Problem communicating via serial port in Linux

Question

Hello,
I am trying to transfer data via serial port, in Linux.
But it is impossible till now!
I get Runtime exception.
Here is my code:
public class Main {
    public Main() {
    int num=5;
    int[] array = new int[5];
    public static void main(String args[])  {
        java.awt.EventQueue.invokeLater(new Runnable() {
            public void run() {
                array[0]=1;
                array[1]=2;
                array[2]=3;
                array[3]=4;
                array[4]=5;
                new ParallelCommunication(num,array);
import java.io.*;
import java.util.*;
import javax.comm.*; // for SUN's serial/parallel port libraries
//import gnu.io.*; // for rxtxSerial library
public class ParallelCommunication implements Runnable, SerialPortEventListener {
   static CommPortIdentifier portId;
   static CommPortIdentifier saveportId;
   static Enumeration portList;
   InputStream inputStream;
   SerialPort serialPort;
   Thread readThread;
   static OutputStream outputStream;
   static boolean outputBufferEmptyFlag = false;
   int num;
   int[] array;
   public ParallelCommunication(int this_num,int[] this_array) {
      boolean portFound = false;
      String defaultPort;
      num = this_num;
     array=new int[this_array.length];     
      array = this_array;     
      // determine the name of the serial port on several operating systems
      String osname = System.getProperty("os.name","").toLowerCase();
      if ( osname.startsWith("windows") ) {
         // windows
         defaultPort = "COM1";
      } else if (osname.startsWith("linux")) {
         // linux
        defaultPort = "/dev/ttyS0";
      } else {
         System.out.println("Sorry, your operating system is not supported");
         return;
//      if (args.length > 0) {
//         defaultPort = args[0];
      System.out.println("Set default port to "+defaultPort);
      // parse ports and if the default port is found, initialized the reader
      portList = CommPortIdentifier.getPortIdentifiers();
      while (portList.hasMoreElements()) {
         portId = (CommPortIdentifier) portList.nextElement();
         if (portId.getPortType() == CommPortIdentifier.PORT_SERIAL) {
            if (portId.getName().equals(defaultPort)) {
               System.out.println("Found port: "+defaultPort);
               portFound = true;
               // init reader thread              
               initialize();
               break;
      if (!portFound) {
         System.out.println("port " + defaultPort + " not found.");
   public void initwritetoport() {
      // initwritetoport() assumes that the port has already been opened and
      //    initialized by "public void initialize()"
      try {
         // get the outputstream
         outputStream = serialPort.getOutputStream();
      } catch (IOException e) {}
      try {
         // activate the OUTPUT_BUFFER_EMPTY notifier
         serialPort.notifyOnOutputEmpty(true);
      } catch (Exception e) {
         System.out.println("Error setting event notification");
         System.out.println(e.toString());
         System.exit(-1);
   public void writetoport(int counter) {
      try {
         // write string to serial port
         outputStream.write(String.valueOf(array[counter]).getBytes());
      } catch (IOException e) {}
   public void initialize() {
      // initalize serial port
      try {
         serialPort = (SerialPort) portId.open("SimpleReadApp", 2000);
      } catch (PortInUseException e) {System.out.println("Port In Use.");}  //******Here is the Exception******
      try {
         inputStream = serialPort.getInputStream();
      } catch (IOException e) {}
      try {
         serialPort.addEventListener(this);
      } catch (TooManyListenersException e) {}
      // activate the DATA_AVAILABLE notifier
      serialPort.notifyOnDataAvailable(true);
      try {
         // set port parameters
         serialPort.setSerialPortParams(9600, SerialPort.DATABITS_8,
                     SerialPort.STOPBITS_1,
                     SerialPort.PARITY_NONE);
      } catch (UnsupportedCommOperationException e) {}
      // start the read thread
      readThread = new Thread(this);
      readThread.start();
   public void run() {
      // first thing in the thread, we initialize the write operation
     initwritetoport();     
     for(int i=0; i<=num_of_inputs; i++) {
        // write string to port, the serialEvent will read it
        writetoport(i);
     serialPort.close();     
   public void serialEvent(SerialPortEvent event) {
      switch (event.getEventType()) {
      case SerialPortEvent.BI:
      case SerialPortEvent.OE:
      case SerialPortEvent.FE:
      case SerialPortEvent.PE:
      case SerialPortEvent.CD:
      case SerialPortEvent.CTS:
      case SerialPortEvent.DSR:
      case SerialPortEvent.RI:
      case SerialPortEvent.OUTPUT_BUFFER_EMPTY:
         break;
      case SerialPortEvent.DATA_AVAILABLE:
         // we get here if data has been received
         byte[] readBuffer = new byte[20];
         try {
            // read data
            while (inputStream.available() > 0) {
               int numBytes = inputStream.read(readBuffer);
            // print data
            String result  = new String(readBuffer);
            System.out.println("Read: "+result);
         } catch (IOException e) {}
         break;
}...and the outcome is :
Exception in thread "AWT-EventQueue-0" java.lang.RuntimeException:
Error opening "/dev/ttyS0"
tcgetattr(): Input/output error
at com.sun.comm.LinuxDriver.getCommPort(LinuxDriver.java:66)
at javax.comm.CommPortIdentifier.open(CommPortIdentifier.java:369)
at ParallelCommunication.initialize(ParallelCommunication.java:128)
I have searched a lot and I couldn't find a solution.
Thank you.

Answer 1

I'm having the same problem this helped somewhat debug the problem
http://bloggerdigest.blogspot.com/2006/11/linux-serial-com-port-diagnostic-test.html
I'm running Suse 10.3 and apparently it does not recognize my serial ports. So before
you can test your Java code you have to figure out how to make linux see the ports.
If I find a solution I'll let you know but if you find one first let me know. Thanks.