How to get NRF52840 into deep sleep while power supply is low?

[Sealedfire]

Chip: NRF52840

Firmware platform: Wirepas V5

Hello!

I am now writing firmware for a product based on HW&SW mentioned above.

It is powered by battery and sends data periodically.

I want to halt or deep-sleep the chip after detecting the supply voltage is low enough(~2.5V), and resume after voltage is normal.

Problem is that Wirepas SDK doesn't provide such APIs, so I have to implement it in application code.

Will you please provide some advice? Where to find related APIs, and how to implement them correctly?

Best regards,

Daniel Duan

[Shaney]

Hi,

I've done something similar and I used the ADC https://docs.zephyrproject.org/latest/reference/peripherals/adc.html#adc to measure the battery levels and then I forced the system in to deep sleep when the sampled value where lower than a threshold.

Putting the system to deep sleep can be done by first enabling it in your Kconfig file using:

CONFIG_SYS_POWER_DEEP_SLEEP_STATES=y
CONFIG_SYS_PM_STATE_LOCK=y

And then using

sys_pm_force_power_state(SYS_POWER_STATE_DEEP_SLEEP_1);

To put the system in deep sleep.

To avoid the system shutting down on its own when you have long idle time I suggest disabling automatic deep sleep first thing you do using

 sys_pm_ctrl_disable_state(SYS_POWER_STATE_DEEP_SLEEP_1);

These functions can be found in power/power.h.

Before you enter deep sleep, ensure that you have enabled any of the peripherals that can wake the system from deep sleep, otherwise it will sleep forever or until the power dips so low that the system resets.

You can wake the system with these methods:

https://infocenter.nordicsemi.com/topic/ps_nrf52840/power.html?cp=4_0_0_4_2_2#unique_1384365742

Hope it'll help you get started.

[Sealedfire]

Hi Shaney,

Thanks for your suggestion!

Sorry I can't implement this since the Wirepas stack takes control of related registers and no APIs to share with application.

I also asked them for suggestion, seems the best way is to turn off the radio part, and I am waiting for their suggestion.

Anyway I really appreciate your immediate help.

Thanks and best regards!

DanielDuan

[Shaney]

Ah I see sorry that I couldn't be of any more help. I hope you find a solution to your problem.

Have good one!

[Edvin]

Hello Daniel,

I guess you would have to check with the authors of the Wirepas stack to make sure that you don't break anything by entering system off at the wrong time. Check whether there are some graceful shutdown considerations you need to take. I am not familiar with Wirepas, but based on a quick Google search, it looks like some sort of (Bluetooth?) Mesh stack.

So I guess it holds some network information that may or may not need to be stored in flash before entering system off.

However, there is an API to enter system off, found in nrf_power.h in NCS:

__STATIC_INLINE void nrf_power_system_off(void)
{
    NRF_POWER->SYSTEMOFF = POWER_SYSTEMOFF_SYSTEMOFF_Enter;
    __DSB();

    /* Solution for simulated System OFF in debug mode */
    while (true)
    {
        __WFE();
    }
}

You can check out the implementation of nrf_power_system_off. It tells you the address of the system off register, which you can also find here.

Best regards,

Edvin

[Sealedfire]

Hi Shaney,

Don't worry man, I already got feedback from Wirepas support.

Thanks and have a good day!

DanielDuan