PCM Interface

Data Structures

struct  snd_pcm_channel_area_t
union  snd_pcm_sync_id_t

Modules

 Stream Information
 Hardware Parameters
 Software Parameters
 Access Mask Functions
 Format Mask Functions
 Subformat Mask Functions
 Status Functions
 Description Functions
 Debug Functions
 Direct Access (MMAP) Functions
 Helper Functions
 Hook Extension
 Scope Plugin Extension
 Simple setup functions
 Deprecated Functions

Files

file  pcm.c
 

PCM Interface.


file  pcm_plugin.c
 

PCM Interface.


Defines

#define SND_PCM_DLSYM_VERSION   _dlsym_pcm_001
#define SND_PCM_NONBLOCK
#define SND_PCM_ASYNC
#define SND_PCM_NO_AUTO_RESAMPLE   0x00010000
#define SND_PCM_NO_AUTO_CHANNELS   0x00020000
#define SND_PCM_NO_AUTO_FORMAT   0x00040000
#define SND_PCM_NO_SOFTVOL   0x00080000

Typedefs

typedef struct _snd_pcm_info snd_pcm_info_t
typedef struct _snd_pcm_hw_params snd_pcm_hw_params_t
typedef struct _snd_pcm_sw_params snd_pcm_sw_params_t
typedef struct _snd_pcm_status snd_pcm_status_t
typedef struct _snd_pcm_access_mask snd_pcm_access_mask_t
typedef struct _snd_pcm_format_mask snd_pcm_format_mask_t
typedef struct
_snd_pcm_subformat_mask 
snd_pcm_subformat_mask_t
typedef unsigned long snd_pcm_uframes_t
typedef long snd_pcm_sframes_t
typedef struct _snd_pcm snd_pcm_t
typedef enum _snd_pcm_type snd_pcm_type_t
typedef struct _snd_pcm_scope snd_pcm_scope_t

Enumerations

enum  snd_pcm_class_t {
  SND_PCM_CLASS_GENERIC = 0, SND_PCM_CLASS_MULTI, SND_PCM_CLASS_MODEM, SND_PCM_CLASS_DIGITIZER,
  SND_PCM_CLASS_LAST = SND_PCM_CLASS_DIGITIZER
}
enum  snd_pcm_subclass_t { SND_PCM_SUBCLASS_GENERIC_MIX = 0, SND_PCM_SUBCLASS_MULTI_MIX, SND_PCM_SUBCLASS_LAST = SND_PCM_SUBCLASS_MULTI_MIX }
enum  snd_pcm_stream_t { SND_PCM_STREAM_PLAYBACK = 0, SND_PCM_STREAM_CAPTURE, SND_PCM_STREAM_LAST = SND_PCM_STREAM_CAPTURE }
enum  snd_pcm_access_t {
  SND_PCM_ACCESS_MMAP_INTERLEAVED = 0, SND_PCM_ACCESS_MMAP_NONINTERLEAVED, SND_PCM_ACCESS_MMAP_COMPLEX, SND_PCM_ACCESS_RW_INTERLEAVED,
  SND_PCM_ACCESS_RW_NONINTERLEAVED, SND_PCM_ACCESS_LAST = SND_PCM_ACCESS_RW_NONINTERLEAVED
}
enum  snd_pcm_format_t {
  SND_PCM_FORMAT_UNKNOWN = -1, SND_PCM_FORMAT_S8 = 0, SND_PCM_FORMAT_U8, SND_PCM_FORMAT_S16_LE,
  SND_PCM_FORMAT_S16_BE, SND_PCM_FORMAT_U16_LE, SND_PCM_FORMAT_U16_BE, SND_PCM_FORMAT_S24_LE,
  SND_PCM_FORMAT_S24_BE, SND_PCM_FORMAT_U24_LE, SND_PCM_FORMAT_U24_BE, SND_PCM_FORMAT_S32_LE,
  SND_PCM_FORMAT_S32_BE, SND_PCM_FORMAT_U32_LE, SND_PCM_FORMAT_U32_BE, SND_PCM_FORMAT_FLOAT_LE,
  SND_PCM_FORMAT_FLOAT_BE, SND_PCM_FORMAT_FLOAT64_LE, SND_PCM_FORMAT_FLOAT64_BE, SND_PCM_FORMAT_IEC958_SUBFRAME_LE,
  SND_PCM_FORMAT_IEC958_SUBFRAME_BE, SND_PCM_FORMAT_MU_LAW, SND_PCM_FORMAT_A_LAW, SND_PCM_FORMAT_IMA_ADPCM,
  SND_PCM_FORMAT_MPEG, SND_PCM_FORMAT_GSM, SND_PCM_FORMAT_SPECIAL = 31, SND_PCM_FORMAT_S24_3LE = 32,
  SND_PCM_FORMAT_S24_3BE, SND_PCM_FORMAT_U24_3LE, SND_PCM_FORMAT_U24_3BE, SND_PCM_FORMAT_S20_3LE,
  SND_PCM_FORMAT_S20_3BE, SND_PCM_FORMAT_U20_3LE, SND_PCM_FORMAT_U20_3BE, SND_PCM_FORMAT_S18_3LE,
  SND_PCM_FORMAT_S18_3BE, SND_PCM_FORMAT_U18_3LE, SND_PCM_FORMAT_U18_3BE, SND_PCM_FORMAT_LAST = SND_PCM_FORMAT_U18_3BE,
  SND_PCM_FORMAT_S16 = SND_PCM_FORMAT_S16_LE, SND_PCM_FORMAT_U16 = SND_PCM_FORMAT_U16_LE, SND_PCM_FORMAT_S24 = SND_PCM_FORMAT_S24_LE, SND_PCM_FORMAT_U24 = SND_PCM_FORMAT_U24_LE,
  SND_PCM_FORMAT_S32 = SND_PCM_FORMAT_S32_LE, SND_PCM_FORMAT_U32 = SND_PCM_FORMAT_U32_LE, SND_PCM_FORMAT_FLOAT = SND_PCM_FORMAT_FLOAT_LE, SND_PCM_FORMAT_FLOAT64 = SND_PCM_FORMAT_FLOAT64_LE,
  SND_PCM_FORMAT_IEC958_SUBFRAME = SND_PCM_FORMAT_IEC958_SUBFRAME_LE
}
enum  snd_pcm_subformat_t { SND_PCM_SUBFORMAT_STD = 0, SND_PCM_SUBFORMAT_LAST = SND_PCM_SUBFORMAT_STD }
enum  snd_pcm_state_t {
  SND_PCM_STATE_OPEN = 0, SND_PCM_STATE_SETUP, SND_PCM_STATE_PREPARED, SND_PCM_STATE_RUNNING,
  SND_PCM_STATE_XRUN, SND_PCM_STATE_DRAINING, SND_PCM_STATE_PAUSED, SND_PCM_STATE_SUSPENDED,
  SND_PCM_STATE_DISCONNECTED, SND_PCM_STATE_LAST = SND_PCM_STATE_DISCONNECTED
}
enum  snd_pcm_start_t { SND_PCM_START_DATA = 0, SND_PCM_START_EXPLICIT, SND_PCM_START_LAST = SND_PCM_START_EXPLICIT }
enum  snd_pcm_xrun_t { SND_PCM_XRUN_NONE = 0, SND_PCM_XRUN_STOP, SND_PCM_XRUN_LAST = SND_PCM_XRUN_STOP }
enum  snd_pcm_tstamp_t { SND_PCM_TSTAMP_NONE = 0, SND_PCM_TSTAMP_ENABLE, SND_PCM_TSTAMP_MMAP = SND_PCM_TSTAMP_ENABLE, SND_PCM_TSTAMP_LAST = SND_PCM_TSTAMP_ENABLE }
enum  _snd_pcm_type {
  SND_PCM_TYPE_HW = 0, SND_PCM_TYPE_HOOKS, SND_PCM_TYPE_MULTI, SND_PCM_TYPE_FILE,
  SND_PCM_TYPE_NULL, SND_PCM_TYPE_SHM, SND_PCM_TYPE_INET, SND_PCM_TYPE_COPY,
  SND_PCM_TYPE_LINEAR, SND_PCM_TYPE_ALAW, SND_PCM_TYPE_MULAW, SND_PCM_TYPE_ADPCM,
  SND_PCM_TYPE_RATE, SND_PCM_TYPE_ROUTE, SND_PCM_TYPE_PLUG, SND_PCM_TYPE_SHARE,
  SND_PCM_TYPE_METER, SND_PCM_TYPE_MIX, SND_PCM_TYPE_DROUTE, SND_PCM_TYPE_LBSERVER,
  SND_PCM_TYPE_LINEAR_FLOAT, SND_PCM_TYPE_LADSPA, SND_PCM_TYPE_DMIX, SND_PCM_TYPE_JACK,
  SND_PCM_TYPE_DSNOOP, SND_PCM_TYPE_DSHARE, SND_PCM_TYPE_IEC958, SND_PCM_TYPE_SOFTVOL,
  SND_PCM_TYPE_IOPLUG, SND_PCM_TYPE_EXTPLUG, SND_PCM_TYPE_MMAP_EMUL, SND_PCM_TYPE_LAST = SND_PCM_TYPE_MMAP_EMUL
}

