C# SerialPort EventHandler in Unity

Question

I am writing C# code for Unity. Just reading SerialPort value in EventHandler. The problem is that the handler is not called. here's the code

using UnityEngine;
using System.Collections;
using System;
using System.IO.Ports;

public class MainScript : MonoBehaviour {

public SerialPort mySerialPort;
public static float speed=100;
GameObject cube ;
public GUIStyle style ;
// Use this for initialization
void Start () {

    cube = GameObject.FindGameObjectWithTag ("cube");

    if(mySerialPort.IsOpen)
        mySerialPort.Close();

    mySerialPort = new SerialPort("com5");
    mySerialPort.BaudRate = 9600;
    mySerialPort.Parity = Parity.None;
    mySerialPort.StopBits = StopBits.None;
    mySerialPort.DataBits = 8;
    mySerialPort.Handshake = Handshake.None;
    mySerialPort.DataReceived += new SerialDataReceivedEventHandler (DataReceivedHandler);

    if(mySerialPort.IsOpen == false)
        mySerialPort.Open();
}


void OnGUI(){
    GUI.Box (new Rect(100,100,100,100),"Speed : " + speed , style);
}
// Update is called once per frame
void Update () {
// speed = mySerialPort.ReadTo ("\r");
// update My View with the speed new value

    cube.transform.Rotate(Vector3.up * speed *Time.deltaTime);

}


public static void DataReceivedHandler(object sender, SerialDataReceivedEventArgs e)
{
    SerialPort sp = (SerialPort)sender;
    speed = float.Parse( sp.ReadTo ("\r") ) ;
    print ("Data Recieved : " + speed);
}
}

the problem is not in the serial port as, when i read it in the update function for unity it reads the right value but, there's a performance issue updating the UI.

thanks

Answer 1

As you said, the handler for 'DataReceived' event would not be called and it's a known issue with Unity (as of today). My workaround was to use a separate thread to read the port (polling):

private bool _looping;
private SerialPort _port;
public string _comPort; // e.g. "COM3"
private const int _baudRate = 921600;
private Thread portReadingThread;
private string strData;

private void OnEnable()
{
    _looping = true;
    portReadingThread = new Thread(ReadArduino);
    portReadingThread.Start();
}

private void OnDestroy()
{
    _looping = false;  // This is a necessary command to stop the thread.
                       // if you comment this line, Unity gets frozen when you stop the game in the editor.                           
    portReadingThread.Join();
    portReadingThread.Abort();
    _port.Close();
}

void ReadArduino()
{        
    // For any COM number larger than 9, you should add prefix of \\\\.\\ to it. 
    // For example for COM15, you should write it as "\\\\.\\COM15" instead of "COM15".
    _port = new SerialPort(_comPort, _baudRate);
    if (_port == null)
    {
        Debug.LogError("_port is null");
        return;
    }

    _port.Handshake = Handshake.None;
    _port.DtrEnable = true;
    //myPort.RtsEnable = true;
    _port.ReadTimeout = 500; // NOTE: Don't Reduce it or the communication might break!
    _port.WriteTimeout = 1000;
    _port.Parity = Parity.None;
    _port.StopBits = StopBits.One;
    _port.DataBits = 8;
    _port.NewLine = "\n";

    _port.Open();
    if (!_port.IsOpen)
        print("PORT HAS NOT BEEN OPEN!");
    // Send "START" command to the arduino.
    _port.WriteLine("START");
    // Start reading the data coming through the serial port.
    while (_looping)
    {
        strData = _port.ReadLine(); // blocking call.
        print(strData);
        Thread.Sleep(0);
    }
}

The reading happens in the following line:

strData = _port.ReadLine(); // blocking call.

but it does not block or freeze unity because it's happening in a separate thread.

By the way, if you wanted to write something to the port, simply write:

  public void WriteToArduino()
  {
        _port.WriteLine("YourMessageHere");
  }

You can call WriteToArduino() anywhere in your game. It does not need to be in any special thread or something.