/************************************************************************/
/*                                                                      */
/*                      Reading rotary encoder                          */
/*                      one, two and four step encoders supported       */
/*                                                                      */
/*             Author : Uwe Kolz ( encode function )                    */
/*      Example frame : Peter Dannegger                                 */
/*                                                                      */
/************************************************************************/
#include <avr/io.h>
#include <avr/interrupt.h>

// target: ATtiny2313 ( was ATmega16 in original )
//------------------------------------------------------------------------

#define	XTAL		8e6			// 8MHz

#define PHASE_A		(PIND & 1<<PD0)
#define PHASE_B		(PIND & 1<<PD1)

#define LEDS_DDR	DDRB
#define	LEDS		PORTB			// LEDs against VCC

int8_t enc_delta;				// -128 ... 127

void encode_init( void )
{
	TCCR0A = 1<<WGM01;								// CTC
	TCCR0B = 1<<CS01^1<<CS00;						// XTAL / 64
	OCR0A = (uint8_t)(XTAL / 64.0 * 1e-3 - 0.5);	// 1ms
	TIMSK |= 1<<OCIE0A;
}

// return 1 for forward and -1 for backward
uint8_t encode(int8_t dgA, uint8_t dgB) {
	static uint8_t dgHist = 0;          // values history
	uint8_t dgVal         = 0;          // current value Bit 1 and 2

	dgVal = 0;
	if (dgA != 0) dgVal |= 0b01;
	if (dgB != 0) dgVal |= 0b10;

	if ( ( dgHist & 0b11 ) == dgVal) return 0; // no change --> return

	dgHist = dgHist<<2;
	dgHist = ( dgHist | dgVal ) & 0b00111111;

	////////////////////////////////////////////////////////////////////
	// Uncomment one of the switch statement to select the resolution //
	////////////////////////////////////////////////////////////////////


	switch (dgHist) // 1:1 single step encoders
	{
	case 0b100001: return  1; break;
	case 0b010010: return -1; break;

	default: return 0;	break;
	}


	/*
	switch (dgHist) // 1:2 two step encoders
	{
	case 0b111000: return  1; break;
	case 0b000111: return  1; break;
	case 0b110100: return -1; break;
	case 0b001011: return -1; break;

	default: return 0;	break;
	}
	*/

	/*
	switch (dgHist) // 1:4 four step encoders
	{
		case 0b111000: return  1; break;
		case 0b100001: return  1; break;
		case 0b000111: return  1; break;
		case 0b011110: return  1; break;
		case 0b110100: return -1; break;
		case 0b010010: return -1; break;
		case 0b001011: return -1; break;
		case 0b101101: return -1; break;

		default: return 0;	break;
	}
	*/

	return 0;
}


ISR( TIMER0_COMPA_vect )				// 1ms for manual movement
{
	enc_delta += encode( PHASE_A, PHASE_B );
}

int8_t encode_read( void )			// read single step encoders
{
	int8_t val;

	cli();
	val = enc_delta;
	enc_delta = 0;
	sei();
	return val;					// counts since last call
}


int main( void )
{
	int32_t val = 0;

	LEDS_DDR = 0xFF;
	PIND = 0b11;
	encode_init();
	sei();
	val = 0b11111111;

	while (1)
	{
		val += encode_read();			// read a single step encoder
		LEDS = val;
	}
}