.\" $NetBSD: audio.4,v 1.90.2.2 2020/12/19 13:52:36 martin Exp $
.\"
.\" Copyright (c) 1996 The NetBSD Foundation, Inc.
.\" All rights reserved.
.\"
.\" This code is derived from software contributed to The NetBSD Foundation
.\" by John T. Kohl.
.\"
.\" Redistribution and use in source and binary forms, with or without
.\" modification, are permitted provided that the following conditions
.\" are met:
.\" 1. Redistributions of source code must retain the above copyright
.\" notice, this list of conditions and the following disclaimer.
.\" 2. Redistributions in binary form must reproduce the above copyright
.\" notice, this list of conditions and the following disclaimer in the
.\" documentation and/or other materials provided with the distribution.
.\"
.\" THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS
.\" ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
.\" TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
.\" PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS
.\" BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
.\" CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
.\" SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
.\" INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
.\" CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
.\" ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
.\" POSSIBILITY OF SUCH DAMAGE.
.\"
.Dd May 8, 2019
.Dt AUDIO 4
.Os
.Sh NAME
.Nm audio
.Nd device-independent audio driver layer
.Sh SYNOPSIS
.In 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 .
.Pp
.Pa /dev/audio
and
.Pa /dev/sound
are used for recording or playback of digital samples.
.Pp
.Pa /dev/mixer
is used to manipulate volume, recording source, or other audio mixer
functions.
.Pp
.Pa /dev/audioctl
accepts the same
.Xr ioctl 2
operations as
.Pa /dev/sound ,
but no other operations.
It 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 sets the track to manipulate
monaural 8-bit mu-law 8000Hz.
When
.Pa /dev/sound
is opened, it maintains the audio format and pause/unpause
state of the most recently opened track.
In all other respects
.Pa /dev/audio
and
.Pa /dev/sound
are identical.
.Pp
On a full-duplex device, reads and writes may operate concurrently
without interference.
.Pp
On a half-duplex device, if there are any recording descriptors already,
opening with write mode will fail.
Similarly, if there are any playback descriptors already,
opening with read mode will fail.
If both playback and recording are requested on a half-duplex device,
it will be treated as playback mode.
.Pp
On either type of device, opening with write mode will start in playback mode,
opening with read mode will start in recording mode.
.Pp
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 a reading process does not call
.Xr read 2
frequently enough, it will simply miss samples.
.Pp
The audio driver supports track multiplexing.
All sampling devices can be opened at any time without interference.
For playback, all tracks opened simultaneously are mixed,
even if their specified format is different.
For recording, recorded data is distributed to all opened tracks,
even if their specified format is different.
To achieve this, the audio driver has a small efficient encoding converter,
a channel mixer, and a frequency converter.
The frequency conversion adapts the simplest way
(interpolation method for upward, and simple thinning method for downward)
due to restriction in kernel resources and processing time.
It will work well in most case but don't expect excessive quality.
.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 .
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 mmap'ped buffer appears as a block of memory of size
.Va buffersize
(as available via
.Dv AUDIO_GETINFO
or
.Dv AUDIO_GETBUFINFO ) .
The audio driver will continuously move data from this buffer
from/to the mixing buffer, 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.
Note that
.Xr mmap 2
no longer maps hardware buffers directly.
Now it is achieved by emulation so don't expect any improvements excessively
rather than normal
.Xr write 2 .
For historical reasons, only encodings that are not set
.Dv AUDIO_ENCODINGFLAG_EMULATED
are able to
.Xr mmap 2 .
.Pp
The audio device, like most devices, can be used in
.Xr select 2 ,
can be set in non-blocking mode and can be set (with a
.Dv FIOASYNC
ioctl) 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:
.Bl -tag -width indent
.It Dv AUDIO_FLUSH
This command stops all playback and recording, clears all queued
buffers, resets error counters on this track,
and restarts recording and playback as
appropriate for the current sampling mode.
