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

[RK]

Yes it will pause until woken from sleep mode. So you are being woken from sleep mode, hence it's counting very, very slowly because you're being woken very, very occasionally, but you are being woken.

So again, for the n'th time, feed the watchdog. When you are in your low power mode and sleeping for a long, long time with your watchdog timer disabled, any time you are woken up from __wfe(), feed the watchdog, that will prevent any occasional events which are occurring and causing the CPU to run even just a few microseconds, from causing the watchdog reset.

__wfe()
if( in_deep_sleep_mode )
    feed_watchog()