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Describe the safety mechanism execution timing of the safety manual

Arriy
Expert 1720 points

I'm reading "Safety Manual for TMS570LS31x and TMS570LS21x Hercules™ ARM®-Based Safety Critical Microcontrollers(SPNU511D)".

I have a question,safety mechanism execution timing described in "Appendix A Summary of Recommended Safety Feature Usage".

For example, "CPU2B : Boot Time Execution of LBIST STC" at page 78.

Safety mechanism name is "Boot Time Execution", But Diagnonstic Operation is "Periodic / On-Demand".


This is a "At Boot Time" is right ?

Best Regards.

  • 0
    TI__Guru 65480 points
    Arriy,

    So this column either says 'Continous' or "Periodic / On Demand'.

    Best way to explain might be to contrast CPU2B with CPU1.

    CPU1 is the CPU Lockstep Comparator and listed as "Continous".
    This means:
    a. it operates while your application is running
    b. it's effective all the time (continually) ... it checks every cycle for
    a mismatch between the two lockstep CPUs.

    CPU2B is the LBIST test of the CPU. It is listed as "Periodic / On Demand"
    It only operates for a finite time from when the safety lib. initiates the test until the test completes.

    I'll just stop the explanation there for now to focus on what 'Periodic / On Demand' means rather than elaborating on the pros/cons; but let's say each has it's important role to play.
  • 0 in reply to Anthony F. Seely
    Expert 1720 points

    Anthony

    Thank you your answer.

    I understand it is either 'Continous' or "Periodic / On Demand' that enters this line.

    Is it correct with the recognition that you selected the closest one among them?

    Best Regards.

  • 0 in reply to Arriy
    TI__Guru 65480 points
    Hi Arriy,

    I am not sure what you mean by 'select' because the way I look at it, this is a description of the 'type' of the test ... either online or offline.

    It's not like there is any selection to make.

    You do need to know that the offline ones need to be explicitly triggered, in some cases your safety analysis may say you depend on one of the periodic tests and that it is important that it is repeated within some particular time interval.

    Whereas the 'continuous' diagnostics are on in the background and you don't need to explicitly execute them.

    do you have anything to add to make this more clear?
  • 0 in reply to Arriy
    TI__Guru 59540 points

    I agree with Anthony's comments for sure on this.

    However, I am not certain what is meant by:

    Arriy said:
    Is it correct with the recognition that you selected the closest one among them?

    Arriy, could you explain further what you you mean by this statement? The column is intended to describe how the diagnostic mechanism is instantiated. It is either continuous or it has to be executed/called on a onetime basis (boot time) or on a periodic basis. In either case of boot time or periodically it is an on demand diagnostic because the code has to deliberately call the SW that exercises the diagnostic.i.e., it doesn't happen automatically. Does this clear up the two selection possibilities?