man/man4/audio.4

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.\"	$NetBSD: audio.4,v 1.20 1998/05/28 17:27:15 augustss Exp $
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.Dd $Mdocdate: November 1 2020 $
.Dt AUDIO 4
.Os
.Sh NAME
.Nm audio ,
.Nm audioctl
.Nd device-independent audio driver layer
.Sh SYNOPSIS
.Cd "audio* at ..."
.Pp
.In sys/types.h
.In sys/ioctl.h
.In sys/audioio.h
.In string.h
.Sh DESCRIPTION
The
.Nm audio
driver provides support for various audio peripherals.
It provides a uniform programming interface layer above different
underlying audio hardware drivers.
.Pp
In addition to hardware mixer controls like those
documented in
.Xr azalia 4 ,
the
.Nm
driver exposes the
.Va record.enable
control.
The superuser can change it with
.Xr mixerctl 8 .
It accepts the following values:
.Pp
.Bl -tag -offset indent -width "sysctl" -compact
.It Cm on
Recording is enabled.
.It Cm off
Silence is returned instead of the recorded samples.
.It Cm sysctl
Behavior is controlled by the
.Va kern.audio.record
.Xr sysctl 2
variable.
This is the default.
.El
.Pp
There are two types of device files available for audio operation:
.Bl -dash -offset indent
.It
Audio devices are used for recording or playback of digital samples.
.It
Control devices are used to manipulate audio device
parameters like volume or recording source.
They can also read certain
.Nm
driver variables while it is in use.
.El
.Sh AUDIO DEVICES
When audio devices are opened,
they attempt to maintain the previous audio 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.
.Pp
If a writing process does not call
.Xr write 2
frequently enough to provide samples at the pace the hardware
consumes them silence is inserted.
If a reading process does not call
.Xr read 2
frequently enough, it will simply miss samples.
.Pp
The following
.Xr ioctl 2
commands are supported on the sample devices:
.Pp
.Bl -tag -width Ds -compact
.It Dv AUDIO_GETDEV Fa "audio_device_t *"
This command fetches the current hardware device information into the
.Vt audio_device_t *
argument.
.Bd -literal
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;
.Ed
.Pp
.It Dv AUDIO_SETPAR Fa "struct audio_swpar *"
.It Dv AUDIO_GETPAR Fa "struct audio_swpar *"
Set or get audio parameters as encoded in the
.Vt audio_swpar
structure.
.Bd -literal
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 */
};
.Ed
.Pp
When setting the device parameters with
.Dv AUDIO_SETPAR ,
the
.Vt audio_swpar
structure should first be initialized with
.Bd -literal
struct audio_swpar ap;

AUDIO_INITPAR(&ap);
.Ed
.Pp
and then only the values to be changed should be set.
This ensures 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
.Dv AUDIO_GETPAR
to obtain the parameters in use.
.Pp
The parameters are as follows:
.Bl -tag -width "round"
.It Va bits
Number of bits per sample: must be between 1 and 32.
.It Va 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
.Va bits .
.It Va sig
If set (i.e. non-zero) then the samples are signed;
otherwise they are unsigned.
.It Va le
If set then the byte order is little endian;
if not it is big endian.
It is meaningful only if
.Va bps
> 1.
.It Va msb
If set, then the
.Va bits
are aligned in the packet to the most significant bit
(i.e. lower bits are padded),
otherwise to the least significant bit
(i.e. higher bits are padded).
It's meaningful only if
.Va bits
<
.Va bps
* 8.
.It Va rchan
The number of recorded channels; meaningful only if the
device is opened for reading.
.It Va pchan
The number of channels playing; meaningful only if
the device is opened for writing.
.It Va rate
The sampling frequency in Hz.
.It Va nblks
The number of blocks in the play buffer.
.It Va round
The audio block size.
.El
.Pp
.It Dv 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
.Xr write 2
syscall.
The buffer size is obtained by multiplying
the
.Va nblks ,
.Va round ,
and
.Va bps
parameters obtained with
.Dv AUDIO_GETPAR .
.Pp
.It Dv AUDIO_STOP
Stop playback and recording immediately.
.Pp
.It Dv AUDIO_GETPOS Fa "struct audio_pos *"
Fetch an atomic snapshot of device timing information in the
.Vt audio_pos
structure.
.Bd -literal
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 */
};
.Ed
.Pp
The properties have the following meaning:
.Bl -tag -width "play_xrun"
.It Va play_pos
Total number of bytes played by the device since playback started
(a.k.a the device wall clock).
.It Va play_xrun
The number of bytes corresponding to silence played because
.Xr write 2
wasn't called fast enough.
.It Va rec_pos
Total number of bytes recorded by the device since recording started
(a.k.a the device wall clock).
.It Va rec_xrun
The number of bytes dropped because
.Xr read 2
wasn't called fast enough.
