How to keep RTC running while in system off mode?

[lilealyh]

hi all:

      NRFSDK_16. I want to get timestamp from rtc,but my device need run with low power,so when the device in idle mode(no user use),will put it in system off mode.

But when wake up from system off with button the rtc is reset.So is there any way to avoid RTC reset after system wakeup ?or have other best methods?

please help me ?thanks  a lot!

[Jørgen Holmefjord]

Hi,

It is not possible to run RTC in System OFF mode. All clock sources are turned off in System OFF mode. If you want to run the RTC, you can only go to System ON mode. 

The Sleep Current with RTC running in System ON mode is 1.50 uA (with no RAM retention). If you need the low power of System OFF, there exists external low-power RTCs that can wake the chip from System OFF through a GPIO pin sense.

Best regards,
Jørgen

[lilealyh]

Hi jorgen:

Thanks for quickly replay.Now I understand the system off mode not possible to run RTC,I can wakeup from system off mode using GPIO pin sense,but i don't kown how to wake up from sleep mode.

1、Using sd_app_evt_wait() api whether can into sleep mode,if can and how to wake up from sleep mode?

2、If using external low-power RTCs and what should i do ?

[Jørgen Holmefjord]

1. sd_app_evt_wait() will enter System ON idle mode. The CPU will wake on any generated event, i.e., if you have RTC running, the CPU will wake on the COMPAREx event.
2. There is an example for wakeup on GPIO in this GitHub repository.

[lilealyh]

Hi jorgen.I genuinely appreciate your help and support.