AW: [En-Nut-Discussion] The Watchdog timer

[Oliver Schulz]

Hi Sigurd,

> Hey!
> I'm trying to program the watchdog timer in my application. I 
> have red the datasheat for at Atmega128. When i delay the 
Please read the datasheet more carefully! Did you omit the chapter describing the timed sequence to change the watchdog timeout?

I assume, that you don't operate themega128 in 103 compatibility mode and you didn't program the fuse WDTON (which is the default for atmega128, I think)

To set the watchdog timeout or disable the watchdog, you have to follow this sequence:

1. Set the bits WDCE and WDE in WDTCR in one instruction.
2. Set the desired bits for timeout or disabling in one instruction that follows step 1 immediately.

Beware, step 1 also enables the watchdog.

To be sure, the these instructions are not interrupted, I would surround them with calls to NutEnterCritical() and NutExitCritical() (or cli() and sei()).

So you code must read like this:

for(;;) {
 NutEnterCritical();
 WDTCR = 0x18;
 WDTCR = 0x0F;
 NutExitCritical();

 NutSleep(100);

 NutEnterCritical(); 
 WDTCR = 0x18;
 WDTCR = 0;
 NutExitCritical();
}


Usually, if the watchdog is enabled, you can reset the watchdog timer by using the WDR assembler instruction (asm("wdr");).

For more simplier life, just use the macros defined in avr/wdt.h from avr-libc.

Hope that helps...

Oliver.