AVR morse hello world

main.c

#include <avr/io.h>
#include <avr/interrupt.h>
#include <avr/sleep.h>
#include <stdint.h>

// First four bits encode morse code - 1 is dash and 0 is dot
// then goes length of code
char message[] = {
    0x04, // .... - H
    0x01, //    . - E
    0x44, // .-.. - L
    0x44, // .-.. - L
    0x73, //  --- - O
    0x00, // space
    0x33, //  .-- - W
    0x73, //  --- - O
    0x23, //  .-. - R
    0x44, // .-.. - L
    0x43, //  -.. - D
};

// index of letter
uint8_t messageIndex = 0;
// index of morse symbol, 0 - leftmost
uint8_t subIndex = 0;
// flag, whether it is pause between morse symbols 
// not necessary, PORTD7 bit can be used, but more readable
uint8_t pause = 1;

const uint8_t MaxIndex = sizeof(message)/sizeof(char);
// number of cycles for single morse dot symbol
const uint16_t DotCyclesNum = 5000;


int main(void)
{
    //Setup the clock
    cli();            //Disable global interrupts
    TCCR1B |= 1<<CS11 | 1<<CS10;  //Divide by 64
    TCCR1B |= 1<<WGM12;     //Put Timer/Counter1 in CTC mode
    OCR1A = DotCyclesNum;    //set timer period
    TIMSK |= 1<<OCIE1A;        //enable timer compare interrupt

    //Setup the I/O for the LED

    DDRD |= (1<<DDD7);     //Set PortD Pin7 as an output
    PORTD |= (0<<PORTD7);        //Set PortD Pin7 low to turn off LED

    set_sleep_mode(SLEEP_MODE_IDLE);
    sleep_enable();

    sei();            //Enable global interrupts

    
    while(1) { sleep_cpu(); }          //Loop forever, interrupts do the rest
}

// signal dot or dash
void proceedMessageDisplay() {
    uint8_t maxSubIndex = message[messageIndex] & 0x0F; // length of letter in morse code
    // if one - signal dash, else dot
    if (message[messageIndex] & (0x1 << (3 + maxSubIndex - subIndex))) {
        OCR1A = 3*DotCyclesNum;
    } else {
        OCR1A = DotCyclesNum;
    }
}

void pauseMessageDisplay() {
    // there are three types of pauses:
    uint8_t symbolPause = 1,
         characterPause = 0,
              wordPause = 0;

    subIndex += 1;
    if (subIndex >= (message[messageIndex] & 0x0F)) {
        // moving to next letter 
        symbolPause = 0;
        characterPause = 1;
        subIndex = 0;
        messageIndex += 1;
    } 

    uint8_t overflow = messageIndex == MaxIndex;
    if (overflow || message[messageIndex] == 0x00) {
        // moving to next word or cycling
        characterPause = 0;
        wordPause = 1;
        if (overflow) {
            messageIndex = 0;
        } else {
            messageIndex += 1;
        }
    }
    
    if (symbolPause) {
        OCR1A = DotCyclesNum;
    } else if (characterPause) {
        OCR1A = 3*DotCyclesNum;
    } else {
        OCR1A = 7*DotCyclesNum;
    }
}

ISR(TIMER1_COMPA_vect)      //Interrupt Service Routine
{
    cli();
    if (pause) {
        proceedMessageDisplay();
    } else {
        pauseMessageDisplay();
    }
    
    pause ^= 1;

    SFIOR |= 1<<PSR10; // reseting timer
    sei();

    PORTD ^= (1<<PORTD7); // switching led
}