Hyams Iftach wrote:
The idea of using watchdog timers work very well since those areThe idea behind a watchdog timer is that it makes sure that you can reach the system, assuming you don't fuck up in a too major a way that the system does not work even after a reboot. This concept is kinda aimed at Windows, where a reboot will often really solve your problems.
usually accessed directly (just map the memory over PCI or whatever
bus you have).
Those timers start the countdown once they set an initial value and
then you have to set them all along the life cycle. One have to estimate
the time till next refresh and hope the timer had such long intervals ...
It is useless in general purpose system since you don't have and fixed
periodic task. Yes, the ticks ISR is but what it does not indicate any
soundness of your application (nor OS) so adding it to such procedure
will keep you from immediate reset but will not save you in case of
severe failure.
The idea is that you have a hardware device that is constantly threatening your system to reboot it. In order to pacify it, a user space process must constantly tell it "It's ok, we're still ok". You can set that process to check whatever you like before saying that. So, you can try and get a web page from you local server, try to connect to the controlling system, or whatever, and pacify the watchdog if everything's ok.
There are several problems with this:
1. It doesn't work if the corruption will prevent a clean reboot.
2. One such card I found costs in excess of 130$. That's way too much for an embedded system (about 20% of the cost)
as a result
3. It's not that useful for task specific repeated work based on linux.
It MAY be useful for general purpose servers. Also, it will be useful for Windows, in case the machine crashes. Then again, I'm not sure remote consoles won't be better.
Shachar
-- Shachar Shemesh Lingnu Open Source Consulting http://www.lingnu.com/
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