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

#define F_CPU 16500000L

#define SERIAL_TX PB3
#define SERIAL_RX PB0

SoftwareSerial mySerial(SERIAL_RX, SERIAL_TX);

int main(void) {
    uint8_t ch;

    mySerial.begin(9600);
    _delay_ms(100); // Waits serial initialization

    sei(); // Enables the global interrupt

    DDRB |= (0x01 << PB1); // Set PB1 (6) as OUTPUT

    mySerial.write("Type in character or string...\n");

    while (1) {
        if (mySerial.available()) {
            PORTB ^= (1 << PB1); // Toggle on/off LED
            ch = mySerial.read();
            mySerial.write(ch);
        }
        _delay_ms(5);
        PORTB = ~(1 << PB1); // Turn off LED
    }

    return (0);
}