I just bought the nRF9160 DK. How do I put it in deep sleep mode?
The "REGULATORS" peripheral, where the SYSTEMOFF register resides, is in the secure mode by default.
To add this to the non-secure region (the application space), you need to modify the spm.c file as explained here:
After this modification, you should be able to enter SYSTEMOFF mode:
NRF_REGULATORS_NS->SYSTEMOFF = 1;
That's what I suspected.
Thank you very much.