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

#define True	1
#define False	0

//Global variables:
// Although one should generally try to avoid the use of global variables
// in normal c programming, they are sometimes required when working 
// with programs for microcontrollers. Here we define a global variable
// so that we can share data between a ISR and and the main(). Also note the
// volatile keyword. This just tells the compiler to not try and do any fancy
// optimizations on this variable.

volatile int32_t position = 0; //Signed 32bit integer
volatile uint8_t do_speed_calc = False;

//ISR that gets triggered on Timer1 OCRA compare, about every 500 ms.
ISR(TIMER1_COMPA_vect)
{
	//While we could do the actual speed calculation and UART output here in
	// this ISR, we want to avoid doing that as the ATmega's can only handle
	// one interrupt at a time. If we're busy doing calculations in this ISR
	// while a rising edge from the encoder comes in, the other ISR won't fire.
	// So we just set a variable here and check for it in main().

	do_speed_calc = True;
}

//This ISR gets called on every rising edge of the encoder A signal. If the B
// signal is high we increment the position counter. Otherwise we decrement.
ISR(INT0_vect)
{
	if (PIND & _BV(PD3))
		position++;
	else
		position--;
}

void init();

int main()
{
	int32_t current_position = 0;
	int32_t previous_position = 0;
	int32_t position_change = 0;

	init();

	printf("\x1B[2J\x1B\x63");	//VT100 clear screen command.
	printf("Welcome to the Encoder Lab!");

	while(1)
	{
		if(do_speed_calc)
		{
			current_position = position;
			position_change = current_position - previous_position;

			printf("\x1B[2;1H");	//VT100 set position command. Row:2 Column:1
			printf("Current speed: %+.5li, Current position: %+.8li", position_change*2, current_position);

			previous_position = current_position;

			do_speed_calc = False;
		}
	}

	return 0;
}

void init()
{
	//Init Ports
	PORTD |= _BV(PD2) | _BV(PD3);	//Turn on pull-up resistors on pin D2 and D3.

	//Enable global interrupts
	sei();

	//Init UART
	uart_init();

	//Init Timer 1
	TCCR1A = 0; //Normal timer operation.
	TCCR1B = _BV(WGM12) | _BV(CS12);	//Clear Timer on Compare Match (CTC) Mode, Set timer clock signal to system clock/256
	OCR1AH = (15624 & 0xFF00) >> 8;	//Setting the Output Compare Register to 15624 gives us an interrupt about every
	OCR1AL = (15624 & 0x00FF);		// 500ms. Note that we have to first write to the high byte and then the low.
	TIMSK = _BV(OCIE1A);

	//Init External Interrupt on PD2
	MCUCR |= _BV(ISC01) | _BV(ISC00);	//Trigger interrupt on rising edge.
	GICR |= _BV(INT0);					//Enable interrupts.
}