Rerouting AT interface for power measurement using external supply

RE: Rerouting AT interface for power measurement using external supply

Frikkie Badenhorst — Thu, 08 Jul 2021 10:38:30 GMT

Thanks Stian, your help has been extremely helpful in testing the module! Have a lovely summer time!

RE: Rerouting AT interface for power measurement using external supply

Stian Røed Hafskjold — Wed, 07 Jul 2021 11:16:54 GMT

And:

The default keepalive time can be specified with the `CONFIG_MQTT_KEEPALIVE` Kconfig option.

RE: Rerouting AT interface for power measurement using external supply

Stian Røed Hafskjold — Wed, 07 Jul 2021 09:39:39 GMT

Feedback from the SW developers:

MQTT is over TLS or TCP, which is restricted by MSS of modem IP stack (708) for one packet. But APP side does not really need to care about this, as MQTT lib loops to send out MQTT payload in multiple packets.

https://github.com/zephyrproject-rtos/zephyr/blob/main/subsys/net/lib/mqtt/mqtt_transport_socket_tcp.c#L69
https://github.com/zephyrproject-rtos/zephyr/blob/main/subsys/net/lib/mqtt/mqtt_transport_socket_tls.c#L107

To publish in normal AT command mode, it’s limited by MQTT_MESSAGE_BUFFER_LEN defined for SLM/MQTT service, which has a default value of below:

#define MQTT_MESSAGE_BUFFER_LEN NET_IPV4_MTU

You can increase the MQTT_MESSAGE_BUFFER_LEN to send/receive larger payload. The other limitation are the size of AT command/response. Current AT command size is limited to 4096:

https://github.com/nrfconnect/sdk-nrf/blob/master/applications/serial_lte_modem/src/slm_at_host.c#L32

And the AT response size is limited to 1152 (twice of CONFIG_SLM_SOCKET_RX_MAX):

https://github.com/nrfconnect/sdk-nrf/blob/master/applications/serial_lte_modem/src/slm_at_host.c#L72

These values can be changed too.

In NCSv1.6.0, we added support for datamode for MQTT publish, for which the MQTT payload is only limited by datamode buffer limitation, i.e. half of AT command buffer size – DMA block size = 4096/2 – 256 = 1792 bytes.

RE: Rerouting AT interface for power measurement using external supply

Stian Røed Hafskjold — Tue, 06 Jul 2021 12:20:35 GMT

Hi I'm sorry, waiting for feedback from one of the SW engineers. Due to summer holidays many of the modem experts are out of office, so things take a bit longer. Anyways, I don't think this is any hard limitation of the modem. If you just set up a TCP socket connection, the network MTU should be at least 1500 (if I remember correctly). I don't know how this translates into the MQTT protocol though. Maybe Didrik's answer here can shed some light: https://devzone.nordicsemi.com/f/nordic-q-a/58357/nrf9160-packet-data-receive-buffer-size/238816#238816

RE: Rerouting AT interface for power measurement using external supply

Frikkie Badenhorst — Mon, 05 Jul 2021 15:13:50 GMT

Hi Stian,

Could you please provide some clarity on this as soon as possible?

RE: Rerouting AT interface for power measurement using external supply

Frikkie Badenhorst — Thu, 01 Jul 2021 16:38:25 GMT

Hi Stian, I have identified another important question:

According to the MQTT AT command used with this Serial LTE Modem app allows only a max publish payload of 576 bytes. Is this only limited by the application itself and can be increased by simply adjusting a variable, or is this a hard limitation of the modem? I cant think 576 is the max payload, thus I believe it is the former.

I also believe we will be able to specify our own MQTT keep-alive time, and not the default 60 seconds?

I am asking this on this ticket, as this is still related to the hex file you prepared for us!

Thanks!

RE: Rerouting AT interface for power measurement using external supply

Frikkie Badenhorst — Thu, 01 Jul 2021 14:23:08 GMT

Ok for now we are still not able to get it in a lower power between DRX cycles. Will have to look into the setting of the field on the SIM. When testing a modem from a different manufacturer however, we are not seeing this, which makes me wonder if it is indeed the SIM.

Nonetheless for now we can work with this value we are seeing as a test.

Thanks for all your assistance, Stian.

RE: Rerouting AT interface for power measurement using external supply

Stian Røed Hafskjold — Thu, 01 Jul 2021 13:27:33 GMT

The text marked in red in the previous answer is kind of important as well. This field has to be set in the SIM, which it's usually not by default. If you have a regular test-SIM for your callbox, you probably have the ADM key and can change this field.

