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AUDIO(4)	       FreeBSD Kernel Interfaces Manual		      AUDIO(4)

NAME
     audio, audioctl --	device-independent audio driver	layer

SYNOPSIS
     audio* at ...

     #include <sys/types.h>
     #include <sys/ioctl.h>
     #include <sys/audioio.h>
     #include <string.h>

DESCRIPTION
     The audio driver provides support for various audio peripherals.  It pro-
     vides a uniform programming interface layer above different underlying
     audio hardware drivers.

     In	addition to hardware mixer controls like those documented in
     azalia(4),	the audio driver exposes the record.enable control.  The supe-
     ruser can change it with mixerctl(8).  It accepts the following values:

	   on	   Recording is	enabled.
	   off	   Silence is returned instead of the recorded samples.
	   sysctl  Behavior is controlled by the kern.audio.record sysctl(2)
		   variable.  This is the default.

     There are two types of device files available for audio operation:

	   -   Audio devices are used for recording or playback	of digital
	       samples.

	   -   Control devices are used	to manipulate audio device parameters
	       like volume or recording	source.	 They can also read certain
	       audio driver variables while it is in use.

AUDIO DEVICES
     When audio	devices	are opened, they attempt to maintain the previous au-
     dio sample	format and record/playback mode.  In addition, if one is
     opened read-only (write-only) the device is set to	record-only (play-
     only) mode	with recording (playing) unpaused.

     If	a writing process does not call	write(2) frequently enough to provide
     samples at	the pace the hardware consumes them silence is inserted.  If a
     reading process does not call read(2) frequently enough, it will simply
     miss samples.

     The following ioctl(2) commands are supported on the sample devices:

     AUDIO_GETDEV audio_device_t *
	     This command fetches the current hardware device information into
	     the audio_device_t	* argument.

	     typedef struct audio_device {
		     char name[MAX_AUDIO_DEV_LEN];
		     char version[MAX_AUDIO_DEV_LEN];
		     char config[MAX_AUDIO_DEV_LEN];
	     } audio_device_t;

     AUDIO_SETPAR struct audio_swpar *
     AUDIO_GETPAR struct audio_swpar *
	     Set or get	audio parameters as encoded in the audio_swpar struc-
	     ture.

	     struct audio_swpar	{
		     unsigned int sig;	     /*	if 1, encoding is signed */
		     unsigned int le;	     /*	if 1, encoding is little-endian	*/
		     unsigned int bits;	     /*	bits per sample	*/
		     unsigned int bps;	     /*	bytes per sample */
		     unsigned int msb;	     /*	if 1, bits are msb-aligned */
		     unsigned int rate;	     /*	common play & rec sample rate */
		     unsigned int pchan;     /*	play channels */
		     unsigned int rchan;     /*	rec channels */
		     unsigned int nblks;     /*	number of blocks in play buffer	*/
		     unsigned int round;     /*	common frames per block	*/
	     };

	     When setting the device parameters	with AUDIO_SETPAR, the
	     audio_swpar structure should first	be initialized with

	     struct audio_swpar	ap;

	     AUDIO_INITPAR(&ap);

	     and then only the values to be changed should be set.  This en-
	     sures that	the software will work with future versions of the
	     driver.  The driver will attempt to set the given parameters; if
	     the device	doesn't	support	them, it will choose other parameters.
	     Then the software must call AUDIO_GETPAR to obtain	the parameters
	     in	use.

	     The parameters are	as follows:

	     bits   Number of bits per sample: must be between 1 and 32.

	     bps    Bytes per sample; if specified, it must be large enough to
		    hold all bits.  By default it's set	to the smallest	power
		    of two large enough	to hold	bits.

	     sig    If set (i.e. non-zero) then	the samples are	signed;	other-
		    wise they are unsigned.

	     le	    If set then	the byte order is little endian; if not	it is
		    big	endian.	 It is meaningful only if bps >	1.

	     msb    If set, then the bits are aligned in the packet to the
		    most significant bit (i.e. lower bits are padded), other-
		    wise to the	least significant bit (i.e. higher bits	are
		    padded).  It's meaningful only if bits < bps * 8.

	     rchan  The	number of recorded channels; meaningful	only if	the
		    device is opened for reading.

	     pchan  The	number of channels playing; meaningful only if the de-
		    vice is opened for writing.

	     rate   The	sampling frequency in Hz.

	     nblks  The	number of blocks in the	play buffer.

	     round  The	audio block size.