Functions

int snd_pcm_open (snd_pcm_t **pcm, const char *name, snd_pcm_stream_t stream, int mode)
 Opens a PCM.
int snd_pcm_open_lconf (snd_pcm_t **pcm, const char *name, snd_pcm_stream_t stream, int mode, snd_config_t *lconf)
 Opens a PCM using local configuration.
int snd_pcm_close (snd_pcm_t *pcm)
 close PCM handle
const char * snd_pcm_name (snd_pcm_t *pcm)
 get identifier of PCM handle
snd_pcm_type_t snd_pcm_type (snd_pcm_t *pcm)
 get type of PCM handle
snd_pcm_stream_t snd_pcm_stream (snd_pcm_t *pcm)
 get stream for a PCM handle
int snd_pcm_poll_descriptors_count (snd_pcm_t *pcm)
 get count of poll descriptors for PCM handle
int snd_pcm_poll_descriptors (snd_pcm_t *pcm, struct pollfd *pfds, unsigned int space)
 get poll descriptors
int snd_pcm_poll_descriptors_revents (snd_pcm_t *pcm, struct pollfd *pfds, unsigned int nfds, unsigned short *revents)
 get returned events from poll descriptors
int snd_pcm_nonblock (snd_pcm_t *pcm, int nonblock)
 set nonblock mode
int snd_async_add_pcm_handler (snd_async_handler_t **handler, snd_pcm_t *pcm, snd_async_callback_t callback, void *private_data)
 Add an async handler for a PCM.
snd_pcm_tsnd_async_handler_get_pcm (snd_async_handler_t *handler)
 Return PCM handle related to an async handler.
int snd_pcm_info (snd_pcm_t *pcm, snd_pcm_info_t *info)
 Obtain general (static) information for PCM handle.
int snd_pcm_hw_params_current (snd_pcm_t *pcm, snd_pcm_hw_params_t *params)
 Retreive current PCM hardware configuration chosen with snd_pcm_hw_params.
int snd_pcm_hw_params (snd_pcm_t *pcm, snd_pcm_hw_params_t *params)
 Install one PCM hardware configuration chosen from a configuration space and snd_pcm_prepare it.
int snd_pcm_hw_free (snd_pcm_t *pcm)
 Remove PCM hardware configuration and free associated resources.
int snd_pcm_sw_params_current (snd_pcm_t *pcm, snd_pcm_sw_params_t *params)
 Return current software configuration for a PCM.
int snd_pcm_sw_params (snd_pcm_t *pcm, snd_pcm_sw_params_t *params)
 Install PCM software configuration defined by params.
int snd_pcm_prepare (snd_pcm_t *pcm)
 Prepare PCM for use.
int snd_pcm_reset (snd_pcm_t *pcm)
 Reset PCM position.
int snd_pcm_status (snd_pcm_t *pcm, snd_pcm_status_t *status)
 Obtain status (runtime) information for PCM handle.
int snd_pcm_start (snd_pcm_t *pcm)
 Start a PCM.
int snd_pcm_drop (snd_pcm_t *pcm)
 Stop a PCM dropping pending frames.
int snd_pcm_drain (snd_pcm_t *pcm)
 Stop a PCM preserving pending frames.
int snd_pcm_pause (snd_pcm_t *pcm, int enable)
 Pause/resume PCM.
snd_pcm_state_t snd_pcm_state (snd_pcm_t *pcm)
 Return PCM state.
int snd_pcm_hwsync (snd_pcm_t *pcm)
 (DEPRECATED) Synchronize stream position with hardware
int snd_pcm_delay (snd_pcm_t *pcm, snd_pcm_sframes_t *delayp)
 Obtain delay for a running PCM handle.
int snd_pcm_resume (snd_pcm_t *pcm)
 Resume from suspend, no samples are lost.
int snd_pcm_htimestamp (snd_pcm_t *pcm, snd_pcm_uframes_t *avail, snd_htimestamp_t *tstamp)
 Obtain last position update hi-res timestamp.
snd_pcm_sframes_t snd_pcm_avail (snd_pcm_t *pcm)
 Return number of frames ready to be read (capture) / written (playback).
snd_pcm_sframes_t snd_pcm_avail_update (snd_pcm_t *pcm)
 Return number of frames ready to be read (capture) / written (playback).
int snd_pcm_avail_delay (snd_pcm_t *pcm, snd_pcm_sframes_t *availp, snd_pcm_sframes_t *delayp)
 Combine snd_pcm_avail and snd_pcm_delay functions.
snd_pcm_sframes_t snd_pcm_rewindable (snd_pcm_t *pcm)
 Get safe count of frames which can be rewinded.
snd_pcm_sframes_t snd_pcm_rewind (snd_pcm_t *pcm, snd_pcm_uframes_t frames)
 Move application frame position backward.
snd_pcm_sframes_t snd_pcm_forwardable (snd_pcm_t *pcm)
 Get safe count of frames which can be forwarded.
snd_pcm_sframes_t snd_pcm_forward (snd_pcm_t *pcm, snd_pcm_uframes_t frames)
 Move application frame position forward.
snd_pcm_sframes_t snd_pcm_writei (snd_pcm_t *pcm, const void *buffer, snd_pcm_uframes_t size)
 Write interleaved frames to a PCM.
snd_pcm_sframes_t snd_pcm_readi (snd_pcm_t *pcm, void *buffer, snd_pcm_uframes_t size)
 Read interleaved frames from a PCM.
snd_pcm_sframes_t snd_pcm_writen (snd_pcm_t *pcm, void **bufs, snd_pcm_uframes_t size)
 Write non interleaved frames to a PCM.
snd_pcm_sframes_t snd_pcm_readn (snd_pcm_t *pcm, void **bufs, snd_pcm_uframes_t size)
 Read non interleaved frames to a PCM.
int snd_pcm_wait (snd_pcm_t *pcm, int timeout)
 Wait for a PCM to become ready.
int snd_pcm_link (snd_pcm_t *pcm1, snd_pcm_t *pcm2)
 Link two PCMs.
int snd_pcm_unlink (snd_pcm_t *pcm)
 Remove a PCM from a linked group.
int snd_pcm_recover (snd_pcm_t *pcm, int err, int silent)
 Recover the stream state from an error or suspend.
int snd_pcm_set_params (snd_pcm_t *pcm, snd_pcm_format_t format, snd_pcm_access_t access, unsigned int channels, unsigned int rate, int soft_resample, unsigned int latency)
 Set the hardware and software parameters in a simple way.
int snd_pcm_get_params (snd_pcm_t *pcm, snd_pcm_uframes_t *buffer_size, snd_pcm_uframes_t *period_size)
 Get the transfer size parameters in a simple way.

Detailed Description

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


Define Documentation

#define SND_PCM_ASYNC

Async notification (flag for open mode)

#define SND_PCM_DLSYM_VERSION   _dlsym_pcm_001

dlsym version for interface entry callback

#define SND_PCM_NO_AUTO_CHANNELS   0x00020000

Disable automatic (but not forced!) channel conversion

#define SND_PCM_NO_AUTO_FORMAT   0x00040000

Disable automatic (but not forced!) format conversion

#define SND_PCM_NO_AUTO_RESAMPLE   0x00010000

Disable automatic (but not forced!) rate resamplinig

#define SND_PCM_NO_SOFTVOL   0x00080000

Disable soft volume control

#define SND_PCM_NONBLOCK

Non blocking mode (flag for open mode)

Examples:
/test/latency.c.

Typedef Documentation

typedef struct _snd_pcm_access_mask snd_pcm_access_mask_t

PCM access types mask

typedef struct _snd_pcm_format_mask snd_pcm_format_mask_t

PCM formats mask

typedef struct _snd_pcm_hw_params snd_pcm_hw_params_t

PCM hardware configuration space container

Examples:
/test/latency.c, and /test/pcm.c.
typedef struct _snd_pcm_info snd_pcm_info_t

PCM generic info container

typedef struct _snd_pcm_scope snd_pcm_scope_t

SND_PCM_TYPE_METER scope handle

typedef long snd_pcm_sframes_t

Signed frames quantity

Examples:
/test/pcm.c, and /test/pcm_min.c.
typedef struct _snd_pcm_status snd_pcm_status_t

PCM status container

Examples:
/test/latency.c.
typedef struct _snd_pcm_subformat_mask snd_pcm_subformat_mask_t

PCM subformats mask

typedef struct _snd_pcm_sw_params snd_pcm_sw_params_t

PCM software configuration container

Examples:
/test/latency.c, and /test/pcm.c.
typedef struct _snd_pcm snd_pcm_t

PCM handle

Examples:
/test/latency.c, /test/pcm.c, and /test/pcm_min.c.