RE: Rerouting AT interface for power measurement using external supply

Stian Røed Hafskjold — Thu, 01 Jul 2021 13:22:58 GMT

Sorry, forgot to mention, you need to set the power saving profile. Use the AT%XDATAPRFL command and set the level to 0.

The power saving level has an effect on the shutdown of the UICC during Extended Discontinuous Reception (eDRX) cycles. On power level 0, the modem deactivates the UICC if the eDRX period is longer than 60 seconds and UICC deactivation is allowed through EF-AD under USIM ADF. The modem activates the UICC and performs the necessary checks before setting up any signaling or data connections with the network. Otherwise, the UICC is not activated because of modem functionality.

On power levels 1–4, the modem deactivates the UICC if the eDRX cycles are longer than 10 minutes. The UICC is activated before any signaling or data connections are set up with the network and when waking up from eDRX. This means that the UICC is deactivated and activated at every eDRX cycle.

RE: Rerouting AT interface for power measurement using external supply

Frikkie Badenhorst — Thu, 01 Jul 2021 12:49:38 GMT

Thanks Stian, we have a fully configurable test network and base station (Amarisoft Callbox Mini), so we force the network to basically accept any timer request by the UEs.

When using the 5 minute TAU wakeup and 0 minute active time as you mentioned, I can see the device going into a 3uA state.

However, as a test I am setting the following:

Active timer: 30minutes

TAU: 7 hours

eDRX cycle: 655sec (+- 11 minutes)

PTW: 5.12 sec

From this,

[quote userid="4556" url="~/f/nordic-q-a/76896/rerouting-at-interface-for-power-measurement-using-external-supply/318180#318180"]This is probably due to the SIM card being active. The SIM is active if the DRX interval (the spikes you see every 640ms (?)) is less than 1 minute[/quote]

I would think that the SIM should be deactived since the DRX cycle is larger than 1minute, but we still see the 39uA current after the PTW is complete:

Is this expected behaviour? Then I guess that the SIM card is always active during the active time, regardless of the DRX cycle?

RE: Rerouting AT interface for power measurement using external supply

Stian Røed Hafskjold — Thu, 01 Jul 2021 11:59:19 GMT

This is probably due to the SIM card being active. The SIM is active if the DRX interval (the spikes you see every 640ms (?)) is less than 1 minute.

You can check this by measuring the voltage on the SIM current measurement header. If it's 1.8V the SIM is in clock stop mode and is consuming between 20-100 uA depending on the SIM card. It should be 0V when the SIM is shut down.

Try to put the modem in PSM mode, which will turn off the SIM, to get the lowest current consumption. The following AT command requests PSM mode with a 5 minute ("10001010") TAU wakeup interval, and the active time set to 0 ("00000000"). The active time specifies how long the modem should stay in DRX mode after going to PSM, after each wakeup.

AT+CPSMS=1,"","","10001010","00000000"

You should also enable unsolicited notifications at level 5, which will return the PSM settings which is actually given by the network. It does not always match the requested ones.

AT+CEREG=5
AT+CEREG?

The response should look something like this:

+CEREG: 1,"7BD5","0106C601",7,0,2,"00000000","10001010"

If the fields in red above are set to 11100000, PSM is not activated and might not be supported by the network

https://infocenter.nordicsemi.com/topic/ref_at_commands/REF/at_commands/nw_service/cereg_set.html?cp=2_1_7_7_0

https://infocenter.nordicsemi.com/topic/ref_at_commands/REF/at_commands/nw_service/cpsms_set.html?cp=2_1_7_2_0

RE: Rerouting AT interface for power measurement using external supply

Frikkie Badenhorst — Thu, 01 Jul 2021 11:09:20 GMT

Hi Stian, it looks as if we are still seeing a base current of 30-40uA with 8547.merged.hex in the idle state.

We have tried both AT#XSLEEP=0 and AT#XSLEEP=1

RE: Rerouting AT interface for power measurement using external supply

Frikkie Badenhorst — Thu, 01 Jul 2021 10:22:08 GMT

Excellent, thanks Stian! Your help is greatly appreciated

RE: Rerouting AT interface for power measurement using external supply

Stian Røed Hafskjold — Thu, 01 Jul 2021 10:15:28 GMT

Yes, here is a new hex file with the expected idle current: devzone.nordicsemi.com/.../8547.merged.hex

RE: Rerouting AT interface for power measurement using external supply

Frikkie Badenhorst — Thu, 01 Jul 2021 08:35:23 GMT

Thanks Stian.

