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TPS65381 Window watchdog timeout

Is there an error in the datasheet for the TPS65381?

It says that WDT_WIN1_CFG sets the Open window duration for Q&A mode and the Closed window for windowed watchdog. Does this register really do 2 jobs?

The default values described in the datasheet says that the closed window will be 13.75mS and the open window will be 70.4mS, but when I set the time of the WDI signal to 40mS it doesn't work, where a time of 70mS does.

Can someone clarify how to set the window periods please?

Thanks

Andy

  • Andy,

    Yes the configuration bits are used for both the default external trigger mode WDT and the Q&A mode WDT. You cannot have these two modes enabled at the same time so the register isn't really doing two jobs, but rather one job depending on the WDT mode chosen.  The opposite is true for WDT_WIN2_CFG. 

    Using the WDT with external trigger input (Default Mode) is described on page 45 of the datasheet section 5.4.1.13 and  WDT_WIN1_CFG is used to configure the closed window with the formula:  tWCW (WDTI) = (RT[6:0] + 1) × 0.55 ms (Bits RT[6:0] are located in the SPI register, WDT_WIN1_CFG)

    Using the WDT with in Question and answer mode is done via SPI reconfiguring as explained in section 5.4.1.14 starting on page 47 and WDT_WIN1_CFG is used to configure the open window with the formula:  tWOW (Q&A) = (RT[6:0] + 1) × 0.55 ms (The bits RT[6:0] are located in the SPI register, WDT_WIN1_CFG)

    Can you confirm you are using external trigger input mode and what you are triggering on or how you are measuring the WDI signal so we can check exactly what you mean by saying you set WDI signal to 40ms or 70ms.

    Also, figure 5-7 and 5-8 notes about the windows were recently clarified in an updated datasheet.  Which version of the datasheet are you using?  Please make sure you have downloaded the latest version so we are both refering to the same document as we move forward.

    Thanks. Scott

  • Hi Scott,

    I think you've missed the point of what I was saying with reference to the WDT_WIN1_CFG register. I understand there are two modes of operation, but in the datasheet it says in one mode it defines the OPEN window and in the other mode it defines the CLOSED window. So, it's doing two jobs, right?

    The datasheet I'm using is SLVSBC4B –MAY 2012–REVISED JULY 2014.

    I have wired the NRES pin to a port on the TMS570 rather than the RESET pin. I don't want the micro resetting whilst I'm trying to debug. Another port pin drives the WDI input. The code uses the NRES signal to initiate counting, then it simply counts up 1mS ticks until the desired interval has been reached then it toggles the WDI for one loop (1mS). I have a 'scope connected to these signals, so I can see what's going on.

    The NRES signal becomes active again when the interval is around 60mS, which is where I have the problem. With the default settings the CLOSED window should be 13.75mS and the OPEN window 70.4mS, which should put a 60mS interval easily inside the open window, so why am I seeing resets?

    Regards

    Andy

  • Andy, 

    It does two jobs but not at the same time, as you cannot have the watchdog running in both modes at the same time.  The job it does depends on which watchdog mode you have congigured:  Q&A mode or external trigger mode (See section 5.4.1.11).  Bit 5 ,  WD_CFG, controlls the watchdog timer configuration and thus will determine which way  WDT_WIN1_CFG register is used, hence my comment hence my comment the register can only be doing one thing at a time since the modes are mutully excluse.   

    I have assume you have set the watchdog timer up for external trigger mode, but would need you to confirm this. 

    Next have you followed the watchdog sync flow outlined on page 94, figure 6-5.   Synchronization routine is critical so you know when you start sending triggers you know if you sent them during open or closed window. For synchronization you can wait for a timeout or change the WD configuration which will force a reset cycle on the WD. 

    If you could send the scope shots we can try to see what is going on like the period and duty cycle you are giving on the WDI to try and help determine what is going on.  Another way to debug is use the register setting do disable WD reset. 

    Are you polling the WD fail counter at any point to see if you are incrementing the counter due to timeouts or edge in the closed window? 

    - Scott