How to recover a nRF9160 from sporadic ENETDOWN

[Achim Kraus]

Using a Thingy!91 (v1.0.0 and v1.4.0, firmware 1.2.3, 1.2.7) I get sometimes (every couple of days) a ENETDOWN when sending data out. Before that ENETDOWN, the device was usually able to exchange 100 and more UDP messages.

Currently I do a "sys_reboot(SYS_REBOOT_COLD)", but I'm wondering, if there are less massive ways to recover.   

I found other questions, but I'm still struggling to see an "useful" answer. e.g.

https://devzone.nordicsemi.com/f/nordic-q-a/57642/nrf9160-lte-modem-documentation

but the link at the end, ends in "NOT FOUND".

So, what is the recommended way to recover from ENETDOWN?

[Achim Kraus]

Though this case is rare in reality, I'm still not that sure. Anyway, that are my results so far:

On reboot, I use

   lte_lc_init();

   lte_lc_connect_async(lte_handler)

and

   socket(AF_INET, SOCK_DGRAM, IPPROTO_UDP)

With that, the device is able to exchange UDP messages. In rare cases, sendto returns an error, and errno is ENETDOWN.

In that case, I wait now, until the registered lte_handler (see above) reports, that the device is connected again. After that, I close the old socket and open a new one with    

   socket(AF_INET, SOCK_DGRAM, IPPROTO_UDP)

again.

So far, that works. Lets see, if it still works in 2-3 weeks :-).