WDT interrupt not firing

RE: WDT interrupt not firing

Susheel Nuguru — Mon, 15 Oct 2018 07:50:55 GMT

Rob,

I made a small change to remove all resets to see if the WDT interrupt is being fired or not. And it seems that it is being fired normally. I think the problem was that the logs of the interrupt will not come out before the reset and also I think something was wrong with my no init configuration. So I used Keil and forced the no init on RAM location. Please see the changed main.c file

devzone.nordicsemi.com/.../main.c

Then the results got are as expected

...

RE: WDT interrupt not firing

RobMeades — Mon, 08 Oct 2018 17:41:56 GMT

Hmmm. I've added that but it makes no difference for me I'm afraid. I get this output:

    @time 0: starting up and enable LF clock.
    @time 0: setting the watchdog timer to 5 seconds.
    @time 0: retained RAM variable is 0.
    @time 0: retained RAM variable incremented to 1.
    @time 0: resetting...

    @time 0: starting up and enable LF clock.
    @time 0: setting the watchdog timer to 5 seconds.
    @time 0: retained RAM variable is 1.
    @time 0: retained RAM variable incremented to 2.
    @time 0: no longer feeding the watchdog; it should go off and increment the retained RAM variable to 3.

    @time 0: starting up and enable LF clock.
    @time 0: setting the watchdog timer to 5 seconds.
    @time 0: retained RAM variable is 2.

...

...with this code:

#include "mbed.h"
#include <SerialWireOutput.h>

// An unsigned int in an uninitialised RAM area
#if defined(__CC_ARM) || (defined(__ARMCC_VERSION) && (__ARMCC_VERSION >= 6010050))
__attribute__ ((section(".bss.noinit"),zero_init))
unsigned int gRetained;
#elif defined(__GNUC__)
__attribute__ ((section(".noinit")))
unsigned int gRetained;
#elif defined(__ICCARM__)
unsigned int gRetained @ ".noinit";
#endif

// Hook into the weak function to allow Serial Wire Output (because that's how my board speaks to the world)
namespace mbed {
    FileHandle *mbed_target_override_console(int)
    {
        static SerialWireOutput swo;
        return &swo;
    }
}

// Watchdog interrupt handler
void WDT_IRQHandler(void)
{
    gRetained++;
    NRF_WDT->EVENTS_TIMEOUT = 0;
}

// Start LF clock, required by watchdog
void lfclk_start()
{
    NRF_CLOCK->EVENTS_LFCLKSTARTED = 0;
    NRF_CLOCK->LFCLKSRC = (CLOCK_LFCLKSRC_SRC_Xtal << CLOCK_LFCLKSRC_SRC_Pos);
    __DSB();     //<-- This will wait until write buffers are emptied.
    NRF_CLOCK->TASKS_LFCLKSTART = 1;
    while (NRF_CLOCK->EVENTS_LFCLKSTARTED == 0){ }
}

// Entry point
int main()
{
    wait_ms(1000);

    // Start LF clock
    printf("\n@time %2d: starting up and enable LF clock.\n", (int) time(NULL));
    lfclk_start();

    printf("@time %2d: setting the watchdog timer to 5 seconds.\n", (int) time(NULL));
    // Setting watchdog to 5 seconds
    // Set timeout value timeout [s] = ( CRV + 1 ) / 32768
    NRF_WDT->CRV = (5 * 32768) - 1;
    NVIC_SetPriority(WDT_IRQn, 7);
    NVIC_ClearPendingIRQ(WDT_IRQn);
    NVIC_EnableIRQ(WDT_IRQn);
    NRF_WDT->INTENSET = 1;
    NRF_WDT->TASKS_START = 1;

    printf("@time %2d: retained RAM variable is %d.\n", (int) time(NULL), gRetained);
    if (gRetained > 2) {
        printf("Setting retained RAM variable to 0 and resetting...\n");
        gRetained = 0;
        wait_ms(1000);
        NVIC_SystemReset();
    }

    gRetained++;
    printf("@time %2d: retained RAM variable incremented to %d.\n", (int) time(NULL), gRetained);

    if (gRetained < 2) {
        printf("@time %2d: resetting...\n", (int) time(NULL));
        wait_ms(1000);
        NVIC_SystemReset();
    } else {
        printf("@time %2d: no longer feeding the watchdog; it should go off and increment the retained RAM variable to %d.\n",
               (int) time(NULL), gRetained + 1);
        for (unsigned int x = 0; x < 0xFFFFFFFF; x++) {
             __asm__ __volatile__ ("nop");
        }
    }

    printf("@time %2d: Should never get here.\n", (int) time(NULL));
    while(1) {}
}

RE: WDT interrupt not firing

Susheel Nuguru — Mon, 08 Oct 2018 07:55:04 GMT

seems like we forgot to enable the lfclock.

