OpenBSD-4.6/share/man/man4/audio.4
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.\" by John T. Kohl.
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.Dd $Mdocdate: June 27 2009 $
.Dt AUDIO 4
.Os
.Sh NAME
.Nm audio ,
.Nm mixer
.Nd device-independent audio driver layer
.Sh SYNOPSIS
.Cd "audio* at ..."
.Pp
.Fd #include <sys/types.h>
.Fd #include <sys/ioctl.h>
.Fd #include <sys/audioio.h>
.Fd #include <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.
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
.Nm audio
device while it is in use.
.Sh SAMPLING DEVICES
When
.Pa /dev/audio
is opened, it automatically configures the underlying driver for the
hardware's default sample format, or monaural 8-bit mu-law if a default
sample format has not been specified by the underlying driver.
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 format 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
.Nm audio
device is opened for both reading and writing,
it will start in half-duplex play mode with recording paused.
For proper full-duplex operation, after the device is opened for reading
and writing, full-duplex mode must be set and then recording must be unpaused.
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
.Dq 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
.Nm 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 buffer_size
(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
.Nm audio
device, like most devices, can be used in
.Xr select 2 ,
can be set in non-blocking mode, and can be set (with an
.Dv FIOASYNC
.Xr ioctl 2 )
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 Ds -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.
.Pp
.It Dv AUDIO_RERROR Fa "int *"
.It Dv AUDIO_PERROR Fa "int *"
These commands fetch the count of dropped input or output samples into
the
.Vt int *
argument, respectively.
There is no information regarding when in the sample stream
they were dropped.
.Pp
.It Dv AUDIO_WSEEK Fa "u_long *"
This command fetches the count of bytes that are queued ahead of the
first sample in the most recent sample block written into its
.Vt u_long *
argument.
.Pp
.It Dv AUDIO_DRAIN
This command suspends the calling process until all queued playback
samples have been played by the hardware.
.Pp
.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_GETFD Fa "int *"
This command returns the current setting of the full-duplex mode.
.Pp
.It Dv AUDIO_GETENC Fa "audio_encoding_t *"
This command is used iteratively to fetch sample encoding
.Va name Ns s
and
.Va format_id Ns s
into the input/output
.Vt 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
.Pp
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.
.Pp
.It Dv AUDIO_SETFD Fa "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.
.Pp
.It Dv AUDIO_GETPROPS Fa "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:
.Pp
.Bl -tag -width AUDIO_PROP_INDEPENDENT -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
.Pp
.It Dv AUDIO_GETIOFFS Fa "audio_offset_t *"
.It Dv AUDIO_GETOOFFS Fa "audio_offset_t *"
These commands fetch the current offset in the input (output) buffer where
the audio hardware's DMA engine will be putting (getting) data.
They are mostly useful when the device
buffer is available in user space via the
.Xr mmap 2
call.
The information is returned in the
.Vt 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
.Pp
.It Dv AUDIO_GETRRINFO Fa "audio_bufinto_t *"
.It Dv AUDIO_GETPRINFO Fa "audio_bufinfo_t *"
These commands fetch the current information about the input or
output buffer, respectively.
The block size, high and low water marks and current position
are returned in the
.Vt audio_bufinfo
structure.
.Bd -literal
typedef struct audio_bufinfo {
u_int blksize; /* block size */
u_int hiwat; /* high water mark */
u_int lowat; /* low water mark */
u_int seek; /* current position */
} audio_bufinfo_t;
.Ed
.Pp
This information is mostly useful in input or output loops to determine
how much data to read or write, respectively.
Note, these ioctls were added to aid in porting third party applications
and libraries, and should not be used in new code.
.Pp
.It Dv AUDIO_GETINFO Fa "audio_info_t *"
.It Dv AUDIO_SETINFO Fa "audio_info_t *"
Get or set audio information as encoded in the
.Vt 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; /* input to output mix */
/* 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_char output_muted; /* toggle play mute */
u_char cspare[3];
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 */
} audio_info_t;
.Ed
.Pp
When setting the current state with
.Dv AUDIO_SETINFO ,
the
.Vt audio_info
structure should first be initialized with
.Pp
.Dl "AUDIO_INITINFO(&info);"
.Pp
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 blocksize
is used to attempt to set both play and record block sizes
to the same value, it is left for compatibility only and
its use is discouraged.