.It Dv AUDIO_PERROR (int)
.It Dv AUDIO_RERROR (int)
This command fetches the count of dropped output (input)
bytes into its integer argument.
There is no information regarding when in the sample stream
they were dropped.
.It Dv AUDIO_WSEEK (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 integer argument.
.It Dv AUDIO_DRAIN
This command suspends the calling process until all queued playback
samples have been played.
.It Dv AUDIO_GETDEV (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
.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.
The encoding returned by the command is user accessible encoding and
is not hardware supported encoding.
.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.
.It Dv AUDIO_GETFD (int)
This command is obsolete.
.It Dv AUDIO_SETFD (int)
This command is obsolete.
.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:
.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.
.It Dv AUDIO_PROP_PLAYBACK
the device is capable of audio playback.
.It Dv AUDIO_PROP_CAPTURE
the device is capable of audio capture.
.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 track mixer will be 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
.Vt audio_offset_t
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_GETBUFINFO (audio_info_t)
.It Dv AUDIO_SETINFO (audio_info_t)
Get or set audio information as encoded in the audio_info structure.
For historical reasons, the audio_info structure has three different
layer's parameters: track, track mixer and hardware rich mixer.
.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 [HWmixer] */
/* BSD extensions */
u_int blocksize; /* read/write block size [track] */
u_int hiwat; /* output high water mark [track] */
u_int lowat; /* output low water mark [track] */
u_int _ispare1;
u_int mode; /* current operation mode [track] */
#define AUMODE_PLAY 0x01
#define AUMODE_RECORD 0x02
#define AUMODE_PLAY_ALL 0x04 /* Not used anymore */
} audio_info_t;
.Ed
.Pp
When setting the current state with
.Dv AUDIO_SETINFO ,
the audio_info structure should first be initialized with
.Li AUDIO_INITINFO(&info)
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
or
.Dv AUDIO_GETBUFINFO
first.
.Pp
The
.Va mode
field indicates current operation mode, either one of
.Dv AUMODE_PLAY
or
.Dv AUMODE_RECORD .
These two flags can not be changed once this descriptor is opened.
For playback mode, the obsolete
.Dv AUMODE_PLAY_ALL
flag can be set but has no effect.
.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.
Normally the
.Va blocksize
is calculated to correspond to 40ms
(for some hardware, this value may be different due to
the hardware restrictions)
of sound and it is recalculated
when the encoding parameters change.
If the descriptor is opened for read only,
.Va blocksize
indicates the blocksize for the recording track.
Otherwise,
.Va blocksize
indicates the blocksize for the playback track.
.Bd -literal
struct audio_prinfo {
u_int sample_rate; /* sample rate in samples/s [track] */
u_int channels; /* number of channels, usually 1 or 2 [track] */
u_int precision; /* number of bits/sample [track] */
u_int encoding; /* data encoding (AUDIO_ENCODING_* below) [track] */
u_int gain; /* volume level [HWmixer] */
u_int port; /* selected I/O port [HWmixer] */
u_long seek; /* BSD extension [track] */
u_int avail_ports; /* available I/O ports [HWmixer] */
u_int buffer_size; /* total size audio buffer [track] */
u_int _ispare[1];
u_int samples; /* number of samples [track] */
u_int eof; /* End Of File (zero-size writes) counter [track] */
u_char pause; /* non-zero if paused, zero to resume [track] */
u_char error; /* non-zero if underflow/overflow occurred [track] */
u_char waiting; /* non-zero if another process hangs in open [track] */
u_char balance; /* stereo channel balance [HWmixer] */
u_char cspare[2];
u_char open; /* non-zero if currently open [trackmixer] */
u_char active; /* non-zero if I/O is currently active [trackmixer] */
};
.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:
.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
.It Dv AUDIO_ENCODING_AC3
Dolby Digital AC3
.El
.Pp
The
.Nm
driver accepts the following formats.