PCM type

typedef unsigned long snd_pcm_uframes_t

Unsigned frames quantity

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

Enumeration Type Documentation

PCM type

Enumerator:
SND_PCM_TYPE_HW 

Kernel level PCM

SND_PCM_TYPE_HOOKS 

Hooked PCM

SND_PCM_TYPE_MULTI 

One or more linked PCM with exclusive access to selected channels

SND_PCM_TYPE_FILE 

File writing plugin

SND_PCM_TYPE_NULL 

Null endpoint PCM

SND_PCM_TYPE_SHM 

Shared memory client PCM

SND_PCM_TYPE_INET 

INET client PCM (not yet implemented)

SND_PCM_TYPE_COPY 

Copying plugin

SND_PCM_TYPE_LINEAR 

Linear format conversion PCM

SND_PCM_TYPE_ALAW 

A-Law format conversion PCM

SND_PCM_TYPE_MULAW 

Mu-Law format conversion PCM

SND_PCM_TYPE_ADPCM 

IMA-ADPCM format conversion PCM

SND_PCM_TYPE_RATE 

Rate conversion PCM

SND_PCM_TYPE_ROUTE 

Attenuated static route PCM

SND_PCM_TYPE_PLUG 

Format adjusted PCM

SND_PCM_TYPE_SHARE 

Sharing PCM

SND_PCM_TYPE_METER 

Meter plugin

SND_PCM_TYPE_MIX 

Mixing PCM

SND_PCM_TYPE_DROUTE 

Attenuated dynamic route PCM (not yet implemented)

SND_PCM_TYPE_LBSERVER 

Loopback server plugin (not yet implemented)

