#define F_CPU 16000000UL
#include <avr/io.h>
#include <avr/interrupt.h>

void pin_setup(void)
{
	DDRC=(1<<PC0)|(1<<PC1); //Prepare to give power to the radios
	PORTC=(1<<PC0)|(1<<PC1); //Give power to the radios
	DDRB=(1<<PB3); //Transmit pin as output
	EICRA=(1<<ISC00); //Select level change interrupt on int0
	EIMSK=(1<<INT0); //Enable int0
}

void uart_setup(void)
{
	UCSR0A=(1<<U2X0); //Double speed uart
	UCSR0B=(1<<RXCIE0)|(1<<RXEN0)|(1<<TXEN0); //Enable rx and tx circuitry and rx interrupt
	UCSR0C=(1<<UCSZ01)|(1<<UCSZ00); //Select 8-bit data
	UBRR0=1; //Select 1MBaud speed
}

	void uart_write(unsigned char c)
	{
		while(!(UCSR0A&(1<<UDRE0))); //Block until ready to write
		UDR0=c; //Write
	}

	void uart_write_s(char *s) //Write normal string
	{
		while(*s)
		{
			uart_write((unsigned char)*s);
			s++;
		}
	}

void timer_setup(void)
{
	TCCR1B=(1<<CS11); //Select 8 as timer1 divisor
	TCNT1=0; //Clear timer1

	TCCR2A=(1<<WGM21); //Select CTC mode
	TCCR2B=(1<<CS22); //Select 64 as timer2 divisor
	OCR2A=99; //1250 updates a seconds
	TCNT2=0; //Clear timer2
}

ISR(INT0_vect) //Interrupt executed on int0 level change
{
	unsigned char tl=TCNT1L; //Capture lower byte first
	unsigned char th=TCNT1H; //Capture upper byte second
	TCNT1=0; //Clear timer1
	if(TIFR1&(1<<TOV1)) //Check if timer1 has overflown
	{
		uart_write('R'); //Notify of timer1 overflow
		TIFR1=(1<<TOV1); //Clear timer1 overflow flag
	}
	if(th) //Only send the upper byte if it is not zero
	{
		uart_write((th>>4)+'A'); //Send first half
		uart_write((th&15)+'A'); //Send second half
	}
	uart_write((tl>>4)+'A'); //Send lower byte's upper half
	uart_write((tl&15)+'A'); //Send lower byte's lower half
	uart_write('\n'); //Frame end symbol
}

unsigned char isn(unsigned char c)
{
	return('0'<=c && c<='9');
}

ISR(USART_RX_vect)
{
	unsigned char rx=UDR0, d=0;
	static unsigned char b[3]={0,0,0}, i=0;
	EIMSK=0;
	if(rx=='\n')
	{
		if(i==0)
		{
			TCCR2A&=~(1<<COM2A0);
			EIMSK=(1<<INT0);
		}
		else if(isn(b[0]))
		{
			d=(b[0]-'0');
			if(isn(b[1]))
			{
				d*=10;
				d+=(b[1]-'0');
				if(isn(b[2]))
				{
					d*=10;
					d+=(b[2]-'0');
				}
			}
			OCR2A=d;
			TCCR2A|=(1<<COM2A0);
			uart_write_s(" OK");
		}
		else
		{
			uart_write_s(" ERR");
		}
		b[0]=0;
		b[1]=0;
		b[2]=0;
		i=0;
	}
	else
	{
		if(i>2)
		{
			i=0;
		}
		b[i++]=rx;
	}
	uart_write(rx);
}

int main(void)
{
	pin_setup(); //Setup pins and pin interrupts
	uart_setup(); //Setup uart
	timer_setup(); //Setup timer
	sei(); //Enable global interrupts
	while(1); //Everything is interrupt driven <3
	return(0);
}