/**
* MetkuMods - http://metku.net/
* How to get started with AVR microcontrollers, part 2
* Example 2.2 - Fading led
*
* Author: Aki Korhonen
* Date: 2009-04-29
*/

// If clock speed isn't set in the project settings then it is set here
#ifndef F_CPU
	#define F_CPU 1000000UL // 1 MHz
#endif

#include <avr/io.h>

#include <inttypes.h>

#include <util/delay.h>

// Led at PB0, OCR0A
#define LED 0

// Min and max values for the PWM
// You can fine tune how bright and dim the led goes
// Minimum for MIN is 0 and maximum for MAX is 255
#define PWM_MIN 0
#define PWM_MAX 128

int main(void)
{
	DDRB = 0xFF;
	PORTB = 0x00;
	
	// Value for the register and step size
	// "value" equals brightness of the led
	// 0 = off | 255 = full brightness
	uint8_t value = 0;
	uint8_t step = 1;

	// -------------------------
	// Initialize PWM

	// 8-bit PWM, Phase correct
	// 8 bits give us 256 levels of brightness
	TCCR0A |= (1<<WGM00);

	// Clear OC0A/OC0B on Compare Match
	// Set OC0A/OC0B at BOTTOM (non-inverting mode)
	TCCR0A |= (1<<COM0A1);

	// Set prescaler to 8
	// 1 MHz / 8*256 = ~490 Hz PWM frequency
	TCCR0B |= (1<<CS01);

	// -------------------------
	
	// The program fades the led from off to on and vice versa
	while(1)
	{
		// Write the value to the Output Compare Register A
		OCR0A = value;

		// Increment the value by step
		value += step;
		
		// If we reach the maximum value, invert the direction and vice versa
		if(value >= PWM_MAX)
			step *= -1;
		else if(value <= PWM_MIN)
			step = 1;
		
		// Wait for 40 ms
		_delay_ms(40);
	}

	return 0;
}