Watchdog timer issue - AVR ATmega324PA

Question

I was using ATmega32A before and now I am migrating to ATmega324PA just to enhance power management. Now I am testing the new controller in every aspect. This is a simple code to check the watchdog timer but it keeps resetting the controller.

Code:

int main(void)
{
  uart_init();
  PORTA|=(1<<PORTA1);
  _delay_ms(1500);
  PORTA&=~(1<<PORTA1);
  _delay_ms(2000);
  uart_array("FFFFFFFFFFFFFFFFFF");
  wdt_enable(WDTO_2S);
  _delay_ms(5000);
}

void uart_init()
{
 /*set PinA1 as output for LED*/
 DDRA|=(1<<1);

 /*set PinD3 as output for UART*/
 DDRD|=(1<<3);

 /*set pinD2 as input for UART*/
 DDRD&=~(1<<2);

 /*enabling TX and RX*/
 UCSR1B |=(1<<TXEN1) | (1<<RXEN1);

 /*asynchronous mode selection*/
 UCSR1C&=~(1<<UMSEL11);
 UCSR1C&=~(1<<UMSEL10);

 /*setting data format to 8 bit*/
 UCSR1B &=~(1<<UCSZ12);
 UCSR1C|=(1<<UCSZ11)|(1<<UCSZ10);

 /* setting one bit as stop bit*/
 UCSR1C &=~(1<<USBS1);

 /*Disabling parity*/
 UCSR1C &= ~((1<<UPM11) | (1<<UPM10));

 /* loading 8 LSB to UBRRL*/
 UBRR1L = UBRRL_VALUE;

 /* loading 4 MSB to UBRRH*/
 UBRR1H = UBRRH_VALUE;
}

The code works well for the first time, but after that, LED keeps blinking.

Note: watchdog (WDTON) fuse bit is disabled.

Answer 1

Yeah, that is because after the watchdog fires, you have to reset the corresponding flag before main starts again (there is a register where you can read out, what caused the reset) and to disable the watchdog from firing over and over.

This code will fix your problem:

    // This function is called upon a HARDWARE RESET:
void reset(void) __attribute__((naked)) __attribute__((section(".init3")));

/*! Clear SREG_I on hardware reset. */
void reset(void)
{
     cli();
    // Note that for newer devices (any AVR that has the option to also
    // generate WDT interrupts), the watchdog timer remains active even
    // after a system reset (except a power-on condition), using the fastest
    // prescaler value (approximately 15 ms). It is therefore required
    // to turn off the watchdog early during program startup.
    MCUSR = 0; // clear reset flags
    wdt_disable();
}

This .init3 thing is a special code section where you can put code that is run before main starts. Here is a link that describes that, but you shouldn't worry too much about it, the code above will work just fine when put into the main.c.

Answer 2

Beyond previous reset() function advice you need disable watchdog in bootloader (if used of course). There is/was e.g. known bug of original Arduino bootloader which did not disable watchdog.