// ATtiny824

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

uint8_t i;                                                  // SW counter
uint8_t j;                                                  // SW counter

ISR(RTC_PIT_vect)
{
  RTC.PITINTFLAGS = RTC_PI_bm;                              // clear PIT flag
}

int main(void)
{
  _PROTECTED_WRITE(CLKCTRL.MCLKCTRLB, CLKCTRL_PDIV_10X_gc | CLKCTRL_PEN_bm);  // 2MHz main clock

  PORTA.PIN1CTRL = PORT_ISC_INPUT_DISABLE_gc;               // disable PA1 digital input buffer
  PORTA.PIN2CTRL = PORT_ISC_INPUT_DISABLE_gc;               // disable PA2 digital input buffer
  PORTA.PIN3CTRL = PORT_ISC_INPUT_DISABLE_gc;               // disable PA3 digital input buffer
  PORTA.PIN4CTRL = PORT_ISC_INPUT_DISABLE_gc;               // disable PA4 digital input buffer
  PORTA.PIN5CTRL = PORT_ISC_INPUT_DISABLE_gc;               // disable PA5 digital input buffer
  PORTA.PIN6CTRL = PORT_ISC_INPUT_DISABLE_gc;               // disable PA6 digital input buffer
  PORTA.PIN7CTRL = PORT_ISC_INPUT_DISABLE_gc;               // disable PA7 digital input buffer
  PORTB.PIN0CTRL = PORT_ISC_INPUT_DISABLE_gc;               // disable PB0 digital input buffer
  PORTB.PIN1CTRL = PORT_ISC_INPUT_DISABLE_gc;               // disable PB1 digital input buffer
  PORTB.PIN2CTRL = PORT_ISC_INPUT_DISABLE_gc;               // disable PB2 digital input buffer
  PORTB.PIN3CTRL = PORT_ISC_INPUT_DISABLE_gc;               // disable PB3 digital input buffer

  RTC.CLKSEL = RTC_CLKSEL_INT1K_gc;                         // 1024 Hz from OSCULP32K
  while(RTC.PITSTATUS > 0) {}                               // wait for RTC.PITCTRLA synchronization
  RTC.PITINTCTRL = RTC_PI_bm;                               // enable periodic interrupt
  RTC.PITCTRLA = RTC_PERIOD_CYC8192_gc | RTC_PITEN_bm;      // 8s, enable PIT

  TCB0.CCMP = 0x9C3F;                                       // 40ms @ 1MHz TCB0 clock
  TCB0.CTRLA = TCB_CLKSEL_DIV2_gc | TCB_ENABLE_bm;          // 1 MHz clock, enable TCB0


  PORTA.DIRSET = PIN3_bm;                                   // PA3 output (LED)

  SLPCTRL.CTRLA = SLPCTRL_SMODE_PDOWN_gc | SLPCTRL_SEN_bm;  // POWER-DOWN sleep mode, Sleep Enable

  sei();                                                    // enable interrupts

  while(1)
  {
    if(TCB0.INTFLAGS)
    {
      TCB0.INTFLAGS = TCB_CAPT_bm;                          // clear TCB0 interrupt flag
      i++;
      if(i == 4)                                            // 160 ms
      {
        PORTA.OUTSET = PIN3_bm;                             // PA3 on
      }
      else if(i == 5)                                       // 200 ms
      {
        PORTA.OUTCLR = PIN3_bm;                             // PA3 off
        i = 0;
        j++;
        if(j == 6)                                          // 6 pulses
        {
          j = 0;
          TCB0.CNT = 0;                                     // clear TCB0
          __asm__ __volatile__ ("sleep" "\n\t" :: );
        }
      }  
    } 
  } 
}