title: no audio data from PC send to STM32F4 audio class USB
body: <p>I'm working in an audio project. We use stm32f407 like a USB audio device to get audio data from PC then send out by I2S module. We are using stm32f4 Discovery kit and STM32cubeMX. After generate code by following this <a href="https://www.youtube.com/watch?v=0NnIum2hAWg" rel="nofollow noreferrer">video</a>, i change nothing and flash to Kit; my PC identifies that STM Audio device but there isn't any data send to my kit when play music, except MuteCMD . My question is:</p>
  
  <ul>
  <li><p>i don't know which function is callback when data stream from PC to Kit.</p></li>
  <li><p>why PC identifies that my kit is an audio output device but the callback of volume control isn't called when I config volume on PC and there isn't any data of music send to my device. The only one mute control callback function is called when i mute the PC. </p></li>
  </ul>
  
  <p>this is my config in STM32cubeMX</p>
  
  <p>pinout config figure
  <a href="https://i.stack.imgur.com/VyN25.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/VyN25.png" alt="pinout config figure"></a></p>
  
  <p>USB device config figure 1
  <a href="https://i.stack.imgur.com/pSske.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/pSske.png" alt="USB device config figure 1"></a></p>
  
  <p>USB device config figure 2
  <a href="https://i.stack.imgur.com/1ouh9.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/1ouh9.png" alt="USB device config figure 2"></a></p>
  
  <p>USB device config figure 3
  <a href="https://i.stack.imgur.com/nzrvb.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/nzrvb.png" alt="USB device config figure 3"></a></p>
  
  <p>PC identifies AUDIO device figure
  <a href="https://i.stack.imgur.com/z1HDv.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/z1HDv.png" alt="PC identifies AUDIO device figure"></a></p>
  
  <p>choosing PC's audio output device figure
  <a href="https://i.stack.imgur.com/1vYy3.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/1vYy3.png" alt="choosing PC&#39;s audio output device figure"></a></p>
  
  <p>fail to play test tone figure
  <a href="https://i.stack.imgur.com/ifbg3.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/ifbg3.png" alt="fail to play test tone figure"></a></p>