.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 .
.Bd -literal
struct audio_prinfo {
u_int sample_rate; /* sample rate in bit/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_* below) */
u_int gain; /* volume level */
u_int port; /* selected I/O port */
u_int seek; /* BSD extension */
u_int avail_ports; /* available I/O ports */
u_int buffer_size; /* total size audio buffer */
u_int block_size; /* size a block */
/* 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 occurred */
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
.Va encoding
parameter can have the following values:
.Pp
.Bl -tag -width AUDIO_ENCODING_SLINEAR_BE -compact
.It Dv AUDIO_ENCODING_ULAW
mu-law encoding, 8 bits/sample
.It Dv AUDIO_ENCODING_ALAW
A-law 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 big endian byte order
.El
.Pp
The
.Va precision
parameter describes the number of bits of audio data per sample.
For sample formats such as 8, 16, and 32-bit, where the number of audio data
bits is a power of 2,
.Va precision
is also exactly the size of each sample.
For other sample formats the sample size is the smallest power of
2 bits that the data can fit into.
For example the sample size of 20 and 24-bit formats is 32 bits.
.Pp
The
.Va gain ,
.Va port ,
and
.Va balance
settings provide simple shortcuts to the richer
.Nm mixer
interface described below.
The
.Va 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
with the normal setting at
.Dv AUDIO_MID_BALANCE .
.Pp
The input port should be a combination of:
.Pp
.Bl -tag -width AUDIO_MICROPHONE -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
.Pp
The output port should be a combination of:
.Pp
.Bl -tag -width AUDIO_HEADPHONE -compact
.It Dv AUDIO_SPEAKER
to select speaker output.
.It Dv AUDIO_HEADPHONE
to select headphone output.
.It Dv AUDIO_LINE_OUT
to select line output.
.El
.Pp
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 block_size
gives the maximum value for
.Va hiwat .
Currently the
.Va buffer_size
can only be read and not set.
.Pp
.Va block_size
sets the current audio block size.
The generic
.Nm 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 block_size set is returned in this field.
Normally the
.Va block_size
is calculated to correspond to 50ms of sound and it is recalculated
when the encoding parameter changes, but if the
.Va block_size
is set explicitly this value becomes sticky, i.e., it remains
even when the encoding is changed.
The stickiness can be cleared by reopening the device or setting the
.Va block_size
to 0.
.Pp
Care should be taken when setting the
.Va block_size
before other parameters.
If the device does not natively support the audio parameters, then the
internal block size may be scaled to a larger size to accommodate
conversion to a native format.
If the
.Va block_size
has been set, the internal block size will not be rescaled when the
parameters, and thus possibly the scaling factor, change.
This can result in a block size much larger than was originally requested.
It is recommended to set
.Va block_size
at the same time as, or after, all other parameters have been set.
.Pp
The
.Va seek
and
.Va samples
fields are only used for
.Dv AUDIO_GETINFO .
.Va seek
represents the count of
bytes 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
.Nm 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:
.Pp
.Bl -tag -width Ds -compact
.It Dv AUDIO_GETDEV Fa "audio_device_t *"
This command is the same as described above for the sampling devices.
.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
By convention, all the mixer devices can be distinguished from other
mixer controls because they use a name from one of the
.Dv 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 aucat 1 ,
.Xr audioctl 1 ,
.Xr cdio 1 ,
.Xr mixerctl 1 ,
.Xr ioctl 2 ,
.Xr ossaudio 3 ,
.Xr sio_open 3 ,
.Xr ac97 4 ,
.Xr uaudio 4 ,
.Xr audio 9
.Sh BUGS
If the device is used in
.Xr mmap 2
it is currently always mapped for writing (playing) due to
VM system weirdness.