// This pgm just blinks D.2 for testing the protoboard.
#include <inttypes.h>
#include <avr/io.h>
#include <avr/interrupt.h>

//timeout values for each task
#define t1 250   
#define begin {
#define end }
 
// task subroutines
void task1(void);  	//blink at 2 or 8 Hz 
void initialize(void); //all the usual mcu stuff 
          
volatile unsigned char time1;	//timeout counter 
unsigned char led;				//light states  
         
//**********************************************************
//timer 0 compare ISR
ISR (TIMER0_COMP_vect)
begin      
  //Decrement the  time if they are not already zero
  if (time1>0)	--time1;
end  

//**********************************************************       
//Entry point and task scheduler loop
int main(void)
begin  
  	initialize();
  
  	//main task scheduler loop 
  	while(1)
  	begin     
		if (time1==0){time1=t1;	task1();}
  	end
end  
  
//**********************************************************          
//Task 1
void task1(void) 
begin  
  	//toggle the second bit
  	led = led ^ 0b00000100;
  	PORTD = led;
end  
 

//********************************************************** 
//Set it all up
void initialize(void)
begin
	//set up the ports
  	DDRD=0b00000100;	// PORT D.2 is an ouput
           
  	//set up timer 0  
  	TIMSK=2;		//turn on timer 0 cmp match ISR 
  	OCR0 = 249;  	//set the compare re to 250 time ticks
  	//prescalar to 64 and turn on clear-on-match
  	TCCR0=0b00001011;	
    
  	//init the LED status (all off)
  	led=0xff; 
  
  	//init the task timer
  	time1=t1;  
      
  	//crank up the ISRs
  	sei();
end