nRF91 modem connection blackout after SIM disable loops

Question

Hello! Based on some tests, I've seen that modem disables attach logic for at least half an hour in case it has tried to connect to network at least twice with disabled SIM. My assumption is that the same Modem Reset Loop restriction kicks in, because even the SIM is again enabled, modem need to be running for some time (once it was around 30 minutes, sometimes its longer) before it can again establish connection successfully or AT%XFCTORYRESET=0 need to be issued to modem - the same behavior as with reset loop restriction. I have seen the same issue on multiple devices As far as my testing went I did not manage to receive any specific notification about this event by setting %MDMEV=2 AT command (I was kinda hoping to see LTE_LC_MODEM_EVT_RESET_LOOP). The SIM disabling is a necessary feature for devices that are not used in field, so that we don't have to pay for data, that actually are not necessary. Turning off the device in that case is not an option. 
 
 It is pretty easy to replicate. Program the sample on device, disable SIM and let connect logic go in a loop few times. If you let only one connection loop to go thru, after power reset device manages to regain connection to network. I let it run for 3 loops, then enabled SIM and did a power reset. The mentioned timeout appears only after at least 2 (based on couple of tests) unsuccessful connect events. And no this is not the actual modem loop reset restriction because of the resets, in field device is never reset manually, I tested our FW with a continuously running device firmware which has a connect/reconnect logic with timeouts implemented and the same timeout appeared. 
 1200.udp.zip 
 
 I am using mfw_nrf91x1_2.0.4 and nRF SDK v3.2.4 
 
 Question is can I somehow detect when this happens on MCU side? Because currently it brings in a connection delay. We have a battery powered device and keeping the modem on for 30 minutes non stop is not really an option here. As mentioned we have implemented reconnect/retry logic with increasing timeout attempts (modem shut down gracefully between each attempt) and with that device connects to server almost half day later when SIM was enabled and device had power reset.

Øyvind · Accepted Answer

Hello again Andris, apologies for the late reply. 
 Our team have looked through the modem traces and point out the following: 
 
 From the logs it appears the application is repeatedly power cycling / software resetting the modem after the SIM is disabled. That can trigger Radio Policy Manager (RPM). Per GSMA TS .34_8.2.2_REQ_003, in permanent reject scenarios the modem allows only a limited number of application-initiated software resets, typically 1 per hour by default. The number of re-attempts depends on the SIM configuration. 
 Please try the following setup

Subscribe to + CNEC and + CGEV

If the modem notifies (+CNEC) that the reject cause “ EPS services and non-EPS services not allowed " was received, deactivate the modem (+ CFUN =4) and reactivate it after 20-30 minutes. Rebooting immediately is pointless because the SIM subscription likely won't be fixed so soon. Since Attach attempts are typically limited, use them wisely and avoid triggering them all at once.

If the modem reports the RPM restriction became active (+CGEV), wait for RPM to trigger the Attach re-attempt. The application should not trigger a reboot until the next reject (+CNEC) because the modem reboots internally once the RPM restriction ends. Do not shut down the modem completely (cut power), as it won't know how long it was off and can't determine if the RPM restriction ended.

+CGEV: RESTR 1,2 (with +CGEREP=1) can be used to detect when RPM restriction has been activated.

Let me know how this works for you. 
 Kind regards, Øyvind

nRF91 modem connection blackout after SIM disable loops

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