SND_PCM_TYPE_LINEAR_FLOAT 

Linear Integer <-> Linear Float format conversion PCM

SND_PCM_TYPE_LADSPA 

LADSPA integration plugin

SND_PCM_TYPE_DMIX 

Direct Mixing plugin

SND_PCM_TYPE_JACK 

Jack Audio Connection Kit plugin

SND_PCM_TYPE_DSNOOP 

Direct Snooping plugin

SND_PCM_TYPE_DSHARE 

Direct Sharing plugin

SND_PCM_TYPE_IEC958 

IEC958 subframe plugin

SND_PCM_TYPE_SOFTVOL 

Soft volume plugin

SND_PCM_TYPE_IOPLUG 

External I/O plugin

SND_PCM_TYPE_EXTPLUG 

External filter plugin

SND_PCM_TYPE_MMAP_EMUL 

Mmap-emulation plugin

PCM access type

Enumerator:
SND_PCM_ACCESS_MMAP_INTERLEAVED 

mmap access with simple interleaved channels

SND_PCM_ACCESS_MMAP_NONINTERLEAVED 

mmap access with simple non interleaved channels

SND_PCM_ACCESS_MMAP_COMPLEX 

mmap access with complex placement

SND_PCM_ACCESS_RW_INTERLEAVED 

snd_pcm_readi/snd_pcm_writei access

SND_PCM_ACCESS_RW_NONINTERLEAVED 

snd_pcm_readn/snd_pcm_writen access

PCM class

Enumerator:
SND_PCM_CLASS_GENERIC 

standard device

SND_PCM_CLASS_MULTI 

multichannel device

SND_PCM_CLASS_MODEM 

software modem device

SND_PCM_CLASS_DIGITIZER 

digitizer device

PCM sample format

Enumerator:
SND_PCM_FORMAT_UNKNOWN 

Unknown

SND_PCM_FORMAT_S8 

Signed 8 bit

SND_PCM_FORMAT_U8 

Unsigned 8 bit

SND_PCM_FORMAT_S16_LE 

Signed 16 bit Little Endian

SND_PCM_FORMAT_S16_BE 

Signed 16 bit Big Endian

SND_PCM_FORMAT_U16_LE 

Unsigned 16 bit Little Endian

SND_PCM_FORMAT_U16_BE 

Unsigned 16 bit Big Endian

SND_PCM_FORMAT_S24_LE 

Signed 24 bit Little Endian using low three bytes in 32-bit word

SND_PCM_FORMAT_S24_BE 

Signed 24 bit Big Endian using low three bytes in 32-bit word

SND_PCM_FORMAT_U24_LE 

Unsigned 24 bit Little Endian using low three bytes in 32-bit word

SND_PCM_FORMAT_U24_BE 

Unsigned 24 bit Big Endian using low three bytes in 32-bit word

SND_PCM_FORMAT_S32_LE 

Signed 32 bit Little Endian

SND_PCM_FORMAT_S32_BE 

Signed 32 bit Big Endian

SND_PCM_FORMAT_U32_LE 

Unsigned 32 bit Little Endian

SND_PCM_FORMAT_U32_BE 

Unsigned 32 bit Big Endian

SND_PCM_FORMAT_FLOAT_LE 

Float 32 bit Little Endian, Range -1.0 to 1.0

SND_PCM_FORMAT_FLOAT_BE 

Float 32 bit Big Endian, Range -1.0 to 1.0

SND_PCM_FORMAT_FLOAT64_LE 

Float 64 bit Little Endian, Range -1.0 to 1.0

SND_PCM_FORMAT_FLOAT64_BE 

Float 64 bit Big Endian, Range -1.0 to 1.0

SND_PCM_FORMAT_IEC958_SUBFRAME_LE 

IEC-958 Little Endian

SND_PCM_FORMAT_IEC958_SUBFRAME_BE 

IEC-958 Big Endian

SND_PCM_FORMAT_MU_LAW 

Mu-Law

SND_PCM_FORMAT_A_LAW 

A-Law

SND_PCM_FORMAT_IMA_ADPCM 

Ima-ADPCM

SND_PCM_FORMAT_MPEG 

MPEG

SND_PCM_FORMAT_GSM 

GSM

SND_PCM_FORMAT_SPECIAL 

Special

SND_PCM_FORMAT_S24_3LE 

Signed 24bit Little Endian in 3bytes format

SND_PCM_FORMAT_S24_3BE 

Signed 24bit Big Endian in 3bytes format

SND_PCM_FORMAT_U24_3LE 

Unsigned 24bit Little Endian in 3bytes format

SND_PCM_FORMAT_U24_3BE 

Unsigned 24bit Big Endian in 3bytes format

SND_PCM_FORMAT_S20_3LE 

Signed 20bit Little Endian in 3bytes format

SND_PCM_FORMAT_S20_3BE 

Signed 20bit Big Endian in 3bytes format

SND_PCM_FORMAT_U20_3LE 

Unsigned 20bit Little Endian in 3bytes format

SND_PCM_FORMAT_U20_3BE 

Unsigned 20bit Big Endian in 3bytes format

SND_PCM_FORMAT_S18_3LE 

Signed 18bit Little Endian in 3bytes format

SND_PCM_FORMAT_S18_3BE 

Signed 18bit Big Endian in 3bytes format

SND_PCM_FORMAT_U18_3LE 

Unsigned 18bit Little Endian in 3bytes format

SND_PCM_FORMAT_U18_3BE 

Unsigned 18bit Big Endian in 3bytes format

SND_PCM_FORMAT_S16 

Signed 16 bit CPU endian

SND_PCM_FORMAT_U16 

Unsigned 16 bit CPU endian

SND_PCM_FORMAT_S24 

Signed 24 bit CPU endian

SND_PCM_FORMAT_U24 

Unsigned 24 bit CPU endian

SND_PCM_FORMAT_S32 

Signed 32 bit CPU endian

SND_PCM_FORMAT_U32 

Unsigned 32 bit CPU endian

SND_PCM_FORMAT_FLOAT 

Float 32 bit CPU endian

SND_PCM_FORMAT_FLOAT64 

Float 64 bit CPU endian

SND_PCM_FORMAT_IEC958_SUBFRAME 

IEC-958 CPU Endian

PCM start mode

Enumerator:
SND_PCM_START_DATA 

