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

#define F_CPU 24000000UL

#define setbit(P,BIT)        ((P) |= (1<<(BIT)))
#define clearbit(P,BIT)       ((P) &= ~(1<<(BIT)))

#define LED_RED_PORT        PORTF
#define LED_RED_BIT         1
#define LED_red_on()        setbit(LED_RED_PORT.OUT,LED_RED_BIT)
#define LED_red_off()       clearbit(LED_RED_PORT.OUT,LED_RED_BIT)

#define LED_GREEN_PORT      PORTF
#define LED_GREEN_BIT       0
#define LED_green_on()      setbit(LED_GREEN_PORT.OUT,LED_GREEN_BIT)
#define LED_green_off()     clearbit(LED_GREEN_PORT.OUT,LED_GREEN_BIT)

volatile uint16_t sys_tick_ms = 0;
uint16_t sec_counter = 0;


ISR(TCA1_CMP0_vect)
{
    LED_green_on();

    sys_tick_ms++;

    setbit(TCA1_SINGLE_INTFLAGS,TCA_SINGLE_CMP0_bp);

    LED_green_off();
}


int main(void)
{
    // crystal
    #define CPP_value 0xD8        // 0xD8 IOREG Unlock protected I/O reg

    CPU_CCP = CPP_value;        // unlock protected register for 4 cycles
    CLKCTRL.MCLKCTRLA = 0x03;      // Main clk src: ext clock (on evaluation board: 16MHz)
    CPU_CCP = CPP_value;

    CLKCTRL.XOSCHFCTRLA = 0b00010101;  // crystal; startup time 1000 cycles,

    // oscillator enabled

    // overrides normal pin function

	// LEDs

	LED_red_off();
	setbit(LED_RED_PORT.DIR,LED_RED_BIT);

	LED_green_off();
	setbit(LED_GREEN_PORT.DIR,LED_GREEN_BIT);

    // 1. timer enable, Prescaler:1
    clearbit(TCA1.SINGLE.CTRLA,TCA_SINGLE_CLKSEL_2_bp);
    clearbit(TCA1.SINGLE.CTRLA,TCA_SINGLE_CLKSEL_1_bp);
    clearbit(TCA1.SINGLE.CTRLA,TCA_SINGLE_CLKSEL_0_bp);
    setbit(TCA1.SINGLE.CTRLA,TCA_SINGLE_ENABLE_bp);
	
    // 2. Vergleichswert: OCR2 = F.CPU / PRESCALER * seconds;
    TCA1.SINGLE.CMP0 = F_CPU / 1 * 0.001;

    // 3. compare0 enable, clear timer on compare
    clearbit(TCA1.SINGLE.CTRLB,TCA_SINGLE_CMP0EN_bp);
    clearbit(TCA1.SINGLE.CTRLB,TCA_SINGLE_WGMODE_2_bp);
    clearbit(TCA1.SINGLE.CTRLB,TCA_SINGLE_WGMODE_1_bp);
    setbit(TCA1.SINGLE.CTRLB,TCA_SINGLE_WGMODE_0_bp);
	
    // 4. enable output compare match interrupt
    setbit(TCA1.SINGLE.INTCTRL,TCA_SINGLE_CMP0_bp);

    sei();

    while (1)
    {
		ATOMIC_BLOCK(ATOMIC_RESTORESTATE)
		{
			if (sys_tick_ms > 999)
			{
				sys_tick_ms -= 1000;
				sec_counter++;
			}
		}
		
		if (sec_counter >= 1)
		{
			LED_red_on();
			sec_counter = 0;
			LED_red_off();
		}
	}
}