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.Dd March 11, 1997 .Dt AUDIO 4 .Os NetBSD .Sh NAME .Nm audio .Nd device-independent audio driver layer .Sh SYNOPSIS .Fd #include <sys/types.h> .Fd #include <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.
p There are three device files available for audio operation:
a /dev/sound are used for recording or playback of digital samples.
a /dev/mixer is used to manipulate volume, recording source, or other audio mixer functions. .Sh SAMPLING DEVICES When
a /dev/audio is opened, it automatically directs the underlying driver to manipulate monaural 8-bit mulaw samples. 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
a /dev/sound is opened, it maintains the previous audio sample mode and record/playback mode. In all other respects
p 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).
p Reads and writes to a sampling device should be in multiples of the current audio block size which can be queried and set using the interfaces described below. Writes which are not multiples of the block size will be padded to a block boundary with silence. Reads which are not multiples of the block size will consume a block from the audio hardware but only return the requested number of bytes.
p 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. 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.
p If a writing process does not call .Xr write 2 frequently enough to provide audio playback blocks in time for the next hardware interrupt service, one or more audio silence blocks will be queued for playback, unless the .Dv AUMODE_PLAY_ALL mode is set. The writing process must provide enough data via subsequent write calls to ``catch up'' in time to the current audio block before any more process-provided samples will be played. [Alternatively, the playing process can use one of the interfaces below to halt and later restart audio playback.] 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 indent -compact t 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. t Dv AUDIO_RERROR (int) This command fetches the count of dropped input samples into its integer argument. There is no information regarding when in the sample stream they were dropped. t Dv AUDIO_WSEEK (int) This command fetches the count of samples are queued ahead of the first sample in the most recent sample block written into its integer argument. t Dv AUDIO_DRAIN This command suspends the calling process until all queued playback samples have been played by the hardware. t Dv AUDIO_GETDEV (audio_device_t) This command fetches the current hardware device information into the 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 t 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. d -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 To query all the supported encodings, start with an index field of zero and continue with successive encodings (1, 2, ...) until the command returns an error. t Dv AUDIO_GETFD (int) This command fetches a non-zero value into its integer argument if the hardware supports full-duplex operation, or a zero value if the hardware only supports half-duplex operation. t Dv AUDIO_SETFD (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. t Dv AUDIO_GETINFO (audio_info_t) t Dv AUDIO_SETINFO (audio_info_t) Get or set audio information as encoded in the audio_info structure. d -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 buffersize; /* total size audio buffer */ /* 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_int backlog; /* samples of output backlog to gen. */ u_int mode; /* current device mode */ #define AUMODE_PLAY 0x01 #define AUMODE_RECORD 0x02 #define AUMODE_PLAY_ALL 0x04 /* play all samples--no real-time correction */ }; .Ed
p When setting the current state with .Dv AUDIO_SETINFO , the audio_info structure should first be initialized with .Li Dv AUDIO_INITINFO Po &info Pc 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.
p 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. .Dv AUMODE_PLAY and .Dv AUMODE_PLAY_ALL are mutually exclusive, and only full-duplex audio devices support simultaneous record and playback.
p .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).
p .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. Upon return from an .Dv AUDIO_SETINFO call, the actual blocksize set is returned in this field.
p .Va backlog is currently unused. d -literal struct audio_prinfo { u_int sample_rate; /* sample rate in samples/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_* above) */ u_int gain; /* volume level */ u_int port; /* selected I/O port */ u_long seek; /* BSD extension */ u_int ispare[3]; /* 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 ocurred */ u_char waiting; /* non-zero if another process hangs in open */ u_char cspare[3]; u_char open; /* non-zero if currently open */ u_char active; /* non-zero if I/O is currently active */ }; .Ed
p [Note: many hardware audio drivers require identical playback and recording sample rates, sample encodings, and channel counts. The recording information is always set last and will prevail on such hardware.]
p The encoding parameter can have the following values: l -tag -width indent -compact t Dv AUDIO_ENCODING_ULAW mulaw encoding, 8 bits/sample t Dv AUDIO_ENCODING_ALAW alaw encoding, 8 bits/sample t Dv AUDIO_ENCODING_LINEAR two's complement signed linear encoding with the platform byte order t Dv AUDIO_ENCODING_ULINEAR unsigned linear encoding with the platform byte order t Dv AUDIO_ENCODING_ADPCM ADPCM encoding, 8 bits/sample t Dv AUDIO_ENCODING_LINEAR_LE two's complement signed linear encoding with little endian byte order t Dv AUDIO_ENCODING_LINEAR_BE two's complement signed linear encoding with big endian byte order t Dv AUDIO_ENCODING_ULINEAR_LE unsigned linear encoding with little endian byte order t Dv AUDIO_ENCODING_ULINEAR_BE unsigned linear encoding with little big byte order .El
p The gain and port settings provide simple shortcuts to the richer mixer interface described below. The gain should be in the range q Dv AUDIO_MIN_GAIN , Dv AUDIO_MAX_GAIN . The port value is hardware-dependent and should be selected (if setting with .Dv AUDIO_SETINFO ) based upon return values from the mixer query functions below or from a prior .Dv AUDIO_GETINFO .
p The .Va seek and .Va samples fields are only used for .Dv AUDIO_GETINFO . .Va seek represents the count of samples pending; .Va samples represents the total number of samples recorded or played, less those that were dropped due to inadequate consumption/production rates.
p .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 mixer device,
a /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: l -tag -width indent -compact t Dv AUDIO_GETDEV (audio_device_t) This command is the same as described above for the sampling devices. t Dv AUDIO_MIXER_READ (mixer_ctrl_t) t Dv AUDIO_MIXER_WRITE (mixer_ctrl_t) 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; .Ed 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 mixer_ctrl_t argument. For a mixer value, the .Va value field specifies both the number of channels and the values for each of the channels. 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 . t Dv AUDIO_MIXER_DEVINFO (mixer_devinfo_t) This command is used iteratively to fetch audio mixer device information into the input/output mixer_devinfo_t argument. To query all the supported encodings, start with an index field of zero and continue with successive encodings (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; } v; } un; } mixer_devinfo_t; .Ed 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).
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. For example, a mixer level controlling the input gain on the ``line in'' circuit would be a class that matches an input class device with the name ``Inputs'' (AudioCInputs). 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.
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 "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
AudioNon and AudioNoff.
For
.Dv AUDIO_MIXER_VALUE
mixer control types, the channel count is
returned; the units name specifies what the level controls (typical
values are AudioNvolume, AudioNtreble, AudioNbass).
For AUDIO_MIXER_SET mixer control types, what is what?
.El
p By convention, all the mixer device indices for generic class grouping are at the end of the index number space for a particular hardware device, and can be distinguished from other mixer controls because they use a name from one of the AudioC* string values. .Sh FILES l -tag -width /dev/audio -compact t Pa /dev/audio t Pa /dev/sound t Pa /dev/mixer .El .Sh SEE ALSO .Xr ioctl 2 .
For ports using the ISA bus: .Xr gus 4 , .Xr pas 4 , .Xr pss 4 , .Xr sb 4 , .Xr wss 4 . .Sh BUGS The device class conventions are just a wish and not yet reality.
p Audio playback can be scratchy with pops and crackles due to the audio layer's buffering scheme. Using a bigger blocksize will help reduce such annoyances.