Asynchronous Serial-to-Ethernet Device Servers

Overview

RS-232 Serial Port

Space and Mark

DCE and DTE

Flow Control

Speed, Data Bits, Stop Bits, and Parity

TINI and Networking

Examples

Figure 1.

Virtual Modems

      public static void main(String args[])
      {
         TINIOS.setSerialBootMessagesState(false);
         TINIOS.setDebugMessagesState(false);
         TINIOS.setConsoleOutputEnabled(false);

         System.out.println("Connecting to serial0 at 9600bps, "
                            "listening on TCP port 8001");

         try {
            CommPortIdentifier portId = CommPortIdentifier.getPortIdentifier("serial0");
            SerialPort port = (SerialPort) portId.open("VModemTINI", 10000);

            TINIOS.setRTSCTSFlowControlEnable(1, false);
            TINIOS.setRTSCTSFlowControlEnable(0, true);

            TCPSerialVirtualModem modem = new TCPSerialVirtualModem(port,
                                  /* Comm speed */ 9600, /*TCP Port */ 8001);

            modem.processInput();
         }
         catch (Exception e) {
         System.out.println("Exception: "+e.toString());
         }
      }

      /** Creates a new VirtualModem connected to a serial port on
       * one end and a TCP port on the data side.
       * serial -- the serial port this VirtualModem talks to.
       * speed -- the speed the serial port should be set to.
       * tcpport -- the TCP port this VirtualModem listens on.
       * throws IOException when there's a problem with the serial or TCP port.
       */
      public TCPSerialVirtualModem(SerialPort serial, int speed, int tcpport)
             throws IOException
      {
         super(serial);

         try {
            serial.setSerialPortParams(speed, SerialPort.DATABITS_8,
                                       SerialPort.STOPBITS_1, SerialPort.PARITY_NONE);
         }
         catch (UnsupportedCommOperationException e) {
            throw new IOException();
         }

         ...

         serverSock = new ServerSocket(tcpport, 1); // backlog of one
         listenThread = new listenInbound();
         listenThread.start();
      }

      public void run()
         {
            int rc;
            Socket s;

            while (running) {
               s = null; // No incoming connection request
               try {
                  answered = false;
                  s = serverSock.accept();

                  // Discard incoming connection if already connected
                  if (connected)
                     throw new IOException();

                  sock = s; // for answer()
                  ...

UPS Monitor

         ...
         // Listen for DTR changes
         try {
            port.addEventListener(this);
         } catch (TooManyListenersException e) {
            ...
         }
         port.notifyOnDSR(true);
         ...

      public void serialEvent(SerialPortEvent ev)
      {
         try {
            if (ev.getEventType() == SerialPortEvent.DSR)
               ...
         } catch ...
         ...
      }

      // Listen to incoming UDP requests
      private class listenUDPThread extends Thread
      {
         private DatagramSocket sock;
         private byte[] buffer;
         private DatagramPacket dp;

         public listenUDPThread(DatagramSocket s)
         {
            sock = s;
            buffer = new byte[BUF_SIZE];
            dp = new DatagramPacket(buffer, buffer.length);
         }

         public void run()
         {
            while (running) {
               try {
                  sock.receive(dp);
                  byte[] data = parseCommand(buffer, dp.getLength());
                  sock.send(new DatagramPacket(data, data.length,
                            dp.getAddress(), dp.getPort()));
               }
               catch (Exception e) {
               }
            }
            try {
               sock.close();
            }
            catch (Exception e) {
            }
         }
      }

Generic Serial-to-Ethernet Application

      public GenericBridge()
      {
         ...
         running = true;
         dcThread = new dataCopy();
         dcThread.start();
      }

      // Thread that copies everything from dataIn to dataOut
      private class dataCopy extends Thread
      {
         public void run()
         {
            int r = 0;
            while (running && r >= 0) {
               try {
                  synchronized (threadLock) {
                     r = dataIn.read(dataBuffer);
                     if (r > 0)
                        dataOut.write(dataBuffer, 0, r);
                  }
               }
               catch (Exception e) {
                  r = -1;
                  ...       // Handle error
               }
            }
         }
      }

Conclusion

1. NASA has trouble deciphering computer tapes from this area, so the comparison is valid.
2. Refer to application note 196, "Designing a Virtual Modem Using TINI."
3. See www.networkupstools.org/