I have accidentally closed the ticket, but I believe you are still preparing the update LTE Serial Modem app which will allow the expected idle current.

RE: Rerouting AT interface for power measurement using external supply

Stian Røed Hafskjold — Thu, 01 Jul 2021 08:18:30 GMT

Hi, button 1 on the DK should wake the device up again

RE: Rerouting AT interface for power measurement using external supply

Frikkie Badenhorst — Thu, 01 Jul 2021 07:50:50 GMT

Hi Stian,

after calling AT#XSLEEP, how can we wake the device/UARTs up again so that we can send some more AT commands?

RE: Rerouting AT interface for power measurement using external supply

Frikkie Badenhorst — Wed, 30 Jun 2021 10:40:33 GMT

Thank you Stian! Looking forward to seeing the device in operation!

Please keep me updated on the updated hex file, thanks

RE: Rerouting AT interface for power measurement using external supply

Stian Røed Hafskjold — Wed, 30 Jun 2021 10:22:15 GMT

Hi, sorry for the late reply. Here a hex file for you: devzone.nordicsemi.com/.../3005.merged.hex

It is currently consuming 30 uA in idle, after calling AT#XSLEEP=0, ideally you should see around 2-3 uA. So I will have to look into what changes they made in the newest NCS release v1.6.0 in order to get it down to the expected idle current. Anyways, you should be able to get started with the hex I posted above, and I will get back to you shortly with an updated one.

RE: Rerouting AT interface for power measurement using external supply

Frikkie Badenhorst — Wed, 30 Jun 2021 09:44:59 GMT

Hi Stian, will you be able to provide the hex files of the Serial LTE Modem app? It is very urgent as we need to do testing on the hardware as soon as possible.

We are having issues with installing the SDK and SES as mentioned here, https://devzone.nordicsemi.com/f/nordic-q-a/76895/zephyr-base-not-set-and-open-ide-not-present-in-toolchain-manager/317882#317882 , so cant build the application ourselves.

Thanks a lot for your help so far!

Regards,

Frikkie

RE: Rerouting AT interface for power measurement using external supply

Frikkie Badenhorst — Tue, 29 Jun 2021 14:25:13 GMT

Setting up our own test environment, is exactly what we want to do and the Serial LTE Modem application sounds perfect. As mentioned, for now we are having issues installing the SDK and SES.

Would you be so kind to provide me with the HEX files of this application, which I can use with the Programmer tool provided in nRF Connect for Desktop to flash the app?

Thanks so much, Stian.

RE: Rerouting AT interface for power measurement using external supply

Stian Røed Hafskjold — Tue, 29 Jun 2021 14:13:26 GMT

I don't think we have any precompiled examples in the SDK, but I could probably create some hex files for you if you want.

I would recommend starting with the UDP sample. It transfers a UDP packet at a regular interval and going into PSM or eDRX idle between the transfers. It's power optimized and easily configurable from the .conf file. If you want I can create a hex file with the parameters you want.

Alternatively, you can use the Serial LTE Modem application. This is based on using a terminal to submit AT commands to the modem over UART, so you can set up your own test environment. Then before doing current measurements you can issue the AT+XSLEEP command to turn off UART and putting the nRF91 in the lowest power mode.

RE: Rerouting AT interface for power measurement using external supply

Frikkie Badenhorst — Tue, 29 Jun 2021 11:57:59 GMT

Hi Stian,

Thank you for your response. Yes the SMU looks as if it will work.

Also, what application can we flash onto the the SiP in order to do manual current testing?

We currently have the asset tracker application flashed onto the module, however we are having issues installing the nRD Connect SDK and getting it running with SEGGER Embedded Studio (I have created a seperate ticked for that), so thus for now cannot create our own custom apps.

Should simply erasing the firmware on the app processor be fine?

RE: Rerouting AT interface for power measurement using external supply

Stian Røed Hafskjold — Tue, 29 Jun 2021 11:47:37 GMT

Hi, please follow my guide here on how to measure current on the nRF9160 DK: https://devzone.nordicsemi.com/nordic/cellular-iot-guides/b/hardware-design/posts/getting-started-with-current-measurements-on-the-nrf9160

I think the easiest way is using the SMU method, then you can supply P22 directly with the voltage you need and measure current at the same time. You leave the USB cable plugged in for UART/debugging, and the USB will then power everything on the DK except the nRF91 VDD itself. So there will be now leakage current from the nRF91 to the rest of the DK, nor will the nRF91 be powered by the USB.

No modifications to the DK are needed, and SW6 can be left in the default position.