How to enable NRF52840 RTC using Zephyr?

[ahmedwahdan]

First of all, I see that NRF52840 doesn't have a Real Time Clock but it has a Real Time Counter which is not working in case of sleep and low power mode, am I correct?

Second, How to enable this RTC (What ever it is) , set the current data/time and be able to get the epoch.

Board: NRF52840DK

SDK: NRF Connect 2.1.0

Thanks in advance! 

[Kazi Afroza Sultana]

Hello,

''I see that NRF52840 doesn't have a Real Time Clock but it has a Real Time Counter which is not working in case of sleep and low power mode,'' It is not correct.

 RTC peripheral has low-power timer on the low-frequency clock source. then it (counter) enables the real-time clock.  LFCLK XTAl oscillator is for generating low power. So, the RTC still works in System ON sleep mode. It's only in System OFF mode it's completely turned off.

For use in Zephyr, you should use kernel timer. https://docs.zephyrproject.org/latest/kernel/services/timing/clocks.html

Thanks.

BR

Kazi

[ahmedwahdan]

Thanks Kazi
Does Kernel timer uses RTC? or Do I need to configure something?

Any example or guidance on how to get thing working?

Thanks in advance!

[Kazi Afroza Sultana]

yes. Kernel timer uses RTC. 

You can read this https://docs.zephyrproject.org/latest/kernel/services/timing/timers.html documentation to know how to define timer and how to use this. 

For example: A timer is defined using a variable of type k_timer. It must then be initialized by calling k_timer_init()

Timer expiry funciton works like this-

void my_work_handler(struct k_work *work)
{
    /* do the processing that needs to be done periodically */
    ...
}

K_WORK_DEFINE(my_work, my_work_handler);

void my_timer_handler(struct k_timer *dummy)
{
    k_work_submit(&my_work);
}

[ahmedwahdan]

Thanks
I tried using this timer as suggested and it works just fine,
I still can't figure out how to connect the dots.

I need to set the current epoch, and in run time will get the updated epoch on specific event.
How to do so, is there direct way or need to handle it myself? And will counter keeps it's state in deep sleep?

Thanks for the support!