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Macros | Functions
Software Parameters
PCM Interface

Macros

#define snd_pcm_sw_params_alloca(ptr)
 allocate an invalid snd_pcm_sw_params_t using standard alloca

Functions

size_t snd_pcm_sw_params_sizeof (void)
 get size of snd_pcm_sw_params_t
int snd_pcm_sw_params_malloc (snd_pcm_sw_params_t **ptr)
 allocate an invalid snd_pcm_sw_params_t using standard malloc
void snd_pcm_sw_params_free (snd_pcm_sw_params_t *obj)
 frees a previously allocated snd_pcm_sw_params_t
void snd_pcm_sw_params_copy (snd_pcm_sw_params_t *dst, const snd_pcm_sw_params_t *src)
 copy one snd_pcm_sw_params_t to another
int snd_pcm_sw_params_get_boundary (const snd_pcm_sw_params_t *params, snd_pcm_uframes_t *val)
 Get boundary for ring pointers from a software configuration container.
int snd_pcm_sw_params_set_tstamp_mode (snd_pcm_t *pcm, snd_pcm_sw_params_t *params, snd_pcm_tstamp_t val)
 Set timestamp mode inside a software configuration container.
int snd_pcm_sw_params_get_tstamp_mode (const snd_pcm_sw_params_t *params, snd_pcm_tstamp_t *val)
 Get timestamp mode from a software configuration container.
int snd_pcm_sw_params_set_avail_min (snd_pcm_t *pcm, snd_pcm_sw_params_t *params, snd_pcm_uframes_t val)
 Set avail min inside a software configuration container.
int snd_pcm_sw_params_get_avail_min (const snd_pcm_sw_params_t *params, snd_pcm_uframes_t *val)
 Get avail min from a software configuration container.
int snd_pcm_sw_params_set_period_event (snd_pcm_t *pcm, snd_pcm_sw_params_t *params, int val)
 Set period event inside a software configuration container.
int snd_pcm_sw_params_get_period_event (const snd_pcm_sw_params_t *params, int *val)
 Get period event from a software configuration container.
int snd_pcm_sw_params_set_start_threshold (snd_pcm_t *pcm, snd_pcm_sw_params_t *params, snd_pcm_uframes_t val)
 Set start threshold inside a software configuration container.
int snd_pcm_sw_params_get_start_threshold (const snd_pcm_sw_params_t *paramsm, snd_pcm_uframes_t *val)
 Get start threshold from a software configuration container.
int snd_pcm_sw_params_set_stop_threshold (snd_pcm_t *pcm, snd_pcm_sw_params_t *params, snd_pcm_uframes_t val)
 Set stop threshold inside a software configuration container.
int snd_pcm_sw_params_get_stop_threshold (const snd_pcm_sw_params_t *params, snd_pcm_uframes_t *val)
 Get stop threshold from a software configuration container.
int snd_pcm_sw_params_set_silence_threshold (snd_pcm_t *pcm, snd_pcm_sw_params_t *params, snd_pcm_uframes_t val)
 Set silence threshold inside a software configuration container.
int snd_pcm_sw_params_get_silence_threshold (const snd_pcm_sw_params_t *params, snd_pcm_uframes_t *val)
 Get silence threshold from a software configuration container.
int snd_pcm_sw_params_set_silence_size (snd_pcm_t *pcm, snd_pcm_sw_params_t *params, snd_pcm_uframes_t val)
 Set silence size inside a software configuration container.
int snd_pcm_sw_params_get_silence_size (const snd_pcm_sw_params_t *params, snd_pcm_uframes_t *val)
 Get silence size from a software configuration container.

Detailed Description

See the PCM (digital audio) interface page for more details.


Macro Definition Documentation

#define snd_pcm_sw_params_alloca (   ptr)

allocate an invalid snd_pcm_sw_params_t using standard alloca

Parameters:
ptrreturned pointer
Examples:
/test/latency.c, and /test/pcm.c.

Function Documentation

void snd_pcm_sw_params_copy ( snd_pcm_sw_params_t dst,
const snd_pcm_sw_params_t src 
)

copy one snd_pcm_sw_params_t to another

Parameters:
dstpointer to destination
srcpointer to source
void snd_pcm_sw_params_free ( snd_pcm_sw_params_t obj)

frees a previously allocated snd_pcm_sw_params_t

Parameters:
objpointer to object to free
int snd_pcm_sw_params_get_avail_min ( const snd_pcm_sw_params_t params,
snd_pcm_uframes_t val 
)

Get avail min from a software configuration container.

Parameters:
paramsSoftware configuration container
valreturned minimum available frames to consider PCM ready
Returns:
0 otherwise a negative error code
int snd_pcm_sw_params_get_boundary ( const snd_pcm_sw_params_t params,
snd_pcm_uframes_t val 
)

Get boundary for ring pointers from a software configuration container.

Parameters:
paramsSoftware configuration container
valReturned boundary in frames
Returns:
0 otherwise a negative error code
int snd_pcm_sw_params_get_period_event ( const snd_pcm_sw_params_t params,
int *  val 
)

Get period event from a software configuration container.

Parameters:
paramsSoftware configuration container
valreturned period event state
Returns:
0 otherwise a negative error code
int snd_pcm_sw_params_get_silence_size ( const snd_pcm_sw_params_t params,
snd_pcm_uframes_t val 
)

Get silence size from a software configuration container.

Parameters:
paramsSoftware configuration container
valReturned silence size in frames (0 for disabled)
Returns:
0 otherwise a negative error code

A portion of playback buffer is overwritten with silence when playback underrun is nearer than silence threshold (see snd_pcm_sw_params_set_silence_threshold)

int snd_pcm_sw_params_get_silence_threshold ( const snd_pcm_sw_params_t params,
snd_pcm_uframes_t val 
)

Get silence threshold from a software configuration container.

