Strange current consumption events during sleep using iBeacon example

RE: Strange current consumption events during sleep using iBeacon example

Susheel Nuguru — Fri, 12 Aug 2022 09:29:17 GMT

Sorry for the late reply Jeremy. Was away for few days.

There was a bug in the RC calibration in Zephyr in SDK version 1.9.0 which is fixed in SDK version 2.0.0.

We have also backported this fix to SDK 1.9.2. You need to use our softdevice controller for this and not Zephyr Controller.

RE: Strange current consumption events during sleep using iBeacon example

jeremyherbert — Tue, 02 Aug 2022 11:32:45 GMT

Hi Susheel,

Yes, I understand that it works in terms of providing a clock source, but the problem is that it draws more than 100x more current than the power profiler states it should, even on the nrf52840dk which is supposed to be a reference design. Could you help me understand why that is?

RE: Strange current consumption events during sleep using iBeacon example

Susheel Nuguru — Fri, 29 Jul 2022 09:09:49 GMT

RC 32k is usable but it is less accurate and needs more power to calibrate it constantly from hfclk crystal for the BLE protocol to work. The calibration time varies and can be power intensive over time. There are lots of discussion in this forum regarding using Rc 32k instead of XTAL

RE: Strange current consumption events during sleep using iBeacon example

jeremyherbert — Mon, 25 Jul 2022 21:27:21 GMT

In this case, I am using a device to test if I can remove the 32k XTAL and what the consequences would be. But this is not the consequence I expected... It seems that the RC oscillator is completely unusable?

RE: Strange current consumption events during sleep using iBeacon example

Susheel Nuguru — Mon, 25 Jul 2022 13:30:05 GMT

[quote user="jeremyherbert"]then the events go away on the nrf52840dk_nrf52811. So it seems like this is probably the RC oscillator calibration loop, except it is taking way too long to calibrate or not returning to sleep correctly after calibration[/quote]

It seems like the calibration of the RC is taking much longer than expected. We have seen this on devices that have a wrong PPM setting given to the calibrating module, But if you already have an XTAL on your device, why use RC?

RE: Strange current consumption events during sleep using iBeacon example

jeremyherbert — Fri, 22 Jul 2022 23:43:27 GMT

Some more testing reveals that if I remove

CONFIG_CLOCK_CONTROL_NRF_K32SRC_RC=y
CONFIG_CLOCK_CONTROL_NRF_K32SRC_RC_CALIBRATION=y
CONFIG_CLOCK_CONTROL_NRF_K32SRC_500PPM=y

and add

CONFIG_CLOCK_CONTROL_NRF_K32SRC_XTAL=y
CONFIG_CLOCK_CONTROL_NRF_K32SRC_50PPM=y

then the events go away on the nrf52840dk_nrf52811. So it seems like this is probably the RC oscillator calibration loop, except it is taking way too long to calibrate or not returning to sleep correctly after calibration. I think this is a bug in the calibration loop code, because if I use the online power estimator: https://devzone.nordicsemi.com/power/w/opp/2/online-power-profiler-for-bluetooth-le the LF clock calibration current should only be 1uA, not the 50uA I measured on my custom board:

RE: Strange current consumption events during sleep using iBeacon example

jeremyherbert — Fri, 22 Jul 2022 23:27:54 GMT

If I build for the nrf52840dk_nrf52811 the same events still appear (the floor current is different though because I haven't optimised any GPIO levels or anything like that). I only changed the config to CONFIG_BOARD_ENABLE_DCDC=n so that the switching noise would go away.

5s interval:

1s interval:

RE: Strange current consumption events during sleep using iBeacon example

jeremyherbert — Fri, 22 Jul 2022 23:04:53 GMT

I have just tried changing the advertising interval to 1 second, and the spikes still persist but they are much shorter than before (note that the x axis is now 10s instead of 1 minute):

RE: Strange current consumption events during sleep using iBeacon example

jeremyherbert — Fri, 22 Jul 2022 12:31:03 GMT

Hi Susheel,

yes, the sample was “ibeacon” and I only changed a single line which increases the advertising interval. I did tinker with some settings in the prj.conf around disabling the console and logging, but they didn’t make a difference.

I haven’t had a chance to try to reproduce on the DK, but also I am not sure if it is equivalent because it has an nrf52840, not the 52811.

RE: Strange current consumption events during sleep using iBeacon example

Susheel Nuguru — Fri, 22 Jul 2022 12:26:54 GMT

I haven't looked into your code yet but it looks like the spikes are in regular interval. Have you tested this on the DK? If not can you test it?

Also can you briefly explain which example you took as example and what changes you did?