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Pablo Devanne
Pablo Devanne
Associate
March 20, 2017
Solved

STM32F407 : IWDG and erase flash sector

  • March 20, 2017
  • 2 replies
  • 3491 views
Posted on March 20, 2017 at 15:53

Hi,

In my application I'm using the Independent watchdog on a STM32F407 with a maximum reload period of 2 ms. During some maintenance operations, we need to save some configuration parameters in flash memory. Even if we use the 16 kB sector, the erase time is greater than 2 ms and the IWDG make the MCU reset. Because there is only on flash bank on the 407 I can't kick the watchdog during the flash erase operation (and the bus stalls anyway), and it is not possible to disable the IWDG.

In order to avoid these resets, I tried to reconfigure the IWDG with a max reload period of a few seconds which is, I measured, way greater than the time needed for the erase operation.

In debug, the registers of the IWDG looks fine after the reconfiguration but when I tried in release or in debug but with no break point near the erase sector routine I have a IWDG reset.

Is there any way to avoid this behavior or am I just not correctly reconfiguring the IWDG ?

Many thanks in advance,

Pablo

    This topic has been closed for replies.
    Best answer by waclawek.jan
    Posted on March 23, 2017 at 23:59

    OK so I played for some more and I'd recommend you in any watchdog timing change to:

      IWDG->KR = 0x5555;  // allow accessing other registers

      IWDG->RLR = 4; // any timeout you want

      while (IWDG->SR AND IWDG_SR_RVU) != 0) {  // this takes 6 LSI clocks

        IWDG->KR = 0xAAAA; // kick the dog (*)

      }

    // okay by here the dog timing according to the new setting is active

    I tried only the lowest prescaler (i.e. IWDG->PR = 0) so there might be gotchas with other prescaler settings.

    I'll describe my detailed findings in a separate thread and some time later, it's almost midnight here and I desperately need some sleep, tomorrow workday again.

    JW

    2 replies

    Pablo Devanne
    Pablo DevanneAuthor
    Associate
    March 23, 2017
    Posted on March 23, 2017 at 09:47

    A solution could be to locate the IVT in RAM and to use a timer to generate a 1ms interrupt, the ISR would be in ram and would kick the watchdog. Then, when the maintenance operation is done, de-initialize the timer for normal behavior. But I am not really seduced by this method.

    Do you have another idea ?

    AvaTar
    AvaTar
    Senior III
    March 23, 2017
    Posted on March 23, 2017 at 12:14

    A possible solution might be to reset the MCU, and re-initialize without the IWDG for flashing. When done, either init the IWDG, or reset again and proceed with a 'normal' startup.

    waclawek.jan
    waclawek.jan
    Super User
    March 23, 2017
    Posted on March 23, 2017 at 10:03

    IMO there are details in the IWDG working which are not properly documented, see for example

    https://community.st.com/0D50X00009XkYEQSA3

     

    The freshly loaded values might not get active until one 'old period' elapsed for example. Try waiting 1-2ms after changing the IWDG parameters, while kicking the dog otten enough, after that try the FLASH programming.

    ST might want to comment both here and in the linked thread.

    JW

    Pablo Devanne
    Pablo DevanneAuthor
    Associate
    March 23, 2017
    Posted on March 23, 2017 at 16:47

    Thanks I will try this solution and come back to you.

    But if I understand well, if I configure the watchdog for a 2 seconds period in order to erase my sectors and write them, I will have to wait for 2 seconds to get back to the 2ms behavior after reconfiguration ... That's not really what you could expect from a watchdog peripheral ...

    waclawek.jan
    waclawek.jan
    Super User
    March 23, 2017
    Posted on March 23, 2017 at 16:51

    I didn't say that's how it's exactly behaving, all what I said was that the RM does not give an exact description of the behaviour.

    You can try this quickly on a simplified minimal example, you don't need to implement it into your actual machine.

    JW

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