MIXER(4I) 4I MIXER(4I)

NAME


mixer - generic mixer device interface

SYNOPSIS


#include <sys/soundcard.h>

DESCRIPTION


Mixer Pseudo-Device
The /dev/mixer pseudo-device is provided for two purposes:

+o 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 /dev/mixer pseudo-device provides interfaces to enumerate all
of the audio devices on the system.

+o 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.

Ordinary audio applications should not attempt to adjust their playback or
record volumes or other device settings using this device. Instead, they
should use the SNDCTL_DSP_SETPLAYVOL and SNDCTL_DSP_SETRECVOL ioctls that
are documented in dsp(4I).

Sndstat Device


The /dev/sndstat device supports 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.

IOCTLS


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 /dev/mixer, or a against a file descriptor open to
any other audio device in the system.

Applications should issue SNDCTL_SYSINFO first to learn what audio devices
and mixers are available on the system, and then use SNDCTL_AUDIOINFO or
SNDCTL_MIXERINFO to obtain more information about the audio devices or
mixers, respectively.

OSS_GETVERSION The argument is a pointer to an integer, which retrieves
the version of the 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.

SNDCTL_SYSINFO The argument is a pointer to an oss_sysinfo structure,
which has the following definition:

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;

The important fields here are numaudios, which is used to
determine the number of audio devices that can be queried
with SNDCTL_AUDIOINFO, nummixers which provides a count
of mixers on the system, and numcards which counts to
total number of aggregate devices. A 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.

SNDCTL_AUDIOINFO The argument is a pointer to an oss_audioinfo structure,
which has the following structure:

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;

In the above structure, all of the fields are reserved
except the following: dev, name, card_number, mixer_dev,
caps, min_rate, max_rate, min_channels, max_channels, and
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.

The 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 numaudios
(exclusive) returned by SNDCTL_SYSINFO. Alternatively,
when issuing the ioctl against a real mixer or dsp
device, the special value -1 can be used to indicate that
the query is being made against the device opened. If -1
is used, the field is overwritten with the device number
for the current device on successful return.

No other fields are significant upon entry, but a
successful return contains details of the device.

The name field is a human readable name representing the
device. Applications should not try to interpret it.

The card_number field indicates the number assigned to
the aggregate device. This can be used with the
SNDCTL_CARDINFO ioctl.

The mixer_dev is the mixer device number for the mixing
device associated with the audio device. This can be
used with the SNDCTL_MIXERINFO ioctl.

The caps field contains any of the bits PCM_CAP_INPUT,
PCM_CAP_OUTPUT, and PCM_CAP_DUPLEX. Indicating whether
the device support input, output, and whether input and
output can be used simultaneously. All other bits are
reserved.

The min_rate and 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.

The min_channels and 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.

The devnode field contains the actual full path to the
device node for this device, such as
/dev/sound/audio810:0dsp. Applications should open this
file to access the device.

SNDCTL_CARDINFO The argument is a pointer to a struct oss_card_info,
which has the following definition:

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;

This ioctl is used to query for information about the
aggregate audio device.

The card field should be initialized by the application
to the number of the card to query. This is a number
between zero (inclusive) and value of numcards
(exclusive) returned by SNDCTL_SYSINFO. Alternatively,
when issuing the ioctl against a real mixer or dsp
device, the special value -1 can be used to indicate that
the query is being made against the device opened. If -1
is used, the field is overwritten with the number for the
current hardware device on successful return.

The shortname, longname, and hw_info contain ASCIIZ
strings describing the device in more detail. The
hw_info member can contain multiple lines of detail, each
line ending in a NEWLINE.

The flag, intr_count, and ack_count fields are not used
by this implementation.

SNDCTL_MIXERINFO The argument is a pointer to a struct oss_mixer_info,
which has the following definition:

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;

In the above structure, all of the fields are reserved
except the following: dev, name, modify_counter,
card_number, nrext, priority, and 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.

The 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 nummixers (exclusive)
returned by SNDCTL_SYSINFO, or by SNDCTL_MIX_NRMIX.
Alternatively, when issuing the ioctl against a real
mixer or dsp device, the special value -1 can be used to
indicate that the query is being made against the device
opened. If -1 is used, the field is overwritten with the
mixer number for the current open file on successful
return.

No other fields are significant upon entry, but on
successful return contains details of the device.

The name field is a human readable name representing the
device. Applications should not try to interpret it.

The 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.

The card_number field is the number of the aggregate
audio device this mixer is located on. It can be used
with the SNDCTL_CARDINFO ioctl.

The nrext field is the number of mixer extensions
available on this mixer. See the SNDCTL_MIX_NREXT
description.

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.

The devnode field contains the actual full path to the
device node for the physical mixer, such as
/dev/sound/audio810:0mixer. Applications should open
this file to access the mixer settings.

Mixer Extension IOCTLs


The pseudo /dev/mixer device supports ioctls that can change the oarious
settings for the audio hardware in the system.

Those ioctls should only be used by dedicated mixer applications or desktop
olumme 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 SNDCTL_DSP_SETPLAYVOL or SNDCTL_DSP_SETRECVOL
ioctls for that purpose. See dsp(4I) for more information. Ordinary
applications should never attempt to change master port selection or
hardware settings such as monitor gain settings.

The ioctls in this section can only be used to access the mixer device that
is associated with the current file descriptor.

Applications should not assume that a single /dev/mixer node is able to
access any physical settings. Instead, they should use the ioctl
SNDCTL_MIXERINFO to determine the device path for the real mixer device,
and issue ioctls on a file descriptor opened against the corresponding
devnode field.

When a dev member is specified in each of the following ioctls, the
application should specify -1, although for compatibility the mixer allows
the application to specify the mixer device number.

