~4Dgifts/toolbox/src/exampleCode/irix/playEngine README
This file describes the purpose and use of the
functions defined in the source file PlayEngine.c.
OVERVIEW:
---------
The purpose of this source file is to provide a set of routines
that will permit an audio track to be played without interference
from operating system multitasking activities.
The way it works is to sproc (similar to fork) a sub-process that
raises its priority high enough so that the other operating system
activities cannot preempt it. The main application provides this
new process with a pointer to the data to be played and starts and
stops the process through signals and/or semaphores.
For more details on this implemetation, beyond what is contained in
this README, see the comments throughout the PlayEngine.c file.
DESCRIPTION:
------------
This set of routines can be used for other purposes other than as
an audio player but the demo program demonstrates the functions by
playing audio tracks.
Also, this demonstration program doesn't take full advantage of
some of the capabilities of multiprocessing. For example, a flag
could be provided in the audio loop that would allow the parent
application to communicate commands to the child process, like to
abort early, go back some number of records, etc.
Entry points:
-------------
CreateSubProcess
This routine is called once to create the subprocess. If
semaphores are to be used, it will also create the semaphores.
Synopsis:
CreateSubProcess ();
StartSubProcess
This routine is called to tell the subprocess to do something.
It must be preceded by a call to 'CreateSubProcess'. It is
called each time the subprocess is to perform some task.
Synopsis:
StartSubProcess ();
DestroySubProcess
This routine destroys the subprocess and returns the semaphore
arena to the system. It *must* be called otherwise, the
semaphore arena is not returned to the system.
Synopsis:
DestroySubProcess ();
COMPILATION:
------------
There are two symbols of interest when compiling the PlayEngine.
One is USE_SEMAPHORES, which will compile in code to use
semaphores between the parent and child, and the other is
DEBUG_SP, which compiles in debug print statements to allow the
developer to see what is going on as it happens.
Parts of the demo.c program were cut and pasted from the program
~4Dgifts/examples/libaudio/playaifc.c.
Source
Documentation
Reference
OR, ...