read from com port

Jeg har problemer med at når min kode når til ReadData = comport.ReadExisting(); så får jeg denne felj nogen der har en løsning på mit problem (An unhandled exception of type 'System.StackOverflowException' occurred in System.dll)



public void InitializeBackgroundWorker()
        {
           
            backgroundWorker1.WorkerSupportsCancellation = true;
            backgroundWorker1.DoWork += new DoWorkEventHandler(backgroundWorker1_DoWork);
            backgroundWorker1.RunWorkerCompleted += new RunWorkerCompletedEventHandler(backgroundWorker1_RunWorkerCompleted);
           
           
        }

private void backgroundWorker1_DoWork(object sender, DoWorkEventArgs e)
        {
            BackgroundWorker worker = sender as BackgroundWorker;
            e.Result = readstring(worker, e); //Jeg kalder readstring
           
        }   
public void openport()
        {
            //, parity: Parity.Even, dataBits: 8, stopBits: StopBits.One
            BaudRateInt = Convert.ToInt32(BaudRate);
            comport = new SerialPort(portName: Port, baudRate: BaudRateInt);
            //comport.ReadTimeout = 100000;
            comport.Handshake = Handshake.None;
            //comport.DataReceived += SerialDataReceivedEventHandler(readstring);

            comport.Open();
        }

string readstring(BackgroundWorker worker, DoWorkEventArgs e)
        {         
            if (worker.CancellationPending)
            {
                e.Cancel = true;
            }
               
            else
            {
                if (results != "!PA1")
                {
                    try
                    {
                        ReadData = comport.ReadExisting();
                        char[] delimiterChars = { ',' };
                        string[] words = ReadData.Split(delimiterChars);
                        data = words[0];
                        results = data;
                        readstring(worker, e);
                     
                    }
                    catch (TimeoutException)
                    {
                        readstring(worker, e);
                    }
                    catch (IOException)
                    {
                        readstring(worker, e);
                    }

                }
            }
           
            return ReadData;
        }