AT%XVBAT behavior on different mode.

[Balamurugan]

Hi,

We are using  AT%XVBAT command to get battery voltage and detect low battery.

We facing issue in CFUN=20 mode, sometimes  AT%XVBAT is returning latest voltage and sometimes returns last know voltage continuously until power off . But in  CFUN=4 always reruns current voltage as expecetd.

we would like to know the AT%XVBAT on different modem modes. 

Network mode	Current value	Last know value
CFUN=1 Mode active(RX/TX)
CFUN=1 PSM
CFUN=21  Mode active(RX/TX)
CFUN=21 PSM
CFUN=4 offline
CFUN=44 Offline mode without shutting down UICC
CFUN=0 Power Off
CFUN =30
CFUN =31

Please fill table with YES or NO for AT%XVBAT command behavior.

Modem version using:1.1.1

Thanks,

Bala

[Øyvind]

Hello, 

I have forwarded your inquiry to our R&D department. I'm assuming you are using Thingy:91? Please have a look at this answer from my colleague. 

Also, when are you seeing these issues, as the note in the +XVBAT documentation:
Note: Longer sleeps, such as eDRX and PSM, are modem active time. Therefore, in those cases the %XVBAT value returned is from the time just before entering the sleep or from previous GPS reception during the eDRX/PSM gap.

Kind regards,

Øyvind

[Balamurugan]

Hi,

we are using nrf9160 in our product. its custom board. since behavior of %XVBAT  is not consistent with "CFUN=20' during our testing. we request you to share behavior on different mode in the table.

As mentioned in doc +XVBAT documentation. we are clear with PSM mode and its working expected.

we are just concerned  about other modes.

Awaiting for the reply.

Thanks,

Bala

[Øyvind]

Hello Bala, 

The answer regarding the table is that it is too difficult to provide. There are several factors that would not give the correct answer.

Our engineers' response based on the description in AT reference guide: 

The battery level is measured and stored when RF circuits are used for transmission or reception. This value is returned when the modem is activated with CFUN=1/21/31. There is no difference between active CFUN modes. If there is no activity in the modem, RF circuits are off and the battery level is not measured. During long sleeps like PSM, this will cause some inaccuracy to reported voltage as the stored value may be somewhat old.

This means that if AT+CFUN=20 has been given, then GNSS is still active, which prevents measuring battery voltage when the AT%XVBAT is given. Thus the last previously measured value is returned at that point. In AT+CFUN=4 mode, the modem is fully shut down, so AT%XVBAT can wake it up, do the measurement, report value, and go back to sleep. 

Regarding CFUN=20 mode... if the GPS receiver has not been started or is stopped using the GPS socket options (e.g. NRF_SO_GNSS_STOP), then the GPS receiver is not really active and also the runtime VBAT measurement is not enabled. In that case, the VBAT will return the value that it has previously measured. But if GPS is active in CFUN=20 mode (started with NRF_SO_GNSS_START) then it should return the current value. The same goes for mode CFUN=30. If mode is in PSM, the reported value is old. Also, the customer might have a fix_interval or fix_retry setting in GPS that disables the receiver for a set time. If he modifies the voltage during that time and sends the AT%VBAT, he will not get a current value.

GNSS only mode can be activated with CFUN=31 but GNSS tracking is not started from the RPC interface. Also, the application does not have knowledge about PSM or other sleep modes inside modem. The customer may get the last known value instead of the current value because the application doesn't have all the modem status information.

Let me know if anything is unclear. 

Kind regards,

Øyvind

[Balamurugan]

Its Clear. Thanks for the detailed explanation.