AVR Timer Compare Interrupt

Recently I plan to make a Bluetooth receiver myself and connect it to the quadcopter, so I study how to output 4-channel PWM.

The plan is to use the timer interrupt, calculate the duty cycle during the interrupt, and then switch the specified PIN pin between high and low levels.

It took me a long time to understand the usage of this. The following code implements an interrupt once per second on the 16M ATMEGA8 chip.

void setup() {

    pinMode(13, OUTPUT);

   //Disable interrupts 

    cli();

    //TCNT1 is the accumulator register here, which increases once per clock

    //TCNT1 = 0;

    //TCCR1 control register

    TCCR1A = 0;

    TCCR1B = 0;

    //OCR1A is the accumulation upper limit register. Adjusting this value can control the frequency.

    // Here 15625 is calculated as follows: 16M / 1024 = 15625

    OCR1A = 15625;

    // Set the frequency division to 1024

    // Here _BV is a macro, which is the function of 1 << n. The various ways of setting bits feel quite fragmented.

    TCCR1B |= (_BV(CS12) | _BV(CS10));

    // The CTC mode controlled by WGM12 means that TCNT1 will be cleared to 0 by itself, otherwise it needs to be cleared to 0 manually

    TCCR1B |= 1 << WGM12;

    // Set up comparison interrupt

    bitSet(TIMSK, OCIE1A);

    // Enable interrupt

    be();

}

int flag = 0;

void loop() {

  // put your main code here, to run repeatedly:

}

ISR(TIMER1_COMPA_vect) {

    if (flag == 0) 

    {

        flag = 1;

        digitalWrite(13, HIGH);

    }

    else

    {

        flag = 0;

        digitalWrite(13, LOW);

    }

}