Doc/lib/libsunaudio.tex

   1 \section{\module{sunaudiodev} ---
   2          Access to Sun audio hardware.}
   3 \declaremodule{builtin}{sunaudiodev}
   4
   5 \modulesynopsis{Access to Sun audio hardware.}
   6
   7
   8 This module allows you to access the Sun audio interface. The Sun
   9 audio hardware is capable of recording and playing back audio data
  10 in u-LAW\index{u-LAW} format with a sample rate of 8K per second. A
  11 full description can be found in the \manpage{audio}{7I} manual page.
  12
  13 The module defines the following variables and functions:
  14
  15 \begin{excdesc}{error}
  16 This exception is raised on all errors. The argument is a string
  17 describing what went wrong.
  18 \end{excdesc}
  19
  20 \begin{funcdesc}{open}{mode}
  21 This function opens the audio device and returns a Sun audio device
  22 object. This object can then be used to do I/O on. The \var{mode} parameter
  23 is one of \code{'r'} for record-only access, \code{'w'} for play-only
  24 access, \code{'rw'} for both and \code{'control'} for access to the
  25 control device. Since only one process is allowed to have the recorder
  26 or player open at the same time it is a good idea to open the device
  27 only for the activity needed. See \manpage{audio}{7I} for details.
  28
  29 As per the manpage, this module first looks in the environment
  30 variable \code{AUDIODEV} for the base audio device filename.  If not
  31 found, it falls back to \file{/dev/audio}.  The control device is
  32 calculated by appending ``ctl'' to the base audio device.
  33 \end{funcdesc}
  34
  35
  36 \subsection{Audio Device Objects}
  37 \label{audio-device-objects}
  38
  39 The audio device objects are returned by \function{open()} define the
  40 following methods (except \code{control} objects which only provide
  41 \method{getinfo()}, \method{setinfo()}, \method{fileno()}, and
  42 \method{drain()}):
  43
  44 \begin{methoddesc}[audio device]{close}{}
  45 This method explicitly closes the device. It is useful in situations
  46 where deleting the object does not immediately close it since there
  47 are other references to it. A closed device should not be used again.
  48 \end{methoddesc}
  49
  50 \begin{methoddesc}[audio device]{fileno}{}
  51 Returns the file descriptor associated with the device.  This can be
  52 used to set up \code{SIGPOLL} notification, as described below.
  53 \end{methoddesc}
  54
  55 \begin{methoddesc}[audio device]{drain}{}
  56 This method waits until all pending output is processed and then returns.
  57 Calling this method is often not necessary: destroying the object will
  58 automatically close the audio device and this will do an implicit drain.
  59 \end{methoddesc}
  60
  61 \begin{methoddesc}[audio device]{flush}{}
  62 This method discards all pending output. It can be used avoid the
  63 slow response to a user's stop request (due to buffering of up to one
  64 second of sound).
  65 \end{methoddesc}
  66
  67 \begin{methoddesc}[audio device]{getinfo}{}
  68 This method retrieves status information like input and output volume,
  69 etc. and returns it in the form of
  70 an audio status object. This object has no methods but it contains a
  71 number of attributes describing the current device status. The names
  72 and meanings of the attributes are described in
  73 \file{/usr/include/sun/audioio.h} and in the \manpage{audio}{7I}
  74 manual page.  Member names
  75 are slightly different from their \C{} counterparts: a status object is
  76 only a single structure. Members of the \cdata{play} substructure have
  77 \samp{o_} prepended to their name and members of the \cdata{record}
  78 structure have \samp{i_}. So, the \C{} member \cdata{play.sample_rate} is
  79 accessed as \member{o_sample_rate}, \cdata{record.gain} as \member{i_gain}
  80 and \cdata{monitor_gain} plainly as \member{monitor_gain}.
  81 \end{methoddesc}
  82
  83 \begin{methoddesc}[audio device]{ibufcount}{}
  84 This method returns the number of samples that are buffered on the
  85 recording side, i.e.\ the program will not block on a
  86 \function{read()} call of so many samples.
  87 \end{methoddesc}
  88
  89 \begin{methoddesc}[audio device]{obufcount}{}
  90 This method returns the number of samples buffered on the playback
  91 side. Unfortunately, this number cannot be used to determine a number
  92 of samples that can be written without blocking since the kernel
  93 output queue length seems to be variable.
  94 \end{methoddesc}
  95
  96 \begin{methoddesc}[audio device]{read}{size}
  97 This method reads \var{size} samples from the audio input and returns
  98 them as a Python string. The function blocks until enough data is available.
  99 \end{methoddesc}
 100
 101 \begin{methoddesc}[audio device]{setinfo}{status}
 102 This method sets the audio device status parameters. The \var{status}
 103 parameter is an device status object as returned by \function{getinfo()} and
 104 possibly modified by the program.
 105 \end{methoddesc}
 106
 107 \begin{methoddesc}[audio device]{write}{samples}
 108 Write is passed a Python string containing audio samples to be played.
 109 If there is enough buffer space free it will immediately return,
 110 otherwise it will block.
 111 \end{methoddesc}
 112
 113 There is a companion module,
 114 \module{SUNAUDIODEV}\refstmodindex{SUNAUDIODEV}, which defines useful
 115 symbolic constants like \constant{MIN_GAIN}, \constant{MAX_GAIN},
 116 \constant{SPEAKER}, etc. The names of the constants are the same names
 117 as used in the \C{} include file \code{<sun/audioio.h>}, with the
 118 leading string \samp{AUDIO_} stripped.
 119
 120 The audio device supports asynchronous notification of various events,
 121 through the SIGPOLL signal.  Here's an example of how you might enable
 122 this in Python:
 123
 124 \begin{verbatim}
 125 def handle_sigpoll(signum, frame):
 126     print 'I got a SIGPOLL update'
 127 pp
 128 import fcntl, signal, STROPTS
 129
 130 signal.signal(signal.SIGPOLL, handle_sigpoll)
 131 fcntl.ioctl(audio_obj.fileno(), STROPTS.I_SETSIG, STROPTS.S_MSG)
 132 \end{verbatim}