Hardware Parameters

Macros
#define	snd_pcm_hw_params_alloca(ptr)
	allocate an invalid snd_pcm_hw_params_t using standard alloca

Functions
int	snd_pcm_hw_params_any (snd_pcm_t *pcm, snd_pcm_hw_params_t *params)
	Fill params with a full configuration space for a PCM.
int	snd_pcm_hw_params_can_mmap_sample_resolution (const snd_pcm_hw_params_t *params)
	Check if hardware supports sample-resolution mmap for given configuration.
int	snd_pcm_hw_params_is_double (const snd_pcm_hw_params_t *params)
	Check if hardware does double buffering for start/stop for given configuration.
int	snd_pcm_hw_params_is_batch (const snd_pcm_hw_params_t *params)
	Check if hardware does double buffering for data transfers for given configuration.
int	snd_pcm_hw_params_is_block_transfer (const snd_pcm_hw_params_t *params)
	Check if hardware does block transfers for samples for given configuration.
int	snd_pcm_hw_params_is_monotonic (const snd_pcm_hw_params_t *params)
	Check if timestamps are monotonic for given configuration.
int	snd_pcm_hw_params_can_overrange (const snd_pcm_hw_params_t *params)
	Check if hardware supports overrange detection.
int	snd_pcm_hw_params_can_pause (const snd_pcm_hw_params_t *params)
	Check if hardware supports pause.
int	snd_pcm_hw_params_can_resume (const snd_pcm_hw_params_t *params)
	Check if hardware supports resume.
int	snd_pcm_hw_params_is_half_duplex (const snd_pcm_hw_params_t *params)
	Check if hardware does half-duplex only.
int	snd_pcm_hw_params_is_joint_duplex (const snd_pcm_hw_params_t *params)
	Check if hardware does joint-duplex (playback and capture are somewhat correlated)
int	snd_pcm_hw_params_can_sync_start (const snd_pcm_hw_params_t *params)
	Check if hardware supports synchronized start with sample resolution.
int	snd_pcm_hw_params_can_disable_period_wakeup (const snd_pcm_hw_params_t *params)
	Check if hardware can disable period wakeups.
int	snd_pcm_hw_params_is_perfect_drain (const snd_pcm_hw_params_t *params)
	Check if hardware is capable of perfect drain.
int	snd_pcm_hw_params_supports_audio_wallclock_ts (const snd_pcm_hw_params_t *params)
	Check if hardware supports audio wallclock timestamps.
int	snd_pcm_hw_params_supports_audio_ts_type (const snd_pcm_hw_params_t *params, int type)
	Check if hardware supports type of audio timestamps.
int	snd_pcm_hw_params_get_rate_numden (const snd_pcm_hw_params_t *params, unsigned int *rate_num, unsigned int *rate_den)
	Get rate exact info from a configuration space.
int	snd_pcm_hw_params_get_sbits (const snd_pcm_hw_params_t *params)
	Get sample resolution info from a configuration space.
int	snd_pcm_hw_params_get_fifo_size (const snd_pcm_hw_params_t *params)
	Get hardware FIFO size info from a configuration space.
const unsigned char *	snd_pcm_hw_params_get_sync (const snd_pcm_hw_params_t *params)
	Get hardware synchronization ID from a PCM info container.
size_t	snd_pcm_hw_params_sizeof (void)
	get size of snd_pcm_hw_params_t
int	snd_pcm_hw_params_malloc (snd_pcm_hw_params_t **ptr)
	allocate an invalid snd_pcm_hw_params_t using standard malloc
void	snd_pcm_hw_params_free (snd_pcm_hw_params_t *obj)
	frees a previously allocated snd_pcm_hw_params_t
void	snd_pcm_hw_params_copy (snd_pcm_hw_params_t *dst, const snd_pcm_hw_params_t *src)
	copy one snd_pcm_hw_params_t to another
int	snd_pcm_hw_params_get_min_align (const snd_pcm_hw_params_t *params, snd_pcm_uframes_t *val)
	Get the minimum transfer align value in samples.

