/*
//*****************************************************************************
//
// File Name	: 'blink.c'
// Title	: Interrupt Driven LED Blink
// Author	: William Riley
// Date		: 10/13/2005
// Revised	: 10/13/2005
// Version	: 1.0
// Target MCU	: Atmel AVR
// Editor Tabs	: 4
//
//*****************************************************************************

Blinks an LED connected to pin PB0 using timer0 overflow interrupt.


                   +5V
		   |
                   |
                  |-|
                  |-| R1
                  |-|
          LED      |
         | /|      |
PB0 -----|< |------*
         | \|
*/

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

#define MAX_INT_COUNT	31250	// with 16MHz clock and /256 prescale gives a 500ms cycle

int main(void)
{
	PORTA = 0xFF;
	PORTB = 0xFF;
	PORTC = 0xFF;
	PORTD = 0xFF;

	DDRB = 0xFF;

/*

CS02	CS01	CS00
-------------------------
0	0	1	|	No Prescaling
0	1	0	|	/8
0	1	1	|	/64
1	0	0	|	/256
1	0	1	|	/1024


*/

	TCCR0 = ( 1 << CS02 ) | ( 0 << CS01 ) | ( 0 << CS00 );	// set prescale to /256
	TIMSK |= _BV( TOIE0 );					// enable Timer/Counter0 interrupt

	sei();							// enable global interrupts

	for(;;)
	{
	}

	return 0;
}

SIGNAL(SIG_OVERFLOW0)
{
	static uint16_t interrupt_count = 0;
	TCNT0 = 0;
	interrupt_count++;

	if(interrupt_count > MAX_INT_COUNT)
	{
		PORTB ^= 0x01;					// toggle pin PB0
		interrupt_count = 0;
	}
}