//---------------------------------------------------------------------------------------
// Programm Nr.: 16
// Content     : dimming a LED with timer2 fast pulse width modulation mode (PWM)
// Author      : digital AG Halle
// Date        : 27.07.2008
// System      : ATmega8-16PU - Dai Hoc Hue Development Board
//---------------------------------------------------------------------------------------

//The hardware-implemented fast PWM does NOT use calculation time of the MC. It works
//indipendent!

//--included Files-----------------------------------------------------------------------

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

//--declarations-------------------------------------------------------------------------

#ifndef F_CPU
#define F_CPU 8000000	//CPU frequency = 8 MHz
#endif


uint8_t KEYS;
uint8_t KEYS_OLD;

//--INTERRUPT SERVICE ROUTINES (ISR)-----------------------------------------------------

SIGNAL( TIMER2_COMP_vect ) 
{
}

//The ISR is empty but has to be written in the program. If it wasn't - the MC would jump
//to the RESET routine at every timer2 interrupt. 

//--MAIN PROGRAMM------------------------------------------------------------------------

int main(void)
{

	//--INITIALISATION---------------------------------------------------------------

	//INTERRUPTS:

		TIMSK = (1<<OCIE2); 	//activate compare match interrupt of timer2
		OCR2 = 127; 		//preload the compare vlaue register for timer2
					//timer2 is a 8-bit timer -> 127 are 50%

		TCCR2 = (1<<WGM21) | (1<<WGM20) | (1<<COM21);
			// WGM - FAST PWM MODE
			// COM - non inverted pwm

	//PORT_INIT:

		DDRB=8;		//PWM controlled LED at PB3/OC2
		PORTB=8;	//LED off		

		DDRC=224;	//Port C key inputs and bit0 analog channel 0 input
		PORTC=30;	//Pullup (keys and analog input)

		DDRD=255; 	//Port D: all bits defined as output (for the status LEDs)
		PORTD=255; 	//all LEDs off

	//--PROGRAMM CODE BEFORE MAIN LOOP (USED JUST ONE TIME)--------------------------
		
		sei(); 			//ALL INT ENABLE
		TCCR2 |= (1<<CS22);	//set prescaler for timer2 after sei or it will
					//hang imideately - CS22 -> prescaler = 64
					//8 MHz / 64 -> PWM frequency = 125 kHz	
		KEYS_OLD=PINC;

	//--MAIN LOOP--------------------------------------------------------------------
	
	while(1)
	{
	 	KEYS=PINC;

		if (KEYS_OLD!=KEYS) 
		{
			//mask  = 1110 0010 = 226 dec.
			if ((KEYS&226)==!(0x02))	//if key 1 was pressed
			{

				OCR2=OCR2+5;		//increase OCR2 -> brigther
				PORTD=OCR2;		//binary state output
			
			}
			//mask  = 1110 0100 = 228 dec.
			if ((KEYS&228)==!(0x04))	//if key 2 was pressed
			{

				OCR2=OCR2-5;		//decrease OCR2 -> darker
				PORTD=OCR2;		//binary state output
			
			}
		}
		KEYS_OLD=KEYS;
	}
	return 0;
}

//--MAIN PROGRAMM END--------------------------------------------------------------------

//--EXTERNAL ROUTINES--------------------------------------------------------------------

//--PROGRAMM END-------------------------------------------------------------------------