#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 initRTC (void)
{ 
  // Initialize RTC //   

  RTC.CLKSEL = 0;                           // internal 32kHz, Periodendauer 30,518µs
  RTC.PER = 32;                             // set period -->> 1000ms / 31,25ms
  RTC.CMP = 16;
  //RTC.INTCTRL = RTC_CMP_bm | RTC_OVF_bm; 
     
  uint8_t temp = 0;   
  temp |= RTC_PRESCALER_DIV1024_gc;     // Prescaler 1024 -->> 30,518µs * 1024 = 31,250ms
  temp |= RTC_RUNSTDBY_bm;
  temp |= RTC_RTCEN_bm;                 // enabled  
  RTC.CTRLA = temp;                     // set Config  
  
  while (RTC.STATUS > 0) { ; }          // wait for all register to be synchronized
}

ISR(RTC_CNT_vect)
{
    PORTA_OUTTGL = PIN3_bm;
    RTC.INTFLAGS = RTC_CMP_bm | RTC_OVF_bm; 
}

int main(void)
{	
    initInternal20MHzOscillator();
    initRTC();
    PORTA_DIR = PIN3_bm;

    while (1) 
    {	
        if (RTC.INTFLAGS > 0) {
            PORTA_OUTTGL = PIN3_bm;
            RTC.INTFLAGS = RTC_CMP_bm | RTC_OVF_bm;   
        }

    }
}