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SunOS 5.5 Ioctl Requests audio(7I)

structure and output is stopped until additional data is written. If an application

attempts to write a number of bytes that is not a multiple of the current sample frame

size, an error will be generated and the device will need to be closed before any future

writes will succeed.

Asynchronous I/O TheI_SETSIG STREAMS ioctl enables asynchronous notiﬁcation, through theSIGPOLL

signal, of input and output ready conditions. TheO_NONBLOCK ﬂag may be set using

the F_SETFL fcntl(2) to enable non-blocking read() and write() requests. This is normally

sufﬁcient for applications to maintain an audio stream in the background.

Audio Control

Pseudo-Device

It is sometimes convenient to have an application, such as a volume control panel,

modify certain characteristics of the audio device while it is beingused by an unrelated

process. The /dev/audioctl pseudo-device is provided for this purpose. Anynumber of

processes may open /dev/audioctl simultaneously. However, read() and write() system

calls are ignored by /dev/audioctl. TheAUDIO_GETINFO and AUDIO_SETINFO ioctl

commands may be issued to /dev/audioctl to determine the status or alter the behavior of

/dev/audio. Note: In general, the audio control device name is constructed by appending

the letters"ctl" to the path name of the audio device.

Audio Status Change

Notiﬁcation

Applications that open the audio control pseudo-device may request asynchronous

notiﬁcation of changes in the state of the audio device by settingthe S_MSG ﬂag in an

I_SETSIG STREAMS ioctl. Such processes receive aSIGPOLL signal when any of the fol-

lowing events occur:

An AUDIO_SETINFO ioctl has altered the device state.

An input overﬂow or output underﬂow has occurred.

An end-of-ﬁle record (zero-length buffer) has been processed on output.

An open() or close() of /dev/audio has altered the device state.

An external event (such as speakerbox volume control) has altered the

device state.

IOCTLS

Audio Information

Structure

The state of the audio device may be polled or modiﬁed using theAUDIO_GETINFO and

AUDIO_SETINFO ioctl commands. These commands operate on the audio_info struc-

ture as deﬁned, in <sys/audioio.h>, as follows:

/∗ This structure contains state information for audio device

IO streams ∗/

struct audio_prinfo {

/∗ The following values describe the audio data encoding ∗/

uint_t sample_rate; /∗ samples per second ∗/

uint_t channels; /∗ number of interleaved channels ∗/

uint_t precision; /∗ number of bits per sample ∗/

uint_t encoding; /∗ data encoding method ∗/

/∗ The following values control audio device conﬁguration ∗/

uint_t gain; /∗ volume level ∗/

uint_t port; /∗ selected I/O port ∗/

uint_t buffer_size; /∗ I/O buffer size ∗/

/∗ The following values describe the current device state ∗/

modiﬁed 21 Mar 1995 7I-27

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