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

volatile uint8_t button;             // flag "button"
volatile uint8_t indicate;           // flag "indicate"
volatile uint8_t tcb;                // TCB SW flag
uint16_t adc_bat;                    // battery voltage ADC Value

ISR(PORTA_PORT_vect)                 // button
{
  button = 1;                         // set "button" flag
  indicate = 1;                       // set "indicate" flag
  PORTA.INTFLAGS = PORT_INT2_bm;      // clear PA2 interrupt flag
}

ISR(TCB0_INT_vect)                // 50ms after button pressed
{
  tcb = 1;                        // set TCB SW flag
  TCB0.CTRLA = 0;                 // disable TCB
  TCB0.CNT = 0;                   // clear TCB
  TCB0.INTFLAGS = TCB_CAPT_bm;    // clear TCB interrupt flag
}

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

  PORTA.PIN3CTRL = PORT_ISC_INPUT_DISABLE_gc;   // disable PA3 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

  PORTA.DIRSET = PIN1_bm;                       // PA1 output
  PORTA.PIN2CTRL = PORT_PULLUPEN_bm | PORT_ISC_LEVEL_gc;  // PA2 pull-up, low level sense interrupt

  VREF.CTRLA = VREF_ADC0REFSEL_2V5_gc;         // 2.5V ADC voltage reference

  ADC0.CTRLC = ADC_REFSEL_VDDREF_gc | ADC_PRESC_DIV8_gc;  // VDD as reference, 250kHz ADC clock
  ADC0.MUXPOS = ADC_MUXPOS_INTREF_gc;          // internal reference VREF as ADC input
  ADC0.CTRLD = ADC_INITDLY_DLY64_gc;           // initialization/start-up delay (256µs)
  ADC0.CTRLB = ADC_SAMPNUM_ACC4_gc;            // accumulate 4 ADC sampling results
  ADC0.CTRLA = ADC_ENABLE_bm;                  // enable ADC

  TCB0.CCMP = 0xC350;                          // timeout value (50ms @ 1MHz TCB clock)
  TCB0.INTCTRL = TCB_CAPT_bm;                  // enable TCB capture or timeout interrupt

  SLPCTRL.CTRLA = SLPCTRL_SMODE_STDBY_gc;      // select STANDBY sleep mode

  sei();                                       // enable global interrupts

  while(1)
  {
    if(button)
    {
      button = 0;                                              // clear the flag
      ADC0.COMMAND = ADC_STCONV_bm;                            // start conversion
      while(!(ADC0.INTFLAGS & ADC_RESRDY_bm)){}                // wait until conversion done
      adc_bat = ADC0.RES;                                      // read accumulated result
      adc_bat >>= 2;                                           // divide by 4 
      if(adc_bat > 730)                                        // if V_bat < 3.5V
      {
        PORTA.OUTSET = PIN1_bm;                                // PA1 on
      }
      TCB0.CTRLA = TCB_CLKSEL_CLKDIV2_gc | TCB_ENABLE_bm;      // 1MHz TCB clock, enable TCB
    }
    if(tcb)                                                    // TCB for debouncing without delay
    {
      if(PORTA.IN & PIN2_bm)                                   // if PA2 button released
      {
        PORTA.OUTCLR = PIN1_bm;                                // PA1 off
        tcb = 0;                                               // clear the flag
        indicate = 0;                                          // clear the flag
      }
    }
    if(!indicate)
    {
      PORTA.PIN2CTRL = PORT_PULLUPEN_bm | PORT_ISC_LEVEL_gc;   // PA2 pull-up, low level sense interrupt
      sleep_mode();
      PORTA.PIN2CTRL = PORT_PULLUPEN_bm;                       // PA2 pull-up, disable interrupt
    }
  }
}