Detailed Description

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

Macro Definition Documentation

snd_pcm_hw_params_alloca

#define snd_pcm_hw_params_alloca

(

ptr

)

allocate an invalid snd_pcm_hw_params_t using standard alloca

Parameters

ptr	returned pointer

Examples

/test/latency.c, and /test/pcm.c.

Function Documentation

snd_pcm_hw_params_any()

int snd_pcm_hw_params_any	(	snd_pcm_t *	pcm,
		snd_pcm_hw_params_t *	params )

Fill params with a full configuration space for a PCM.

Parameters

pcm	PCM handle
params	Configuration space

The configuration space will be filled with all possible ranges for the PCM device.

Note that the configuration space may be constrained by the currently installed configuration on the PCM device. To remove any constrains, free the configuration with snd_pcm_hw_free first.

Examples

/test/latency.c, and /test/pcm.c.

snd_pcm_hw_params_can_disable_period_wakeup()

int snd_pcm_hw_params_can_disable_period_wakeup

(

const snd_pcm_hw_params_t *

params

)

Check if hardware can disable period wakeups.

Parameters

params

Configuration space

Return values

0	Hardware cannot disable period wakeups
1	Hardware can disable period wakeups

Examples

/test/latency.c.

snd_pcm_hw_params_can_mmap_sample_resolution()

int snd_pcm_hw_params_can_mmap_sample_resolution

(

const snd_pcm_hw_params_t *

params

)

Check if hardware supports sample-resolution mmap for given configuration.

Parameters

params

Configuration space

Return values

0	Hardware doesn't support sample-resolution mmap
1	Hardware supports sample-resolution mmap

This function should only be called when the configuration space contains a single configuration. Call snd_pcm_hw_params to choose a single configuration from the configuration space.

snd_pcm_hw_params_can_overrange()

int snd_pcm_hw_params_can_overrange

(

const snd_pcm_hw_params_t *

params

)

Check if hardware supports overrange detection.

Parameters

params

Configuration space

Return values

0	Hardware doesn't support overrange detection
1	Hardware supports overrange detection

This function should only be called when the configuration space contains a single configuration. Call snd_pcm_hw_params to choose a single configuration from the configuration space.

snd_pcm_hw_params_can_pause()

int snd_pcm_hw_params_can_pause

(

const snd_pcm_hw_params_t *

params

)

Check if hardware supports pause.

Parameters

params

Configuration space

Return values

0	Hardware doesn't support pause
1	Hardware supports pause

This function should only be called when the configuration space contains a single configuration. Call snd_pcm_hw_params to choose a single configuration from the configuration space.

snd_pcm_hw_params_can_resume()

int snd_pcm_hw_params_can_resume

(

const snd_pcm_hw_params_t *

params

)

Check if hardware supports resume.

Parameters

params

Configuration space

Return values

0	Hardware doesn't support resume
1	Hardware supports resume

This function should only be called when the configuration space contains a single configuration. Call snd_pcm_hw_params to choose a single configuration from the configuration space.

snd_pcm_hw_params_can_sync_start()

int snd_pcm_hw_params_can_sync_start

(

const snd_pcm_hw_params_t *

params

)

Check if hardware supports synchronized start with sample resolution.

Parameters

params

Configuration space

Return values

0	Hardware doesn't support synchronized start
1	Hardware supports synchronized start

This function should only be called when the configuration space contains a single configuration. Call snd_pcm_hw_params to choose a single configuration from the configuration space.

snd_pcm_hw_params_copy()

void snd_pcm_hw_params_copy	(	snd_pcm_hw_params_t *	dst,
		const snd_pcm_hw_params_t *	src )

copy one snd_pcm_hw_params_t to another

Parameters

dst	pointer to destination
src	pointer to source

Examples

/test/latency.c.

snd_pcm_hw_params_free()

void snd_pcm_hw_params_free

(

snd_pcm_hw_params_t *

obj

)

frees a previously allocated snd_pcm_hw_params_t

Parameters

obj	pointer to object to free

snd_pcm_hw_params_get_fifo_size()

int snd_pcm_hw_params_get_fifo_size

(

const snd_pcm_hw_params_t *

params

)

Get hardware FIFO size info from a configuration space.