Can you enable by defining and calling this function in your code. I can see that the WDT interrupt is being called after this.

void lfclk_start()
{
    NRF_CLOCK->EVENTS_LFCLKSTARTED = 0;
    NRF_CLOCK->LFCLKSRC = (CLOCK_LFCLKSRC_SRC_Xtal << CLOCK_LFCLKSRC_SRC_Pos);
    __DSB();     //<-- This will wait until write buffers are emptied.
    NRF_CLOCK->TASKS_LFCLKSTART = 1;
    while (NRF_CLOCK->EVENTS_LFCLKSTARTED == 0){  }
}

call this in main before initializing the WDT registers

RE: WDT interrupt not firing

RobMeades — Fri, 05 Oct 2018 10:02:36 GMT

Tried that, no change I'm afraid:

@time 0: starting up and setting the watchdog timer to 5 seconds.
@time 0: retained RAM variable is 0.
@time 0: retained RAM variable incremented to 1.
@time 0: resetting...

@time 0: starting up and setting the watchdog timer to 5 seconds.
@time 0: retained RAM variable is 1.
@time 0: retained RAM variable incremented to 2.
@time 0: waiting for 10 seconds while feeding the watchdog every second...
@time 1: feeding watchdog...
@time 2: feeding watchdog...
@time 3: feeding watchdog...
@time 4: feeding watchdog...
@time 5: feeding watchdog...
@time 6: feeding watchdog...
@time 7: feeding watchdog...
@time 8: feeding watchdog...
@time 9: feeding watchdog...
@time 10: feeding watchdog...
@time 10: no longer feeding the watchdog; it should go off and the interrupt should increment the retained RAM variable to 3.

@time 0: starting up and setting the watchdog timer to 5 seconds.
@time 0: retained RAM variable is 2.

Any other things I can try? FYI, I also tried changing the wait_ms() call while we're waiting for the watchdog to go off into a busy-wait (calling nop), just to make sure that the processor was not sleeping (and hence definitely running off HFCLK), and that made no difference, still the interrupt didn't go off.

RE: WDT interrupt not firing

Susheel Nuguru — Fri, 05 Oct 2018 07:17:29 GMT

CPU runs on 64MHz, so two 32 KHz clocks means around 3900 cpu cycles which should be more than enough for the saving some state in the watchdog interrupt. I have not seen anything like this before, but the code is so simple to fail. I think we are missing something very obvious. I am home with sick kids so, cannot run the code here. Can you see if configuring the RR registers makes any difference here. I understand that you do not want to kick the watchdog as you want it to expire and reset the chip. But I am just wondering if the functioning of the watchdog depends on configuring the RR register and enabling it. Can you please give it a try..

RE: WDT interrupt not firing

RobMeades — Wed, 03 Oct 2018 18:17:43 GMT

A possibility that exists, but which I've been afraid to mention, is that when the watchdog interrupt goes off the clock is still 32 kHz and so you actually only get two CPU clock cycles, at 32 kHz, to do anything. This would hardly be enough to run one assembler instruction before the device was reset, making the watchdog interrupt feature virtually useless. So I hope I'm wrong :-)

RE: WDT interrupt not firing

RobMeades — Wed, 03 Oct 2018 12:39:27 GMT

How interesting. Unfortunately it's a bit complicated for me to run my board under the debugger right now or I'd try that myself. Any suggestions as to what I might try to workaround/explore the issue are welcomed.

RE: WDT interrupt not firing

Susheel Nuguru — Wed, 03 Oct 2018 12:34:12 GMT

i do not have softdevice in the image, but i see that i spoke too quickly. I see that the interrupt is only being fired when i am in debug mode with a breakpoint. This is very strange. I see nothing wrong with your code at all. I believe that the bss RAM area is being properly set to no_init as i can see the variable init address to be 1 after the first reset.

RE: WDT interrupt not firing

RobMeades — Wed, 03 Oct 2018 11:50:51 GMT

Thanks for doing that. Are you sure your code is exactly the same? I've just built under ARM, GCC and IAR and under no toolchain do I see the watchdog interrupt firing. Your SoftDevice is present in the image (but not being called): could that be having an effect?

RE: WDT interrupt not firing

Susheel Nuguru — Wed, 03 Oct 2018 11:25:52 GMT

I did a quick test on my desk and the interrupt was firing ok with your code. The only differenceis that i tested this in keil, exact same code