How implement Watch dog timer ?

shivamallu

Hi all,
I am an embedded developer currently working on a board with PowerPC processor(MPC8260)
my question is
the processor(MPC8260) i am using is having an internal watch dog timer but i dont' have any externel
watch dog timer on the board.
In my board there will be 2 images
1.bootloader
2.linux image
how shall i make use of internal watch dog timer to reset my board when the s/w running on the board hangs ?

thanks in advance
shiva

PBXMAN

: Hi all,
: I am an embedded developer currently working on a board with PowerPC processor(MPC8260)
: my question is
: the processor(MPC8260) i am using is having an internal watch dog timer but i dont' have any externel
: watch dog timer on the board.
: In my board there will be 2 images
: 1.bootloader
: 2.linux image
: how shall i make use of internal watch dog timer to reset my board when the s/w running on the board hangs ?
:
: thanks in advance
: shiva
:

Hello there,

You have a number or options. I roccomend using the Max 824. It's cheap and runs at 3v3 or 5v. Connect it to the /HRES pin of you processor and kick it at least every 250mS. If your software hangs, and let's face most sw does, the watchdog will time out and reset your hardware. The 824 has the added advantage or brown out or dc dip detection, after which it will also cause a reset. The best way to implement it to arbitratily invoke a DDWatchdogKick function throughout your code. Avoid doing so within any loops however !


Generally speaking the so-called watchdog timers within processors are pretty useless because their time-out time is typically far too quick and, because they are part of the same silicon as the processor, they are equally vunerable to EMI. In short, they are not independant Watchdogs.

Cheers,

Pat
: