Unexpected consumption using System OFF Sample & nRF52840DK

[clockis]

Greetings,

I have been measuring the current consumption of our custom FW in our custom board using PPK2 and found some unexpected spikes in the current consumption curve.

I decided to look deeper into this so programmed our custom FW to the nRF52840 DK and the behavior remained the same.

Finally I decide to test some samples with absolutely no changes on the nRF52840DK to confirm the normal behavior of the current curves I should see when the system is Active, in Sleep (system ON Idle) & finally System OFF(which is irrelevant for my application).

It seems that flashing the nRF System OFF sample (unchanged, as it was in the NCS) to the nRF52840 DK produces the same current curve. As mentioned in other tickets ( I have searched and read all of the relevant ones in existence) the current curve in System Sleep (with UART off) should be a few tens of microamps but I am consistently getting the current curve shown below.

Connection diagram (PPK2 in Ampere mode) 
I have also measured with the SW6 to the DEFAULT and nRF ONLY positions but the results were the same.

!!!Below you can see the current curve for the nRF52840DK flashed with the nRF System OFF sample and focus on the duration that corresponds to the System Sleep (System ON Idle) part of the duration ( the sample enters the SYstem Sleep state for two seconds, this what is shown below)

System Sleep (System ON Idle)

System Sleep (System ON Idle) the curve shown above ZOOMED IN ( to be able to distinguish the spikes)

The whole current curve for the System OFF sample

I have tried all different methods of measurement using the PPK2 (Ampere mode & Source mode by providing the external supply from the PPK2) but in all instances, I am getting the same current curve(shown above).

I have also tried the beacon sample (with no changes/modification, as is) and gotten the same curve in Idle mode (apart from when the device wakes up to advertise), between the advertising events I get the same spikes up to 3mA with the current never falling bellow 100's of microamps.

Beacon sample

Beacon sample ZOOMED IN

Even more ZOOMED IN

According to other tickets as well as this one that contains current curves for the Beacon sample this is not at all the Normal curve I should see for this sample

(this is what the people in the ticket mentioned report as the normal current curves for this sample)

which is completely different from my curves.

What could be the cause for the behavior and current curves I am observing when loading the nRF System OFF & Beacon samples to the nRF52840DK and measuring using the PPK2?

Please get back to me for any further information needed, I can also provide the data for the curves shown above.

I look forward to hearing from you.

Best regards,

Stavros

[runsiv]

Hi Stravos 

We are about to enter Christmas vacation on support, so the support will be slow/limted until start of January. 
Just to verify. Is the DK prepared for current measurement as it is described in the Current measurement guide?

I would also recommend to not power the DK over USB when you do current measurement as it might affect the measurement. 

Regards

Runar

[clockis]

Hi runsiv,

A kind reminder, for any updates or information about this would be very helpful as this is a critical issue for us.

I look forward to hearing from you.

Best regards,

Stavros

[clockis]

Hi Vidar,

Thank you very much for your immediate reply!

I just loaded the system_on_demo.hex you sent to the nRF52840DK (using the nRF Connect Programmer app)  & then set up the PPK2 & nRF52840DK as you mentioned ( all switches in the positions you mentioned and Supply Voltage to 3.0V as in your screenshot) 

 

The current curve I got is shown below

which is still very different from what you are getting. What could be the reason for this?

Thank you!

Stavros

[Vidar Berg]

Hi Stavros,

I see that the USB is not connected, please try plugging it in. Also, have you cut the solder bridge next to P22? From your picture, it appears to be shorted with solder.

Best regards,

Vidar

[clockis]

Hi Vidar,

I plugged the USB to the nRF52840DK and to my PC and I get the measurement shown below

Vidar Berg said:

Also, have you cut the solder bridge next to P22? From your picture, it appears to be shorted with solder.

I previously used the PPK2 in Ampere mode to measure the current so I needed to cut the SB40 (as the screenshot from the guide you posted suggests) so for this measurement I shorted it again (using solder) as the nRF52840DK would not be powered at all if I didn't, is that not correct? The nRF52840DK Guide (pg. 38) also mentions this.

Best regards,

Stavros

[Vidar Berg]

Hi Stavros, 

The solder bridge (SB) must be cut when measuring current. Otherwise, the nRF52840 will be powered by the USB-to-3V buck regulator when the USB is connected. Also, with the SB shorted, the PPK voltage applied on P22 may be fed into other parts of the board's circuitry, which should not be included in the measurement. 

I recommend using a jumper, as it allows you to easily switch between current measuring mode and the regular mode.

Best regards,

Vidar

[clockis]

Hi Vidar,

Thank you very much for your patience and support, from what I was seeing this makes sense. I desoldered the SB40. I hope the measurement setup for the nRF52840DK is now correct.

Now with the correct setup, the same as yours, with the system_on_demo.hex & system_off_demo.hex loaded. I am getting the current curves shown below. They look very similar to the ones you observed. The system_on_demo seems to be exactly the same but slightly shifted higher by about 1 uA.

system_off_demo.hex

system_on_demo.hex

Is this expected? Are these measurements normal? Am I missing something else on my setup?

Thank you and I look forward to hearing from you!

Best regards,

Stavros

[Vidar Berg]

Hi Stavros,

Yes, this looks much better. Thank you for the update. The system ON measurement is slightly higher on your board, but it's still within the expected range. This can be explained by variation in sleep current from chip to chip. 

Best regards,

Vidar

[clockis]

Hi Vidar,

That is great news and very reassuring, still, I would like now that the measurement setup has been verified as correct to explain the current curves that I observe when measuring the System ON IDle (System Sleep) current curve using the unmodified nrf/system_off sample ( NCS v2.1.0 ).

With the same verified measurement setup that we confirmed in the previous message I have measured again the current consumption for the sample.

The full curve for all 5 states, of the sample, is shown below.

The state I am interested in confirming and measuring correctly is the 4th, namely the System Sleep (System ON Idle) with UART OFF, for which the current curve is shown below (zoomed in from the curve above).

more zoomed in

As you can observe the current never drops to the typical values seen in the system_on_demo.hex you sent, and they never drop below ~100uA in contrast with the system_on_demo.hex in which I get always below ~10uA. Shouldn't I get the current curve seen with system_on_demo.hex as well as the average current at least much closer than this?

I am also attaching the image used which was generated by building the nrf/system_off sample for the nRF52840DK (NCS 2.1.0) nrf_system_off_sample_v2.1.0.hex

nrf_system_off_sample_v2.1.0.hex

Could you please check this with your setup as well, because it does not make sense for the average current to be 682 uA compared to the 3.59 uA measured with the system_on_demo.hex you sent me. Also the current curve never reaches below ~100uA which also does not conform to the current curve observed with the system_on_demo.hex you sent.

Thank you very much and I look forward to hearing from you.

Best regards,

Stavros

[Vidar Berg]

How did you turn off the UART? When UART reception is enabled in sleep mode, the HF clock remains active to allow data reception. This means the sleep current will be around .5 to 1 mA in System ON.

You can disable the UART before entering sleep using the pm_device_* APIs as shown in the code snippet I posted here:  RE: How to put the UART to sleep (low power mode) 

[clockis]

I used the nrf/system_off sample without any modifications. I did not set this up, it is provided with the nRF Connect SDK v2.1.0 in samples folder.

I am pasting the code of the sample below (only has two files a main.c and a retained.c which is not used as the config option for this is disabled)

main.c (FYI CONFIG_APP_RETENTION is disabled)

/*
 * Copyright (c) 2019 Nordic Semiconductor ASA
 *
 * SPDX-License-Identifier: Apache-2.0
 */

#include <stdio.h>
#include <zephyr/zephyr.h>
#include <zephyr/device.h>
#include <zephyr/init.h>
#include <zephyr/pm/pm.h>
#include <zephyr/pm/device.h>
#include <zephyr/pm/policy.h>
#include <soc.h>
#include "retained.h"
#include <hal/nrf_gpio.h>

