The AT+CFUN=0 take long time sometimes

[Tim Chao]

Hi,

I am developing a low-power device to periodically publish data.

I need to turn off the modem after the publishing task is completed.

And I found that sometimes the AT+CFUN=0 takes a long time to get response.

Below is the code piece for turn-off the modem.

// turn-off modem ~
int64_t start = k_uptime_get();
err = lte_lc_power_off();
int64_t end = k_uptime_get();
LOG_DBG("AT+CFUN=0 done (%5llu ms)", end - start);

And here are some logs I got.

[00:11:31.559,295] <dbg> modem: modem_power_off: AT+CFUN=0 done (  707 ms)
[00:12:35.537,811] <dbg> modem: modem_power_off: AT+CFUN=0 done ( 3034 ms)
[00:14:09.772,918] <dbg> modem: modem_power_off: AT+CFUN=0 done (37793 ms)
[00:15:29.533,721] <dbg> modem: modem_power_off: AT+CFUN=0 done (  651 ms)
[00:17:45.127,807] <dbg> modem: modem_power_off: AT+CFUN=0 done (33883 ms)
[00:18:04.649,200] <dbg> modem: modem_power_off: AT+CFUN=0 done (  681 ms)
[00:18:32.629,821] <dbg> modem: modem_power_off: AT+CFUN=0 done (  745 ms)
----
[00:22:01.609,619] <dbg> modem: modem_power_off: AT+CFUN=0 done ( 3701 ms)
[00:23:00.044,921] <dbg> modem: modem_power_off: AT+CFUN=0 done (  747 ms)
[00:24:01.036,315] <dbg> modem: modem_power_off: AT+CFUN=0 done ( 1497 ms)
[00:25:39.506,195] <dbg> modem: modem_power_off: AT+CFUN=0 done (40664 ms)
[00:26:47.982,025] <dbg> modem: modem_power_off: AT+CFUN=0 done (41370 ms)
[00:27:14.052,673] <dbg> modem: modem_power_off: AT+CFUN=0 done (  733 ms)

You can see that sometimes it takes more than 30 seconds to finish.

Is this normal behavior?

PS. I am using NCS 2.3.0 with Modem FW 1.3.3