How to enter Sys ON low power mode on nRF52 series and wake up by RTC

[Mr_BLE]

Hello,

we want to evaluate the nRF52832 chip with a example project. This project has the following functions:

- low power

- system wakeup by RTC running with external 32 kHz crystal

- while in idle or sleep 64 k RAM retention

- when RTC wakes the chip up: Advertising with one event 3 Channels every 3 s

Where do I start developing this? I have example projects regarding to Advertising, this should be no problem. But I dont know how to enter the low power mode in System ON with RTC wakeup interrupt? Also with RAM retention. Do you have examples for that or a documentation how to enter this modes? 

Thank you!

[haakonsh]

See nrf_pwr_mgmt_run API docs. It puts the system into SystemON by running the following three lines of code after doing some graceful shutdown stuff:
__WFE;
__SEV;
__WFE;

Any interrupt or peripheral EVENT will wake up the CPU, you can therefore set up the RTC to fire a COMPARE MATCH EVENT after 3s with the RTC example in SDK15\examples\peripheral\rtc, or by using the Application Timer library. 

RAM is always retained in SystemON sleep, see nrf_power_rampower_mask_on to set the RAM retention if you're going into SystemOff.