path: root/share/man/man4/audio.4

.\"	$OpenBSD: audio.4,v 1.5 1998/04/30 22:28:58 provos Exp $
.\"	$NetBSD: audio.4,v 1.3 1996/02/27 22:42:05 jtc Exp $
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.\" by John T. Kohl.
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.Dd March 11, 1997
.Dt AUDIO 4
.Os 
.Sh NAME
.Nm audio
.Nd
device-independent audio driver layer
.Sh SYNOPSIS
.Fd #include <sys/types.h>
.Fd #include <sys/audioio.h>
.Sh DESCRIPTION
The
.Nm
driver provides support for various audio peripherals.  It provides a
uniform programming interface layer above different underlying audio
hardware drivers.  The audio layer provides full-duplex operation if the
underlying hardware configuration supports it.
.Pp
There are four device files available for audio operation:
.Pa /dev/audio ,
.Pa /dev/sound ,
.Pa /dev/audioctl ,
and
.Pa /dev/mixer .
.Pa /dev/audio
and
.Pa /dev/sound
are used for recording or playback of digital samples.
.Pa /dev/mixer
is used to manipulate volume, recording source, or other audio mixer
functions.
.Pa /dev/audioctl
accepts the same
.Xr ioctl 2
operations as
.Pa /dev/sound ,
but no other operations.  In contrast to
.Pa /dev/sound
which has the exclusive open property
.Pa /dev/audioctl
can be opened at any time and can be used to manipulate the audio device
while it is in use.
.Sh SAMPLING DEVICES
When
.Pa /dev/audio
is opened, it automatically directs the underlying driver to manipulate
monaural 8-bit mulaw samples.  In addition, if it is opened read-only
(write-only) the device is set to half-duplex record (play) mode with
recording (playing) unpaused and playing (recording) paused.
When
.Pa /dev/sound
is opened, it maintains the previous audio sample mode and
record/playback mode.  In all other respects
.Pa /dev/audio
and
.Pa /dev/sound
are identical.
.Pp
Only one process may hold open a sampling device at a given time
(although file descriptors may be shared between processes once the
first open completes).
.Pp
On a half-duplex device, writes while recording is in progress will be
immediately discarded.  Similarly, reads while playback is in progress
will be filled with silence but delayed to return at the current
sampling rate.  If both playback and recording are requested on a half-duplex
device, playback mode takes precedence and recordings will get silence.
On a full-duplex device, reads and writes may operate
concurrently without interference.
If a full-duplex capable audio device is opened for both reading and writing 
it will start in half-duplex play mode; full-duplex mode has to be set 
explicitely.
On either type of device, if the playback mode is paused then silence is
played instead of the provided samples, and if recording is paused then
the process blocks in
.Xr read 2
until recording is 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 the 
.Dv AUMODE_PLAY_ALL 
mode is not set the writing process must 
provide enough data via
subsequent write calls to ``catch up'' in time to the current audio
block before any more process-provided samples will be played.
If a reading process does not call
.Xr read 2
frequently enough, it will simply miss samples.
.Pp
The audio device is normally accessed with
.Xr read 2
or
.Xr write 2
calls, but it can also be mapped into user memory with
.Xr mmap 2 
(when supported by the device).
Once the device has been mapped it can no longer be accessed
by read or write; all access is by reading and writing to
the mapped memory.  The device appears as a block of memory
of size
.Va buffersize
(as available via 
.Dv AUDIO_GETINFO ).
The device driver will continuously move data from this buffer
from/to the audio hardware, wrapping around at the end of the
buffer.  To find out where the hardware is currently accessing
data in the buffer the
.Dv AUDIO_GETIOFFS
and
.Dv AUDIO_GETOOFFS
calls can be used.
The playing and recording buffers are distinct and must be
mapped separately if both are to be used.
Only encodings that are not emulated (i.e. where
.Dv AUDIO_ENCODINGFLAG_EMULATED
is not set) work properly for a mapped device.
.Pp
The audio device, like most devices, can be used in
.Va select,
can be set in non-blocking mode and can be set to send a
.Dv SIGIO
when I/O is possible.
