$NetBSD: audio.4,v 1.20 1998/05/28 17:27:15 augustss Exp $
Copyright (c) 1996 The NetBSD Foundation, Inc.
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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 ..."
p n sys/types.h n sys/ioctl.h n sys/audioio.h n 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.
p 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:
p l -tag -offset indent -width "sysctl" -compact t Cm on Recording is enabled. t Cm off Silence is returned instead of the recorded samples. t Cm sysctl Behavior is controlled by the .Va kern.audio.record .Xr sysctl 2 variable. This is the default. .El
p There are two types of device files available for audio operation: l -dash -offset indent t Audio devices are used for recording or playback of digital samples. t 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.
p 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.
p The following .Xr ioctl 2 commands are supported on the sample devices:
p l -tag -width Ds -compact t Dv AUDIO_GETDEV Fa "audio_device_t *" This command fetches the current hardware device information into the .Vt audio_device_t * argument. d -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
p t Dv AUDIO_SETPAR Fa "struct audio_swpar *" t Dv AUDIO_GETPAR Fa "struct audio_swpar *" Set or get audio parameters as encoded in the .Vt audio_swpar structure. d -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
p When setting the device parameters with .Dv AUDIO_SETPAR , the .Vt audio_swpar structure should first be initialized with d -literal struct audio_swpar ap; AUDIO_INITPAR(&ap); .Ed
p 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.
p The parameters are as follows: l -tag -width "round" t Va bits Number of bits per sample: must be between 1 and 32. t 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 . t Va sig If set (i.e. non-zero) then the samples are signed; otherwise they are unsigned. t 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. t 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. t Va rchan The number of recorded channels; meaningful only if the device is opened for reading. t Va pchan The number of channels playing; meaningful only if the device is opened for writing. t Va rate The sampling frequency in Hz. t Va nblks The number of blocks in the play buffer. t Va round The audio block size. .El
p t 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 .
p t Dv AUDIO_STOP Stop playback and recording immediately.
p t Dv AUDIO_GETPOS Fa "struct audio_pos *" Fetch an atomic snapshot of device timing information in the .Vt audio_pos structure. d -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
p The properties have the following meaning: l -tag -width "play_xrun" t Va play_pos Total number of bytes played by the device since playback started (a.k.a the device wall clock). t Va play_xrun The number of bytes corresponding to silence played because .Xr write 2 wasn't called fast enough. t Va rec_pos Total number of bytes recorded by the device since recording started (a.k.a the device wall clock). t Va rec_xrun The number of bytes dropped because .Xr read 2 wasn't called fast enough. .El
p t 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. d -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
p The properties have the following meaning: l -tag -width "active" t Va mode The current mode determined by .Xr open 2 flags. t Va pause If set, indicates that .Dv AUDIO_STOP was called, and the device is not attempting to start. t 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:
p l -tag -width Ds -compact t Dv AUDIO_GETDEV Fa "audio_device_t *" t Dv AUDIO_GETPOS Fa "struct audio_pos *" t Dv AUDIO_GETSTATUS Fa "struct audio_status *" t Dv AUDIO_GETPAR Fa "struct audio_swpar *" t 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.
p t Dv AUDIO_MIXER_READ Fa "mixer_ctrl_t *" t 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. d -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
p 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 .
p t 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. d -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
p 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.
p 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
q 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.
p 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.
p
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
p 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 .
p
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
l -tag -width /dev/audioctlN -compact t Pa /dev/audio Ns Ar N Audio device.
t 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