snd_pcm_channel_params()

Set PCM communication parameters

Synopsis:

#include <sys/asoundlib.h>

int snd_pcm_channel_params( 
                    snd_pcm_t * handle, 
                    snd_pcm_channel_params_t * params );

Description:

The snd_pcm_channel_params() function sets up the transfer parameters according to the params structure. All members are write-only.

The function may be called in SND_PCM_STATUS_NOTREADY (initial) and SND_PCM_STATUS_READY states; otherwise, -EBADFD is returned. If the parameters are valid (zero is returned), then the driver state is changed to SND_PCM_STATUS_READY.

typedef struct snd_pcm_format {
    int interleave: 1;   /* data are interleaved */
    int format;          /* SND_PCM_SFMT_XXXX */
    int rate;            /* rate in Hz */
    int voices;          /* voices */
    int special;         /* special (custom) description of format */
    char reserved[124];  /* must be filled with zero */
} snd_pcm_format_t;

where:

interleave: If set, stream contains interleaved samples.
format: Format number (SND_PCM_SFMT_* constants).
rate: Requested rate in Hz.
voices: Number of voices (1-N).
special: Special (custom) description of format. Use when SND_PCM_SFMT_SPECIAL is specified.

typedef struct snd_pcm_channel_params
{
    int32_t             channel;
    int32_t             mode;
    snd_pcm_sync_t      sync;               /* hardware synchronization ID */
    snd_pcm_format_t    format;
    snd_pcm_digital_t   digital;
    int32_t             start_mode;
    int32_t             stop_mode;
    int32_t             time:1, ust_time:1;
    uint32_t            why_failed;         /* SND_PCM_PARAMS_BAD_??? */
    union
    {
        struct
        {
            int32_t     queue_size;
            int32_t     fill;
            int32_t     max_fill;
            uint8_t     reserved[124];      /* must be filled with zero */
        }       stream;
        struct
        {
            int32_t     frag_size;
            int32_t     frags_min;
            int32_t     frags_max;
            uint8_t     reserved[124];      /* must be filled with zero */
        }       block;
        uint8_t     reserved[128];      /* must be filled with zero */
    }       buf;
    uint8_t     reserved[128];      /* must be filled with zero */
}       snd_pcm_channel_params_t;

where:

channel: Specified channel direction. One of SND_PCM_CHANNEL_PLAYBACK or SND_PCM_CHANNEL_CAPTURE.
mode: Specifies channel mode. One of SND_PCM_MODE_STREAM or SND_PCM_MODE_BLOCK.
format: Specifies data format.
digital: Specifies digital setup.
start_mode: Specifies start mode (SND_PCM_START_* constants.
stop_mode: Specifies stop mode (SND_PCM_STOP_* constants).
time: If set, the driver offers the time in the status structure, when the transfer begun. The time is in gettimeofday format.
ust_time: If set, the driver offers the time in the status structure, when the transfer begun. The time is in UST format.
sync: Specifies the synchronization group.
queue_size: Specifies queue size in bytes for the stream mode. The queue size may specify the final transfer latency.
fill: Specifies the fill mode (SND_PCM_FILL_* constants).
max_fill: Specifies the count of bytes to be filled ahead with silence.
frag_size: Specifies the size of fragment in bytes.
frags_min: Capture: Specifies the minimum filled fragments to allow wakeup (usually one). Playback: Specifies the minimum free fragments to allow wakeup (usually one).
frags_max: Playback: Specifies the maximum filled fragments to allow wakeup. Value also specifies the maximum used fragments plus one.

Value (start condition)	Description
SND_PCM_START_DATA	Start when some data are written (playback) or requested (capture).
SND_PCM_START_FULL	Start when whole queue is filled (playback).
SND_PCM_START_GO	Start on the go command.

Value (stop condition)	Description
SND_PCM_STOP_STOP	Stop when underrun/overrun occurs.
SND_PCM_STOP_ERASE	Stop and erase whole buffer when overrun (capture only).
SND_PCM_STOP_ROLLOVER	Rollover when overrun/underrun occurs.

Value (file mode)	Description
SND_PCM_FILL_NONE	Don't fill the buffer with silence samples.
SND_PCM_FILL_SILENCE_WHOLE	Fill the whole buffer with silence.
SND_PCM_FILL_SILENCE	Fill the partial buffer with silence.