SerialPort.ReadExisting workaround needed

Hello everyone,

I'm having an issue with the SerialPort.ReadExisting method, which I think is neccessary for my purpose.

I have a set of inertial movement sensors (up to 16) which deliver data every 1 ms via bluetooth serial port profile. So each sensor streams every 16 ms. In Unity, I want to move the parts of a body (arms, legs etc.) depending on these sensor values.

My first approach with C# was with WinForms, where I could have a DataReceivedHandler and use the ReadExisting() method, then split for lines automatically. In Unity, ReadExisting() seems to be buggy, so I would have to use ReadLine() method instead. But, with ReadLine(), I would have to call this method asynchronously really fast (around 1 ms) in order to not lose received lines via COM port.

My current codes is a copy of some other code I found on the internet:

  public IEnumerator AsynchronousReadFromSerialPort(Action<string> callback, Action fail = null, float timeout = float.PositiveInfinity)
     {
         DateTime initialTime = DateTime.Now;
         DateTime nowTime;
         TimeSpan diff = default(TimeSpan);
      
         string dataString = null;
         //string[] serialPortLines;
      
         do
         {
             try
             {
                 dataString = serialPort.ReadLine();
                 //serialPortLines = serialPort.ReadExisting().Split(new string[] {"\n"}, StringSplitOptions.RemoveEmptyEntries);
             }
             catch (TimeoutException)
             {
                 dataString = null;
                 //serialPortLines = null;
             }
      
             if (dataString != null)
             {
                 callback(dataString);
                 //callback(serialPortLines[0]);
                 yield return null;
             }
             else
             {
                 yield return new WaitForSeconds(0.1f);
             }
      
             nowTime = DateTime.Now;
             diff = nowTime - initialTime;
      
         } while (diff.Seconds < timeout);
      
         if (fail != null)
             fail();
         yield return null;
     }
 
 
     void Update()
         {        
             if (comOpen == true)
             {
                 
                 StartCoroutine
                 (
                     AsynchronousReadFromSerialPort
                     (   (string s) => Debug.Log(s),     // Callback
                         () => Debug.LogError("Error!"), // Error callback
                         10f                             // Timeout (seconds)
                     )
                 );
 }

As you can see, currently I'm using ReadLine() in the Update() function, with is too slow. When I switch the code (commented lines in asynchronous read function) to make use of ReadExisting(), I'm getting this error everytime the ReadExisting() gets called.

 NullReferenceException: Object reference not set to an instance of an object
 System.IO.Ports.WinSerialStream.get_BytesToRead ()
 System.IO.Ports.SerialPort.get_BytesToRead ()
 System.IO.Ports.SerialPort.ReadExisting ()
 (wrapper remoting-invoke-with-check) System.IO.Ports.SerialPort:ReadExisting ()
 SerialComm+<AsynchronousReadFromSerialPort>c__Iterator0.MoveNext () (at Assets/UnityVS/Comports/SerialComm.cs:134)
 UnityEngine.MonoBehaviour:StartCoroutine(IEnumerator)
 SerialComm:Update() (at Assets/UnityVS/Comports/SerialComm.cs:50)

Any help or advice?