.El
.Pp
.It Dv AUDIO_GETSTATUS Fa "struct audio_status *"
Fetch the current device status from the audio driver in the
.Vt audio_status
structure.
This
.Xr ioctl 2
is intended for use with diagnostic tools
and is of no use to audio programs.
.Bd -literal
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 */
};
.Ed
.Pp
The properties have the following meaning:
.Bl -tag -width "active"
.It Va mode
The current mode determined by
.Xr open 2
flags.
.It Va pause
If set, indicates that
.Dv AUDIO_STOP
was called, and the device is not attempting to start.
.It Va active
If set, indicates that the device is playing and/or recording.
.El
.El
.Sh CONTROL DEVICES
Control devices support the following
.Xr ioctl 2
commands:
.Pp
.Bl -tag -width Ds -compact
.It Dv AUDIO_GETDEV Fa "audio_device_t *"
.It Dv AUDIO_GETPOS Fa "struct audio_pos *"
.It Dv AUDIO_GETSTATUS Fa "struct audio_status *"
.It Dv AUDIO_GETPAR Fa "struct audio_swpar *"
.It Dv AUDIO_SETPAR Fa "struct audio_swpar *"
These commands are the same as described above for the audio devices.
While the audio device is open,
.Dv AUDIO_SETPAR
may not be used.
.Pp
.It Dv AUDIO_MIXER_READ Fa "mixer_ctrl_t *"
.It Dv AUDIO_MIXER_WRITE Fa "mixer_ctrl_t *"
These commands read the current mixer state or set new mixer state for
the specified device
.Va dev .
.Va type
identifies which type of value is supplied in the
.Vt mixer_ctrl_t *
argument.
.Bd -literal
#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
.Ed
.Pp
For a mixer value, the
.Va 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 implementation).
For an enumeration value, the
.Va ord
field should be set to one of the possible values as returned by a prior
.Dv AUDIO_MIXER_DEVINFO
command.
The type
.Dv AUDIO_MIXER_CLASS
is only used for classifying particular
.Nm mixer
device types and is not used for
.Dv AUDIO_MIXER_READ
or
.Dv AUDIO_MIXER_WRITE .
.Pp
.It Dv AUDIO_MIXER_DEVINFO Fa "mixer_devinfo_t *"
This command is used iteratively to fetch audio
.Nm mixer
device information into the input/output
.Vt 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
command returns an error.
.Bd -literal
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;
.Ed
.Pp
The
.Va label
field identifies the name of this particular mixer control.
The
.Va index
field may be used as the
.Va dev
field in
.Dv AUDIO_MIXER_READ
and
.Dv AUDIO_MIXER_WRITE
commands.
The
.Va 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 input source from CD, line in, or microphone).
Set types are similar to enumeration types but any combination
of the mask bits can be used.
.Pp
The
.Va mixer_class
field identifies what class of control this is.
This value is set to the index value used to query the class itself.
The
.Pq arbitrary
value set by the hardware driver may be determined by examining the
.Va mixer_class
field of the class itself,
a mixer of type
.Dv AUDIO_MIXER_CLASS .
For example, a mixer level controlling the input gain on the
.Dq line in
circuit would have a
.Va mixer_class
that matches an input class device with the name
.Dq inputs
.Dv ( AudioCinputs )
and would have a
.Va label
of
.Dq line
.Dv ( 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.
.Pp
The
.Va next
and
.Va 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
.Dq next
value).
If there is no relevant next or previous value,
.Dv AUDIO_MIXER_LAST
is specified.
.Pp
For
.Dv 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
.Dv AudioNon
and
.Dv AudioNoff .
For the
.Dv AUDIO_MIXER_VALUE
and
.Dv AUDIO_MIXER_SET
mixer control types, the channel count is
returned; the units name specifies what the level controls (typical
values are
.Dv AudioNvolume ,
.Dv AudioNtreble ,
and
.Dv AudioNbass ) .
.\" For AUDIO_MIXER_SET mixer control types, what is what?
.El
.Pp
A process may read the control device to get notifications about
mixer changes.
Whenever a control changes, the
.Xr read 2
function fetches an integer identifying the control.
It may be used in the
.Va dev
field of the
.Va mixer_ctrl
structure to call
.Dv AUDIO_MIXER_READ .
.Pp
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.
.Sh FILES
.Bl -tag -width /dev/audioctlN -compact
.It Pa /dev/audio Ns Ar N
Audio device.
.It Pa /dev/audioctl Ns Ar N
Control device.
.El
.Sh SEE ALSO
.Xr aucat 1 ,
.Xr cdio 1 ,
.Xr sndioctl 1 ,
.Xr ioctl 2 ,
.Xr sio_open 3 ,
.Xr sioctl_open 3 ,
.Xr ac97 4 ,
.Xr uaudio 4 ,
.Xr sndio 7 ,
.Xr audioctl 8 ,
.Xr mixerctl 8 ,
.Xr sndiod 8 ,
.Xr audio 9
.\" .Sh BUGS