nRF9160 PSM active time problem

[akofoed]

Hi Nordic,

Using nrf-connect 1.9.99 and Zephyr 2.7.99 (*** Booting Zephyr OS build v2.7.99-ncs1-1 ***)

I am using then nRF9160-DK and everything is fine. Getting 40uA in LTE-M PSM mode when sleeping. However, am trying to control the active time and no matter what I do to the CONFIG_LTE_PSM_REQ_RAT, it seems to be be active in about 7 seconds. RPTAU is responding as expected.

# Config (90 secs / 2 secs)
CONFIG_LTE_PSM_REQ_RPTAU="10000011"
CONFIG_LTE_PSM_REQ_RAT="00000001"

Power consumption with active:

As you can see, the modem is active in 6.88 seconds, I would have expected it to be online in 2 seconds (RPTAU). The code running during in active mode has long finished at this point.

I would have hoped that the modem falls asleep again after 2 seconds (RPTAU).

Is there any way to get it to sleep after 2 seconds?

Kind regards

Anders
https://DataHamster.io

[Øyvind]

Hello, 

What does the network provide? I.e. issue the following command "AT+CEREG?"

From the LTE link Controller documentation under Enabling power-saving features:

A timer value that is requested by the modem is not necessarily given by the network. The event callbacks LTE_LC_EVT_PSM_UPDATE and LTE_LC_EVT_EDRX_UPDATE contain the values that are actually decided by the network.

Kind regards,
Øyvind

[akofoed]

Thanks, it says:

+CEREG: 0,4
OK

From this I gather it means:

4 – Subscribe unsolicited result codes +CEREG: <stat>[,[<tac>],[<ci>],[<AcT>][,,[,[<Active-Time>],[<Periodic-TAU>]]]]

Meaning that I active time can be set. I am using 1NCE as provider in Denmark and only using PSM mode.

Kind regards

Anders

[Øyvind]

Hi Anders, 

Is there a reason for using latest/main nRF Connect SDK branch? Can you please retry with tag v1.9.1 to verify with stable release?

akofoed said:

+CEREG: 0,4
OK

No, the response from CEREG? (read command) is

+CEREG: <n>,<stat>[,[<tac>],[<ci>],[<AcT>][,<cause_type>],[<reject_cause>][,[<Active-Time>],[<Periodic-TAU>]]]]

in your case <n> and <stat>

0 – Unsubscribe unsolicited result codes

4 – Unknown (for example, out of Evolved Terrestrial Radio Access Network (E-UTRAN) coverage)

What application are you running? Can you connect to your device using the LTE Link Monitor and issue AT+CFUN? command, if CFUN=0, issue AT+CFUN=1 first and then AT+CFUN?

This should print more information. We might also need a modem trace of when you are seeing this issue.

[akofoed]

Yes, I was running the main branch. I have now installed nrf-sdk using "west init -m github.com/.../sdk-nrf --mr v1.9.1"

I am using the sample nrf/samples/nrf9160/at_client to execute the below:

*** Booting Zephyr OS build v2.7.99-ncs1-1 ***
The AT host sample started
AT+CEREG?
+CEREG: 0,4
OK
AT+CFUN?
+CFUN: 0
OK
AT+CFUN=1
OK
AT+CFUN?
+CFUN: 1
OK
AT+CEREG?
+CEREG: 0,5,"5E09","0281150C",7
OK

In my application, I do get the right TAU and active time values in the response from the network in the callback function.

Is the modem supposed to sleep after CONFIG_LTE_PSM_REQ_RAT="00000001" seconds? == 2 seconds ? Or are there some housekeeping going on with Zephyr power management or some LTE modem stuff?

[Øyvind]

akofoed said:

Is the modem supposed to sleep after CONFIG_LTE_PSM_REQ_RAT="00000001" seconds? == 2 seconds ?

From the KCofig reference it states

Power saving mode setting for requested active time.
See 3GPP 27.007 Ch. 7.38.
And 3GPP 24.008 Ch. 10.5.7.3 for data format.

The KConfig configuration sets the PSM using AT command Power Saving mode setting +CPSMS. 
Based on that, the value you refer to is 2 seconds, yes. That is what you request. 

E.g. my CEREG response is 
+CEREG: 5,5,"08FF","0201EE16",7,,,"11100000","11100000"

Where the first number (5) is due to AT+CEREG=5.

[akofoed]

Yes, I can see that what commands are executed in the lte_lc.c file (+CPSMS). I can also confirm that I get the values back from the network - allowing me to be active in 2 seconds. Everything is good.

But my question then: Why is the modem consuming power in 6.88 seconds (JouleScope image above) and not 2 seconds?

Is the modem supposed to be awake 2 seconds and then go to sleep? Or are there some housekeeping going on with Zephyr power management or some LTE modem stuff? I can confirm that my code finishes in less than 1 sec.