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  • Case ID: 114606
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Watchdog while in sd_app_evt_wait

Adrian Eggenberger

Hi

I've discovered last week some unexpected resets by the watchdog. I guess I've the explanation and the workaround for the behavior, but it would be great to have this assumption confirmed. Maybe some other peoples have similar behaviors.

The firmware is built on SDK11 and is based on a simple peripheral project. We have a watchdog configured with a time of five seconds and not running in sleep mode. We establish a connection from a smart device and than do no real data transfer. The call of sd_app_evt_wait by the application never returns, because the application has nothing to do (no interrupt causing the wakeup). After around 80 seconds the system resets caused by the watchdog.

My assumption is, that the softdevice internally wakes up for handling the BLE connection intervals. These ISR's are quite short, but the Watchdog counts up a bit at any wakeup. The application won't reset the watchdog because the call of sd_app_evt_wait never returns.

The solution I have is to configure at least a timer that forces the function sd_app_evt_wait to leave from time to time.

Can someone confirm this behavior? What is the best way to work around it?

Regards Adrian

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    well that wasn't really his problem - because he wasn't stopping advertising etc, he was in connection so it was guaranteed that there would be constant interrupts in the softdevice and the CPU would be coming out of sleep mode on a regular basis, he just wanted to confirm whether those expected short wakeups would increment the watchdog, which they do, without causing sd_app_evt_wait() to return, which they don't.

    So you have found a similar thing, expect it takes much longer, which means the chip is only waking up very, very occasionally, and not, as in his case, all the time. So whatever you still do have left on, eg the softdevice enable, is causing the chip to do something and so the WDT counts.

    So the solution is to either turn off enough stuff that the chip never wakes at all, or feed the watchdog.

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    well that wasn't really his problem - because he wasn't stopping advertising etc, he was in connection so it was guaranteed that there would be constant interrupts in the softdevice and the CPU would be coming out of sleep mode on a regular basis, he just wanted to confirm whether those expected short wakeups would increment the watchdog, which they do, without causing sd_app_evt_wait() to return, which they don't.

    So you have found a similar thing, expect it takes much longer, which means the chip is only waking up very, very occasionally, and not, as in his case, all the time. So whatever you still do have left on, eg the softdevice enable, is causing the chip to do something and so the WDT counts.

    So the solution is to either turn off enough stuff that the chip never wakes at all, or feed the watchdog.

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