The mixer device can be set to generate a
.Dv SIGIO
whenever a mixer value is changed.
.Pp
The following
.Xr ioctl 2
commands are supported on the sample devices:
.Pp
.Bl -tag -width indent -compact
.It Dv AUDIO_FLUSH
This command stops all playback and recording, clears all queued
buffers, resets error counters, and restarts recording and playback as
appropriate for the current sampling mode.
.It Dv AUDIO_RERROR (int)
This command fetches the count of dropped input samples into its integer
argument.  There is no information regarding when in the sample stream
they were dropped.
.It Dv AUDIO_WSEEK (int)
This command fetches the count of samples are queued ahead of the
first sample in the most recent sample block written into its integer argument.
.It Dv AUDIO_DRAIN
This command suspends the calling process until all queued playback
samples have been played by the hardware.
.It Dv AUDIO_GETDEV (audio_device_t)
This command fetches the current hardware device information into the
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
.It Dv AUDIO_GETFD (int)
The command returns the current setting of the full duplex mode.
.It Dv AUDIO_GETENC (audio_encoding_t)
This command is used iteratively to fetch sample encoding names and
format_ids into the input/output audio_encoding_t argument.
.Bd -literal
typedef struct audio_encoding {
	int index;      /* input: nth encoding */
	char name[MAX_AUDIO_DEV_LEN]; /* name of encoding */
	int encoding;   /* value for encoding parameter */
	int precision;  /* value for precision parameter */
	int flags;
#define AUDIO_ENCODINGFLAG_EMULATED 1 /* software emulation mode */
} audio_encoding_t;
.Ed
To query
all the supported encodings, start with an index field of 0 and
continue with successive encodings (1, 2, ...) until the command returns
an error.
.It Dv AUDIO_SETFD (int)
This command sets the device into full-duplex operation if its integer
argument has a non-zero value, or into half-duplex operation if it
contains a zero value.  If the device does not support full-duplex
operation, attempting to set full-duplex mode returns an error.
.It Dv AUDIO_GETPROPS (int)
This command gets a bit set of hardware properties.  If the hardware
has a certain property the corresponding bit is set, otherwise it is not.
The properties can have the following values:
.Bl -tag -width indent -compact
.It Dv AUDIO_PROP_FULLDUPLEX
the device admits full duplex operation.
.It Dv AUDIO_PROP_MMAP
the device can be used with
.Xr mmap 2 .
.It Dv AUDIO_PROP_INDEPENDENT
the device can set the playing and recording encoding parameters
independently.
.El
.It Dv AUDIO_GETIOFFS (audio_offset_t)
.It Dv AUDIO_GETOOFFS (audio_offset_t)
This command fetches the current offset in the input(output) buffer where
the hardware is putting(getting) data.  It mostly useful when the device
buffer is available in user space via the
.Xr mmap 2
call.
The information is returned in the audio_offset structure.
.Bd -literal
typedef struct audio_offset {
	u_int	samples;   /* Total number of bytes transferred */
	u_int	deltablks; /* Blocks transferred since last checked */
	u_int	offset;    /* Physical transfer offset in buffer */
} audio_offset_t;
.Ed
.It Dv AUDIO_GETINFO (audio_info_t)
.It Dv AUDIO_SETINFO (audio_info_t)
Get or set audio information as encoded in the audio_info structure.
.Bd -literal
typedef struct audio_info {
	struct	audio_prinfo play;   /* info for play (output) side */
	struct	audio_prinfo record; /* info for record (input) side */
	u_int	monitor_gain;
	/* BSD extensions */
	u_int	blocksize;	/* H/W read/write block size */
	u_int	hiwat;		/* output high water mark */
	u_int	lowat;		/* output low water mark */
	u_int	_ispare1;
	u_int	mode;		/* current device mode */
#define AUMODE_PLAY	0x01
#define AUMODE_RECORD	0x02
#define AUMODE_PLAY_ALL 0x04	/* do not do real-time correction */
};
.Ed
When setting the current state with
.Dv AUDIO_SETINFO ,
the audio_info structure should first be initialized with
.Li Dv AUDIO_INITINFO Po &info Pc
and then the particular values to be changed should be set.  This
allows the audio driver to only set those things that you wish to
change and eliminates the need to query the device with
.Dv AUDIO_GETINFO
first.
