NRF9160 Modem and Brownouts

[Thomas]

What level of risk is involved with brownouts for the modem? We have seen some modems in the past which have bricked themselves when a brownout has occurred when performing periodic flash maintenance. Is there any chance of something similar happening on the nrf9160? How robust is the modem to the frequent brownout resets that would be seen when batteries are on the way out?

Kind regards,

Thomas

[Heidi]

Hi! I apologize for the delayed response to your inquiry. 

The modem is quite reliable when it comes to power being cut during file system operations. 

File system sync is done occasionally to all files. Although the sync does not always erase the in-use half of file system, it is recommended that we are conservative and the sync is done at most three times a day (this ensures the 10 000 erase cycle limit is not reached within 10 years).

I have never encountered the modem being bricked. I have forwarded this to the developers though, and I'll update you when I hear back.

Best regards,

Heidi

[Thomas]

Thank you Heidi, It is good to hear you have not seen this before. What would happen if power was cut during one of these file syncs?

[Heidi]

The file system is designed to be as robust as possible, so it will survive even if the power is cut during file system operations. However, the latest changes may be lost. 

[Thomas]

Thank you Heidi

[Thomas]

Hi Heidi, sorry one more question. When you say it is recommended the sync is done at most 3 times a day, are you saying the modem handles that, or we as users need to ensure it does not do that? If so, how? We don't have to limit the amount of times we power down the modem with AT+CFUN=0 do we?

[Heidi]

I'm not sure. 

I know there is some limit to running AT+CFUN=0, which is why we recommend customers use AT+CFUN=4 if they're going to be powering down very often, but I don't know if this limitation is due to the file-sync or something else.

But as for the 3 times a day maximum, a believe the modem takes care of that. I have asked a developer to double-check so I'll let you know when I get a reply.