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

void initInternal20MHzOscillator (void)
{    
    // 20MHz mittels Fuse ausgewählt //
    CPU_CCP = CCP_IOREG_gc;
    CLKCTRL.OSCHFCTRLA = CLKCTRL_RUNSTDBY_bm | CLKCTRL_AUTOTUNE_0_bm;

    // Main Clock Prescaler
    CPU_CCP = CCP_IOREG_gc;
    CLKCTRL.MCLKCTRLB = 0;         // disable Prescaler, Default 6

    // wait internal oscillator is stable
    while(!(CLKCTRL.MCLKSTATUS & CLKCTRL_OSCHFS_bm))
    { ; }

    // Select Internal Clock Source and enable Pin Clock Out
    CPU_CCP = CCP_IOREG_gc;
    CLKCTRL.MCLKCTRLA = (CLKCTRL_CLKSEL_OSCHF_gc | CLKCTRL_CLKOUT_bm);        
  
    // wait for system oscillator changing to finish
    while (CLKCTRL.MCLKSTATUS & CLKCTRL_SOSC_bm)
    { ; }
}

void initRTCPIT (void)
{ 
  // Initialize RTC //   

  RTC.CLKSEL = 0;                  // internal 32kHz, Periodendauer 30,518µs
  //RTC.PITINTCTRL = RTC_PI_bm;
  uint8_t temp = 0;
  temp |= RTC_PERIOD_3_bm;   // Bit 6
  temp |= RTC_PERIOD_2_bm;   // Bit 5
  temp |= RTC_PERIOD_0_bm;   // Bit 3
  temp |= RTC_PITEN_bm;
  RTC.PITCTRLA = temp;
  
  while (RTC.PITSTATUS > 0) { ; }       // wait for all register to be synchronized
}

ISR(RTC_PIT_vect)
{
   PORTA_OUTTGL = PIN3_bm;
   RTC.PITINTFLAGS = RTC_PI_bm;
}

int main(void)
{	
    initInternal20MHzOscillator();
    initRTCPIT();
    PORTA_DIR = PIN3_bm;
    PORTA_OUTTGL = PIN3_bm; _delay_ms(250);
    PORTA_OUTTGL = PIN3_bm; _delay_ms(250);
    PORTA_OUTTGL = PIN3_bm; _delay_ms(250);
    PORTA_OUTTGL = PIN3_bm; _delay_ms(250);
    while (1) 
    {	 
   
        if (RTC.PITINTFLAGS > 0) {
            PORTA_OUTTGL = PIN3_bm;
            RTC.PITINTFLAGS = RTC_PI_bm;
        }

  
    }
}