     AUDIO_START
	     Start playback and/or recording immediately.  If the device is
	     open for writing (playback), then the play	buffer must be filled
	     with the write(2) syscall.	 The buffer size is obtained by	multi-
	     plying the	nblks, round, and bps parameters obtained with
	     AUDIO_GETPAR.

     AUDIO_STOP
	     Stop playback and recording immediately.

     AUDIO_GETPOS struct audio_pos *
	     Fetch an atomic snapshot of device	timing information in the
	     audio_pos structure.

	     struct audio_pos {
		     unsigned int play_pos;  /*	total bytes played */
		     unsigned int play_xrun; /*	bytes of silence inserted */
		     unsigned int rec_pos;   /*	total bytes recorded */
		     unsigned int rec_xrun;  /*	bytes dropped */
	     };

	     The properties have the following meaning:

	     play_pos	Total number of	bytes played by	the device since play-
			back started (a.k.a the	device wall clock).

	     play_xrun	The number of bytes corresponding to silence played
			because	write(2) wasn't	called fast enough.

	     rec_pos	Total number of	bytes recorded by the device since
			recording started (a.k.a the device wall clock).

	     rec_xrun	The number of bytes dropped because read(2) wasn't
			called fast enough.

     AUDIO_GETSTATUS struct audio_status *
	     Fetch the current device status from the audio driver in the
	     audio_status structure.  This ioctl(2) is intended	for use	with
	     diagnostic	tools and is of	no use to audio	programs.

	     struct audio_status {
	     #define AUMODE_PLAY     0x01
	     #define AUMODE_RECORD   0x02
		     int mode;	     /*	current	mode */
		     int pause;	     /*	not started yet	*/
		     int active;     /*	playing/recording in progress */
	     };

	     The properties have the following meaning:

	     mode    The current mode determined by open(2) flags.

	     pause   If	set, indicates that AUDIO_STOP was called, and the de-
		     vice is not attempting to start.

	     active  If	set, indicates that the	device is playing and/or
		     recording.

CONTROL	DEVICES
     Control devices support the following ioctl(2) commands:

     AUDIO_GETDEV audio_device_t *
     AUDIO_GETPOS struct audio_pos *
     AUDIO_GETSTATUS struct audio_status *
     AUDIO_GETPAR struct audio_swpar *
     AUDIO_SETPAR struct audio_swpar *
	     These commands are	the same as described above for	the audio de-
	     vices.  While the audio device is open, AUDIO_SETPAR may not be
	     used.

     AUDIO_MIXER_READ mixer_ctrl_t *
     AUDIO_MIXER_WRITE mixer_ctrl_t *
	     These commands read the current mixer state or set	new mixer
	     state for the specified device dev.  type identifies which	type
	     of	value is supplied in the mixer_ctrl_t *	argument.

	     #define AUDIO_MIXER_CLASS	0
	     #define AUDIO_MIXER_ENUM	1
	     #define AUDIO_MIXER_SET	2
	     #define AUDIO_MIXER_VALUE	3
	     typedef struct mixer_ctrl {
		     int dev;			     /*	input: nth device */
		     int type;
		     union {
			     int ord;		     /*	enum */
			     int mask;		     /*	set */
			     mixer_level_t value;    /*	value */
		     } un;
	     } mixer_ctrl_t;

	     #define AUDIO_MIN_GAIN  0
	     #define AUDIO_MAX_GAIN  255
	     typedef struct mixer_level	{
		     int num_channels;
		     u_char level[8];		     /*	[num_channels] */
	     } mixer_level_t;
	     #define AUDIO_MIXER_LEVEL_MONO  0
	     #define AUDIO_MIXER_LEVEL_LEFT  0
	     #define AUDIO_MIXER_LEVEL_RIGHT 1

	     For a mixer value,	the value field	specifies both the number of
	     channels and the values for each channel.	If the channel count
	     does not match the	current	channel	count, the attempt to change
	     the setting may fail (depending on	the hardware device driver im-
	     plementation).  For an enumeration	value, the ord field should be
	     set to one	of the possible	values as returned by a	prior
	     AUDIO_MIXER_DEVINFO command.  The type AUDIO_MIXER_CLASS is only
	     used for classifying particular mixer device types	and is not
	     used for AUDIO_MIXER_READ or AUDIO_MIXER_WRITE.

