Technical data

SunOS 5.5 Ioctl Requests audio(7I)

AUDIO_SETINFO

The argument is a pointer to an audio_info structure. This command may be

issued for either the /dev/audio or the /dev/audioctl device with some restric-

tions. This command conﬁgures the audio device according to the structure sup-

plied and overwrites the structure with the new state of the device. Note: The

play.samples, record.samples, play.error, record.error, and play.eof ﬁelds are modiﬁed

to reﬂect the state of the device when the AUDIO_SETINFO was issued. This

allows programs to automatically modify these ﬁelds while retrievingthe previ-

ous value.

Certain ﬁelds in the information structure, such as the pause ﬂags are treated as

read-only when /dev/audio is not open with the corresponding access permis-

sion. Other ﬁelds, such as the gain levels and encoding information, may have a

restricted set of acceptable values. Applications that attempt to modify such

ﬁelds should check the returned values to be sure that the corresponding change

took effect. The sample_rate, channels, precision, and encoding ﬁelds treated as

read-only for /dev/audioctl, so that applications can be guaranteed that the exist-

ing audio format will stay in place until they relinquish the audio device.

AUDIO_SETINFO will return EINVAL when the desired conﬁguration is not pos-

sible, or EBUSY when another process has control of the audio device.

Once set, the following values persist through subsequent open() and close()

calls of the device: play.gain, record.gain, play.balance, record.balance, output_muted,

monitor_gain, play.port, and record.port. However, an automatic device driver

unload will reset these parameters to their default values on the next load. All

other state is reset when the corresponding I/O stream of /dev/audio is closed.

The audio_info structure may be initializedthrough the use of the

AUDIO_INITINFO macro. This macro sets all ﬁelds in the structure to values that

are ignored by theAUDIO_SETINFO command. For instance, the following code

switches the output port from the built-in speaker to the headphone jack without

modifying any other audio parameters:

audio_info_tinfo;

AUDIO_INITINFO(&info);

info.play.port = AUDIO_HEADPHONE;

err = ioctl(audio_fd, AUDIO_SETINFO, &info);

This technique eliminates problems associated with using a sequence of

AUDIO_GETINFO followed by AUDIO_SETINFO.

ERRORS An open() will fail if:

EBUSY The requested play or record access is busy and either the O_NDELAY or

O_NONBLOCK ﬂag was set in the open() request.

EINTR The requested play or record access is busy and a signal interrupted the

open() request.

modiﬁed 21 Mar 1995 7I-31