Clarification for System OFF mode prerequisites

[spanceac]

Hi,

The nRF52840 manual states here https://docs.nordicsemi.com/bundle/ps_nrf52840/page/power.html#ariaid-title10 that "Before entering System OFF mode, all on-going EasyDMA transactions need to have completed".

But the documentation doesn't mention what happens if you attempt to enter System OFF mode but there are EasyDMA transactions still ongoing. Does the system fail to enter OFF mode?

Something else?

I'm mostly interested in UARTE EasyDMA transactions that might be ongoing when I attempt to enter System OFF mode.

The entering system OFF mode is achieved by calling Zephyr's sys_poweroff() API that translates underneath to writing the SYSTEMOFF register.

Thanks!

[Jared]

Hi,

I think the risk here is that the chip will enter into a state where the EasyDMA resources are not completely turned off and continue to consume current even in "System Off". You should stop and abort any ongoing UARTE transaction before you proceed to system off. 

regards

Jared 

[spanceac]

Thank for the reply!

If looks like there is a risk for an incomplete power off on the nRF chips when an user calls sys_powroff() API, and it's not aware of the underlying mechanism of powering off the chip and the EasyDMA prerequisites of having a correct power off.

[Jared]

That is correct