CONFIG_LTE_MODE_PREFERENCE_LTE_M_PLMN_PRIO Description ambiguity

[thomasGronroos]

In the LTE_MODE_PREFERENCE Kconfig description the CONFIG_LTE_MODE_PREFERENCE_LTE_M_PLMN_PRIO option states that:
"LTE-M, PLMN prioritized

LTE-M is preferred, but PLMN selection is more important. The modem will prioritize to stay on home network and switch over to NB-IoT if LTE-M is not available."

In this description it says that the modem prioritizes to stay on home network, but in %XSYSTEMMODE at command the prioritization states that:
"3 – Network selection priorities override system priority, but if the same network or equal priority networks are found, LTE-M is preferred."

So are these options same underneath and does home network in the first one refer to the sim operator's network or something different? If it does mean sim operator's network does the option have any effect when roaming? 
Also do either of these options affect the modems operation when waking up from PSM?

[Øyvind]

Hello, 

I have been assigned your ticket and will provide an answer by end of today. 

Kind regards,
Øyvind

[Øyvind]

thomasGronroos  here is the answer I got from our team regarding the documentation. 

The modem prefers to stay in the home network. If LTE-M is found, it selects that. If LTE-M is not found, it searches for NB-IoT in the home network.

 If no home network is found, the modem prefers to roam in LTE-M. If LTE-M is not found, it searches for a roaming network on NB-IoT.

Still waiting for more confirmation on the PSM functionality: 

When modem wakes up from PSM, it tries to find the previous cell, after that I believe it searches for another cell in the same network. If nothing is found, I would assume that it enters PLMN selection.

Kind regards,
Øyvind

[Øyvind]

Hello, my sincere apologies for the late reply from my side. This fell off my radar. 

Our modem team points out that the PLMN selection in the code base was incorrect, and that the AT commands documentation is correct:

PLMN selection at PSM wakeup: Regardless what is the preference, modem will search for the last registered PLMN (stored to SIM) in the last registered system. If that is not found, then it falls back to the normal PLMN and system selection rules and follows the LTE preference.

Let me know if this answers your questions. 

Kind regards,
Øyvind