title: Using xaudio2 and a parallel port together
body: <p>I am using C++ to code a neuroscience experiment in my research lab. We are studying tactile perception, and we use a parallel port to trigger our brain stimulating device. The timing is very important.
  We recently started using xaudio2 to play very simple WAV files, which are used to trigger our vibrotactile stimulators (for example, our "tactile" stimuli are 100 and 200 Hz sounds with a duration of 100 ms, that move a piezo-electric stimulator that is placed on the hand).
  Our problem is that we need to send out 3 commands to the brain stimulator via the parallel port: once 40 ms before the tactile stimulus, once 10 ms after the start of the stimulus, and a third time 60 ms into the stimulus. Remember, the tactile stimulus lasts 100 ms.
  However, the way xaudio2 triggers sound is that it plays the wave and blocks until it is finished. As a consequence, the program ignores the two parallel port commands which should be sent during the stimulus.
  Does anybody know how I can make sure the tactile stimulus is still triggered for the entirety of its 100 ms duration, but also send out parallel port commands during it? I am using the MSDN XAudio2Samples as the basic structure for playing the wav files, and the PlayWave function is the one which "blocks" any other input while the Wav file is playing -- but I can't figure out how to modify it so that it will also take my parallel port commands (which are Out32(888,1)) while a sound is being played.
  Thank you!</p>
  
  <p>Here is the code for the PlayWave function:</p>
  
  <pre><code>    //--------------------------------------------------------------------------------------
  // Name: PlayWave
  // Desc: Plays a wave and blocks until the wave finishes playing
  //--------------------------------------------------------------------------------------
  _Use_decl_annotations_
  HRESULT PlayWave( IXAudio2* pXaudio2, LPCWSTR szFilename )
  {
      //
      // Locate the wave file
      //
      WCHAR strFilePath[MAX_PATH];
      HRESULT hr = FindMediaFileCch( strFilePath, MAX_PATH, szFilename );
      if( FAILED( hr ) )
      {
          wprintf( L"Failed to find media file: %s\n", szFilename );
          return hr;
      }
  
      //
      // Read in the wave file
      //
      std::unique_ptr&lt;uint8_t[]&gt; waveFile;
      DirectX::WAVData waveData;
      if ( FAILED( hr = DirectX::LoadWAVAudioFromFileEx( strFilePath, waveFile, waveData ) ) )
      {
          wprintf( L"Failed reading WAV file: %#X (%s)\n", hr, strFilePath );
          return hr;
      }
  
      //
      // Play the wave using a XAudio2SourceVoice
      //
  
      // Create the source voice
      IXAudio2SourceVoice* pSourceVoice;
      if( FAILED( hr = pXaudio2-&gt;CreateSourceVoice( &amp;pSourceVoice, waveData.wfx ) ) )
      {
          wprintf( L"Error %#X creating source voice\n", hr );
          return hr;
      }
  
      // Submit the wave sample data using an XAUDIO2_BUFFER structure
      XAUDIO2_BUFFER buffer = {0};
      buffer.pAudioData = waveData.startAudio;
      buffer.Flags = XAUDIO2_END_OF_STREAM;  // tell the source voice not to expect any data after this buffer
      buffer.AudioBytes = waveData.audioBytes;
  
      if ( waveData.loopLength &gt; 0 )
      {
          buffer.LoopBegin = waveData.loopStart;
          buffer.LoopLength = waveData.loopLength;
          buffer.LoopCount = 1; // We'll just assume we play the loop twice
      }
  
  #if (_WIN32_WINNT &lt; 0x0602 /*_WIN32_WINNT_WIN8*/)
      if ( waveData.seek )
      {
          XAUDIO2_BUFFER_WMA xwmaBuffer = {0};
          xwmaBuffer.pDecodedPacketCumulativeBytes = waveData.seek;
          xwmaBuffer.PacketCount = waveData.seekCount;
          if( FAILED( hr = pSourceVoice-&gt;SubmitSourceBuffer( &amp;buffer, &amp;xwmaBuffer ) ) )
          {
              wprintf( L"Error %#X submitting source buffer (xWMA)\n", hr );
              pSourceVoice-&gt;DestroyVoice();
              return hr;
          }
      }
  #else
      if ( waveData.seek )
      {
          wprintf( L"This platform does not support xWMA or XMA2\n" );
          pSourceVoice-&gt;DestroyVoice();
          return hr;
      }
  #endif
      else if( FAILED( hr = pSourceVoice-&gt;SubmitSourceBuffer( &amp;buffer ) ) )
      {
          wprintf( L"Error %#X submitting source buffer\n", hr );
          pSourceVoice-&gt;DestroyVoice();
          return hr;
      }
  
      hr = pSourceVoice-&gt;Start( 0 );
  
      // Let the sound play
      BOOL isRunning = TRUE;
      while( SUCCEEDED( hr ) &amp;&amp; isRunning )
      {
          XAUDIO2_VOICE_STATE state;
          pSourceVoice-&gt;GetState( &amp;state );
          isRunning = ( state.BuffersQueued &gt; 0 ) != 0;
  
          // Wait till the escape key is pressed
          if( GetAsyncKeyState( VK_ESCAPE ) )
              break;
  
          Sleep( 10 );
      }
  
      // Wait till the escape key is released
      while( GetAsyncKeyState( VK_ESCAPE ) )
          Sleep( 10 );
  
      pSourceVoice-&gt;DestroyVoice();
  
      return hr;
  }
  </code></pre>