.Pp
The
.Va mode
field should be set to
.Dv AUMODE_PLAY ,
.Dv AUMODE_RECORD ,
.Dv AUMODE_PLAY_ALL ,
or a bitwise OR combination of the three.
Only full-duplex audio devices support
simultaneous record and playback.
.Pp
.Va hiwat
and
.Va lowat
are used to control write behavior.  Writes to the audio devices will
queue up blocks until the high-water mark is reached, at which point any
more write calls will block until the queue is drained to the low-water
mark.
.Va hiwat
and
.Va lowat
set those high- and low-water marks (in audio blocks).  The default for
.Va hiwat
is the maximum value and for
.Va lowat
75 % of 
.Va hiwat .
.Pp
.Va blocksize
sets the current audio blocksize.  The generic audio driver layer and
the hardware driver have the opportunity to adjust this block size to
get it within implementation-required limits.  Upon return from an
.Dv AUDIO_SETINFO
call, the actual blocksize set is returned in this field.
Normally the 
.Va blocksize
is calculated to correspond to 50ms of sound and it is recalculated
when the encoding parameter changes, but if the
.Va blocksize
is set explicitely this value becomes sticky, i.e., it is remains
even when the encoding is changed.  The stickyness can be cleared
by reopening the device or setting the
.Va blocksize
to 0.
.Bd -literal
struct audio_prinfo {
	u_int	sample_rate;	/* sample rate in samples/s */
	u_int	channels;	/* number of channels, usually 1 or 2 */
	u_int	precision;	/* number of bits/sample */
	u_int	encoding;	/* data encoding (AUDIO_ENCODING_* above) */
	u_int	gain;		/* volume level */
	u_int	port;		/* selected I/O port */
	u_long	seek;		/* BSD extension */
	u_int	avail_ports;	/* available I/O ports */
	u_int	buffer_size;	/* total size audio buffer */
	u_int	_ispare[1];
	/* Current state of device: */
	u_int	samples;	/* number of samples */
	u_int	eof;		/* End Of File (zero-size writes) counter */
	u_char	pause;		/* non-zero if paused, zero to resume */
	u_char	error;		/* non-zero if underflow/overflow ocurred */
	u_char	waiting;	/* non-zero if another process hangs in open */
	u_char	balance;	/* stereo channel balance */
	u_char	cspare[2];
	u_char	open;		/* non-zero if currently open */
	u_char	active;		/* non-zero if I/O is currently active */
};
.Ed
.Pp
Note:  many hardware audio drivers require identical playback and
recording sample rates, sample encodings, and channel counts.  The
playing information is always set last and will prevail on such hardware.
If the hardware can handle different settings the
.Dv AUDIO_PROP_INDEPENDENT
property is set.
.Pp
The encoding parameter can have the following values:
.Bl -tag -width indent -compact
.It Dv AUDIO_ENCODING_ULAW
mulaw encoding, 8 bits/sample
.It Dv AUDIO_ENCODING_ALAW
alaw encoding, 8 bits/sample
.It Dv AUDIO_ENCODING_SLINEAR
two's complement signed linear encoding with the platform byte order
.It Dv AUDIO_ENCODING_ULINEAR
unsigned linear encoding with the platform byte order
.It Dv AUDIO_ENCODING_ADPCM
ADPCM encoding, 8 bits/sample
.It Dv AUDIO_ENCODING_SLINEAR_LE
two's complement signed linear encoding with little endian byte order
.It Dv AUDIO_ENCODING_SLINEAR_BE
two's complement signed linear encoding with big endian byte order
.It Dv AUDIO_ENCODING_ULINEAR_LE
unsigned linear encoding with little endian byte order
.It Dv AUDIO_ENCODING_ULINEAR_BE
unsigned linear encoding with little big byte order
.El
.Pp
The 
.Va gain ,
.Va port
and
.Va balance
settings provide simple shortcuts to the richer mixer
interface described below.  The gain should be in the range
.Bq Dv AUDIO_MIN_GAIN , Dv AUDIO_MAX_GAIN 
and the balance in the range
.Bq Dv AUDIO_LEFT_BALANCE , Dv AUDIO_RIGHT_BALANCE
withe the normal setting at
.Dv AUDIO_MID_BALANCE .
