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TPS65381A-Q1: If AUTO_BIST_DIS = 1 is used, what happens if DIAG_EXIT is still set to 1 on WD Reset?

Max Wittekind
Expert 1875 points
Part Number: TPS65381A-Q1

Dear TI-Supportteam,

We were wondering what would happen if the AUTO_BIST_DIS bit is set to 1 and a WD reset occurs. According to the documentation DIAG_EXIT gets reset post LBIST., which means that in this configuration DIAG_EXIT would still be set to 1 leading to a transition to either ACTIVE or SAFE state.

(Q1) Is the assumption about the automatic transition out of DIAGNOSTIC state due to DIAG_EXIT still beeing set correct?

(Q2) Is the WD_FAIL bit still set after WD reset and thus leading to a transition to SAFE state or is it reset in RESET state and we would transition to ACTIVE state?

Thank you and best regards,

Max

  • 0
    TI__Genius 12735 points

    Hi Max,

    DIAG_EXIT should default to 0 when a reset event happens. I did not find anywhere in the datasheet that refers to DIAG_EXIT being reset when LBIST is run, can you show me where you found that? DIAG_EXIT_MASK is set to 0 when LBIST is run but this bit is different than DIAG_EXIT. DIAG_EXIT will need to be set to 1 to move from DIAGNOSTIC to ACTIVE state.

    I would recommend referencing Figure 5-16 in the TPS65381A-Q1 datasheet. This figure shows what states the device will go to based on a few different conditions. In the case of a watchdog fail, the device will go to the RESET state and the next step will be DIAGNOSTIC when you transition out of RESET.

    Best regards,

    Layne J

  • 0 in reply to Layne J
    Expert 1875 points

    Hi Layne J,

    Thank you for your quick answer.

    In the datasheet the initialization source for the SAFETY_CHECK_CTRL register, which contains the DIAG_EXIT bit, is listet as NPOR and "post LBIST reinitialization" (page 86).

    (Q3) The discription of the bit does not mention a reset on a reset event. Where is that mentioned in the datasheet?

    I also have a follow up question concerning WD_FAIL_CNT reinitialization. In Figure 5-16 footnote (2) it is mentioned that WD_FAIL_CNT reinitializes to 5 on transition to DIAGNOSTIC state.

    (Q4) Is WD_FAIL_CNT initialized to 5 on transition to DIAGNOSTIC state as well as post LBIST?

    Best regards,

    Max

  • 0 in reply to Max Wittekind
    TI__Genius 17380 points

    Hi Max,

    My apologies - Layne was out of office for the rest of last week and I did not catch this thread to cover.

    He will be back today.

  • 0 in reply to Kevin LaRosa
    TI__Genius 12735 points

    Hi Max,

    I am looking in to this question and will provide an answer Wednesday 9/23.

    Best regards,

    Layne J

  • 0 in reply to Layne J
    TI__Genius 12735 points

    Hi Max,

    Please see my answers below. 

    3. I was not able to find anywhere in the datasheet mentioning this behavior, I will need to review this question further. I will provide an answer here tomorrow.

    4. WD_FAIL_CNT is initialized to 5 on transition to DIAGNOSTIC state as well as post LBIST. This can be found on pages 66 and 31 for the DIAGNOSTIC state and LBIST respectively.

    Best regards,

    Layne J

  • 0 in reply to Layne J
    TI__Genius 12735 points

    Hi Max,

    I went through the datasheet further and what I found is that the Auto BIST function is enabled by default. Auto BIST runs when enabled when the device makes a transition from RESET to DIAGNOSTIC states and Auto BIST includes the LBIST function. As we previously discussed, running LBIST causes this register value to reinitialize and will clear the DIAG_EXIT bit. Hope this makes sense.

    Best regards,

    Layne J

  • 0 in reply to Layne J
    Expert 1875 points

    Hi Layne J,

    Just to check, that my understanding is correct. If we disable the Auto BIST the DIAG_EXIT bit will still be set after a RESET and would lead to an automatic transition from RESET->DIAGNOSTIC->ACTIVE, correct?

    Best regards,

    Max

  • 0 in reply to Max Wittekind
    TI__Genius 12735 points

    Hi Max,

    The datasheet leads me to believe that may be a possibility. I would recommend always leaving Auto BIST enabled for this part as there are no specific situations where it should not be used. The DIAG_EXIT bit may still be cleared without Auto BIST enabled but as long as Auto BIST is enabled then it will definitely be cleared.

    Best regards,

    Layne J