man/man4i/mixer.4i

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.Dd March 13, 2022
.Dt MIXER 4I
.Os
.Sh NAME
.Nm mixer
.Nd generic mixer device interface
.Sh SYNOPSIS
.In sys/soundcard.h
.Sh DESCRIPTION
.Ss "Mixer Pseudo-Device"
The
.Pa /dev/mixer
pseudo-device is provided for two purposes:
.Bl -bullet -offset indent
.It
The first purpose is for applications that wish to learn about the list of
audio devices on the system, so that they can select (or provide for users to
select) an appropriate audio device.
The
.Pa /dev/mixer
pseudo-device
provides interfaces to enumerate all of the audio devices on the system.
.It
The second purpose is for mixer panel type applications which need to control
master settings for the audio hardware in the system, such as gain levels,
balance, port functionality, and other device features.
.El
.Pp
Ordinary audio applications should
.Em not
attempt to adjust their playback
or record volumes or other device settings using this device.
Instead, they
should use the
.Dv SNDCTL_DSP_SETPLAYVOL
and
.Dv SNDCTL_DSP_SETRECVOL
ioctls that are documented in
.Xr dsp 4I .
.Ss "Sndstat Device"
The
.Pa /dev/sndstat
device supports
.Xr read 2 ,
and can be read to
retrieve human-readable information about the audio devices on the system.
Software should not attempt to interpret the contents of this device.
.Sh IOCTLS
.Ss "Information IOCTLs"
The following ioctls are intended to aid applications in identifying the audio
devices available on the system.
These ioctls can be issued against either the
pseudo-device
.Pa /dev/mixer ,
or a against a file descriptor open to any
other audio device in the system.
.Pp
Applications should issue
.Dv SNDCTL_SYSINFO
first to learn what audio
devices and mixers are available on the system, and then use
.Dv SNDCTL_AUDIOINFO
or
.Dv SNDCTL_MIXERINFO
to obtain more information
about the audio devices or mixers, respectively.
.Bl -tag -width SNDCTL_AUDIOINFO
.It Dv OSS_GETVERSION
The argument is a pointer to an integer, which retrieves the version of the
.Sy OSS API
used.
The value is encoded with the major version (currently 4)
encoded in the most significant 16 bits, and a minor version encoded in the
lower 16 bits.
.It Dv SNDCTL_SYSINFO
The argument is a pointer to an
.Vt oss_sysinfo
structure, which has the following definition:
.Bd -literal -offset 2n
typedef struct oss_sysinfo {
   char product[32];     /* E.g. SunOS Audio */
   char version[32];     /* E.g. 4.0a */
   int versionnum;       /* See OSS_GETVERSION */
   char options[128];    /* NOT SUPPORTED */

   int numaudios;        /* # of audio/dsp devices */
   int openedaudio[8];   /* Reserved, always 0 */

   int numsynths;        /* NOT SUPPORTED, always 0 */
   int nummidis;         /* NOT SUPPORTED, always 0 */
   int numtimers;        /* NOT SUPPORTED, always 0 */
   int nummixers;        /* # of mixer devices */

   /* Mask of midi devices are busy */
   int openedmidi[8];

   /* Number of sound cards in the system */
   int numcards;

   /* Number of audio engines in the system */
   int numaudioengines;
   char license[16];         /* E.g. "GPL" or "CDDL" */
   char revision_info[256];  /* Reserved */
   int filler[172];          /* Reserved */
} oss_sysinfo;
.Ed
.Pp
The important fields here are
.Fa numaudios ,
which is used to determine the
number of audio devices that can be queried with
.Dv SNDCTL_AUDIOINFO ,
.Fa nummixers
which provides a count of mixers on the system, and
.Fa numcards
which counts to total number of aggregate devices.
A
.Sy card
can consist of one or more audio devices and one or more mixers, although more
typically there is exactly one audio device and one mixer for each card.
.It Dv SNDCTL_AUDIOINFO
The argument is a pointer to an
.Vt oss_audioinfo
structure, which has the following structure:
.Bd -literal -offset 2n
typedef struct oss_audioinfo {
   int dev;             /* Device to query */
   char name[64];       /* Human readable name */
   int busy;            /* reserved */
   int pid;             /* reserved */

   /* PCM_CAP_INPUT, PCM_CAP_OUTPUT */
   int caps;
   int iformats;        /* Supported input formats */
   int oformats;        /* Supported output formats */
   int magic;           /* reserved */
   char cmd[64];        /* reserved */
   int card_number;
   int port_number;     /* reserved */
   int mixer_dev;