     AUDIO_MIXER_DEVINFO mixer_devinfo_t *
	     This command is used iteratively to fetch audio mixer device in-
	     formation into the	input/output mixer_devinfo_t * argument.  To
	     query all the supported devices, start with an index field	of 0
	     and continue with successive devices (1, 2, ...) until the	com-
	     mand returns an error.

	     typedef struct mixer_devinfo {
		     int index;		     /*	input: nth mixer device	*/
		     audio_mixer_name_t	label;
		     int type;
		     int mixer_class;
		     int next, prev;
	     #define AUDIO_MIXER_LAST	     -1
		     union {
			     struct audio_mixer_enum {
				     int num_mem;
				     struct {
					     audio_mixer_name_t	label;
					     int ord;
				     } member[32];
			     } e;
			     struct audio_mixer_set {
				     int num_mem;
				     struct {
					     audio_mixer_name_t	label;
					     int mask;
				     } member[32];
			     } s;
			     struct audio_mixer_value {
				     audio_mixer_name_t	units;
				     int num_channels;
				     int delta;
			     } v;
		     } un;
	     } mixer_devinfo_t;

	     The label field identifies	the name of this particular mixer con-
	     trol.  The	index field may	be used	as the dev field in
	     AUDIO_MIXER_READ and AUDIO_MIXER_WRITE commands.  The type	field
	     identifies	the type of this mixer control.	 Enumeration types are
	     typically used for	on/off style controls (e.g., a mute control)
	     or	for input/output device	selection (e.g., select	recording in-
	     put source	from CD, line in, or microphone).  Set types are simi-
	     lar to enumeration	types but any combination of the mask bits can
	     be	used.

	     The mixer_class field identifies what class of control this is.
	     This value	is set to the index value used to query	the class it-
	     self.  The	(arbitrary) value set by the hardware driver may be
	     determined	by examining the mixer_class field of the class	it-
	     self, a mixer of type AUDIO_MIXER_CLASS.  For example, a mixer
	     level controlling the input gain on the "line in" circuit would
	     have a mixer_class	that matches an	input class device with	the
	     name "inputs" (AudioCinputs) and would have a label of "line"
	     (AudioNline).  Mixer controls which control audio circuitry for a
	     particular	audio source (e.g., line-in, CD	in, DAC	output)	are
	     collected under the input class, while those which	control	all
	     audio sources (e.g., master volume, equalization controls)	are
	     under the output class.  Hardware devices capable of recording
	     typically also have a record class, for controls that only	affect
	     recording,	and also a monitor class.

	     The next and prev may be used by the hardware device driver to
	     provide hints for the next	and previous devices in	a related set
	     (for example, the line in level control would have	the line in
	     mute as its "next"	value).	 If there is no	relevant next or pre-
	     vious value, AUDIO_MIXER_LAST is specified.

	     For AUDIO_MIXER_ENUM mixer	control	types, the enumeration values
	     and their corresponding names are filled in.  For example,	a mute
	     control would return appropriate values paired with AudioNon and
	     AudioNoff.	 For the AUDIO_MIXER_VALUE and AUDIO_MIXER_SET mixer
	     control types, the	channel	count is returned; the units name
	     specifies what the	level controls (typical	values are
	     AudioNvolume, AudioNtreble, and AudioNbass).

     A process may read	the control device to get notifications	about mixer
     changes.  Whenever	a control changes, the read(2) function	fetches	an in-
     teger identifying the control.  It	may be used in the dev field of	the
     mixer_ctrl	structure to call AUDIO_MIXER_READ.

     In	contrast to audio devices, which have the exclusive open property,
     control devices can be opened at any time in write-only mode.  Only one
     reader is allowed at a time.

FILES
     /dev/audioN     Audio device.
     /dev/audioctlN  Control device.

SEE ALSO
     aucat(1), cdio(1),	sndioctl(1), ioctl(2), sio_open(3), sioctl_open(3),
     ac97(4), uaudio(4), sndio(7), audioctl(8),	mixerctl(8), sndiod(8),
     audio(9)

FreeBSD	13.0		       November	1, 2020			  FreeBSD 13.0

NAME | SYNOPSIS | DESCRIPTION | AUDIO DEVICES | CONTROL DEVICES | FILES | SEE ALSO

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