nRF9160 fails to attach after several RESETs & attach without power cycle

[Michal Mühlpachr]

Hi,

nRF9160 with SLM NCS v1.9.1 fails to attach after 7th RESET (by RESET pin) & attach without power cycle.

There is not any ERROR state reported by modem, modem fails to attach forever without power cycle.

After nRF9160 power cycle it attaches immediately with same AT sequence.

We need reliable initialization of nRF9160 SLM/Modem without nRF9160 power cycle because we do not have load power in production HW - issue threatens device stability in the field.

I prepared Python script to reproduce issue with nRF9160DK, you can find it together with log at https://gist.github.com/muhlpachr/40a4d8f1b332aee8a25fa7e1ad023751
Modify COM port for AT commands according your PC setup please.

Issue is 100% reproducible.

Attached you can find modem trace.

Thank you.

Regards,
Michal

trace-2022-03-24T23-42-16.760Z.bin

[Øyvind]

Hello Michal, 

Can you please verify that you are not seeing the nRF9160 Modem Reset Loop Restriction?

Kind regards,
Øyvind

[Øyvind]

Please try with more than 60 seconds between each reset. This is most likely due to the reset loop restriction which will count every reset done within 60 seconds.  

[Michal Mühlpachr]

Hello Øyvind,

yes, it is %MDMEV: RESET LOOP, we were not aware of nRF9160 Modem Reset Loop Restriction functionality.

Is 60 seconds delay between RESETs mentioned anywhere in documentation please ?

Why there is not ERROR reported  by modem while in RESET LOOP after +CFUN=1 ?

Thank you.

Regards,
Michal

[Øyvind]

Hi, 

Michal Mühlpachr said:

Why there is not ERROR reported  by modem while in RESET LOOP after +CFUN=1 ?

I assume that this is due to not subscribing to the modem domain event notification.

Michal Mühlpachr said:

Is 60 seconds delay between RESETs mentioned anywhere in documentation please ?

No, looks like this is not documented from what I can see. 

Kind regards,
Øyvind

[Michal Mühlpachr]

It is clear, that without %MDMEV=1 we do not get URC. But it is strange to get OK for +CFUN=1 while in RESET LOOP.

I just tested to try attach 1h after %MDMEV: RESET LOOP URC, but I am still getting %MDMEV: RESET LOOP. It does not behave according https://infocenter.nordicsemi.com/index.jsp?topic=%2Fref_at_commands%2FREF%2Fat_commands%2Fmob_termination_ctrl_status%2Fmdmev_set.html

Modem was powered whole 1h and RESETed by pin with CONFIG_SLM_START_SLEEP=y in SLM at the beginning of 1h and at the beginning of next try. Remaining time was not stored in NVM, because after power cycle, modem attaches immediately. Why 30 minutes timeout do not apply ?

[Øyvind]

Hello, 
can you please provide a new modem trace and log from the updated scenario? 

Michal Mühlpachr said:

But it is strange to get OK for +CFUN=1 while in RESET LOOP.

Note that changing function of modem is not equivalent to network attach. Do you use AT+CFUN=0 to gracefully shut down modem?

Thanks. 
Kind regards,
Øyvind

[Michal Mühlpachr]

Hi,

with modem trace enabled I am not able to reproduce RESET LOOP after 40m or 1h.
I am able to reproduce it only without modem trace. Sequence is same as below.

But I am able to reproduce, that even with 2minutes delay between RESETs I am still getting RESET LOOP in 7th cycle after power cycle. Modem trace is attached.

Regads,

Michaltrace-2022-03-28T21-28-11.914Z.bin