   /* Obsolete field.  Replaced by devnode */
   int legacy_device;
   int enabled;         /* reserved */
   int flags;           /* reserved */
   int min_rate;        /* Minimum sample rate */
   int max_rate;        /* Maximum sample rate */
   int min_channels;  /* Minimum number of channels */
   int max_channels;  /* Maximum number of channels */
   int binding;         /* reserved */
   int rate_source;     /* reserved */
   char handle[32];     /* reserved */
   unsigned int nrates;     /* reserved */
   unsigned int rates[20];  /* reserved */
   char song_name[64];  /* reserved */
   char label[16];      /* reserved */
   int latency;         /* reserved */

   /* Device special file name (absolute path) */
   char devnode[32];
   int next_play_engine;    /* reserved */
   int next_rec_engine;     /* reserved */
   int filler[184];         /* reserved */
} oss_audioinfo;
.Ed
.Pp
In the above structure, all of the fields are reserved except the following:
.Fa dev ,
.Fa name ,
.Fa card_number ,
.Fa mixer_dev ,
.Fa caps ,
.Fa min_rate ,
.Fa max_rate ,
.Fa min_channels ,
.Fa max_channels ,
and
.Fa devnode .
The reserved fields are provided for compatibility with other OSS
implementations, and available for legacy applications.
New applications should not attempt to use these fields.
.Pp
The
.Fa dev
field should be initialized by the application to the number of
the device to query.
This is a number between zero (inclusive) and value of
.Fa numaudios
(exclusive) returned by
.Dv SNDCTL_SYSINFO .
Alternatively,
when issuing the ioctl against a real mixer or
.Sy dsp
device, the special
value
.Sy -1
can be used to indicate that the query is being made against the device opened.
If
.Sy -1
is used, the field is overwritten with the device
number for the current device on successful return.
.Pp
No other fields are significant upon entry, but a successful return contains
details of the device.
.Pp
The
.Fa name
field is a human readable name representing the device.
Applications should not try to interpret it.
.Pp
The
.Fa card_number
field indicates the number assigned to the aggregate device.
This can be used with the
.Dv SNDCTL_CARDINFO
ioctl.
.Pp
The
.Fa mixer_dev
is the mixer device number for the mixing device associated
with the audio device.
This can be used with the
.Dv SNDCTL_MIXERINFO
ioctl.
.Pp
The
.Fa caps
field contains any of the bits
.Dv PCM_CAP_INPUT ,
.Dv PCM_CAP_OUTPUT ,
and
.Dv PCM_CAP_DUPLEX .
Indicating whether the device
support input, output, and whether input and output can be used simultaneously.
All other bits are reserved.
.Pp
The
.Fa min_rate
and
.Fa max_rate
fields indicate the minimum and maximum sample rates supported by the device.
Most applications should try to use the maximum supported rate for the best
audio quality and lowest system resource consumption.
.Pp
The
.Fa min_channels
and
.Fa max_channels
provide an indication of the number of channels (1 for mono, 2 for stereo,
6 for 5\&.1, etc\&.) supported by the device.
.Pp
The
.Fa devnode
field contains the actual full path to the device node for this device, such as
.Pa /dev/sound/audio810:0dsp .
Applications should open this file to access the device.
.It Dv SNDCTL_CARDINFO
The argument is a pointer to a
.Vt struct oss_card_info ,
which has the following definition:
.Bd -literal -offset 2n
typedef struct oss_card_info {
   int card;
   char shortname[16];
   char longname[128];
   int flags;          /* reserved */
   char hw_info[400];
   int intr_count;     /* reserved */
   int ack_count;      /* reserved */
   int filler[154];
} oss_card_info;
.Ed
.Pp
This ioctl is used to query for information about the aggregate audio device.
.Pp
The
.Fa card
field should be initialized by the application to the number of
the card to query.
This is a number between zero
.Pq inclusive
and value of
.Fa numcards
.Pq exclusive
returned by
.Dv SNDCTL_SYSINFO .
Alternatively,
when issuing the ioctl against a real mixer or
.Sy dsp
device, the special value
.Sy -1
can be used to indicate that the query is being made against the device opened.
If
.Sy -1
is used, the field is overwritten with the number
for the current hardware device on successful return.
.Pp
The
.Fa shortname ,
.Fa longname ,
and
.Fa hw_info
contain
.Sy ASCIIZ
strings describing the device in more detail.
The
.Fa hw_info
member can contain multiple lines of detail, each line ending in a NEWLINE.
.Pp
The
.Fa flag ,
.Fa intr_count ,
and
.Fa ack_count
fields are not used by this implementation.
.It Dv SNDCTL_MIXERINFO
The argument is a pointer to a
.Vt struct oss_mixer_info ,
which has the following definition:
.Bd -literal -offset 2n
typedef struct oss_mixerinfo {
    int dev;
    char id[16];        /* Reserved */
    char name[32];
    int modify_counter;
    int card_number;
    int port_number;    /* Reserved */
    char handle[32];    /* Reserved */
    int magic;          /* Reserved */
    int enabled;        /* Reserved */
    int caps;           /* Reserved */
    int flags;          /* Reserved */
    int nrext;
    int priority;

