ATTINY804 RTC bekomme ich nicht hin

#define F_CPU 20000000

#include <avr/io.h>

#include <avr/cpufunc.h>

#include <avr/interrupt.h>

#include <util.h>

#include <util/delay.h>

uint64_t systemtick64_10ms = 0;

void CLOCK_init(){

  ccp_write_io((void*)& CLKCTRL.MCLKCTRLA,0);  // Masterclock set to 16/20MHz, CLK_OUT is off

  ccp_write_io((void*)& CLKCTRL.MCLKCTRLB,0);  // no division, prescaler disabled

  RTC.CLKSEL = 0x00;                  // internal rtc

  RTC.CNT = 16384;  // 2Hz for Debugtest, original 327                  // 16Bit counter value for 10ms period @ prescaler 0 & 32768Hz (10.009ms)

  RTC.CTRLA =  0x01;                  // no prescaler - rtc enable

  RTC.INTCTRL = 0b00000001;              // Overflow

}

void pinout_init(){

  PORTA.DIR = 0b01001000;    // PA 3 & 6 are output, others are input

  PORTA.PIN3CTRL = 0x00;    // Signal inverted by transistor - writing 1 to this output will pull the reset on mainboard to 0V

  PORTA.PIN6CTRL = 0x80;    // Signal inverted on µC, writing 1 will pull CFGMODE to 0 (activate mode)

}

int main(){

  CLOCK_init();

  pinout_init();

  sei();

  while (1) {

    ;

  }

}

ISR(RTC_CNT_vect){          // OVF for CTC Mode

  PORTA.OUTTGL |= PIN6_bm;    // toggelt CFGMODE zu Testzwecken

  //RTC.INTFLAGS = RTC_OVF_bm;    // clear interrupt

}