Read packet with serialdevice in UWP

See more:

Windows

USB

UWP

Hello.
I'm developing a UWP application that opens a
"SerialDevice" that is a CYPRESS ARM
micrcontroller with "Azure RTOS" and "USBX" library.

The "USBX" library instantiates CDC ACM connection.

The micrcontroller send every second a USB packet with a unknown length from 8 to 512 bytes.

I have to read this packet in my UWP application.

I use this code.

async void my_routine(SerialDevice serialDevice)
{

  var dataReader = new DataReader(serialDevice.InputStream)
  {
    InputStreamOptions = InputStreamOptions.Partial
  };

  while(true)
  {
     // wait packet
     await dataReader.LoadAsync(512);

     // Read first byte that is an OPERATION_CODE
     var opCode = dataReader.ReadByte();
  }
}

I don't understand why the code stucks at

await dataReader.LoadAsync(512);

even if I set

InputStreamOptions = InputStreamOptions.Partial

where microsoft ensures

Quote:

The asynchronous read operation completes when one or more bytes is available.

Can someone help me ?

What I have tried:

I try not to use

await dataReader.LoadAsync(512);

I try to use

await dataReader.LoadAsync(1);

and calculate how many bytes from OPERATION_CODE