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    SubjectRe: Questions about Watch Dog Timer under Linux.
    > products is usually a seperate chip on the board wich will start to
    > work after power reset and will time out in 2 seconds. The system has
    > to start dog clearing from the very beginning and there have no way to
    > disable WDT.

    That will be fun as you will probably need to start some kind of kernel
    task refereshing it early in boot unless your boot is very quick.

    If it cannot be disabled then you don't need to support the disable
    option. The watchdog API is a range of features designed to cover all
    watchdogs. Many only have a few of the features. A large number of the
    supported watchdogs only support a single timeout rate.

    > Is this the pattern we have to follow to use WDT under Linux? We have
    > to choose a chip as WDT, and it seems the chip we've familiar under
    > embedded systems can't be used under Linux?

    There are two ways to handle this depending on your needs and what the
    applications require. The first is to provide the real hardware interface
    - 2 second fixed timeout, no disable. That's perfectly sufficient.

    The other (which some devices do) is to create a kernel thread that
    refreshes the watchdog each second but *only* if a user application has
    made a watchdog call within the last [whatever] seconds. That also allows
    you to provide a disableable watchdog. More flexible but extra work and
    if your embedded system doesn't need the extra facilities - why bother 8)



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