Automatic start on data read/write

SND_PCM_START_EXPLICIT 

Explicit start

PCM state

Enumerator:
SND_PCM_STATE_OPEN 

Open

SND_PCM_STATE_SETUP 

Setup installed

SND_PCM_STATE_PREPARED 

Ready to start

SND_PCM_STATE_RUNNING 

Running

SND_PCM_STATE_XRUN 

Stopped: underrun (playback) or overrun (capture) detected

SND_PCM_STATE_DRAINING 

Draining: running (playback) or stopped (capture)

SND_PCM_STATE_PAUSED 

Paused

SND_PCM_STATE_SUSPENDED 

Hardware is suspended

SND_PCM_STATE_DISCONNECTED 

Hardware is disconnected

PCM stream (direction)

Enumerator:
SND_PCM_STREAM_PLAYBACK 

Playback stream

SND_PCM_STREAM_CAPTURE 

Capture stream

PCM subclass

Enumerator:
SND_PCM_SUBCLASS_GENERIC_MIX 

subdevices are mixed together

SND_PCM_SUBCLASS_MULTI_MIX 

multichannel subdevices are mixed together

PCM sample subformat

Enumerator:
SND_PCM_SUBFORMAT_STD 

Standard

PCM timestamp mode

Enumerator:
SND_PCM_TSTAMP_NONE 

No timestamp

SND_PCM_TSTAMP_ENABLE 

Update timestamp at every hardware position update

SND_PCM_TSTAMP_MMAP 

Equivalent with SND_PCM_TSTAMP_ENABLE, just for compatibility with older versions

PCM xrun mode

Enumerator:
SND_PCM_XRUN_NONE 

Xrun detection disabled

SND_PCM_XRUN_STOP 

Stop on xrun detection


Function Documentation

int snd_async_add_pcm_handler ( snd_async_handler_t **  handler,
snd_pcm_t pcm,
snd_async_callback_t  callback,
void *  private_data 
)

Add an async handler for a PCM.

Parameters:
handler Returned handler handle
pcm PCM handle
callback Callback function
private_data Callback private data
Returns:
0 otherwise a negative error code on failure

The asynchronous callback is called when period boundary elapses.

Examples:
/test/pcm.c.
snd_pcm_t* snd_async_handler_get_pcm ( snd_async_handler_t handler  ) 

Return PCM handle related to an async handler.

Parameters:
handler Async handler handle
Returns:
PCM handle
Examples:
/test/pcm.c.
snd_pcm_sframes_t snd_pcm_avail ( snd_pcm_t pcm  ) 

Return number of frames ready to be read (capture) / written (playback).

Parameters:
pcm PCM handle
Returns:
a positive number of frames ready otherwise a negative error code

On capture does all the actions needed to transport to application level all the ready frames across underlying layers.

The position is synced with hardware (driver) position in the sound ring buffer in this functions.

int snd_pcm_avail_delay ( snd_pcm_t pcm,
snd_pcm_sframes_t availp,
snd_pcm_sframes_t delayp 
)

Combine snd_pcm_avail and snd_pcm_delay functions.

Parameters:
pcm PCM handle
availp Number of available frames in the ring buffer
delayp Total I/O latency in frames
Returns:
zero on success otherwise a negative error code

The avail and delay values retuned are in sync.

snd_pcm_sframes_t snd_pcm_avail_update ( snd_pcm_t pcm  ) 

Return number of frames ready to be read (capture) / written (playback).

Parameters:
pcm PCM handle
Returns:
a positive number of frames ready otherwise a negative error code

On capture does all the actions needed to transport to application level all the ready frames across underlying layers.

The position is not synced with hardware (driver) position in the sound ring buffer in this function. This function is a light version of snd_pcm_avail() .

Using this function is ideal after poll() or select() when audio file descriptor made the event and when application expects just period timing.

Also this function might be called after snd_pcm_delay() or snd_pcm_hwsync() functions to move private ring buffer pointers in alsa-lib (the internal plugin chain).

Examples:
/test/pcm.c.
int snd_pcm_close ( snd_pcm_t pcm  ) 

close PCM handle

Parameters:
pcm PCM handle
Returns:
0 on success otherwise a negative error code

Closes the specified PCM handle and frees all associated resources.

Examples:
/test/latency.c, /test/pcm.c, and /test/pcm_min.c.
int snd_pcm_delay ( snd_pcm_t pcm,
snd_pcm_sframes_t delayp 
)

Obtain delay for a running PCM handle.

