From: Shachar Shemesh (linux-il_at_nonexisting.hamakor.org.il)
Date: Sun 02 May 2004 - 10:09:45 IDT
Hyams Iftach wrote:
> The idea of using watchdog timers work very well since those are
>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 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.
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/ ================================================================= To unsubscribe, send mail to linux-il-request_at_linux.org.il with the word "unsubscribe" in the message body, e.g., run the command echo unsubscribe | mail linux-il-request_at_linux.org.il
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