NRF9160 Modem CCLK overhead and intended design

[GJSea]

Hi,

Couple of questions:

- I'm finding that querying the Modem clock with AT+CCLK? always returns the network time the instant after it has registered with the LTE network. Should I not assume its availability and need to build in the querying of an NTP server followed by setting the clock with AT+CCLK= in case it is initially not available? In this case does this manually set time get overwritten when an LTE network time has been received?

- Can I assume the modem firmware will use its internal RTC clock to keep the time current even during PSM sleeps?

- What is the overhead of calling AT+CCLK? is it just simply creating the modem recv response string internally within the modem firmware?

Thx!

[Bjørn Kvaale]

Sorry for the delayed response. The clock command should read the real time clock, not the network time. So for me, it does not really make sense why it should return the LTE network time.

I believe this could be the case, as the RTC uses the Low Frequency clock, which is only turned off during System Off mode. However, PSM mode is not system off mode, so I believe this should be fine. I will double check this internally.

Let me check internally & get back to you.

[Bjørn Kvaale]

Received an update from Finland: "Modem internal clock is updated always when time is received from LTE network. If user has set time with AT+CCLK, it is overwritten. It should be noted that not all networks are sending time and date information and thus it can't be guaranteed that correct time exists in modem.

Modem FW keeps the clock also during PSM, however the most strict accuracy requirements can't be fulfilled.

The response to AT+CCLK? is generated internally in modem. No network signalling is needed."

[GJSea]

Thanks Bjorn, I'll make sure there is an HTTP backup to get and set the time from an NTP server if the AT+CCLK is not initially acquired.

[Bjørn Kvaale]

Would you mind upvoting any of the comments you thought were good?