avr-studio C code for sparkfun's LED RingCoder Breakout - RGB https://www.sparkfun.com/products/11040

knob.c

/*
 * knob.c
 *
 * Created: 6/22/2013 9:01:18 PM
 *  Author: dtudury
 */ 

#ifndef F_CPU
#define F_CPU 8000000UL // or whatever may be your frequency
#endif

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

//C0 EN
//C1 LATCH
//C2 CLK
//C3 CLR
//C4 DAT

//C5 SW

//D3 GRN
//D6 BLU
//B1 RED

//D0 A
//D1 B

void pwmInit() {
  //https://sites.google.com/site/qeewiki/books/avr-guide/pwm-on-the-atmega328
	//set up red pin on timer 1, B1 (OCR1A)
	TCCR1A = (1 << WGM12) | (1 << WGM10);
	TCCR1A |= (1 << COM1A1) | (1 << COM1A0);
	TCCR1B = (1 << CS10);
	DDRB |= (1 << DDB1);

	//set up green pin on timer 2, D3 (OCR2B)
	TCCR2A = (1 << WGM21) | (1 << WGM20);
	TCCR2A |= (1 << COM2B1) | (1 << COM2B0);
	TCCR2B = (1 << CS20);
	DDRD |= (1<<DDD3);
	
	//set up blue pin on timer 0, D6 (OCR0A)
	TCCR0A = (1 << WGM01) | (1 << WGM00);
	TCCR0A |= (1 << COM0A1) | (1 << COM0A0);
	TCCR0B = (1 << CS00);
	DDRD |= (1<<DDD6);
}

void interruptInit() {
	//set up A pin on D0 (PCINT16)
	DDRD &= ~(1 << DDD0);
	PORTD |= (1 << PORTD0);
	PCMSK2 |= (1 << PCINT16);
	
	//set up B pin on D1 (PCINT17)
	DDRD &= ~(1 << DDD1);
	PORTD |= (1 << PORTD1);
	PCMSK2 |= (1 << PCINT17);

	PCICR |= (1 << PCIE2);
	
	//set up button (SW) on C5 (PCINT13)
	DDRC &= ~(1 << DDC5);
	PORTC |= (1 << PORTC5);
	PCMSK1 |= (1 << PCINT13);

	PCICR |= (1 << PCIE1);

	sei();                     // turn on interrupts
}

void writePosition(uint16_t d) {
	PORTC &= ~(1 << PORTC1); //latch low
	
	for(uint8_t i = 0; i < 16; i++) {
		if(d % 16 == i) {
			PORTC |= (1 << PORTC4);
		} else {
			PORTC &= ~(1 << PORTC4);
		}
		PORTC |= (1 << PORTC2); //toggle clock
		PORTC &= ~(1 << PORTC2);
	}
	
	PORTC |= (1 << PORTC1); //latch high
}

void writeInit() {
	DDRC |= (1 << DDC0);
	DDRC |= (1 << DDC1);
	DDRC |= (1 << DDC2);
	DDRC |= (1 << DDC3);
	DDRC |= (1 << DDC4);
	PORTC &= ~(1 << PORTC0); //enable
	PORTC &= ~(1 << PORTC1); //start latch low
	PORTC &= ~(1 << PORTC2); //start clock low
	PORTC |= (1 << PORTC3); //start clear high
	PORTC &= ~(1 << PORTC4); //start data low
	writePosition(0);
}

int main(void) {
	pwmInit();
	interruptInit();
	writeInit();
	
    while(1) {
    }
}

int lastA = 0;
int lastB = 0;
int step = 0;

void inc() {
	step++;
}

void dec() {
	step += 63;
}

ISR (PCINT2_vect) {
	int A = PIND & (1 << PIND0);
	int B = PIND & (1 << PIND1);
	/*
	if(A) {
		OCR1A = 255; //red pin
	} else {
		OCR1A = 0;
	}
	if(B) {
		OCR2B = 255; //green pin
	} else {
		OCR2B = 0;
	}
	*/

	if(A && B) {
		if(!lastA && lastB) {
			inc();
		} else if(lastA && !lastB) {
			dec();
		}
	} else if(A) {
		if(lastA && lastB) {
			inc();
		} else if(!lastA && !lastB) {
			dec();
		}
	} else if(B) {
		if(!lastA && !lastB) {
			inc();
		} else if(lastA && lastB) {
			dec();
		}			
	} else {
		if(lastA && !lastB) {
			inc();
		} else if(!lastA && lastB) {
			dec();
		}
	}
	writePosition((step + 1) / 4);
	
	lastA = A;
	lastB = B;
}


ISR (PCINT1_vect) {
	if(PINC & (1 << PINC5)) {
		OCR0A = 255; //blue pin
	} else {
		OCR0A = 0;
	}
}