */
    int32_t         free;           /* bytes in queue still free */
    int32_t         underrun;       /* count of underruns (playback) from last status */
    int32_t         overrun;        /* count of overruns (capture) from last status */
    int32_t         overrange;      /* count of ADC (capture) overrange detections from last status */
    uint8_t         reserved[128];  /* must be filled with zero */
}       snd_pcm_channel_status_t;

where:

channel

Specifies channel direction. One of SND_PCM_CHANNEL_PLAYBACK or SND_PCM_CHANNEL_CAPTURE.

mode

Shows transfer mode. One of SND_PCM_MODE_STREAM or SND_PCM_MODE_BLOCK.

status

Shows channel status. Valid values are:

SND_PCM_STATUS_NOTREADY: The driver isn't prepared for any operation. After a successful snd_pcm_channel_params() call the state's changed to SND_PCM_STATUS_READY.
SND_PCM_STATUS_READY: The driver is ready for operation. The audio buffer may be mmap()ed only at this moment, but the samples can't be still transferred. After successful snd_pcm_channel_prepare() call the state's changed to SND_PCM_STATUS_PREPARED.
SND_PCM_STATUS_PREPARED: The driver is prepared for operation. The samples may be transferred at this moment.
SND_PCM_STATUS_RUNNING: The driver manages running stream. The samples may be transferred at this moment.
SND_PCM_STATUS_UNDERRUN: The playback direction is in underrun state. It means that the driver didn't get the data in right time. Only snd_pcm_playback_drain() may change this state.
SND_PCM_STATUS_OVERRUN: The capture direction is in overrun state. It means that hardware hasn't received the data in right time.
SND_PCM_STATUS_PAUSED: The playback is paused.

scount

Shows the count of bytes processed from the playback/capture start. This value is clipped when reaches the SND_PCM_BOUNDARY value.

stime

Shows the playback/capture start time in gettimeofday format. This member is valid only when the time flags was active in the snd_pcm_channel_params_t structure.

ust_stime

Shows the playback/capture start time in UST format. This member is valid only when the ust_time flags was active in the snd_pcm_channel_params_t structure.

frag