    /* Deice special file name (absolute path) */
    char devnode[32];
    int legacy_device;  /* Reserved */
    int filler[245];    /* Reserved */
} oss_mixerinfo;
.Ed
.Pp
In the above structure, all of the fields are reserved except the following:
.Fa dev ,
.Fa name ,
.Fa modify_counter ,
.Fa card_number ,
.Fa nrext ,
.Fa priority ,
and
.Fa devnode .
The reserved fields are provided for compatibility with other
OSS implementations, and available for legacy applications.
New applications should not attempt to use these fields.
.Pp
The
.Fa dev
field should be initialized by the application to the number of
the device to query.
This is a number between zero inclusive and value of
.Fa nummixers
(exclusive) returned by
.Dv SNDCTL_SYSINFO ,
or by
.Dv SNDCTL_MIX_NRMIX .
Alternatively, when issuing the ioctl against a real mixer or
.Sy dsp
device, the special value
.Sy -1
can be used to indicate
that the query is being made against the device opened.
If
.Sy -1
is used,
the field is overwritten with the mixer number for the current open file on
successful return.
.Pp
No other fields are significant upon entry, but on successful return contains
details of the device.
.Pp
The
.Fa name
field is a human readable name representing the device.
Applications should not try to interpret it.
.Pp
The
.Fa modify_counter
is changed by the mixer framework each time the
settings for the various controls or extensions of the device are changed.
Applications can poll this value to learn if any other changes need to be
searched for.
.Pp
The
.Fa card_number
field is the number of the aggregate audio device this
mixer is located on.
It can be used with the
.Dv SNDCTL_CARDINFO
ioctl.
.Pp
The
.Fa nrext
field is the number of mixer extensions available on this mixer.
See the
.Dv SNDCTL_MIX_NREXT
description.
.Pp
The priority is used by the framework to assign a preference that applications
can use in choosing a device.
Higher values are preferable.
Mixers with priorities less than -1 should never be selected by default.
.Pp
The
.Fa devnode
field contains the actual full path to the device node for
the physical mixer, such as
.Pa /dev/sound/audio810:0mixer .
Applications
should open this file to access the mixer settings.
.El
.Ss "Mixer Extension IOCTLs"
The pseudo
.Pa /dev/mixer
device supports ioctls that can change the
various settings for the audio hardware in the system.
.Pp
Those ioctls should only be used by dedicated mixer applications or desktop
volume controls, and not by typical ordinary audio applications such as media
players.
Ordinary applications that wish to adjust their own volume settings
should use the
.Dv SNDCTL_DSP_SETPLAYVOL
or
.Dv SNDCTL_DSP_SETRECVOL
ioctls for that purpose.
See
.Xr dsp 4I
for more information.
Ordinary
applications should never attempt to change master port selection or hardware
settings such as monitor gain settings.
.Pp
The ioctls in this section can only be used to access the mixer device that is
associated with the current file descriptor.
.Pp
Applications should not assume that a single
.Pa /dev/mixer
node is able to access any physical settings.
Instead, they should use the ioctl
.Dv SNDCTL_MIXERINFO
to determine the device path for the real mixer device,
and issue ioctls on a file descriptor opened against the corresponding
.Fa devnode
field.
.Pp
When a
.Fa dev
member is specified in each of the following ioctls, the
application should specify
.Sy -1 ,
although for compatibility the mixer
allows the application to specify the mixer device number.
.Pp
.Bl -tag -width SNDCTL_MIX_ENUMINFO -compact
.It Dv SNDCTL_MIX_NRMIX
The argument is a pointer to an integer, which receives the number of mixer
devices in the system.
Each can be queried by using its number with the
.Dv SNDCTL_MIXERINFO
ioctl.
The same information is available using the
.Fa SNDCTL_SYSINFO
ioctl.
.Pp
.It Dv SNDCTL_MIX_NREXT
The argument is a pointer to an integer.
On entry, the integer should contain
the special value
.Sy -1 .
On return the argument receives the number of mixer
extensions (or mixer controls) supported by the mixer device.
More details
about each extension can be obtained by
.Fa SNDCTL_MIX_EXTINFO
ioctl.
.Pp
.It Dv SNDCTL_MIX_EXTINFO
The argument is a pointer to an
.Vt oss_mixext
structure which is defined as follows:
.Bd -literal -offset 2n
typedef struct oss_mixext {
   int dev;            /* Mixer device number */
   int ctrl;           /* Extension number */
   int type;           /* Entry type */
   int maxvalue;
   int minvalue;
   int flags;
   char id[16];  /* Mnemonic ID (internal use) */
   int parent;   /* Entry# of parent (-1 if root) */
   int dummy;          /* NOT SUPPORTED */
   int timestamp;
   char data[64];      /* Reserved */

