//Watchdog code  
//R. Traylor 11.18.09

//this code does not require that the Extended fuse bits
//M103C or WDTON be set.  This code runs the WDT in safety
//level 1. So, the WDT can be disabled or the timeout interval 
//may be changed with a timed sequence.

#define F_CPU 16000000UL     //16Mhz clock

#include <avr/io.h>
#include <util/delay.h>
#include <avr/interrupt.h>
#include <avr/wdt.h>

/********************************** tcnt0_init ********************************/
//timer counter 0 setup
void tcnt0_init(){
ASSR  |= (1<<AS0);               //ext osc TOSC running at 32.768kHz
TIMSK |= (1<<OCIE0);             //enable interrupts for compare register match
TCCR0 |= (1<<CS00) | (1<<WGM01); //CTC mode, no prescale
OCR0   = 0x03;                   //4 cycles between interrupts is 122uS
}
/******************************************************************************/

/***************************  debounce_switch0  ********************************/
//check PORTD.0 switch
uint8_t debounce_switch0(){
  static uint16_t state = 0;     //holds present state
  state = (state << 1) | (! bit_is_clear(PIND, 0)) | 0xE000;
  if (state == 0xF000) return 1;
  return 0;
}
/******************************************************************************/

/***************************  debounce_switch1  ********************************/
//check PORTD.1 switch
uint8_t debounce_switch1(){
  static uint16_t state = 0;     //holds present state
  state = (state << 1) | (! bit_is_clear(PIND, 1)) | 0xE000;
  if (state == 0xF000) return 1;
  return 0;
}
/******************************************************************************/

/******************************  TIMER 0 ISR  *********************************/
ISR(TIMER0_COMP_vect){ //this code is entered every 122us approx
  if(debounce_switch0() == 1){
    wdt_reset();//execute the wdr instruction to reset the WDT 
  }    
  if(debounce_switch1() == 1){
    MCUCSR = 0x00; //clear out the reset source resgister
  }    
}
/******************************************************************************/

int main(){
uint8_t i;

//this block sets all ports to inputs with pullups on except PORTB
  PORTA = 0xFF; //inputs with pullups
  DDRB = 0xFF;  PORTB = 0x00; //blink lights with PORTB 
  PORTC = 0xFF; //inputs with pullups
  PORTD = 0xFF; //inputs with pullups
  PORTE = 0xFF; //inputs with pullups
  PORTF = 0xFF; //inputs with pullups
  PORTG = 0xFF; //inputs with pullups

  tcnt0_init();//initalize timer counter zero to interrupt at 122us intervals
  sei(); //interrupts enabled 

  wdt_enable(WDTO_2S);  //enable WDT with timeout of 2Sec (1.9sec typically)

  while(1){ 
    PORTB = MCUCSR;  //display the MCUCSR register value
    _delay_ms(500);  //delay .5 sec
    PORTB = 0x00;                        //clear PORTB LEDs 
  }//while(1)

} //main