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TMS320F28335: Watchdog application

Frank Lee96
Intellectual 830 points
Part Number: TMS320F28335


Hi TI，

I‘m using TMS320F28335 in our project.And we use a standalone watchdog chip in the TMS320F28335's peripheral circuit which need to be fed during 1.6 seconds.I want to know why there is a watchdog in the peripheral circuit and the real meaning of the adding of watchdog?Using it to check the CPU's abnormal work state or to check the timer used in the CPU? 

Regards,

Frank

  • 0
    TI__Guru** 115881 points
    Hi Frank,

    In general external watchdog is used to check the correct operation of device. There could be many reason why external watchdog is not fed. It could be that CPU is not working as expected or a particular peripheral is not working as expected. It all depends on how the application is written.

    Regards,

    Vivek Singh
  • 0 in reply to Vivek Singh
    Intellectual 830 points
    Hi Vivek,
    Thanks.Can the watchdog be used to supervise the on-chip Timer?Because the watchdog must be fed within 1.6s.
    Regards,
    Frank
  • 0 in reply to Frank Lee96
    TI__Guru** 115881 points

    Frank,

    Can you describe little bit more on your question?

    Vivek Singh

  • 0 in reply to Frank Lee96
    Intellectual 830 points
    Hi Vivek,
    In our application that is safe related,we holp adopt some measures to check a few microprocessor abnormities such as the RAM is stuck,the I/O is broken and so on when the microprocessor is running.We also use the timer to timing,so we want to adopt efficient way to check the punctuality of the timer.Because we use a standalone wtchdog chip and the reset time is 1.6 seconds,so I want to know whether it's reasonable to using the fixed 1.6s to check the timer.In detail,I use the timer producing a interrupt about 1.5s and fed the watchdog right away,if the timer is abnormal,the microprocessor would be reset by the watchdog chip,then the device will go wrong but there is no dangerous output.
    Best regards.
    Frank
  • 0 in reply to Frank Lee96
    TI__Guru** 115881 points

    Frank,

    It depends on your application. As long as you are sure that incase of correct operation, timer interrupt will be serviced by CPU within 1.6second hence WD will be serviced then this should work. What you need to consider is that when timer interrupt happens, if CPU is busy handling some other interrupt and it also has some other high priority interrupt pending then timer interrupt will be pending for some time and may take more than 1.6 second to get serveiced. As long as you are sure that such thing should never happens and if it happens then you want to consider that as error condition and reset the device then it is fine.

    Hope it is clear to you. I am also looping in our safety expert in this post to answer any additional question you have on this.

    Regards,

    Vivek Singh