   /* Mask of allowed enum values */
   unsigned char enum_present[32];
   int control_no;     /* Reserved */
   unsigned int desc;  /* NOT SUPPORTED */
   char extname[32];
   int update_counter;
   int filler[7];      /* Reserved */
} oss_mixext;
.Ed
.Pp
On entry, the
.Fa dev
field should be initialized to the value
.Sy -1 ,
and
the
.Fa ctrl
field should be initialized with the number of the extension
being accessed.
Between 0, inclusive, and the value returned by
.Dv SNDCTL_MIX_NREXT ,
exclusive.
.Pp
Mixer extensions are organized as a logical tree, starting with a root node.
The root node always has a
.Fa ctrl
value of zero.
The structure of the tree can be determined by looking at the parent field,
which contains the extension number of the parent extension, or
.Sy -1
if the extension is the root extension.
.Pp
The type indicates the type of extension used.
This implementation supports the following values:
.Bl -column -offset 2n "MIXT_STEREOSLIDER" "Enumerated value, 0 to maxvalue"
.It Dv MIXT_DEVROOT      Ta Root node for extension tree
.It Dv MIXT_GROUP        Ta Logical grouping of controls
.It Dv MXIT_ONOFF        Ta Boolean value, 0 = off, 1 = on.
.It Dv MIXT_ENUM         Ta Enumerated value, 0 to maxvalue.
.It Dv MIXT_MONOSLIDER   Ta Monophonic slider, 0 to 255.
.It Dv MIXT_STEREOSLIDER Ta Stereophonic slider, 0 to 255 (encoded as lower two bytes in value.)
.It Dv MIXT_MARKER       Ta Place holder, can ignore.
.El
.Pp
The flags field is a bit array.
This implementation makes use of the following
possible bits:
.Bl -column -offset 2n "MIXF_WRITEABLE" "Extensions value is modifiable"
.It Dv MIXF_READABLE  Ta Extension's value is readable.
.It Dv MIXF_WRITEABLE Ta Extension's value is modifiable.
.It Dv MIXF_POLL      Ta Extension can self-update.
.It Dv MIXF_PCMVOL    Ta Extension is for master PCM playback volume.
.It Dv MIXF_MAINVOL   Ta Extension is for a typical analog volume
.It Dv MIXF_RECVOL    Ta Extension is for master record gain.
.It Dv MIXF_MONVOL    Ta Extension is for a monitor source's gain.
.El
.Pp
The
.Fa id
field contains an
.Sy ASCIIZ
identifier for the extension.
.Pp
The timestamp field is set when the extension tree is first initialized.
Applications must use the same timestamp value when attempting to change the
values.
A change in the timestamp indicates a change a in the structure of the
extension tree.
.Pp
The
.Fa enum_present
field is a bit mask of possible enumeration values.
If a
bit is present in the
.Fa enum_present
mask, then the corresponding enumeration value is legal.
The mask is in little endian order.
.Pp
The
.Fa desc
field provides information about scoping, which can be useful as
layout hints to applications.
The following hints are available:
.Bl -column -offset 2n "MIXEXT_SCOPE_MONITOR" "No scoping hint provided."
.It Dv MIXEXT_SCOPE_MASK    Ta Mask of possible scope values.
.It Dv MIXEXT_SCOPE_INPUT   Ta Extension is an input control.
.It Dv MIXEXT_SCOPE_OUTPUT  Ta Extension is an output control.
.It Dv MIXEXT_SCOPE_MONITOR Ta Extension relates to input monitoring.
.It Dv MIXEXT_SCOPE_OTHER   Ta No scoping hint provided.
.El
.Pp
The
.Fa extname
is the full name of the extension.
.Pp
The
.Fa update_counter
is incremented each time the control's value is changed.
.Pp
.It Dv SNDCTL_MIX_ENUMINFO
The argument is a pointer to an
.Vt oss_mixer_enuminfo
structure, which is defined as follows:
.Bd -literal -offset 2n
typedef struct oss_mixer_enuminfo {
   int dev;
   int ctrl;
   int nvalues;
   int version;
   short strindex[255];
   char strings[3000];
} oss_mixer_enuminfo;
.Ed
.Pp
On entry, the
.Fa dev
field should be initialized to the value
.Sy -1 ,
and
the
.Fa ctrl
field should be initialized with the number of the extension being accessed.
Between 0, inclusive, and the value returned by
.Dv SNDCTL_MIX_NREXT ,
exclusive.
.Pp
On return the
.Fa nvalues
field contains the number of values, and
.Fa strindex
contains an array of indices into the strings member, each index
pointing to an
.Sy ASCIIZ
describing the enumeration value.
.Pp
.It Dv SNDCTL_MIX_READ
.It Dv SNDCTL_MIX_WRITE
The argument is a pointer to an
.Vt oss_mixer_value
structure, defined as follows:
.Bd -literal -offset 2n
typedef struct oss_mixer_value {
   int dev;
   int ctrl;
   int value;