Parameters:
pcm PCM handle
delayp Returned delay in frames
Returns:
0 on success otherwise a negative error code

For playback the delay is defined as the time that a frame that is written to the PCM stream shortly after this call will take to be actually audible. It is as such the overall latency from the write call to the final DAC.

For capture the delay is defined as the time that a frame that was digitized by the audio device takes until it can be read from the PCM stream shortly after this call returns. It is as such the overall latency from the initial ADC to the read call.

Please note that hence in case of a playback underrun this value will not necessarily got down to 0.

If the application is interested in the fill level of the playback buffer of the device, it should use snd_pcm_avail*() functions. The value returned by that call is not directly related to the delay, since the latter might include some additional, fixed latencies the former does not.

Note this function does not update the actual r/w pointer for applications. The function snd_pcm_avail_update() have to be called before any begin+commit operation.

int snd_pcm_drain ( snd_pcm_t pcm  ) 

Stop a PCM preserving pending frames.

Parameters:
pcm PCM handle
Returns:
0 on success otherwise a negative error code
Return values:
-ESTRPIPE a suspend event occurred

For playback wait for all pending frames to be played and then stop the PCM. For capture stop PCM permitting to retrieve residual frames.

For stopping the PCM stream immediately, use ::snd_pcm_drop() instead.

Examples:
/test/latency.c.
int snd_pcm_drop ( snd_pcm_t pcm  ) 

Stop a PCM dropping pending frames.

Parameters:
pcm PCM handle
Returns:
0 on success otherwise a negative error code

This function stops the PCM immediately. The pending samples on the buffer are ignored.

For processing all pending samples, use ::snd_pcm_drain() instead.

Examples:
/test/latency.c.
snd_pcm_sframes_t snd_pcm_forward ( snd_pcm_t pcm,
snd_pcm_uframes_t  frames 
)

Move application frame position forward.

Parameters:
pcm PCM handle
frames wanted skip in frames
Returns:
a positive number for actual skip otherwise a negative error code
Return values:
0 means no action
snd_pcm_sframes_t snd_pcm_forwardable ( snd_pcm_t pcm  ) 

Get safe count of frames which can be forwarded.

Parameters:
pcm PCM handle
Returns:
a positive number of frames or negative error code

Note: The snd_pcm_forward() can accept bigger value than returned by this function. But it is not guaranteed that output stream will be consistent with bigger value.

int snd_pcm_get_params ( snd_pcm_t pcm,
snd_pcm_uframes_t buffer_size,
snd_pcm_uframes_t period_size 
)

Get the transfer size parameters in a simple way.

Parameters:
pcm PCM handle
buffer_size PCM ring buffer size in frames
period_size PCM period size in frames
Returns:
0 on success otherwise a negative error code
int snd_pcm_htimestamp ( snd_pcm_t pcm,
snd_pcm_uframes_t avail,
snd_htimestamp_t tstamp 
)

Obtain last position update hi-res timestamp.

Parameters:
pcm PCM handle
avail Number of available frames when timestamp was grabbed
tstamp Hi-res timestamp
Returns:
0 on success otherwise a negative error code

Note this function does not update the actual r/w pointer for applications.

int snd_pcm_hw_free ( snd_pcm_t pcm  ) 

Remove PCM hardware configuration and free associated resources.

Parameters:
pcm PCM handle
Returns:
0 on success otherwise a negative error code
Examples:
/test/latency.c.
int snd_pcm_hw_params ( snd_pcm_t pcm,
snd_pcm_hw_params_t params 
)

Install one PCM hardware configuration chosen from a configuration space and snd_pcm_prepare it.

Parameters:
pcm PCM handle
params Configuration space definition container
Returns:
0 on success otherwise a negative error code

The configuration is chosen fixing single parameters in this order: first access, first format, first subformat, min channels, min rate, min period time, max buffer size, min tick time

After this call, snd_pcm_prepare() is called automatically and the stream is brought to SND_PCM_STATE_PREPARED state.

The hardware parameters cannot be changed when the stream is running (active). The software parameters can be changed at any time.

Examples:
/test/latency.c, and /test/pcm.c.
int snd_pcm_hw_params_current ( snd_pcm_t pcm,
snd_pcm_hw_params_t params 
)

Retreive current PCM hardware configuration chosen with snd_pcm_hw_params.

Parameters:
pcm PCM handle
params Configuration space definition container
Returns:
0 on success otherwise a negative error code
int snd_pcm_hwsync ( snd_pcm_t pcm  ) 

(DEPRECATED) Synchronize stream position with hardware

Parameters:
pcm PCM handle
Returns:
0 on success otherwise a negative error code

Note this function does not update the actual r/w pointer for applications. The function snd_pcm_avail_update() have to be called before any mmap begin+commit operation.

int snd_pcm_info ( snd_pcm_t pcm,
snd_pcm_info_t info 
)

Obtain general (static) information for PCM handle.

Parameters:
pcm PCM handle
info Information container
Returns:
0 on success otherwise a negative error code
int snd_pcm_link ( snd_pcm_t pcm1,
snd_pcm_t pcm2 
)

Link two PCMs.

Parameters:
pcm1 first PCM handle
pcm2 first PCM handle
Returns:
0 on success otherwise a negative error code

The two PCMs will start/stop/prepare in sync.

Examples:
/test/latency.c.
const char* snd_pcm_name ( snd_pcm_t pcm  ) 

get identifier of PCM handle

Parameters:
pcm PCM handle
Returns:
ascii identifier of PCM handle

Returns the ASCII identifier of given PCM handle. It's the same identifier specified in snd_pcm_open().

int snd_pcm_nonblock ( snd_pcm_t pcm,
int  nonblock 
)

set nonblock mode

Parameters:
pcm PCM handle
nonblock 0 = block, 1 = nonblock mode
Returns:
0 on success otherwise a negative error code
Examples:
/test/latency.c.
int snd_pcm_open ( snd_pcm_t **  pcmp,
const char *  name,
snd_pcm_stream_t  stream,
int  mode 
)

Opens a PCM.