Parameters:
paramsSoftware configuration container
valReturned silence threshold in frames
Returns:
0 otherwise a negative error value

A portion of playback buffer is overwritten with silence (see snd_pcm_sw_params_set_silence_size) when playback underrun is nearer than silence threshold.

int snd_pcm_sw_params_get_start_threshold ( const snd_pcm_sw_params_t params,
snd_pcm_uframes_t val 
)

Get start threshold from a software configuration container.

Parameters:
paramsSoftware configuration container
valReturned start threshold in frames
Returns:
0 otherwise a negative error code

PCM is automatically started when playback frames available to PCM are >= threshold or when requested capture frames are >= threshold

int snd_pcm_sw_params_get_stop_threshold ( const snd_pcm_sw_params_t params,
snd_pcm_uframes_t val 
)

Get stop threshold from a software configuration container.

Parameters:
paramsSoftware configuration container
valReturned stop threshold in frames
Returns:
0 otherwise a negative error code

PCM is automatically stopped in SND_PCM_STATE_XRUN state when available frames is >= threshold. If the stop threshold is equal to boundary (also software parameter - sw_param) then automatic stop will be disabled (thus device will do the endless loop in the ring buffer).

int snd_pcm_sw_params_get_tstamp_mode ( const snd_pcm_sw_params_t params,
snd_pcm_tstamp_t val 
)

Get timestamp mode from a software configuration container.

Parameters:
paramsSoftware configuration container
valReturned timestamp
Returns:
0 otherwise a negative error code
int snd_pcm_sw_params_malloc ( snd_pcm_sw_params_t **  ptr)

allocate an invalid snd_pcm_sw_params_t using standard malloc

Parameters:
ptrreturned pointer
Returns:
0 on success otherwise negative error code
int snd_pcm_sw_params_set_avail_min ( snd_pcm_t pcm,
snd_pcm_sw_params_t params,
snd_pcm_uframes_t  val 
)

Set avail min inside a software configuration container.

Parameters:
pcmPCM handle
paramsSoftware configuration container
valMinimum avail frames to consider PCM ready
Returns:
0 otherwise a negative error code

Note: This is similar to setting an OSS wakeup point. The valid values for 'val' are determined by the specific hardware. Most PC sound cards can only accept power of 2 frame counts (i.e. 512, 1024, 2048). You cannot use this as a high resolution timer - it is limited to how often the sound card hardware raises an interrupt.

Examples:
/test/latency.c, and /test/pcm.c.
int snd_pcm_sw_params_set_period_event ( snd_pcm_t pcm,
snd_pcm_sw_params_t params,
int  val 
)

Set period event inside a software configuration container.

Parameters:
pcmPCM handle
paramsSoftware configuration container
val0 = disable period event, 1 = enable period event
Returns:
0 otherwise a negative error code

An poll (select) wakeup event is raised if enabled.

Examples:
/test/pcm.c.
int snd_pcm_sw_params_set_silence_size ( snd_pcm_t pcm,
snd_pcm_sw_params_t params,
snd_pcm_uframes_t  val 
)

Set silence size inside a software configuration container.

Parameters:
pcmPCM handle
paramsSoftware configuration container
valSilence size in frames (0 for disabled)
Returns:
0 otherwise a negative error code

A portion of playback buffer is overwritten with silence when playback underrun is nearer than silence threshold (see snd_pcm_sw_params_set_silence_threshold)

The special case is when silence size value is equal or greater than boundary. The unused portion of the ring buffer (initial written samples are untouched) is filled with silence at start. Later, only just processed sample area is filled with silence. Note: silence_threshold must be set to zero.

int snd_pcm_sw_params_set_silence_threshold ( snd_pcm_t pcm,
snd_pcm_sw_params_t params,
snd_pcm_uframes_t  val 
)

Set silence threshold inside a software configuration container.

Parameters:
pcmPCM handle
paramsSoftware configuration container
valSilence threshold in frames
Returns:
0 otherwise a negative error code

A portion of playback buffer is overwritten with silence (see snd_pcm_sw_params_set_silence_size) when playback underrun is nearer than silence threshold.

int snd_pcm_sw_params_set_start_threshold ( snd_pcm_t pcm,
snd_pcm_sw_params_t params,
snd_pcm_uframes_t  val 
)

Set start threshold inside a software configuration container.

Parameters:
pcmPCM handle
paramsSoftware configuration container
valStart threshold in frames
Returns:
0 otherwise a negative error code

PCM is automatically started when playback frames available to PCM are >= threshold or when requested capture frames are >= threshold

Examples:
/test/latency.c, and /test/pcm.c.
int snd_pcm_sw_params_set_stop_threshold ( snd_pcm_t pcm,
snd_pcm_sw_params_t params,
snd_pcm_uframes_t  val 
)

Set stop threshold inside a software configuration container.

Parameters:
pcmPCM handle
paramsSoftware configuration container
valStop threshold in frames
Returns:
0 otherwise a negative error code

PCM is automatically stopped in SND_PCM_STATE_XRUN state when available frames is >= threshold. If the stop threshold is equal to boundary (also software parameter - sw_param) then automatic stop will be disabled (thus device will do the endless loop in the ring buffer).

int snd_pcm_sw_params_set_tstamp_mode ( snd_pcm_t pcm,
snd_pcm_sw_params_t params,
snd_pcm_tstamp_t  val 
)

Set timestamp mode inside a software configuration container.

Parameters:
pcmPCM handle
paramsSoftware configuration container
valTimestamp mode
Returns:
0 otherwise a negative error code
size_t snd_pcm_sw_params_sizeof ( void  )

get size of snd_pcm_sw_params_t

Returns:
size in bytes