/*
  Takt_M328P.c
  Arduino UNO rev3

  Created: 05.06.2022
  Author : ukhl
*/

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

#define LED (1<<PINB5)

volatile uint16_t CTCon;
volatile uint16_t CTCoff;
volatile uint16_t freq100 = 1000; // Frequenz in 1/100 Hz; 1000 = 10,00 Hz

ISR ( TIMER1_COMPA_vect ) {

  PORTB ^= LED;
  if ( PINB & LED ) {
    OCR1A = CTCon;
  } else {
    OCR1A = CTCoff;
  }
}

void init(void) {
  DDRB |= ( LED );

  ////  Timer
  TCCR1B |= (1 << WGM12) | (0 << CS12) | (1 << CS11) | (1 << CS10); // CTC , clk / 64
  OCR1A = 25000000 / freq100 - 1;  // wird im Timer Interrupt gesetzt.
  TIMSK1 |= (1 << OCIE1A);
}

int main(void) {
  init();
  sei();

  CTCoff = 250 * 1  ;                        // 1 ms Impuls dauer
  CTCon  = 25000000 / freq100 - CTCoff - 1 ; // Frequenz.

  while (1)  {
    /* nichts zu tun */
  }
}