Power Management Clarification

[Jose Forno]

Hi, 

I want to test the power managment on the nRF52840. I plan to make a  simple test application that enter in sleep/systemoff mode every, let's say, 1 minute. After wake up it'll performs some simple tasks and then enter again in sleep/systemoff mode, and so on.

I can use the "pwr_mgmt" example in the SDK as a start, but I'll need to add a timer.

I read the power section in the datasheet, and the power management library documentation but I have some doubts:

1.- On system off, all the device will shutdown, including the timer, so , I can't enter in this mode because the timer won't be able to wake up the device. Am I right?.

2.- If the question above is right, how can I go to sleep mode (or an equivalent mode)? Using the "nrf_pwr_mgmt_run" function will do the job?

3.- Is there another  mode to save power in this type of application, that needs a timer to wake up the system?

Best regards

José Forno

[haakonsh]

1. Correct.

2. Yes, nrf_pwr_mgmt_run puts the MCU into SystemON Idle, a sleep-state where all peripherals are available and the CPU sleeps until woken by any interrupt. 

3.  No, there are only three power states; SystemON, SystemON Idle, and SystemOFF.  There is also a sub-state in SystemON Idle called Constant Latency where the HFCLK is kept running in order to speed up the wake-up time of the CPU and peripherals, but this feature is seldom used as it consumes a lot of power. See POWER — Power supply for details. 

[Jose Forno]

Thanks for your answer. Crystal clear!.