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watchdog count calculations

jayalaxmi b c
Intellectual 320 points

Other Parts Discussed in Thread: TM4C129XNCZAD

 I am using TM4C129xnczad. I am using CCS version is 6.1.1, TI Compiler 5.2.5. My application takes some 2 minutes to complete the execution.

Depending on execution time I want to calculate watchdog count value.  How I can do the calculations to feed the dog.

Thanks in advance.

 

  • 0
    Guru 27665 points
    You mean vary the watchdog time during run? That sounds like a bad idea.

    A two minute watchdog seems very long as well.

    Robert
  • 0 in reply to Robert Adsett
    Intellectual 320 points
    No Sir I am not loading watchdog at run time.Just I want to calculate watchdog load value with respect to my app execution time. If it is like 500ms how i need to calculate the count value.

    Thank you.
  • 0 in reply to jayalaxmi b c
    Guru 27665 points
    OK, we've gone from 2 minutes to 500mS. An improvement but still way too long IMO.

    Watchdogs on the TM4C123 (I suspect the '129 is similar but you need to read the documentation) are clocked from either the system clock or the PIOSC. Each of the watchdogs has a dedicated source, not programmable.

    The oddity is that they are a double triggered watchdog, they need to time out twice before triggering a reset.

    Suggest you include the following in your reading

    e2e.ti.com/.../1699026
    www.ganssle.com/watchdogs.htm
    www.ganssle.com/.../watchdogsredux.htm

    Robert
  • 0 in reply to Robert Adsett
    TI__Guru 59540 points
    Jayalaxmi,

    Just to be clear, as Robert mentions the watchdog is driven by one of the two clocks mentioned. To calculate the time for the watchdog you would simply multiply the WD count by 1/WD_CLK to get the time for the WD. Is this what you are asking for in your question?

    It is important to note that when you determine placement of the WD servicing, you must accommodate potential for latency due to interrupts so simple function time calculations may not be sufficient for identifying the spacing of you when you service your WD.

    Also, as Robert mentions, please have a look at the datasheet/user guide and let me know if you have any additional questions regarding configuring the WD.