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198 lines
6.7 KiB
HTML
198 lines
6.7 KiB
HTML
<!doctype html public "-//w3c//dtd html 4.0 transitional//en">
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<html>
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<head>
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<meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1">
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<meta name="GENERATOR" content="Mozilla/4.79 [en] (Windows NT 5.0; U) [Netscape]">
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<meta name="Author" content="Phil Burk">
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<meta name="Description" content="Internal docs. How a stream is started or stopped.">
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<meta name="KeyWords" content="audio, tutorial, library, portable, open-source, DirectSound,sound, music, JSyn, synthesis,">
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<title>PortAudio Implementation - Start/Stop</title>
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</head>
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<body>
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<center><table COLS=1 WIDTH="100%" BGCOLOR="#FADA7A" >
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<tr>
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<td>
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<center>
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<h1>
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<a href="http://www.portaudio.com">PortAudio</a> Implementation Guide</h1></center>
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</td>
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</tr>
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</table></center>
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<p>This document describes how to implement the PortAudio API on a new
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computer platform. Implementing PortAudio on a new platform, makes it possible
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to port many existing audio applications to that platform.
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<p>By Phil Burk
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<br>Copyright 2000 Phil Burk and Ross Bencina
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<p>Note that the license says: <b>"Any person wishing to distribute modifications
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to the Software is requested to send the modifications to the original
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developer so that they can be incorporated into the canonical version."</b>.
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So when you have finished a new implementation, please send it back to
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us at "<a href="http://www.portaudio.com">http://www.portaudio.com</a>"
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so that we can make it available for other users. Thank you!
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<h2>
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Download the Latest PortAudio Implementation</h2>
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Always start with the latest implementation available at "<a href="http://www.portaudio.com">http://www.portaudio.com</a>".
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Look for the nightly snapshot under the CVS section.
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<h2>
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Select an Existing Implementation as a Basis</h2>
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The fastest way to get started is to take an existing implementation and
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translate it for your new platform. Choose an implementation whose architecture
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is as close as possible to your target.
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<ul>
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<li>
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DirectSound Implementation - pa_win_ds - Uses a timer callback for the
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background "thread". Polls a circular buffer and writes blocks of data
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to keep it full.</li>
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<li>
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Windows MME - pa_win_wmme - Spawns an actual Win32 thread. Writes blocks
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of data to the HW device and waits for events that signal buffer completion.</li>
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<li>
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Linux OSS - pa_linux - Spawns a real thread that writes to the "/dev/dsp"
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stream using blocking I/O calls.</li>
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</ul>
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When you write a new implementation, you will be using some code that is
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in common with all implementations. This code is in the folder "pa_common".
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It provides various functions such as parameter checking, error code to
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text conversion, sample format conversion, clipping and dithering, etc.
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<p>The code that you write will go into a separate folder called "pa_{os}_{api}".
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For example, code specific to the DirectSound interface for Windows goes
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in "pa_win_ds".
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<h2>
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Read Docs and Code</h2>
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Famialiarize yourself with the system by reading the documentation provided.
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here is a suggested order:
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<ol>
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<li>
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User Programming <a href="pa_tutorial.html">Tutorial</a></li>
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<li>
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Header file "pa_common/portaudio.h" which defines API.</li>
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<li>
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Header file "pa_common/pa_host.h" for host dependant code. This definces
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the routine you will need to provide.</li>
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<li>
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Shared code in "pa_common/pa_lib.c".</li>
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<li>
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Docs on Implementation of <a href="pa_impl_startstop.html">Start/Stop</a>
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code.</li>
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</ol>
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<h2>
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Implement Output to Default Device</h2>
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Now we are ready to crank some code. For instant gratification, let's try
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to play a sine wave.
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<ol>
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<li>
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Link the test program "pa_tests/patest_sine.c" with the file "pa_lib.c"
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and the implementation specific file you are creating.</li>
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<li>
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For now, just stub out the device query code and the audio input code.</li>
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<li>
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Modify PaHost_OpenStream() to open your default target device and get everything
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setup.</li>
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<li>
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Modify PaHost_StartOutput() to start playing audio.</li>
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<li>
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Modify PaHost_StopOutput() to stop audio.</li>
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<li>
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Modify PaHost_CloseStream() to clean up. Free all memory that you allocated
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in PaHost_OpenStream().</li>
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<li>
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Keep cranking until you can play a sine wave using "patest_sine.c".</li>
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<li>
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Once that works, try "patest_pink.c", "patest_clip.c", "patest_sine8.c".</li>
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<li>
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To test your Open and Close code, try "patest_many.c".</li>
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<li>
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Now test to make sure that the three modes of stopping are properly supported
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by running "patest_stop.c".</li>
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<li>
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Test your implementation of time stamping with "patest_sync.c".</li>
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</ol>
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<h2>
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Implement Device Queries</h2>
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Now that output is working, lets implement the code for querying what devices
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are available to the user. Run "pa_tests/pa_devs.c". It should print all
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of the devices available and their characteristics.
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<h2>
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Implement Input</h2>
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Implement audio input and test it with:
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<ol>
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<li>
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patest_record.c - record in half duplex, play back as recorded.</li>
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<li>
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patest_wire.c - full duplex, copies input to output. Note that some HW
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may not support full duplex.</li>
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<li>
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patest_fuzz.c - plug in your guitar and get a feel for why latency is an
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important issue in computer music.</li>
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<li>
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paqa_devs.c - try to open every device and use it with every possible format</li>
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</ol>
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<h2>
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Debugging Tools</h2>
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You generally cannot use printf() calls to debug real-time processes because
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they disturb the timing. Also calling printf() from your background thread
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or interrupt could crash the machine. So PA includes a tool for capturing
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events and storing the information while it is running. It then prints
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the events when Pa_Terminate() is called.
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<ol>
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<li>
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To enable trace mode, change TRACE_REALTIME_EVENTS in "pa_common/pa_trace.h"
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from a (0) to a (1).</li>
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<li>
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Link with "pa_common/pa_trace.c".</li>
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<li>
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Add trace messages to your code by calling:</li>
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<br><tt> void AddTraceMessage( char *msg, int data );</tt>
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<br><tt>for example</tt>
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<br><tt> AddTraceMessage("Pa_TimeSlice: past_NumCallbacks ",
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past->past_NumCallbacks );</tt>
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<li>
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Run your program. You will get a dump of events at the end.</li>
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<li>
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You can leave the trace messages in your code. They will turn to NOOPs
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when you change TRACE_REALTIME_EVENTS back to (0).</li>
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</ol>
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<h2>
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Delivery</h2>
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Please send your new code along with notes on the implementation back to
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us at "<a href="http://www.portaudio.com">http://www.portaudio.com</a>".
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We will review the implementation and post it with your name. If you had
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to make any modifications to the code in "pa_common" or "pa_tests" <b>please</b>
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send us those modifications and your notes. We will try to merge your changes
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so that the "pa_common" code works with <b>all</b> implementations.
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<p>If you have suggestions for how to make future implementations easier,
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please let us know.
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<br>THANKS!
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<br>
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</body>
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</html>
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