snd_pcm_channel_info()

Get information about the PCM direction

Synopsis:

#include <sys/asoundlib.h>

int snd_pcm_channel_info( snd_pcm_t * handle, 
                          snd_pcm_channel_info_t * info );

Library:

libasound.so

Description:

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

typedef union snd_pcm_sync
{
    uint8_t     id[16];
    uint16_t    id16[8];
    uint32_t    id32[4];
    uint64_t    id64[2];
}       snd_pcm_sync_t;

typedef struct snd_pcm_digital
{
    uint8_t     dig_status[24];         /* AES/EBU/IEC958 channel status bits */
    uint8_t     dig_subcode[147];       /* AES/EBU/IEC958 subcode bits */
    uint8_t     dig_valid:1;            /* must be non-zero to accept these values */
    uint8_t     dig_subframe[4];        /* AES/EBU/IEC958 subframe bits */
    uint8_t     reserved[128];          /* must be filled with zero */
}       snd_pcm_digital_t;

where:

dig_status[24]

AES/EBU/IEC958 channel status bits.

dig_subcode[147]

AES/EBU/IEC958 subcode bits.

dig_valid: 1

Must be nonzero to accept these values.

dig_subframe[4]

AES/EBU/IEC958 subframe bits.

typedef struct snd_pcm_channel_info
{
    int32_t     subdevice;              
    int8_t      subname[36];            
    int32_t     channel;                
    int32_t     zero1;                  
    int32_t     zero2[4];               
    uint32_t    flags;                  
    uint32_t    formats;                
    uint32_t    rates;                  
    int32_t     min_rate;               
    int32_t     max_rate;               
    int32_t     min_voices;             
    int32_t     max_voices;             
    int32_t     max_buffer_size;        
    int32_t     min_fragment_size;      
    int32_t     max_fragment_size;      
    int32_t     fragment_align;         
    int32_t     fifo_size;              
    int32_t     transfer_block_size;    
    uint8_t     zero3[4];               

    snd_pcm_digital_t dig_mask;         
    uint32_t    zero4;                  
    int32_t     mixer_device;           
    snd_mixer_eid_t mixer_eid;          
    snd_mixer_gid_t mixer_gid;          
    uint8_t     reserved[128];          
}       snd_pcm_channel_info_t;

where:

subdevice

Subdevice number.

subname[32]

Subdevice name.

channel

Channel information.

flags

One of:

SND_PCM_CHNINFO_BLOCK

Hardware supports block mode.

SND_PCM_CHNINFO_BLOCK_TRANSFER

Hardware transfers samples by chunks (for example PCI burst transfers).

SND_PCM_CHNINFO_INTERLEAVE

Hardware accepts interleaved stream samples.

SND_PCM_CHNINFO_MMAP

Hardware supports mmap access.

SND_PCM_CHNINFO_MMAP_VALID

Fragment samples are valid during transfer. It means that the fragment samples may be used when the io member from the mmap control structure snd_pcm_mmap_control_t is set (the fragment is being transferred).

SND_PCM_CHNINFO_NONINTERLEAVE

Hardware accepts non-interleaved stream samples.

SND_PCM_CHNINFO_OVERRANGE

Hardware supports ADC (capture) overrange detection.

SND_PCM_CHNINFO_PAUSE

Hardware supports pause (playback only).

SND_PCM_CHNINFO_STREAM

Hardware supports stream mode.

formats

Supported formats.

rates

Hardware rates.

min_rate

Minimum rate (in Hz).

max_rate

Maximum rate (in Hz).

min_voices

Minimum voices (probably always 1).

max_voices

Maximum voices.

max_buffer_size

Maximum buffer size in bytes.

min_fragment_size

Minimum fragment size in bytes.

max_fragment_size

Maximum fragment size in bytes.

fragment_align

Align fragment value.

fifo_size

Stream FIFO size in bytes.

transfer_block_size

Bus transfer block size in bytes.

dig_mask

AES/EBU/IEC958 supported bits, zero = no AES/EBU/IEC958.

mixer_device

Mixer device for this channel.

mixer_eid

Mixer element identification for this channel.

mixer_gid

Mixer group identification for this channel.

Returns:

Zero on success, or an error code.

Errors:

-EINVAL

Invalid handle.

Examples:

See the example in Configuring the Audio channel in the Playing Audio Data chapter. This call is identical to the snd_pcm_plugin_info() call.

Classification:

ALSA

See also:

snd_pcm_plugin_info()