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Intel and using pins for multiple purposes

Discussion in 'Hobby Electronics' started by Sylvia Else, Sep 21, 2013.

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  1. Sylvia Else

    Sylvia Else Guest

    I was wondering why I couldn't use the watchdog timer function on one of
    my computers - the driver says that it's been disabled in hardware.

    A look at the chipset page reveals that when the system is powered up, a
    pin is sampled, and if it is high, the watchdog timer function is indeed

    The pin has a pulldown resistor, which the spec warns can be as high as 50K.

    Only thing is, the rest of the time, the pin is the output intended to
    drive (indirectly) the computer speaker.

    So if the speaker driver circuitry is implemented in a way that could
    behave as a modest pullup, it could unintentionally disable the watchdog
    timer function. I rather suspect that this is what is happening, since I
    can't see any reason for a MB manufacturer to deliberately disable such
    an obscure function.

    Which leaves two questions.

    1) Was the speaker output pin really the best choice for this?

    2) Where is the need to disable the watchdog timer function at all? If a
    system doesn't program it to operate, then it won't. There seems no
    earthly need to make it impossible for software to use it. It's not even
    the kind of thing that would make for product differentiation (charge
    more for a board without the functionality disabled).

    Interested readers can find the spec here:


    Search for "No Reboot (NR)" without the quotes.


  2. yaputya

    yaputya Guest

    What do you need the watchdog for?
  3. Sylvia Else

    Sylvia Else Guest

    Restart the system if it hangs.

  4. I can only imagine that Intel provided a method for disabling the hardware
    watchdog in order to avoid an infinite boot loop in the event that the timer
    was set to too short a duration.

    I haven't looked into the architecture, but the speaker output would likely
    be the least critical pin (system function wise), and would tie in well with
    the "system diagnostics" side of things - the motherboard manufacturer
    definitely seems to have botched it.

    If you have a decent (i.e., very high impedance) multimeter, check the
    voltage on that pin at boot time. A decent DSO would be even better, but I
    suspect it's a simple resistive pull up to +Vcc rather than a pulse in
    response to something else.

    If it is indeed pulling it up, simply cut the speaker circuit off - I'd
    suspect in your scenario watchdog time functionality would be more
    beneficial than the provision of a power-on beep. If you still want
    provision for power-on diagnostics, put a switch in there, to switch the
    speaker circuit back in if the system fails.
  5. yaputya

    yaputya Guest

    Yeah but why do you need it running unattended?
    If it hangs you must have a software/hardware problem.
    You shouldn't be using a Windoze PC for anything critical anyway.
  6. It could also be something as simple as a flipped bit pursuant to a
    voltage/magnetic surge. There's a reason why 100% of dedicated servers
    actually have a functional watchdog implementation.
    I didn't see anywhere in her post that she'd written she was using Windows.

    Just for the record though, I have a server sitting here which has been
    running Windows (2K Server) continuously since late 2002 and hasn't once
    crashed due to software failure (I'll admit that it's had two PSUs and one
    HDD replaced in that time - but neither of these have anything to do with
    choice of operating system). I also have a Debian machine which falls over
    of its own accord at least once a week due to memory leaks in a driver.
  7. Sylvia Else

    Sylvia Else Guest

    Who said it was Windows?

    I say I want to use the watchdog timer. I can't for the life of me see
    how you can conclude that I shouldn't want to.

  8. Sylvia Else

    Sylvia Else Guest

    Though the only thing that could stuff things up that badly would be the
    BIOS, and if a BIOS developer gets things that wrong on a system with a
    BIOS rom that's soldered into place, and thereby not reflashable, they
    strongly deserve to have to buy a new motherboard.
    After posting, I did reflect on it some more, and it certainly seems
    that the most obvious speaker driver implementation (and we're not
    talking Hi-Fi here), is not likely to function as a pull-up. I've
    entered a support ticket with the board manufacturer - but what are the
    odds that they'll just tell me to reflash to the most recent BIOS? I
    already did anyway, before looking at the hardware details. It didn't
    help, of course.
    Unfortunately, I can't even reach the pin - it's a surface mounted
    device soldered to the board with an array of pins. I've tried
    backtracking from the loudspeaker driver (using a magnifying glass), but
    I quickly get lost, and I suspect this is a multi-layer board. Buying an
    X-ray machine to diagnose this seems a bit over-the-top.
    If necessary, I'll just buy a third-party watchdog card.

  9. yaputya

    yaputya Guest

    I assumed so, around 90% of PCs use it.
    You normally only use a watchdog to reboot when a problem occurs.
    If you are having PC problems this ng might be able to help you fix them directly.
    So, why do you need a watchdog in the first place?
  10. Sylvia Else

    Sylvia Else Guest

    So you assumed that I was doing something critical, but that I was using
    Windows for it, despite, in your view, the inappropriateness of that.
    Seems a bit arrogant to me.
    I can't fix a problem until it exists, and if one arises, then without
    the watchdog timer, the system will hang until such time as I notice,
    which I don't want.

    Pretty much the standard use of watchdog timer, indeed.

  11. yaputya

    yaputya Guest

    Not really, and no offence intended.
    I simply meant *if* it was critical, you shouldn't depend on Windows.
    Since you haven't given a reason why you want to go to the trouble of using
    a watchdog, I still don't know if your application is critical or not.
    If you are using Windows, just say so.
    A watchdog reset won't fix hardware software problems.
    And if you aren't around to notice a crash, you won't be around to see the watchdog stuck
    in an endless reboot sequence either, if the fault is still present. Unless you write recovery
    code your PC will not resume where it left off either.
    You still haven't explained what you are doing with the PC that justifies
    a watchdog. You may be better off with a more stable O/S instead.
  12. Sylvia Else

    Sylvia Else Guest

    It already resumes its critical task on a reboot.
    Remind me why it needs to be justified.

  13. Sylvia Else

    Sylvia Else Guest

    I submitted a support ticket to the board manufacturer, whose initial
    response was that they don't support Linux, and that I should install a
    Windows operating system and try it there.

    I said I'be be willing to try, but that as far I can see there's no
    official driver for the hardware.

    Their response is now that I contact Microsort for further information.

    Perhaps they mean that if I get enough information from Microsoft to
    write a driver for the hardare, do so, and then it doesn't work, they'll
    take the matter seriously.

    The real situation seems to be that they don't support any chipset
    feature that Windows doesn't use, and it's pot-luck whether it'll work.

    The board, BTW, is a GA-H61M-S2PV (rev 2.0). I've also tried a revision
    2.2, with the same result.

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