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TMS320F280049: Watchdog not compatible to other Piccolo devices, force reset not possible when WDDIS set

StephanS
Genius 4087 points

Part Number: TMS320F280049

Hi,

we are forcing Piccolo devices to reset by writing a zero into the WDCR register. The wrong WDCHK value causes an immediate reset.

On the 280049, this does not work if the watchdog is disabled (via WDDIS bit). In this case, any write to the WDCR register that does not include the correct WDCHK value is ignored.

So our "force reset" procedure has to be extended:

First, make sure that the watchdog is enabled by clearing the WDDIS bit (and writing the correct WDCHK value).

Then write an invalid value (zero) to WDCR as before to force a reset.

The changed behaviour is okay for us, but is not code compatible to other Piccolo devices. And - it should be noted in the datasheet.

Regards, Stephan

  • 0
    TI__Guru** 116511 points
    Stephan,

    We are looking into this. One question though, watchdog comes-up enable by default. Are you disabling it in your application and then trying to reset via watchdog ?

    Regards,
    Vivek Singh
  • 0 in reply to Vivek Singh
    Genius 4087 points
    Vivek Singh,

    thanks for looking into this.
    Yes, we are disabling the watchdog in our application for some special actions and trying to reset via watchdog during these actions.
    This was the fastest way for a forced reset.
    Or is there another easy reset-force possibility?

    Regards, Stephan
  • 0 in reply to StephanS
    TI__Guru** 116511 points

    Stephan,

    In old Piccolo device TRM also it is mentioned that WDCHK field should not be written when WD is disable. 

    I agree that functionality may have changed on new device but since device comes up with WD enable and no one should write to WDCHK if WD is disabled hence it should not cause compatibility issue. 

    We'll update the document (clarify in WDCHK bit field definition) for this. Thank you for providing the feedback.

    Regards,

    Vivek Singh

  • 0 in reply to Vivek Singh
    Genius 4087 points
    Vivek Singh,

    I agree that this is no big issue - we can extend the forced reset by first enabling the watchdog.
    But - I have to disagree with the interpretation of the WDCHK 'other' documentation: It clearly says
    "Note that this happens even when watchdog module is disabled."

    Regards, Stephan
  • 0 in reply to StephanS
    TI__Guru** 116511 points
    Yes, I agree. I was just pointing out that there is a statement in TRM not to use it that way though it works. As mentioned, we are going to update the definition of this bit in TRM to make it clear.

    Regards,
    Vivek Singh