NRF9160 watchdog enable during System OFF

[loumay]

Hi,

I have a firmware which need to transit to System-OFF under certain conditions. The startup code of the firmware enables the watchdog timer, which can't be disable once started (register are not available anymore according to NRF9160 specifications).

I observed that the watchdog is still resetting the SoC, even after entering System-OFF. Is it expected behaviour? I didn't found on the NRF9160 specifications if entering System-OFF will disable the watchdog, or keep it running.

Thanks,

Louis

[Elfving]

Hey Loumay!

I'm looking into it, but I will have to get back to you.

Best regards,

Elfving

[Elfving]

Hey again!

This is mentioned a bit in the product specification, though I guess it is more centered on allowing it to be awake than the opposite.

 

This configuration might be what you are looking for.

Best regards,

Elfving

[loumay]

Hi Elfving,

Thanks for your inputs.
I'm aware of this configuration options for the watchdog and it does indeed prevent the SoC from resetting after entering System-OFF.

However, it does more than this if I understand properly: The watchdog won't count down after each call of `wfi` or `wfe`. This is an issue for me, as our firmware is expected to enter sleep mode regularly to save power. The watchdog won't be able to do is duty and reset the firmware if this one is "stuck", e.g.: in longer than expected sleep state, or simply in Idle loop.

As this CONFIG.SLEEP can't be configured after the watchdog is started, this will sadly not be an option for me.

Looking at https://infocenter.nordicsemi.com/topic/ps_nrf9160/pmureset.html, I can see at the bottom "⁵ Watchdog reset is not available in System OFF." .
Doesn't it means that watchdog should not be able to get the nrf9160 out of System-OFF?

[Elfving]

Hey Loumay!

loumay said:

Watchdog reset is not available in System OFF."

It seems that you are right about that, my mistake. In system off all clocks are turned off. 

Are you checking this using debug mode? If that was the case it would change things.

Best regards,

Elfving

[loumay]

Hi Elfving,

Thanks again for your support.

I found out that my issue was due to the modem not turned off properly before requesting System-OFF.

A power measurement helps me to figure this out.

This is stated in infocenter.nordicsemi.com/.../system_off_mode.html:

The LTE modem also needs to be stopped, by issuing a command through the modem API, before entering System OFF mode. Once the command is issued, one should wait for the modem to respond that it actually has stopped, as there may be a delay until modem is disconnected from the network.

Waiting the response from the modem solve the issue.

Thanks again,

Louis