nRF52832 Real Time Counter TICK and PPI question

[Keltyx98]

Good afternoon,

I'm trying to understand how the RTC works on the nRF52.

The RTC can run when HFCLK is OFF and PCLK16M is not available

Section 25.5 describes the TICK event as a source for interrupts allowing the CPU to be "powered down" : is "powered down" the System OFF mode? Or is it also without the PCLK16M?

In Section 25.6 it is written that the TICK event can be deactivated using the EVTEN register because else, it would request PCLK16M and HFCLK and consume more power. 

If I understood correctly he EVTEN register allows to route the different events to the PPI instead of the IRQ, allowing "HFCLK-less" operation.

I would like to have a wake up from the System OFF Mode through a GPIO pin activated by an event on the PPI sent by the RTC but I cannot understand which event is the most power efficient.

What does the TICK event has better than the COMPARE event in order to have specified that the CPU can be "powered down"? Isn't the CPU also powered down when PCLK16M is not available?

Thank you and kind regards

[Kenneth]

Hello,

You can find some current consumption values for different power down modes here:
https://infocenter.nordicsemi.com/topic/com.nordic.infocenter.nrf52832.ps.v1.1/pmu.html#unique_205654252 

The nRF52 will automatically enter low power mode (and automatically stop HFCLK) when the MCU is not executing code. The nRF52 will automatically startup the HFCLK on wakeup.

All the ION (System ON) values you see listed are when MCU is in low power mode (in sleep not executing code), on wakeup from ION the MCU will continue to run code from where it was put to sleep on wakeup. The MCU can wakeup on all kind of events (such as RTC etc) when in System ON mode.

For all IOFF (System OFF) values the MCU will reset on wakeup, and only a few wakeup sources are available (pin, nfc, and lpcomp). There is no RTC available in IOFF. The system OFF can only be entered by calling the SYSTEM OFF command from the MCU, if the System OFF command is not called, then the chip will be in System ON.

For all new development you should use the nRF Connect SDK (NCS), see:
https://devzone.nordicsemi.com/nordic/nordic-blog/b/blog/posts/nrf-connect-sdk-and-nrf5-sdk-statement  

To get started with NCS check out:
https://academy.nordicsemi.com/courses/nrf-connect-sdk-fundamentals/ 

Best regards,
Kenneth

[Keltyx98]

Thank you for your quick answer.
I will then avoid the System OFF mode since it's not possible to reroute the RTC on a PPI that goes to a GPIO pin.
Since both COMPARE and TICK events are available at the same power consumption, I will use the COMPARE event to wake up the MCU via IRQ.

Thank you!