.br
The input port should be a combination of
.Bl -tag -width indent -compact
.It Dv AUDIO_MICROPHONE
to select microphone input.
.It Dv AUDIO_LINE_IN
to select line input.
.It Dv AUDIO_CD
to select CD input.
.El
The output port should be a combination of
.Bl -tag -width indent -compact
.It Dv AUDIO_SPEAKER
to select microphone output.
.It Dv AUDIO_HEADPHONE
to select headphone output.
.It Dv AUDIO_LINE_OUT
to select line output.
.El
The available ports can be found in
.Va avail_ports .
.Pp
.Va buffer_size
is the total size of the audio buffer.  The buffer size divided
by the 
.Va blocksize
gives the maximum value for
.Va hiwat .
Currently the
.Va buffer_size
can only be read and not set.
.Pp
The
.Va seek
and
.Va samples
fields are only used for
.Dv AUDIO_GETINFO .
.Va seek
represents the count of
samples pending;
.Va samples
represents the total number of bytes recorded or played, less those
that were dropped due to inadequate consumption/production rates.
.Pp
.Va pause
returns the current pause/unpause state for recording or playback.
For
.Dv AUDIO_SETINFO ,
if the pause value is specified it will either pause
or unpause the particular direction.
.El
.Sh MIXER DEVICE
The mixer device,
.Pa /dev/mixer ,
may be manipulated with
.Xr ioctl 2 
but does not support
.Xr read 2
or
.Xr write 2 .
It supports the following
.Xr ioctl 2
commands:
.Bl -tag -width indent -compact
.It Dv AUDIO_GETDEV (audio_device_t)
This command is the same as described above for the sampling devices.
.It Dv AUDIO_MIXER_READ (mixer_ctrl_t)
.It Dv AUDIO_MIXER_WRITE (mixer_ctrl_t)
.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;
.Ed
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 
.Va mixer_ctrl_t
argument.  
For a mixer value, the
.Va value
field specifies both the number of channels and the values for each of
the channels.  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 mixer device
types and is not used for
.Dv AUDIO_MIXER_READ
or
.Dv AUDIO_MIXER_WRITE .
.It Dv AUDIO_MIXER_DEVINFO (mixer_devinfo_t)
This command is used iteratively to fetch audio mixer device information
into the input/output mixer_devinfo_t argument.  To query all the
supported encodings, start with an index field of 0 and continue with
successive encodings (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;
		} v;
	} un;
} mixer_devinfo_t;
.Ed
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.  For example, a mixer
level controlling the input gain on the ``line in'' circuit would be a
class that matches an input class device with the name ``Inputs''
(AudioCInputs).
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.
.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 "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
AudioNon and AudioNoff.
For
.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 AudioNvolume, AudioNtreble, AudioNbass).
.\" For AUDIO_MIXER_SET mixer control types, what is what?
.El
.Pp
By convention, all the mixer device can be distinguished from other
mixer controls because they use a name from one of the AudioC* string values.
.Sh FILES
.Bl -tag -width /dev/audioctl -compact
.It Pa /dev/audio
.It Pa /dev/audioctl
.It Pa /dev/sound
.It Pa /dev/mixer
.El
.Sh SEE ALSO
.Xr ioctl 2 .
.br
For ports using the ISA bus:
.Xr gus 4 ,
.Xr pas 4 ,
.Xr pss 4 ,
.Xr sb 4 ,
.Xr wss 4 .
.Sh BUGS
Some of the device-specific manual pages do not yet exist.
.br
If the device is used in
.Xr mmap 2
it is currently always mapped for writing (playing) due to
VM system weirdness.
.Pp