Parameters

params

Configuration space

Returns

FIFO size in frames otherwise a negative error code if the info is not available

This function should only be called when the configuration space contains a single configuration. Call snd_pcm_hw_params to choose a single configuration from the configuration space.

snd_pcm_hw_params_get_min_align()

int snd_pcm_hw_params_get_min_align	(	const snd_pcm_hw_params_t *	params,
		snd_pcm_uframes_t *	val )

Get the minimum transfer align value in samples.

Parameters

params	Configuration space
val	Returned minimum align value

Returns

0 otherwise a negative error code if the configuration space does not contain a single value

snd_pcm_hw_params_get_rate_numden()

int snd_pcm_hw_params_get_rate_numden	(	const snd_pcm_hw_params_t *	params,
		unsigned int *	rate_num,
		unsigned int *	rate_den )

Get rate exact info from a configuration space.

Parameters

params	Configuration space
rate_num	Pointer to returned rate numerator
rate_den	Pointer to returned rate denominator

Returns

0 otherwise a negative error code if the info is not available

This function should only be called when the configuration space contains a single configuration. Call snd_pcm_hw_params to choose a single configuration from the configuration space.

snd_pcm_hw_params_get_sbits()

int snd_pcm_hw_params_get_sbits

(

const snd_pcm_hw_params_t *

params

)

Get sample resolution info from a configuration space.

Parameters

params

Configuration space

Returns

sample resolution (in bits) otherwise a negative error code if the info is not available

For linear formats, this function returns sample resolution - used bits starting from the first usable significant bit defined by the format (e.g. bit 31 for S32_LE format or bit 23 for S24_LE format - starting from bit zero). Application may use full sample bit range defined by the format, but additional bits (outside this sample resolution) are stripped (not processed).

For non-linear formats, this value may have a special meaning which may be defined in future.

This function should only be called when the configuration space contains a single configuration. Call snd_pcm_hw_params to choose a single configuration from the configuration space.

snd_pcm_hw_params_get_sync()

const unsigned char * snd_pcm_hw_params_get_sync

(

const snd_pcm_hw_params_t *

params

)

Get hardware synchronization ID from a PCM info container.

Parameters

params

Configuration space

Returns

16-byte synchronization ID (use SND_PCM_HW_PARAMS_SYNC_SIZE)

This synchronization ID determines the similar clocks for the PCM stream between multiple devices (including different cards). "All zeros" means "not set". The contents of the ID can be used only for a comparison with the contents of another ID returned from this function. Applications should not do a comparison with hard-coded values, because the implementation generating such synchronization IDs may be changed in future.

snd_pcm_hw_params_is_batch()

int snd_pcm_hw_params_is_batch

(

const snd_pcm_hw_params_t *

params

)

Check if hardware does double buffering for data transfers for given configuration.

Parameters

params

Configuration space

Return values

0	Hardware doesn't do double buffering for data transfers
1	Hardware does double buffering for data transfers

This function should only be called when the configuration space contains a single configuration. Call snd_pcm_hw_params to choose a single configuration from the configuration space.

snd_pcm_hw_params_is_block_transfer()

int snd_pcm_hw_params_is_block_transfer

(

const snd_pcm_hw_params_t *

params

)

Check if hardware does block transfers for samples for given configuration.

