Using a watchdog timer to restart an MKR 1010 WiFi

Using Arduino Project Guidance
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Hello all,

I am currently simply trying to figure out how it is possible to create some code that would allow me to execute a reset when the program gets stuck for too long.

I am using some AWS WiFi connectivity functions, and if connection is lost, upon reconnection the program has gotten stuck. So if a reconnection is not found for ~10 mins, then I would like to perform a reset.

I have not had any luck with the other post similar to this which was closed last year.

Best,
Anthony

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have a look at WDTZero library - it gives examples of using WDT - I have tested it on a MKRFOX 1200

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@horace thank you! I will test this out. I appreciate your quick response! I think I tried this and found that the program does not resume again. I think this does some sort of shut off? once the timer runs out it is done forever.

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Hi @anthonylimon

The issue with the WDTZero library is that it doesn't take into account the time taken to synchronise registers on the SAMD21.

The SAMD21 has the advantage of a flexible clock system that allows practically any on-chip or external clock source to drive its peripheral modules, such as its TCC/TC timers, RTC, WDT etc... The disadvantage however is that certain registers have to be read and/or write synchronised between the peripheral and the CPU, this can take up to 5 to 6 clock source cycles.

The problem occurs if the clock source that's driving the peripheral is slow, such as the on-chip, low power 32.768kHz oscillator usually used to clock the watchdog. In this case, resetting the watchdog by writing CLEAR register requires a synchronisation time of 5 to 6 milliseconds.

The standard procedure for write synchronisation is to block and wait for the periperhal's register to synchronise:

WDT->CLEAR.reg = WDT_CLEAR_CLEAR_KEY;      // Reset the watchdog
while(WDT->STATUS.bit.SYNCBUSY);           // Wait for synchronisation

This works just fine if the peripheral is clocked at 48MHz like the CPU, but causes the program to block for 5 to 6 millisconds while writing to the watchdog's CLEAR register. This can be problematic if your program requires a fast loop time.

The solution is to use an if() statement in the loop(), to check whether register synchronisation is taking place, and only reset the watchdog if it isn't:

if (!WDT->STATUS.bit.SYNCBUSY)              // Check if the WDT register CLEAR register is not being synchronized
{
    WDT->CLEAR.reg = WDT_CLEAR_CLEAR_KEY;   // Reset the watchdog timer
}

This allows the watchdog to be reset without blocking. It might be worth modifying WDTZero library's clear() function, since others have raised a pull request for this change on Github, but the owner hasn't responded.

This issue was first described here:

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Wow. I really appreciate this in depth explanation. Exactly what I was looking for! I will try to implement this information. (As soon as I figure out how to reprogram my Arduino after getting it stuck in an infinitely resetting watchdog timer haha.. oops)

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