snd_pcm_channel_params_t

Description:

The snd_pcm_channel_params_t structure describes the parameters of a PCM capture or playback channel. The members include:

channel

The channel direction; one of SND_PCM_CHANNEL_PLAYBACK or SND_PCM_CHANNEL_CAPTURE.

mode

The channel mode: SND_PCM_MODE_BLOCK. (SND_PCM_MODE_STREAM is deprecated.)

You can OR in the following flags:

• SND_PCM_MODE_FLAG_PROTECTED_CONTENT — indicates that the output path may not change without the client's approval. When the output path does change, the client will change to state SND_PCM_STATUS_UNSECURE. The client can then check the current output path, and call snd_pcm_channel_prepare() to continue playback.
• SND_PCM_MODE_FLAG_REQUIRE_PROTECTION — indicates that digital protection is required on the audio path. For example, for HDMI, it indicates that HDCP must be enabled for audio to play.

sync

The synchronization group. Not supported; don't use this member.

format

The data format; see snd_pcm_format_t.

digital

Not currently implemented.

start_mode

The start mode; one of:

• SND_PCM_START_DATA — start when some data is written (playback) or requested (capture).
• SND_PCM_START_FULL — start when the whole queue is filled (playback only).
• SND_PCM_START_GO — start on the Go command.

stop_mode

The stop mode; one of:

• SND_PCM_STOP_STOP — stop when an underrun or overrun occurs.
• SND_PCM_STOP_ROLLOVER_RESET — when recovering from writing or reading more data, reset the counter. Use this option for fault tolerant systems.
• SND_PCM_STOP_ROLLOVER — Rollover the fragments when an underrun or overrun occurs. Use this option to overcome jitter between audio that is being captured or played by the client application.

time

If set, the driver offers, in the status structure, the time when the transfer began. The time is in the format used by gettimeofday() (see the QNX Neutrino C Library Reference).

ust_time

If set, the driver offers, in the status structure, the time when the transfer began. The time is in UST format.

why_failed

An indication why an operation failed; one of:

• SND_PCM_PARAMS_BAD_MODE
• SND_PCM_PARAMS_BAD_START
• SND_PCM_PARAMS_BAD_STOP
• SND_PCM_PARAMS_BAD_FORMAT
• SND_PCM_PARAMS_BAD_RATE
• SND_PCM_PARAMS_BAD_VOICES
• SND_PCM_PARAMS_NO_CHANNEL

queue_size

The queue size, in bytes, for the stream mode. Not supported; don't use this member.

fill

The fill mode (SND_PCM_FILL_* constants). Not supported; don't use this member.

max_fill

The number of bytes to be filled ahead with silence. Not supported; don't use this member.

frag_size

The size of fragment, in bytes.

frags_min

Depends on the mode:

• Capture — the minimum filled fragments to allow wakeup (usually one).
• Playback — the minimum free fragments to allow wakeup (usually one).

frags_max

For playback, the maximum filled fragments to allow wakeup. This value specifies the total number of fragments that could be written to by an application. This excludes the fragment that's currently playing, so the actual total number of fragments is frags_max + 1.

frags_buffered_max

If this is set, io-audio may block the caller after fewer than frags_max fragments have been passed, if it chooses, but won't block the client before frags_buffered_max fragments have been written.

sw_mixer_subchn_name

By default, the name of all sw_mixer subchannel groups is PCM Subchannel; you can use this field to assign a different name.

audio_type_name

The name of the audio type the subchannel is associated with. This is used for audio concurrency management policies, such as audio ducking. For more information, see the Audio Concurrency Management chapter. If there's no matching audio type defined in your audio policy configuration file, then the audio type named default is used. If there's no audio type named default, the lowest priority audio type is used instead.

Classification:

QNX Neutrino