Error message "error disabling serialEvent for "COM3" null" using Arduino

Question

I have simplified the question very much. I am trying to send the encoder motor feed back to Processing which will be displayed on the processing. But the error is coming something like:

error disabling serialEvent for "COM3" null

Processing:

import processing.serial.*;

Serial port;
int index = 0;
String lmotor, rmotor, data, status;

void setup()
{
    size(500, 500);
    port = new Serial(this, "COM3", 9600);
    port.bufferUntil('A');
}

void serialEvent(Serial port)
{
    if(data != null)
    {
        println(data);
        data = port.readStringUntil('A');
        data = data.substring(0, data.length()-1);
        index = data.indexOf(",");
        lmotor = data.substring(0, index);
        rmotor = data.substring(index+1, data.length());
    }
}

void draw()
{
    background(255);
    textSize(100);
    fill(random(0, 255), 0, random(0, 255));
    text(lmotor, 50, 150);
    textSize(100);
    fill(0, random(0, 255), random(0, 255));
    text(rmotor, 300, 150);
}

Arduino/AVR code:

#include <avr/io.h>
#include <util/delay.h>

#define SETBIT(ADDRESS,   BIT) (ADDRESS|=(1<<BIT));
#define CLEARBIT(ADDRESS, BIT) (ADDRESS&=~(1<<BIT));
#define CHECKBIT(ADDRESS, BIT) (ADDRESS & (1<<BIT));

char c;
int sfl=0, sfr=0, y=0, temp;

void interrupt_init()
{
    cli();
    EIMSK = 0x03;
    EICRA = 0x0A;
    sei();
}

void encoder_pin_config_init()
{
    DDRD = DDRD & 0xF3;
    // Internal pull-up resistors
    SETBIT(PORTD, PD3);
    SETBIT(PORTD, PD2);
}

void byte_init (int baud)
{
    UBRR0H = (baud>>8);                  // Shift the register right by 8 bits
    UBRR0L = baud;                       // Set baud rate
    UCSR0B |= (1<<TXEN0)  | (1<<RXEN0);  // Enable receiver and transmitter
    UCSR0C |= (1<<UCSZ00) | (1<<UCSZ01); // 8-bit data format
}

void byte_transmit (unsigned char data)
{
    while (!(UCSR0A & (1<<UDRE0)))  // Wait while register is free
        ;
    UDR0 = data;                    // Load data in the register
}

unsigned char byte_receive (void)
{
    while(!(UCSR0A) & (1<<RXC0))   // Wait while data is being received
        ;
    return UDR0;                   // Return 8-bit data
}

void setup()
{
    interrupt_init();
    byte_init(103);
    encoder_pin_config_init();

    Serial.begin(9600);

    pinMode(4, HIGH);
    pinMode(5, OUTPUT);
    pinMode(6, OUTPUT);
    pinMode(7, OUTPUT);
    pinMode(9, OUTPUT);
    pinMode(10, OUTPUT);

    digitalWrite(9, HIGH);
    digitalWrite(10, HIGH);
}

void loop()
{
    digitalWrite(4, HIGH);
    digitalWrite(5, LOW);
    digitalWrite(6, HIGH);
    digitalWrite(7, LOW);
    temp = sfl;
    while(temp>0)
    {
        y = temp%10;
        c = y + '0';
        byte_transmit(c);
        temp = temp/10;
    }
    byte_transmit(',');
    temp = sfr;
    while(temp>0)
    {
        y = temp%10;
        c = y + '0';
        byte_transmit(c);
        temp = temp/10;
    }
    byte_transmit('A');

    digitalWrite(5, LOW);
    digitalWrite(6, LOW);
    digitalWrite(7, LOW);
    digitalWrite(4, LOW);
}

ISR(INT0_vect)
{
    sfl++;
}

ISR(INT1_vect)
{
    sfr++;
}

Answer 1

You're hardcoding COM3. The port may not be correct.

From the Serial reference:

// Example by Tom Igoe

import processing.serial.*;

// The serial port:
Serial myPort;

// List all the available serial ports:
printArray(Serial.list());

// Open the port you are using at the rate you want:
myPort = new Serial(this, Serial.list()[0], 9600);

// Send a capital A out the serial port:
myPort.write(65);

Notice that this code uses the Serial.list() function to list the valid ports. Try using this to figure out which ports are being used.

Answer 2

One thing you must do is use the volatile keyword for the variables you're modifying inside the ISRs. Please read up here on Stack Overflow—or anywhere—on why you need volatile. Your code is almost guaranteed to not work if you modify a plain int inside an ISR. That's the first thing that jumps right out at me.

The other thing that I wonder about is using low-speed serial to communicate motor position encoding. Unless your motor is moving very slowly, you'll want to use fast interrupts to catch your encoder signals. This is very unconventional and is likely not to work as you expect.