title: USB CDC based on STM32F103 has different transmission effect on Windows7 and Ubuntu
body: <p>I used STM32F103 to send data to the PC via USB CDC at a frequency of 4000Hz, 21 bytes per packet. The code generated by STMCube. And then I found that only 1000 packets can be received per second on Windows7 via serial assistant, but it can normally receive 4000 packets per second on Ubuntu via CuteCOM. How do I achieve the same effect on Windows7? Thank you.</p>
  
  <pre><code>int main(void)
  {
      HAL_Init();
      SystemClock_Config();
      MX_GPIO_Init();
      MX_USB_DEVICE_Init();
      while(1)
      {
          __WFI();
      }
  }
  
  void HAL_SYSTICK_Callback(void)      //4000Hz
  {
      CDC_Transmit_FS(buff, 21);
  }
  </code></pre>
  
  <p>I use python to test, and the result is:
  <a href="https://i.stack.imgur.com/oeHFs.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/oeHFs.png" alt="Windows7"></a></p>
  
  <p><a href="https://i.stack.imgur.com/ftOAN.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/ftOAN.png" alt="Ubuntu"></a></p>