AVR Freaks

Thanks for all the great replies.

I am using a AtMega1281 in the project that I want to be using the Watchdog in.

I have really never ever used the watchdog but it seems to be straight forward in usage.

I always have event based systems and in general make sure these events do not take to long to process, so that seems to be the way to go with using the watchdog.

From what I understand so far is that at initial power on the watchdog is disabled by default ( note that I never program the watchdog fuse)

So then it is not important what is done to it, but after a watchdog generated reset it seems to be such that the watchdog is not turned off, but changes to the shortest interval time possible. Which as said will cause problems if you do not take that into account.

So this means that the second thing I have to do (first is setting the IO ports to a after reset state, just plain PORT & DDR registers writing) is either turn the watchdog off, or set it to a very long time interval.

At this point I think I will opt for leaving/turning it on and setting it to 8seconds time-out which will be way more than needed.

Then I will do the full system initialization and when that is done change the watchdog to 2 seconds. an event should never last longer than a second anyway or the system might run into memory problems. so 2 seconds between ticks should be more than enough. Then I can choose in the special situations to speed up or just let the timer be.

Interestingly while looking at the AVRgcc documentation the wdt library does not have a standard function call to turn the watchdog off.

you call wdt_enable for turning it on and set the interval ( assume that when I want to change the interval I also call this function). and a wdt_reset that you have to cal regularly to not trigger the watchdog.

I have made a file with 4 functions:

1: function to turn watchdog ON

void WDT_Turn_On(const uint8_t a_time)
{
	wdt_enable(a_time);
}

2: function to change the interval

void WDT_Set_Interval(const uint8_t a_time)
{
	wdt_enable(a_time);
}

3: a function that will reset the watchdog

void WDT_Do_Reset(void)
{
	wdt_reset();
}

4: a function that will turn off the watchdog

void WDT_Turn_Off(void)
{
	uint8_t l_Sreg;
		
	l_Sreg = SREG;						// store SREG state specially for global interrupt enable
	cli();								// turn off interrupts
	wdt_reset();						// reset watchdog
	MCUSR &= ~(1<<WDRF);				// make sure WDRF is cleared in MCU status reg or else watchdog cannot be turned off
	WDTCSR |= (1<<WDCE) | (1<<WDE);		// send special value to command register enabling it to be editted
	WDTCSR = 0x00;						// turn off watchdog by clearing WDE & WDIE plus all the rest
	SREG = l_Sreg;						// restore SREG. if interrupts were enabled they will be again
}

now the first 2 are the same, but when you go through the code it is clear what the function is actually doing.

in fact the first 3 are just re-definitions of the functions in the avr/wdt library and are a shell for me to in now and a year to still understand what is going on.

the 4th function I copied from the datasheet

I am just wondering if I need to reset the watchdog myself before changing the interval or if that is done inside the library.

And personally I am still in doubt if I not going to make the "turn on" function turn the wdt on always at 8 seconds, and then use the set interval to change it later on in the process.

That is interesting as the documentation does not mention it.

it only mentions a macro define for the reset command, a couple of defines for the interval time setting and an enable function.