nRF9160 modem: Not reconnecting to network after reset

[JordanYates]

After several resets of an application (Either soft-resets or reprogramming) the nRF9160 will fail to connect back onto the network.
Currently using v1.3.4, but this issue also occurred on v1.3.3

LTE_LC_EVT_NW_REG_STATUS will happen with LTE_LC_NW_REG_SEARCHING, followed by LTE_LC_EVT_CELL_UPDATE with a valid cell.
However LTE_LC_EVT_RRC_UPDATE never occurs. Under normal operation RRC_UPDATE occurs a few hundred milliseconds after CELL_UPDATE.

Additional resets of the the application do not bring the modem back to an operational state.
A hard power cycle brings the application back immediately.

Attached is a modem trace at level NRF_MODEM_LIB_TRACE_ALL of when this issue is occurring.
This was triggered by letting the watchdog expire on the application after 1 minute several times in a row.

modem_trace_1674798274.bin

[dejans]

Hi,

Modem searches the area for networks, but in your case it does not completes the search. The issue might happen due to multiple resets performed by the application. Documentation specifies that for modem firmware version 1.3.1 or newer, maximum 7 resets are allowed before modem RESET LOOP is activated. Once in reset loop, attach requests are restricted in next 30 minutes.

Best regards,
Dejan

[JordanYates]

Hi Dejan,

That makes sense, thanks for the response. Is it expected for GNSS operation to be blocked while it is in the RESET LOOP mode?

Thanks,
Jordan

[dejans]

Hi Jordan,

GNSS can be started when RESET LOOP restriction is active. You can read more about the operation of the GNSS receiver and modem Reset Loop restriction in the documentation. 

Best regards,
Dejan