Parameters:
pcmp Returned PCM handle
name ASCII identifier of the PCM handle
stream Wanted stream
mode Open mode (see SND_PCM_NONBLOCK, SND_PCM_ASYNC)
Returns:
0 on success otherwise a negative error code
Examples:
/test/latency.c, /test/pcm.c, and /test/pcm_min.c.
int snd_pcm_open_lconf ( snd_pcm_t **  pcmp,
const char *  name,
snd_pcm_stream_t  stream,
int  mode,
snd_config_t lconf 
)

Opens a PCM using local configuration.

Parameters:
pcmp Returned PCM handle
name ASCII identifier of the PCM handle
stream Wanted stream
mode Open mode (see SND_PCM_NONBLOCK, SND_PCM_ASYNC)
lconf Local configuration
Returns:
0 on success otherwise a negative error code
int snd_pcm_pause ( snd_pcm_t pcm,
int  enable 
)

Pause/resume PCM.

Parameters:
pcm PCM handle
enable 0 = resume, 1 = pause
Returns:
0 on success otherwise a negative error code

Note that this function works only on the hardware which supports pause feature. You can check it via ::snd_pcm_hw_params_can_pause() function.

int snd_pcm_poll_descriptors ( snd_pcm_t pcm,
struct pollfd *  pfds,
unsigned int  space 
)

get poll descriptors

Parameters:
pcm PCM handle
pfds array of poll descriptors
space space in the poll descriptor array
Returns:
count of filled descriptors

This function fills the given poll descriptor structs for the specified PCM handle. The poll desctiptor array should have the size returned by ::snd_pcm_poll_descriptors_count() function.

The result is intended for direct use with the poll() syscall.

For reading the returned events of poll descriptor after poll() system call, use ::snd_pcm_poll_descriptors_revents() function. The field values in pollfd structs may be bogus regarding the stream direction from the application perspective (POLLIN might not imply read direction and POLLOUT might not imply write), but the ::snd_pcm_poll_descriptors_revents() function does the right "demangling".

You can use output from this function as arguments for the select() syscall, too. Do not forget to translate POLLIN and POLLOUT events to corresponding FD_SET arrays and demangle events using ::snd_pcm_poll_descriptors_revents() .

Examples:
/test/pcm.c.
int snd_pcm_poll_descriptors_count ( snd_pcm_t pcm  ) 

get count of poll descriptors for PCM handle

Parameters:
pcm PCM handle
Returns:
count of poll descriptors
Examples:
/test/pcm.c.
int snd_pcm_poll_descriptors_revents ( snd_pcm_t pcm,
struct pollfd *  pfds,
unsigned int  nfds,
unsigned short *  revents 
)

get returned events from poll descriptors

Parameters:
pcm PCM handle
pfds array of poll descriptors
nfds count of poll descriptors
revents pointer to the returned (single) event
Returns:
zero if success, otherwise a negative error code

This function does "demangling" of the revents mask returned from the poll() syscall to correct semantics (POLLIN = read, POLLOUT = write).

Note: The null event also exists. Even if poll() or select() syscall returned that some events are waiting, this function might return empty set of events. In this case, application should do next event waiting using poll() or select().

Note: Even if multiple poll descriptors are used (i.e. pfds > 1), this function returns only a single event.

Examples:
/test/pcm.c.
int snd_pcm_prepare ( snd_pcm_t pcm  ) 

Prepare PCM for use.

Parameters:
pcm PCM handle
Returns:
0 on success otherwise a negative error code
Examples:
/test/latency.c, and /test/pcm.c.
snd_pcm_sframes_t snd_pcm_readi ( snd_pcm_t pcm,
void *  buffer,
snd_pcm_uframes_t  size 
)

Read interleaved frames from a PCM.

Parameters:
pcm PCM handle
buffer frames containing buffer
size frames to be read
Returns:
a positive number of frames actually read otherwise a negative error code
Return values:
-EBADFD PCM is not in the right state (SND_PCM_STATE_PREPARED or SND_PCM_STATE_RUNNING)
-EPIPE an overrun occurred
-ESTRPIPE a suspend event occurred (stream is suspended and waiting for an application recovery)

If the blocking behaviour was selected and it is running, then routine waits until all requested frames are filled. The returned number of frames can be less only if a signal or underrun occurred.

If the non-blocking behaviour is selected, then routine doesn't wait at all.

Examples:
/test/latency.c.
snd_pcm_sframes_t snd_pcm_readn ( snd_pcm_t pcm,
void **  bufs,
snd_pcm_uframes_t  size 
)

Read non interleaved frames to a PCM.

Parameters:
pcm PCM handle
bufs frames containing buffers (one for each channel)
size frames to be read
Returns:
a positive number of frames actually read otherwise a negative error code
Return values:
-EBADFD PCM is not in the right state (SND_PCM_STATE_PREPARED or SND_PCM_STATE_RUNNING)
-EPIPE an overrun occurred
-ESTRPIPE a suspend event occurred (stream is suspended and waiting for an application recovery)

If the blocking behaviour was selected and it is running, then routine waits until all requested frames are filled. The returned number of frames can be less only if a signal or underrun occurred.

If the non-blocking behaviour is selected, then routine doesn't wait at all.

int snd_pcm_recover ( snd_pcm_t pcm,
int  err,
int  silent 
)

Recover the stream state from an error or suspend.

Parameters:
pcm PCM handle
err error number
silent do not print error reason
Returns:
0 when error code was handled successfuly, otherwise a negative error code

This a high-level helper function building on other functions.

This functions handles -EINTR (interrupted system call), -EPIPE (overrun or underrun) and -ESTRPIPE (stream is suspended) error codes trying to prepare given stream for next I/O.

Note that this function returs the original error code when it is not handled inside this function (for example -EAGAIN is returned back).

Examples:
/test/pcm_min.c.
int snd_pcm_reset ( snd_pcm_t pcm  ) 

Reset PCM position.

Parameters:
pcm PCM handle
Returns:
0 on success otherwise a negative error code

Reduce PCM delay to 0.

int snd_pcm_resume ( snd_pcm_t pcm  ) 

Resume from suspend, no samples are lost.

