[nordic] alarm.pin.PinAlarm(preserve_dios) support for NRF52840

[bikeNomad]

I'm using a Seeed Studio XIAO NRF52840 SENSE board that has a LSM6DS IMU on-board.

This IMU is powered from a GPIO pin on the NRF52840 MCU.

I'd like to have the IMU be able to wake the board from deep-sleep using an alarm.pin.PinAlarm.

It works OK for waking from light sleep, but the GPIOs are turned off during deep sleep.

It appears that it is possible to maintain GPIO states (and also to wake from pin changes) during sleep states in this MCU.

[Sola85]

Have you verified that you actually get a lower power consumption using deep sleep instead of light sleep?

From my experience you can get down to 2uA in light sleep on nrf boards and deep sleep gives basically no further reduction.

So if light sleep works for you, it might be an option to just use that instead.

[bikeNomad]

I'm getting about 650µA in light-sleep (with BLE connected, flash on, and IMU on), and about 90µA in deep-sleep.