SIM shutdown does not happen during the e-DRX cycle greater than 60 seconds on NRF9151 DK

[mnjLC]

We recently got the NRF9151-DK and were trting to measure the e-DRX current on the system working on CAT-M1 network. The NRF9151 DK is loaded with Serial LTE Modem application ( Default application that it was shipped with )and Modem firmware v2.0.0 ( Default FW that it was shipped with ). According to this post we have set the follwing at commands 

at+cfun=0

AT%XDATAPRFL=0 // sets the low power mode

AT+SSRDA=0,1,0 // sim shut shutdown

at+cfun=1

at+cedrx=2,4,”0101”

We are still seeing 35uA of floor current during e-DRX cycle. We feel this is a bug in the pre lodaed FW. Can someone from nordic try it on their NRF9151-DK and share the results?. I all attaching the PPK2 trace with this post.

Thanks!

nrf9151_eDRX_80_PTW_1_1NCE_NoShutoff.ppk

[Didrik Rokhaug]

Hi,

Can you take a modem trace, so that we can see the communication between the SIM card and the modem?

Are you using the same SIM card as in the previous ticket?

Best regards,

Didrik

[mnjLC]

Hi,

Attached is the PPK trace and the modem trace that you requested.nrf9151_eDRX_120_PTW_1_ATT_NoShutoff.mtrace

nrf9151_eDRX_120_PTW_1_ATT_NoShutoff.ppk

Please review and let us know your findings.
Thanks!

[Didrik Rokhaug]

Thanks, I'll have the modem team look at the trace.

From what I can see, you are using a different SIM card this time. Have you tried with the same SIM card as you used last time?

The nRF9151 and nRF9161 runs the same modem FW, so the behaviour should be the same between the two.

[Didrik Rokhaug]

According to the EF-AD, this SIM card does not support deactivation in eDRX.

[mnjLC]

Hi,

We see that there are two options +SSRDA at command,

1) suspend and resume UICC.

2) deactivate and activate UICC

Are both the mentioned options dependent on EF-AD ? From my understanding, deactivate and activate should work regardless of EF-AD register status.

Didrik Rokhaug said:

From what I can see, you are using a different SIM card this time. Have you tried with the same SIM card as you used last time?

Yes, we are using 1NCE sim at San-Francisco, USA location for testing the NRF9161. The previous test on the NRF9161 was done in India on a local NB-IoT operator's network.

Thanks!

[Didrik Rokhaug]

Yes, both those features are dependent on the EF-AD.

Not all SIM cards allows you to turn them off (using either suspend or deactivate) during eDRX, as that would wear out their flash too quickly, leaving you with an unusable SIM card (and product).

[mnjLC]

Thanks!

[mnjLC]

Hello Didrik,

We use MFF2 style hardware sims. Currently we are shutting down the sims ( at+ssrda=0,1,0 ) during the e-drx cycles. Will that also affect the flash on these type of sims?

Thanks!

[Didrik Rokhaug]

I don't think the form factor of the SIM affects anything.

[papatel]

Hello Didrik,
I'd first like to point out that the form factor does indeed make implications on the endurance capability of the NVRAM.  *Usually* MFF2 sims have a significantly higher endurance rating than their plastic counter parts. 

We do have a question regarding suspend vs sim shutoff.  If your comment about wearing flash out applies even to proper implementations of the suspend command, that is an alarming concern.  There are a ton of factors here to consider for a physical SIM:

• Endurance cycle, industrial MFF2 sims claim 500MM write cycles
• Flash wear level implementation
• Flash size (larger flash means less wear per cell if you have good wear leveling implemented)

My point is that Nordic should have good answers to these questions.  I really request we get a full answer on this from the Nordic team.  I will in parallel ask our MVNO to also consider these points.

The best solution would be a software SIM but I'm not getting any answers from my contacts at Nordic or our MVNO as to when that feature will be available.

Thank you!

-Patrick.