Flow Controll Settings for Serial Communication between Java RXTX and Arduino

Question

I have a simple sketch on my Seeeduino Mega 1.22 which just displays the serial input on a LCD Display. Using lynx term and the arduino serial monitor works fine: sent input is being displayed. The trouble starts when I want to start serial communication between my Java programm, running in Eclipse on a Win7 x64 machine, and the Seeeduino. I'm using the RXTX x64 build. The programm is intended to send and receive some string.getBytes() via the open port. Receiving on the Java side works, but receiving on the Arduino side fails.

It seems that the problem is the proper Flow Control setting. I saw that some people had the same issue like here Issues receving in RXTX

But this solution does not work for me. If I set the FlowControl to None, than I get only a block icon on the display, indicating, that the serial connection has been established, but nothing else. If I set the FlowControl to RCTS_IN | RCTS_OUT, then I get the string bytes only on the display when I close the established connection.

Why is the data only send when I close the connection (Flushing the out stream did not help as well) ? What am I doing wrong with the Flow Controll settings?

This is the modified connect() method I'm using.

void connect(String portName) throws Exception {
        CommPortIdentifier portIdentifier = CommPortIdentifier
                .getPortIdentifier(portName);
        if (portIdentifier.isCurrentlyOwned()) {
            System.out.println("Error: Port is currently in use");
        } else {
            CommPort commPort = portIdentifier.open(this.getClass().getName(),
                    2000);

            if (commPort instanceof SerialPort) {
                SerialPort serialPort = (SerialPort) commPort;
                serialPort.setSerialPortParams(115200, SerialPort.DATABITS_8,
                        SerialPort.STOPBITS_1, SerialPort.PARITY_NONE);

                try {
                  serialPort.setFlowControlMode(
                  //      SerialPort.FLOWCONTROL_NONE);
                  // OR
                  // If CTS/RTS is needed
                  //serialPort.setFlowControlMode(
                        SerialPort.FLOWCONTROL_RTSCTS_IN |
                        SerialPort.FLOWCONTROL_RTSCTS_OUT);
                } catch (UnsupportedCommOperationException ex) {
                  System.err.println(ex.getMessage());
                }

                serialPort.setRTS(true);

                in = serialPort.getInputStream();
                out = serialPort.getOutputStream();

                (new Thread(new SerialWriter(out))).start();

                serialPort.addEventListener(new SerialReader(in, this));
                serialPort.notifyOnDataAvailable(true);

            } else {
                System.out.println("Error: Only serial ports are to use!");
            }
        }
    }

Thanks in advance for your time

Answer 1

Solved it. It was not the buffer, as many suggested it. The problem was, that the Seeeduinos RST Switch on the board was set to automatic. Setting it to manual, solved the problem. No Flow-Controll needed.