nRF9160 - SYSTEM OFF Mode Current

Question

Dear colleagues,

with the newer SDK (I am now using NCS v2.5.0 and 2.6.0), I have difficulties finding the right SYSTEM OFF mode current.

Code currently looks like as follows:

#include <zephyr/kernel.h>
#include <modem/lte_lc.h>

int main(void)
{
	printk("Hello World! %s\n", CONFIG_BOARD);
	nrf_modem_lib_init();
	printk("Turn off Modem and switch to SYSTEM OFF\n");
	lte_lc_power_off();
    k_sleep(K_MSEC(1000));
    NRF_REGULATORS->SYSTEMOFF = 1;
	return 0;
}

Based on:

A) Getting started with current measurements on the nRF9160

and B) NRF9160DK & System OFF

prj.conf was extended to: (does not change anything, I only had the LC layer enabled at first)

# Modem library and link control
CONFIG_LTE_LINK_CONTROL=y
CONFIG_LTE_AUTO_INIT_AND_CONNECT=n
CONFIG_NRF_MODEM_LIB=y

I initially had no modem lib included/function call in the main.c (this was my setup from previous NCS releases, and it worked fine) - but also with the suggested change in the devzone ticket, I don't see a difference. I am measuring 2.7mA.

What is interesting to note though:

If I would erase the flash, and program the *.hex file from the DevZone guide from Stian, I reach about about 400uA. If I then re-erase the flash, and program my code snippet, I end up at the expected current consumption of 1.4uA.

I cannot explain this behavior though, and wonder how I reach the SYSTEM OFF current without flashing the hex file from the devzone guide first.

Thanks,
Kevin

Kevin Kotinkar · Accepted Answer

Hi Charlie,

after back and forth testing, and updating my Toolchain + SDK again, I found out the following:

On previous SDK releases, nrf_modem_lib_init() is not required (tested this on NCS v1.8.0)
On current SDK releases (tested NCS v2.5.0,v2.6.0,v2.6.1) - nrf_modem_lib_init() is a MUST / requirement
- Your code provided code in the project *.zip file and the compiled ncs261_systemoff.hex seem to not include this line and thus don't work (for me).
- You should see a higher current when you fully power down the board and SiP and repower after a few seconds.
- It will seem to work, when you had a correct code sample flashed initially, and then reflash your code while measuring the current consumption and not going through a full power down cycle.
With a working code, I am at around 2uA, testing this with SICA B1, nRF9160 DK v1.0.1
I am slightly higher with the old SiP revision but it also works: 2.35 uA on SICA B0, nRF9160 DK v0.14.0
CONFIG_LTE_AUTO_INIT_AND_CONNECT was deprecated and removed with NCS v2.6.0 - but the cmake will report this, so its easy to catch if missing it.

My code looks as follows now. I don't know why I couldn't get the right result previously as I had the modem lib init() call already in my code. A clean SDK & Toolchain installation, plus a pristine build now helped me to find consistent results.

#include <zephyr/kernel.h>
#include <modem/lte_lc.h>
#include <modem/nrf_modem_lib.h>

int main(void)
{
	printk("Hello World! %s\n", CONFIG_BOARD);
	nrf_modem_lib_init();
	printk("Turn off Modem and switch to SYSTEM OFF\n");
	lte_lc_power_off();
	k_sleep(K_MSEC(1000));
    NRF_REGULATORS->SYSTEMOFF = 1;
	return 0;
}

prj.conf:

# Modem library and link control
CONFIG_LTE_LINK_CONTROL=y
CONFIG_NRF_MODEM_LIB=y

Attaching also my compiled hex file:
ncs_261_sysoff_modemlib_init.hex

If someone is interested in NCS v1.8.0 compiled file (code is similar but no modem_lib_init() and the zephyr related includes are different):
ncs_180_systemoff.hex

Best,
Kevin