#include <avr/io.h>

void init();				//set every thing up, look in here for info on setting up timers

int main(){

	const uint32_t TIMER_HZ = 1000000; //The speed of our timerclock, after prescaling.
	uint16_t freq = 0;	//this varible will hold our desired frequency
	uint8_t buttons;	//this holds the state of the buttons

	init();					//set up our timer...

	while(1){				//do this forever...

		buttons = ~PINC;

		switch( buttons ) {
			case 1:
				freq=262;
				PORTA = ~1;
				break;
			case 2:
				freq=294;
				PORTA = ~2;
				break;
			case 4:
				freq=330;
				PORTA = ~4;
				break;
			case 8:
				freq=349;
				PORTA = ~8;
				break;
			case 16:
				freq=392;
				PORTA = ~16;
				break;
			case 32:
				freq=440;
				PORTA = ~32;
				break;
			case 64:
				freq=494;
				PORTA = ~64;
				break;
			case 128:
				freq=523;
				PORTA = ~128;
				break;
			default:
				freq=0;
				PORTA = ~0;
			break;	
		}

		//Now we use the value in `freq' to set up our timer. OCR1A determines the overal period
		// of the waveform and OCR1B determines the duty cycle. In this example, we just want to
		// change the frequency and keep the duty cycle at 50% so we always set OCR1B to be half
		// of ICR1A
		
		OCR1A = (TIMER_HZ/freq + 1)/2;
		OCR1B = OCR1A/2;
	}	
}

void init(){

	/* General Theory of Operation

	* The goal is to be able to output a given frequency, to achieve this...

	* For this program we are going to set up our timer, so that it ticks
	* one million times per second, assuming we use the on board oscillator
	* of 8Mhz, that is 8 million cycles per second. To do this, we need to pre-scale (divide down)
	* the clock by 8.

	* The next trick is to make a pin automagically toggle (change state: 0-->1 or 1-->0) when we reach a
	* designated value, this can be done using an Output Compare Register (OCR)
	* supplied with the timer/counter. For the 16-bit timer on the ATmega16 (timer1)
	* there are 2 channels of OCR (A and B), we need only use:
	    OCR1A... Output Compare Register timer1 channel A...
	* we tell the timer to toggle the pin tied to this function. This pin is given the name
	* OC1A, and is coincident with the 5th pin in PORTD, thus PD5

	* The final touch is to change the timer so its TOP value is equal to the OCR1A value.
	* This allows us to know that the number of tics between overflows is precisely OCR1A,
	* and thus each time OCR1A toggles twice, we have the right period...., and 1 over period is frequency... yay!
	*/
	
	/*and finally..... to set up hardware in the ATmega16, we must manipulate special function registers. These registers
	* tell the hardware how it should behave The datasheet describes all the available hardware and
	* the registers associated with its control.
	*/

	//information on the Timer Control Registers for timer1 on page 110 of the ATmega16 datasheet

	TCCR1A |= _BV(COM1B1);		//toggle the PIN OCR1A when Timer 1 has reach the value stored in OCR1;
	TCCR1B |= _BV(CS11);		//prescale the timer clock by 8
	
	TCCR1A |= _BV(WGM10);		//Set up Waveform Generation Mode 9... OCR1A as TOP, update OCR1A
	TCCR1B |= _BV(WGM13);		//when we reach BOTTOM value

	//summary of all WGMs can be found on page 112 of the ATmega16 datasheet...

	
	//Set up the port we're using for LEDS to be output and set them high (LED's off)
	DDRA = 0xFF;
	PORTA = 0xFF;

	//final make our OC1B pin (output for waveform) an output
	DDRD = _BV(PD4);
	
	//Turn on the internal pull-ups for the switches.
	DDRC = 0x00;
	PORTC = 0xFF;
}