#define BUSY_WAIT_S 2U
#define SLEEP_S 2U

/* Prevent deep sleep (system off) from being entered on long timeouts
 * or `K_FOREVER` due to the default residency policy.
 *
 * This has to be done before anything tries to sleep, which means
 * before the threading system starts up between PRE_KERNEL_2 and
 * POST_KERNEL.  Do it at the start of PRE_KERNEL_2.
 */
static int disable_ds_1(const struct device *dev)
{
	ARG_UNUSED(dev);

	pm_policy_state_lock_get(PM_STATE_SOFT_OFF, PM_ALL_SUBSTATES);
	return 0;
}

SYS_INIT(disable_ds_1, PRE_KERNEL_2, 0);

void main(void)
{
	int rc;
	const struct device *cons = DEVICE_DT_GET(DT_CHOSEN(zephyr_console));

	if (!device_is_ready(cons)) {
		printk("%s: device not ready.\n", cons->name);
		return;
	}

	printk("\n%s system off demo\n", CONFIG_BOARD);

	if (IS_ENABLED(CONFIG_APP_RETENTION)) {
		bool retained_ok = retained_validate();

		/* Increment for this boot attempt and update. */
		retained.boots += 1;
		retained_update();

		printk("Retained data: %s\n", retained_ok ? "valid" : "INVALID");
		printk("Boot count: %u\n", retained.boots);
		printk("Off count: %u\n", retained.off_count);
		printk("Active Ticks: %" PRIu64 "\n", retained.uptime_sum);
	} else {
		printk("Retained data not supported\n");
	}

	/* Configure to generate PORT event (wakeup) on button 1 press. */
	nrf_gpio_cfg_input(NRF_DT_GPIOS_TO_PSEL(DT_ALIAS(sw0), gpios),
			   NRF_GPIO_PIN_PULLUP);
	nrf_gpio_cfg_sense_set(NRF_DT_GPIOS_TO_PSEL(DT_ALIAS(sw0), gpios),
			       NRF_GPIO_PIN_SENSE_LOW);

	printk("Busy-wait %u s\n", BUSY_WAIT_S);
	k_busy_wait(BUSY_WAIT_S * USEC_PER_SEC);

	printk("Busy-wait %u s with UART off\n", BUSY_WAIT_S);
	rc = pm_device_action_run(cons, PM_DEVICE_ACTION_SUSPEND);
	k_busy_wait(BUSY_WAIT_S * USEC_PER_SEC);
	rc = pm_device_action_run(cons, PM_DEVICE_ACTION_RESUME);

	printk("Sleep %u s\n", SLEEP_S);
	k_sleep(K_SECONDS(SLEEP_S));

	printk("Sleep %u s with UART off\n", SLEEP_S);
	rc = pm_device_action_run(cons, PM_DEVICE_ACTION_SUSPEND);
	k_sleep(K_SECONDS(SLEEP_S));
	rc = pm_device_action_run(cons, PM_DEVICE_ACTION_RESUME);

	printk("Entering system off; press BUTTON1 to restart\n");

	if (IS_ENABLED(CONFIG_APP_RETENTION)) {
		/* Update the retained state */
		retained.off_count += 1;
		retained_update();
	}

	/* Above we disabled entry to deep sleep based on duration of
	 * controlled delay.  Here we need to override that, then
	 * force entry to deep sleep on any delay.
	 */
	pm_state_force(0u, &(struct pm_state_info){PM_STATE_SOFT_OFF, 0, 0});

	/* Now we need to go sleep. This will let the idle thread runs and
	 * the pm subsystem will use the forced state. To confirm that the
	 * forced state is used, lets set the same timeout used previously.
	 */
	k_sleep(K_SECONDS(SLEEP_S));

	printk("ERROR: System off failed\n");
	while (true) {
		/* spin to avoid fall-off behavior */
	}
}

This sample can be found in ..\v2.1.0\zephyr\samples\boards\nrf\system_off

[Vidar Berg]

I tried the 'system OFF' sample just now and got similar results. The problem is that the sample does not suspend the UART before entering 'System OFF', causing the UART pin states to be retained during sleep. This leads to current leakage. I will report this as a bug internally. You can comment the  'rc = pm_device_action_run(cons, PM_DEVICE_ACTION_RESUME);' at line 85 for now.

Edit: this was fixed by this commit: https://github.com/nrfconnect/sdk-zephyr/commit/2cbc452d1d0dcf9dc6bc9c6081b4bc54f6a04e89