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
SNDCTL_MIXERINFO ioctl. The same information is
available using the SNDCTL_SYSINFO ioctl.

SNDCTL_MIX_NREXT The argument is a pointer to an integer. On entry,
the integer should contain the special value -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 SNDCTL_MIX_EXTINFO ioctl.

SNDCTL_MIX_EXTINFO The argument is a pointer to an oss_mixext structure
which is defined as follows:

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;

On entry, the dev field should be initialized to the
value -1, and the ctrl field should be initialized
with the number of the extension being accessed.
Between 0, inclusive, and the value returned by
SNDCTL_MIX_NREXT, exclusive.

Mixer extensions are organized as a logical tree,
starting with a root node. The root node always has a
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 -1 if the extension is the root extension.

The type indicates the type of extension used. This
implementation supports the following values:

MIXT_DEVROOT Root node for extension tree
MIXT_GROUP Logical grouping of controls
MXIT_ONOFF Boolean value, 0 = off, 1 = on.
MIXT_ENUM Enumerated value, 0 to maxvalue.
MIXT_MONOSLIDER Monophonic slider, 0 to 255.
MIXT_STEREOSLIDER Stereophonic slider, 0 to 255
(encoded as lower two bytes in
value.)
MIXT_MARKER Place holder, can ignore.

The flags field is a bit array. This implementation
makes use of the following possible bits:

MIXF_READABLE Extension's value is readable.
MIXF_WRITEABLE Extension's value is modifiable.
MIXF_POLL Extension can self-update.
MIXF_PCMVOL Extension is for master PCM
playback volume.
MIXF_MAINVOL Extension is for a typical analog
volume
MIXF_RECVOL Extension is for master record
gain.
MIXF_MONVOL Extension is for a monitor
source's gain.

The id field contains an ASCIIZ identifier for the
extension.

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.

The enum_present field is a bit mask of possible
enumeration values. If a bit is present in the
enum_present mask, then the corresponding enumeration
value is legal. The mask is in little endian order.

The desc field provides information about scoping,
which can be useful as layout hints to applications.
The following hints are available:

MIXEXT_SCOPE_MASK Mask of possible scope
values.
MIXEXT_SCOPE_INPUT Extension is an input
control.
MIXEXT_SCOPE_OUTPUT Extension is an output
control.
MIXEXT_SCOPE_MONITOR Extension relates to input
monitoring.
MIXEXT_SCOPE_OTHER scoping hint provided.

The extname is the full name of the extension.

The update_counter is incremented each time the
control's value is changed.

SNDCTL_MIX_ENUMINFO The argument is a pointer to an oss_mixer_enuminfo
structure, which is defined as follows:

typedef struct oss_mixer_enuminfo {
int dev;
int ctrl;
int nvalues;
int version;
short strindex[255];
char strings[3000];
} oss_mixer_enuminfo;

On entry, the dev field should be initialized to the
value -1, and the ctrl field should be initialized
with the number of the extension being accessed.
Between 0, inclusive, and the value returned by
SNDCTL_MIX_NREXT, exclusive.

On return the nvalues field contains the number of
values, and strindex contains an array of indices into
the strings member, each index pointing to an ASCIIZ
describing the enumeration value.

SNDCTL_MIX_READ
SNDCTL_MIX_WRITE The argument is a pointer to an oss_mixer_value
structure, defined as follows:

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;

On entry, the dev field should be initialized to the
value -1, and the ctrl field should be initialized
with the number of the extension being accessed.
Between 0, inclusive, and the value returned by
SNDCTL_MIX_NREXT, exclusive. Additionally, the
timestamp member must be initialized to the same value
as was supplied in the oss_mixext structure used with
SNDCTL_MIX_EXTINFO.

For SNDCTL_MIX_WRITE, the application should supply
the new value for the extension. For SNDCTL_MIX_READ,
the mixer returns the extensions current value in
value.

Compatibility IOCTLs


The following ioctls are for compatibility use only:

SOUND_MIXER_READ_VOLUME
SOUND_MIXER_READ_PCM
SOUND_MIXER_READ_OGAIN
SOUND_MIXER_READ_RECGAIN
SOUND_MIXER_READ_RECLEV
SOUND_MIXER_READ_IGAIN
SOUND_MIXER_READ_RECSRC
SOUND_MIXER_READ_RECMASK
SOUND_MIXER_READ_DEVMASK
SOUND_MIXER_READ_STEREODEVS
SOUND_MIXER_WRITE_VOLUME
SOUND_MIXER_WRITE_PCM
SOUND_MIXER_WRITE_OGAIN
SOUND_MIXER_WRITE_RECGAIN
SOUND_MIXER_WRITE_RECLEV
SOUND_MIXER_WRITE_IGAIN
SOUND_MIXER_WRITE_RECSRC
SOUND_MIXER_WRITE_RECMASK
SOUND_MIXER_INFO
SNDCTL_AUDIOINFO_EX
SNDCTL_ENGINEINFO

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.

FILES


/dev/mixer Symbolic link to the pseudo mixer device for the system

/dev/sndstat Sound status device

ERRORS


An ioctl(2) fails if:

EINVAL The parameter changes requested in the ioctl are invalid or are not
supported by the device.

ENXIO The device or extension referenced does not exist.

ARCHITECTURE


SPARC x86

INTERFACE STABILITY


The information and mixer extension IOCTLs are Uncommitted. The
Compatibility IOCTLs are Obsolete Uncommitted. The extension names are
Uncommitted.

SEE ALSO


close(2), ioctl(2), open(2), read(2), dsp(4I), attributes(7)

BUGS


The names of mixer extensions are not guaranteed to be predictable.

OmniOS February 1, 2019 OmniOS