   /* Reserved for future use.  Initialize to 0 */
   int flags;

   /* Must be set to oss_mixext.timestamp */
   int timestamp;

   /* Reserved for future use.  Initialize to 0 */
   int filler[8];
} oss_mixer_value;
.Pp
.Ed
On entry, the
.Fa dev
field should be initialized to the value
.Sy -1 ,
and the
.Fa ctrl
field should be initialized with the number of the extension
being accessed.
Between 0, inclusive, and the value returned by
.Dv SNDCTL_MIX_NREXT ,
exclusive.
Additionally, the timestamp member must be
initialized to the same value as was supplied in the
.Vt oss_mixext
structure
used with
.Dv SNDCTL_MIX_EXTINFO .
.Pp
For
.Dv SNDCTL_MIX_WRITE ,
the application should supply the new value for the extension.
For
.Dv SNDCTL_MIX_READ ,
the mixer returns the extensions current value in value.
.El
.Ss "Compatibility IOCTLs"
The following ioctls are for compatibility use only:
.Pp
.Bl -tag -offset 2n -width SNDCTL_MIX_ENUMINFO -compact
.It Dv SOUND_MIXER_READ_VOLUME
.It Dv SOUND_MIXER_READ_PCM
.It Dv SOUND_MIXER_READ_OGAIN
.It Dv SOUND_MIXER_READ_RECGAIN
.It Dv SOUND_MIXER_READ_RECLEV
.It Dv SOUND_MIXER_READ_IGAIN
.It Dv SOUND_MIXER_READ_RECSRC
.It Dv SOUND_MIXER_READ_RECMASK
.It Dv SOUND_MIXER_READ_DEVMASK
.It Dv SOUND_MIXER_READ_STEREODEVS
.It Dv SOUND_MIXER_WRITE_VOLUME
.It Dv SOUND_MIXER_WRITE_PCM
.It Dv SOUND_MIXER_WRITE_OGAIN
.It Dv SOUND_MIXER_WRITE_RECGAIN
.It Dv SOUND_MIXER_WRITE_RECLEV
.It Dv SOUND_MIXER_WRITE_IGAIN
.It Dv SOUND_MIXER_WRITE_RECSRC
.It Dv SOUND_MIXER_WRITE_RECMASK
.It Dv SOUND_MIXER_INFO
.It Dv SNDCTL_AUDIOINFO_EX
.It Dv SNDCTL_ENGINEINFO
.El
.Pp
These ioctls can affect the software volume levels associated with the calling
process.
They have no effect on the physical hardware levels or settings.
They should not be used in new applications.
.Sh FILES
.Bl -tag -width /dev/sndstat
.It Pa /dev/mixer
Symbolic link to the pseudo mixer device for the system
.It Pa /dev/sndstat
Sound status device
.El
.Sh ERRORS
An
.Xr ioctl 2
fails if:
.Bl -tag -width EINVAL
.It Er EINVAL
The parameter changes requested in the ioctl are invalid or are not supported
by the device.
.It Er ENXIO
The device or extension referenced does not exist.
.El
.Sh ARCHITECTURE
SPARC
x86
.Sh INTERFACE STABILITY
The information and mixer extension IOCTLs are Uncommitted.
The Compatibility IOCTLs are Obsolete Uncommitted.
The extension names are Uncommitted.
.Sh SEE ALSO
.Xr close 2 ,
.Xr ioctl 2 ,
.Xr open 2 ,
.Xr read 2 ,
.Xr dsp 4I ,
.Xr attributes 7
.Sh BUGS
The names of mixer extensions are not guaranteed to be predictable.