.Va encoding
and
.Va precision
are one of the values obtained by
.Dv AUDIO_GETENC ,
regardless of formats supported by underlying driver.
.Va frequency
ranges from 1000Hz to 192000Hz,
regardless of frequency (ranges) supported by underlying driver.
.Va channels
depends your underlying driver.
If the underlying driver only supports monaural (1channel)
or stereo (2channels), you can specify 1 or 2 regardless of
number of channels supported by underlying driver.
If the underlying driver supports three or more channels, you can specify
the number of channels supported by the underlying driver or less.
.Pp
The
.Va gain ,
.Va port
and
.Va balance
settings provide simple shortcuts to the richer mixer
interface described below and are not obtained by
.Dv AUDIO_GETBUFINFO .
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
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
.Dv ( AUDIO_GETBUFINFO
only).
.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 by
.Dv AUDIO_GETINFO
and
.Dv AUDIO_GETBUFINFO .
.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.
.It Dv AUDIO_QUERYFORMAT (audio_format_query_t)
This command enumerates formats supported by the hardware.
Similarly to
.Dv AUDIO_GETENC ,
to query all the supported formats,
start with an index field of 0 and continue with successive formats
(1, 2, ...) until the command returns an error.
.Bd -literal
typedef struct audio_format_query {
u_int index;
struct audio_format fmt;
} audio_format_query_t;
.Ed
.It Dv AUDIO_GETFORMAT (audio_info_t)
This command fetches the current hardware format.
Only the following members in audio_info_t are used.
Members which are not listed here or belong in invalid direction are
filled by \-1.
.Bl -bullet
.It
mode
.It
play.encoding
.It
play.precision
.It
play.channels
.It
play.sample_rate
.It
record.encoding
.It
record.precision
.It
record.channels
.It
record.sample_rate
.El
.Pp
.Va mode
indicates which direction is valid.
.It Dv AUDIO_SETFORMAT (audio_info_t)
This command sets the hardware format.
It will fail if there are any opened descriptors.
So obviously, it must be issued on
.Pa /dev/audioctl .
Similarly to
.Dv AUDIO_GETFORMAT ,
only above members in audio_info_t are used.
Members which is not listed or belong in invalid direction are ignored.
The parameters can be chosen from the choices obtained by
.Dv AUDIO_QUERYFORMAT .
.It Dv AUDIO_GETCHAN (int)
This command is obsolete.
.It Dv AUDIO_SETCHAN (int)
This command is obsolete.
.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
.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)
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 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
.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.
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 controlling the input gain on the 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
.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 ,
.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 audiocfg 1 ,
.Xr audioctl 1 ,
.Xr mixerctl 1 ,
.Xr ioctl 2 ,
.Xr ossaudio 3 ,
.Xr midi 4 ,
.Xr radio 4 ,
.Ss ISA bus
.Xr aria 4 ,
.Xr ess 4 ,
.Xr gus 4 ,
.Xr guspnp 4 ,
.Xr pas 4 ,
.Xr sb 4 ,
.Xr wss 4 ,
.Xr ym 4
.Ss PCI bus
.Xr auacer 4 ,
.Xr auich 4 ,
.Xr auixp 4 ,
.Xr autri 4 ,
.Xr auvia 4 ,
.Xr azalia 4 ,
.Xr clcs 4 ,
.Xr clct 4 ,
.Xr cmpci 4 ,
.Xr eap 4 ,
.Xr emuxki 4 ,
.Xr esa 4 ,
.Xr esm 4 ,
.Xr eso 4 ,
.Xr fms 4 ,
.Xr neo 4 ,
.Xr sv 4 ,
.Xr yds 4
.Ss TURBOchannel
.Xr bba 4
.Ss USB
.Xr uaudio 4
.Sh HISTORY
Support for virtual channels and mixing first appeared in
.Nx 8.0 .
.Sh BUGS
If the device is used in
.Xr mmap 2
it is currently always mapped for writing (playing) due to VM system weirdness.