// Debounce program
#include <avr/io.h>
#include <util/delay.h>

#define TRUE 1
#define FALSE 0
#define HIGH 1
#define LOW 0

#define BUTTON_PORT PORTA 
#define BUTTON_PIN PINA
#define BUTTON_BIT PA7

#define LED_PORT PORTB
#define LED_BIT PB2
#define LED_DDR DDRB

#define DEBOUNCE_TIME 25
#define BLOCK_TIME 250

void setup();
int is_pressed();
void toggle_led();

int main()
{
  setup();

  while(TRUE) {
    if (is_pressed()) {
      toggle_led();
      _delay_ms(BLOCK_TIME);
    }
  }
}

void setup()
{
   CLKPR = (1 << CLKPCE);
   CLKPR = (0 << CLKPS3) | (0 << CLKPS2) | (0 << CLKPS1) | (0 << CLKPS0);

  // Set LED as output
  LED_DDR = _BV(LED_BIT);

  // Turn the LED off initially
  LED_PORT &= ~(_BV(LED_BIT));

  // Turn on internal pull-up on button
  BUTTON_PORT = _BV(BUTTON_BIT);
}

int is_pressed()
{
  // check if button pressed
  if (bit_is_clear(BUTTON_PIN, BUTTON_BIT)) {
    // debounce the signal
    _delay_ms(DEBOUNCE_TIME);
    if (bit_is_clear(BUTTON_PIN, BUTTON_BIT)) return TRUE;
  }
  return FALSE;
}

void toggle_led()
{
  LED_PORT ^= _BV(LED_BIT);
}