A game of catch between Arduino and Processing

Question

The following code makes Arduino and Processing pass an 'A' back and forth like hot potato:

PROCESSING SENDS 'A' TO ARDUINO

import processing.serial.*; //import the Serial library
Serial mySerial;  //the Serial port object

void setup() 
{
  mySerial = new Serial(this, Serial.list()[7], 9600); //Pick whichever works
  mySerial.bufferUntil('\n');
}

void serialEvent( Serial mySerial) 
{
  println("writing A...");
  delay(1000);                   //How I defined this is not relevant. Trust me.
  mySerial.write('A');        //Send 'A' to Arduino
}

ARDUINO SENDS 'A' BACK TO PROCESSING

void setup()
{
  Serial.begin(9600);
}

void loop()
{
  delay(1000);
  Serial.println('A');      //Send 'A' back to Processing
}

What happens? Well... the game works for about ten exchanges (how do I know? well I get the "writing A..." message five times, and my use of bufferUntil() tells me that each of those messages were prompted by receiving a Serial.println('A') from the Arduino) BUT then Processing interrupts with the following error:

Error, disabling serialEvent() for /dev/tty.usbmodem1421
null
java.lang.RuntimeException: Error reading from serial port /dev/tty.usbmodem1421: Port not opened
    at processing.serial.Serial.serialEvent(Unknown Source)
    at jssc.SerialPort$LinuxEventThread.run(SerialPort.java:1299)
Could not run the sketch (Target VM failed to initialize).
For more information, read revisions.txt and Help → Troubleshooting.

What's going on?

Dave · Accepted Answer · 2014-06-30 06:01:31Z

Port not opened

was the keyword in the error message: The Serial Port randomly closes from time to time. The solution is to continually force it open in draw:

Serial serial;
boolean serialInited;


void draw () {
    if (serialInited) {
        // serial is up and running
        try {
            byte b = serial.read();
            // fun with serial here...
        } catch (RuntimeException e) {
            // serial port closed :(
            serialInited = false;
        }
    } else {
        // serial port is not available. bang on it until it is.
        initSerial();
    }
}

void initSerial () {
    try {
        serial = new Serial(this, Serial.list()[0], BAUD_RATE);
        serialInited = true;
    } catch (RuntimeException e) {
        if (e.getMessage().contains("<init>")) {
            System.out.println("port in use, trying again later...");
            serialInited = false;
        }
    }
}

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