Parameters:
pcm PCM handle
Returns:
0 on success otherwise a negative error code
Return values:
-EAGAIN resume can't be proceed immediately (audio hardware is probably still suspended)
-ENOSYS hardware doesn't support this feature

This function can be used when the stream is in the suspend state to do the fine resume from this state. Not all hardware supports this feature, when an -ENOSYS error is returned, use the ::snd_pcm_prepare() function to recovery.

Examples:
/test/pcm.c.
snd_pcm_sframes_t snd_pcm_rewind ( snd_pcm_t pcm,
snd_pcm_uframes_t  frames 
)

Move application frame position backward.

Parameters:
pcm PCM handle
frames wanted displacement in frames
Returns:
a positive number for actual displacement otherwise a negative error code
snd_pcm_sframes_t snd_pcm_rewindable ( snd_pcm_t pcm  ) 

Get safe count of frames which can be rewinded.

Parameters:
pcm PCM handle
Returns:
a positive number of frames or negative error code

Note: The snd_pcm_rewind() can accept bigger value than returned by this function. But it is not guaranteed that output stream will be consistent with bigger value.

int snd_pcm_set_params ( snd_pcm_t pcm,
snd_pcm_format_t  format,
snd_pcm_access_t  access,
unsigned int  channels,
unsigned int  rate,
int  soft_resample,
unsigned int  latency 
)

Set the hardware and software parameters in a simple way.

Parameters:
pcm PCM handle
format required PCM format
access required PCM access
channels required PCM channels
rate required sample rate in Hz
soft_resample 0 = disallow alsa-lib resample stream, 1 = allow resampling
latency required overall latency in us
Returns:
0 on success otherwise a negative error code
Examples:
/test/pcm_min.c.
int snd_pcm_start ( snd_pcm_t pcm  ) 

Start a PCM.

Parameters:
pcm PCM handle
Returns:
0 on success otherwise a negative error code
Examples:
/test/latency.c, and /test/pcm.c.
snd_pcm_state_t snd_pcm_state ( snd_pcm_t pcm  ) 

Return PCM state.

Parameters:
pcm PCM handle
Returns:
PCM state snd_pcm_state_t of given PCM handle

This is a faster way to obtain only the PCM state without calling ::snd_pcm_status().

Examples:
/test/pcm.c.
int snd_pcm_status ( snd_pcm_t pcm,
snd_pcm_status_t status 
)

Obtain status (runtime) information for PCM handle.

Parameters:
pcm PCM handle
status Status container
Returns:
0 on success otherwise a negative error code
Examples:
/test/latency.c.
snd_pcm_stream_t snd_pcm_stream ( snd_pcm_t pcm  ) 

get stream for a PCM handle

Parameters:
pcm PCM handle
Returns:
stream of PCM handle

Returns the type snd_pcm_stream_t of given PCM handle.

int snd_pcm_sw_params ( snd_pcm_t pcm,
snd_pcm_sw_params_t params 
)

Install PCM software configuration defined by params.

Parameters:
pcm PCM handle
params Configuration container
Returns:
0 on success otherwise a negative error code

The software parameters can be changed at any time. The hardware parameters cannot be changed when the stream is running (active).

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

Return current software configuration for a PCM.

Parameters:
pcm PCM handle
params Software configuration container
Returns:
0 on success otherwise a negative error code
Examples:
/test/latency.c, and /test/pcm.c.
snd_pcm_type_t snd_pcm_type ( snd_pcm_t pcm  ) 

get type of PCM handle

Parameters:
pcm PCM handle
Returns:
type of PCM handle

Returns the type snd_pcm_type_t of given PCM handle.

int snd_pcm_unlink ( snd_pcm_t pcm  ) 

Remove a PCM from a linked group.

Parameters:
pcm PCM handle
Returns:
0 on success otherwise a negative error code
Examples:
/test/latency.c.
int snd_pcm_wait ( snd_pcm_t pcm,
int  timeout 
)

Wait for a PCM to become ready.

Parameters:
pcm PCM handle
timeout maximum time in milliseconds to wait, a negative value means infinity
Returns:
a positive value on success otherwise a negative error code (-EPIPE for the xrun and -ESTRPIPE for the suspended status, others for general errors)
Return values:
0 timeout occurred
1 PCM stream is ready for I/O
Examples:
/test/latency.c, and /test/pcm.c.
snd_pcm_sframes_t snd_pcm_writei ( snd_pcm_t pcm,
const void *  buffer,
snd_pcm_uframes_t  size 
)

Write interleaved frames to a PCM.

Parameters:
pcm PCM handle
buffer frames containing buffer
size frames to be written
Returns:
a positive number of frames actually written otherwise a negative error code
Return values:
-EBADFD PCM is not in the right state (SND_PCM_STATE_PREPARED or SND_PCM_STATE_RUNNING)
-EPIPE an underrun occurred
-ESTRPIPE a suspend event occurred (stream is suspended and waiting for an application recovery)

If the blocking behaviour is selected and it is running, then routine waits until all requested frames are played or put to the playback ring buffer. The returned number of frames can be less only if a signal or underrun occurred.

If the non-blocking behaviour is selected, then routine doesn't wait at all.

Examples:
/test/latency.c, /test/pcm.c, and /test/pcm_min.c.
snd_pcm_sframes_t snd_pcm_writen ( snd_pcm_t pcm,
void **  bufs,
snd_pcm_uframes_t  size 
)

Write non interleaved frames to a PCM.

Parameters:
pcm PCM handle
bufs frames containing buffers (one for each channel)
size frames to be written
Returns:
a positive number of frames actually written otherwise a negative error code
Return values:
-EBADFD PCM is not in the right state (SND_PCM_STATE_PREPARED or SND_PCM_STATE_RUNNING)
-EPIPE an underrun occurred
-ESTRPIPE a suspend event occurred (stream is suspended and waiting for an application recovery)

If the blocking behaviour is selected and it is running, then routine waits until all requested frames are played or put to the playback ring buffer. The returned number of frames can be less only if a signal or underrun occurred.

If the non-blocking behaviour is selected, then routine doesn't wait at all.

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