/*
Quadrature encoder for the Orangutan, ATmega168

This code assumes that the A and B outputs of a quadrature encoder is connected to PORTC, pins 4&5
If the decoded direction is incorrect, swap the A&B terminals or change the logic of the interrupt
service routine accordingly

The algorithm is from Scott Edwards, in Nuts&Volts Vol 1 Oct. 1995 (Basic Stamp #8) and
is described in an article available on line at http://www.parallax.com/dl/docs/cols/nv/vol1/col/nv8.pdf

Interrupts are required to avoid missing encoder states. However, if skipped states is not a problem
(e.g a volume control), the decoding can take place in the main routine.

*/

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

//global variables: encoder position and direction of rotation
unsigned int enc_pos;
unsigned char enc_dir;

/*
 PORTC Pin change interrupt service routine. Decodes the encoder.
 For algorithm, see Scott Edwards article from Nuts&Volts V1 Oct. 1995 nv8.pdf
 (righthand bit of old A,B) xor (lefthand bit of new A,B) => dir.
 Increment or decrement encoder position accordingly
*/

ISR (PCINT1_vect) {
	static unsigned char enc_last=0,enc_now;
	enc_now = (PINC & (3<<4))>>4;  					//read the port pins and shift result to bottom bits
	enc_dir = (enc_last & 1)^((enc_now & 2) >> 1);	//determine direction of rotation
	if(enc_dir==0) enc_pos++; else enc_pos--;		//update encoder position
	enc_last=enc_now;								//remember last state
}

#include "lcd.c"

int main(void)
{
	unsigned char buf[8];

	enc_pos=0;					//Initialize encoder position

	LCDInit();					//Initialize LCD display

	DDRC &=~(3<<4);  			//Port C pins 4 and 5 as input
	PCMSK1 |= (3<<PCINT12);		//enable interrupt on pin change, bits 4&5 PORTC
	PCICR |= 1<<PCIE1;			//enable interrupt on pin change, PORTC
	sei();						//enable global interrupts

	while (1){
		LCDSendCommand(LCD_Line1);		//display current direction of rotation on line 1
		itoa(enc_dir,buf,10);
		LCDPrintString(buf);
		LCDSendCommand(LCD_Line2);		//display current encoder position on line 2
		itoa(enc_pos,buf,10);
		LCDPrintString(buf);
		}
}