Parameters

params

Configuration space

Return values

0	Hardware doesn't block transfers
1	Hardware does block transfers

This function should only be called when the configuration space contains a single configuration. Call snd_pcm_hw_params to choose a single configuration from the configuration space.

snd_pcm_hw_params_is_double()

int snd_pcm_hw_params_is_double

(

const snd_pcm_hw_params_t *

params

)

Check if hardware does double buffering for start/stop for given configuration.

Parameters

params

Configuration space

Return values

0	Hardware doesn't do double buffering for start/stop
1	Hardware does double buffering for start/stop

This function should only be called when the configuration space contains a single configuration. Call snd_pcm_hw_params to choose a single configuration from the configuration space.

snd_pcm_hw_params_is_half_duplex()

int snd_pcm_hw_params_is_half_duplex

(

const snd_pcm_hw_params_t *

params

)

Check if hardware does half-duplex only.

Parameters

params

Configuration space

Return values

0	Hardware doesn't do half-duplex
1	Hardware does half-duplex

This function should only be called when the configuration space contains a single configuration. Call snd_pcm_hw_params to choose a single configuration from the configuration space.

snd_pcm_hw_params_is_joint_duplex()

int snd_pcm_hw_params_is_joint_duplex

(

const snd_pcm_hw_params_t *

params

)

Check if hardware does joint-duplex (playback and capture are somewhat correlated)

Parameters

params

Configuration space

Return values

0	Hardware doesn't do joint-duplex
1	Hardware does joint-duplex

This function should only be called when the configuration space contains a single configuration. Call snd_pcm_hw_params to choose a single configuration from the configuration space.

snd_pcm_hw_params_is_monotonic()

int snd_pcm_hw_params_is_monotonic

(

const snd_pcm_hw_params_t *

params

)

Check if timestamps are monotonic for given configuration.

Parameters

params

Configuration space

Return values

0	Device doesn't do monotomic timestamps
1	Device does monotonic timestamps

This function should only be called when the configuration space contains a single configuration. Call snd_pcm_hw_params to choose a single configuration from the configuration space.

snd_pcm_hw_params_is_perfect_drain()

int snd_pcm_hw_params_is_perfect_drain

(

const snd_pcm_hw_params_t *

params

)

Check if hardware is capable of perfect drain.

Parameters

params

Configuration space

Return values

0	Hardware doesn't do perfect drain
1	Hardware does perfect drain

This function should only be called when the configuration space contains a single configuration. Call snd_pcm_hw_params to choose a single configuration from the configuration space.

Perfect drain means that the hardware does not use samples beyond the stream application pointer.

snd_pcm_hw_params_malloc()

int snd_pcm_hw_params_malloc

(

snd_pcm_hw_params_t **

ptr

)

allocate an invalid snd_pcm_hw_params_t using standard malloc

Parameters

ptr	returned pointer

Returns

0 on success otherwise negative error code

snd_pcm_hw_params_sizeof()

size_t snd_pcm_hw_params_sizeof

(

void

)

get size of snd_pcm_hw_params_t

Returns

size in bytes

snd_pcm_hw_params_supports_audio_ts_type()

int snd_pcm_hw_params_supports_audio_ts_type	(	const snd_pcm_hw_params_t *	params,
		int	type )

Check if hardware supports type of audio timestamps.

Parameters

params	Configuration space
type	Audio timestamp type

Return values

0	Hardware doesn't support type of audio timestamps
1	Hardware supports type of audio timestamps

This function should only be called when the configuration space contains a single configuration. Call snd_pcm_hw_params to choose a single configuration from the configuration space.

snd_pcm_hw_params_supports_audio_wallclock_ts()

int snd_pcm_hw_params_supports_audio_wallclock_ts

(

const snd_pcm_hw_params_t *

params

)

Check if hardware supports audio wallclock timestamps.

Parameters

params

Configuration space

Return values

0	Hardware doesn't support audio wallclock timestamps
1	Hardware supports audio wallclock timestamps

This function should only be called when the configuration space contains a single configuration. Call snd_pcm_hw_params to choose a single configuration from the configuration space.