116 lines
4.6 KiB
TeX
116 lines
4.6 KiB
TeX
\chapter{SunOS Specific Services}
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The modules described in this chapter provide interfaces to features
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that are unique to the SunOS operating system (versions 4 and 5; the
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latter is also known as Solaris version 2).
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\section{Built-in Module \sectcode{sunaudiodev}}
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\label{module-sunaudiodev}
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\bimodindex{sunaudiodev}
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This module allows you to access the sun audio interface. The sun
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audio hardware is capable of recording and playing back audio data
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in U-LAW format with a sample rate of 8K per second. A full
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description can be gotten with \samp{man audio}.
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The module defines the following variables and functions:
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\setindexsubitem{(in module sunaudiodev)}
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\begin{excdesc}{error}
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This exception is raised on all errors. The argument is a string
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describing what went wrong.
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\end{excdesc}
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\begin{funcdesc}{open}{mode}
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This function opens the audio device and returns a sun audio device
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object. This object can then be used to do I/O on. The \var{mode} parameter
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is one of \code{'r'} for record-only access, \code{'w'} for play-only
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access, \code{'rw'} for both and \code{'control'} for access to the
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control device. Since only one process is allowed to have the recorder
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or player open at the same time it is a good idea to open the device
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only for the activity needed. See the audio manpage for details.
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\end{funcdesc}
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\subsection{Audio Device Objects}
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The audio device objects are returned by \code{open} define the
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following methods (except \code{control} objects which only provide
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getinfo, setinfo and drain):
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\setindexsubitem{(audio device method)}
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\begin{funcdesc}{close}{}
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This method explicitly closes the device. It is useful in situations
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where deleting the object does not immediately close it since there
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are other references to it. A closed device should not be used again.
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\end{funcdesc}
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\begin{funcdesc}{drain}{}
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This method waits until all pending output is processed and then returns.
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Calling this method is often not necessary: destroying the object will
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automatically close the audio device and this will do an implicit drain.
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\end{funcdesc}
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\begin{funcdesc}{flush}{}
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This method discards all pending output. It can be used avoid the
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slow response to a user's stop request (due to buffering of up to one
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second of sound).
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\end{funcdesc}
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\begin{funcdesc}{getinfo}{}
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This method retrieves status information like input and output volume,
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etc. and returns it in the form of
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an audio status object. This object has no methods but it contains a
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number of attributes describing the current device status. The names
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and meanings of the attributes are described in
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\file{/usr/include/sun/audioio.h} and in the audio man page. Member names
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are slightly different from their C counterparts: a status object is
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only a single structure. Members of the \code{play} substructure have
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\samp{o_} prepended to their name and members of the \code{record}
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structure have \samp{i_}. So, the C member \code{play.sample_rate} is
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accessed as \code{o_sample_rate}, \code{record.gain} as \code{i_gain}
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and \code{monitor_gain} plainly as \code{monitor_gain}.
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\end{funcdesc}
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\begin{funcdesc}{ibufcount}{}
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This method returns the number of samples that are buffered on the
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recording side, i.e.
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the program will not block on a \code{read} call of so many samples.
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\end{funcdesc}
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\begin{funcdesc}{obufcount}{}
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This method returns the number of samples buffered on the playback
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side. Unfortunately, this number cannot be used to determine a number
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of samples that can be written without blocking since the kernel
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output queue length seems to be variable.
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\end{funcdesc}
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\begin{funcdesc}{read}{size}
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This method reads \var{size} samples from the audio input and returns
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them as a python string. The function blocks until enough data is available.
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\end{funcdesc}
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\begin{funcdesc}{setinfo}{status}
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This method sets the audio device status parameters. The \var{status}
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parameter is an device status object as returned by \code{getinfo} and
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possibly modified by the program.
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\end{funcdesc}
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\begin{funcdesc}{write}{samples}
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Write is passed a python string containing audio samples to be played.
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If there is enough buffer space free it will immediately return,
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otherwise it will block.
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\end{funcdesc}
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There is a companion module, \code{SUNAUDIODEV}, which defines useful
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symbolic constants like \code{MIN_GAIN}, \code{MAX_GAIN},
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\code{SPEAKER}, etc. The names of
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the constants are the same names as used in the C include file
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\file{<sun/audioio.h>}, with the leading string \samp{AUDIO_}
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stripped.
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\refstmodindex{SUNAUDIODEV}
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Useability of the control device is limited at the moment, since there
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is no way to use the ``wait for something to happen'' feature the
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device provides.
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