Doc/libsunaudio.tex

\section{Built-in Module \sectcode{sunaudiodev}}
\label{module-sunaudiodev}
\bimodindex{sunaudiodev}

This module allows you to access the sun audio interface. The sun
audio hardware is capable of recording and playing back audio data
in U-LAW format with a sample rate of 8K per second. A full
description can be gotten with \samp{man audio}.

The module defines the following variables and functions:

\setindexsubitem{(in module sunaudiodev)}
\begin{excdesc}{error}
This exception is raised on all errors. The argument is a string
describing what went wrong.
\end{excdesc}

\begin{funcdesc}{open}{mode}
This function opens the audio device and returns a sun audio device
object. This object can then be used to do I/O on. The \var{mode} parameter
is one of \code{'r'} for record-only access, \code{'w'} for play-only
access, \code{'rw'} for both and \code{'control'} for access to the
control device. Since only one process is allowed to have the recorder
or player open at the same time it is a good idea to open the device
only for the activity needed. See the audio manpage for details.
\end{funcdesc}

\subsection{Audio Device Objects}

The audio device objects are returned by \code{open} define the
following methods (except \code{control} objects which only provide
getinfo, setinfo and drain):

\setindexsubitem{(audio device method)}

\begin{funcdesc}{close}{}
This method explicitly closes the device. It is useful in situations
where deleting the object does not immediately close it since there
are other references to it. A closed device should not be used again.
\end{funcdesc}

\begin{funcdesc}{drain}{}
This method waits until all pending output is processed and then returns.
Calling this method is often not necessary: destroying the object will
automatically close the audio device and this will do an implicit drain.
\end{funcdesc}

\begin{funcdesc}{flush}{}
This method discards all pending output. It can be used avoid the
slow response to a user's stop request (due to buffering of up to one
second of sound).
\end{funcdesc}

\begin{funcdesc}{getinfo}{}
This method retrieves status information like input and output volume,
etc. and returns it in the form of
an audio status object. This object has no methods but it contains a
number of attributes describing the current device status. The names
and meanings of the attributes are described in
\file{/usr/include/sun/audioio.h} and in the audio man page. Member names
are slightly different from their C counterparts: a status object is
only a single structure. Members of the \code{play} substructure have
\samp{o_} prepended to their name and members of the \code{record}
structure have \samp{i_}. So, the C member \code{play.sample_rate} is
accessed as \code{o_sample_rate}, \code{record.gain} as \code{i_gain}
and \code{monitor_gain} plainly as \code{monitor_gain}.
\end{funcdesc}

\begin{funcdesc}{ibufcount}{}
This method returns the number of samples that are buffered on the
recording side, i.e.
the program will not block on a \function{read()} call of so many samples.
\end{funcdesc}

\begin{funcdesc}{obufcount}{}
This method returns the number of samples buffered on the playback
side. Unfortunately, this number cannot be used to determine a number
of samples that can be written without blocking since the kernel
output queue length seems to be variable.
\end{funcdesc}

\begin{funcdesc}{read}{size}
This method reads \var{size} samples from the audio input and returns
them as a Python string. The function blocks until enough data is available.
\end{funcdesc}

\begin{funcdesc}{setinfo}{status}
This method sets the audio device status parameters. The \var{status}
parameter is an device status object as returned by \function{getinfo()} and
possibly modified by the program.
\end{funcdesc}

\begin{funcdesc}{write}{samples}
Write is passed a Python string containing audio samples to be played.
If there is enough buffer space free it will immediately return,
otherwise it will block.
\end{funcdesc}

There is a companion module, \module{SUNAUDIODEV}, which defines useful
symbolic constants like \constant{MIN_GAIN}, \constant{MAX_GAIN},
\constant{SPEAKER}, etc. The names of
the constants are the same names as used in the \C{} include file
\code{<sun/audioio.h>}, with the leading string \samp{AUDIO_}
stripped.
\refstmodindex{SUNAUDIODEV}

Useability of the control device is limited at the moment, since there
is no way to use the ``wait for something to happen'' feature the
device provides.