Which hardwares in nrf52840 does "nrf_power_system_off()" shut off?

[cpeng]

Hi Devzone:

I am trying to gauge the power consumption after nrf_power_system_off() is called.

So is there a list of the hardwares that "nrf_power_system_off()" shuts off?

The hardwares of my concern are Radio block and SRAM. I would like to know if nrf_power_system_off() would shut off these hardware as well as other blocks. A full list would be appreciated.

Also when the chip reboot from nrf_power_system_off, does it go through the full cycle of rebooting?

What do I mean by full cycle of rebooting:

MBR -> Bootload -> Application

I just need to make sure my main code is properly re-initialized and re-entered.

Thanks!

[Jared]

Hi,

We don't have a list but the product specification explains it pretty good:

"System OFF is the deepest power saving mode the system can enter. In this mode, the system’s core functionality is powered down and all ongoing tasks are terminated.

The device can be put into System OFF mode using the POWER register interface. When in System OFF mode, the device can be woken up through one of the following signals:

1. The DETECT signal, optionally generated by the GPIO peripheral
2. The ANADETECT signal, optionally generated by the LPCOMP module
3. The SENSE signal, optionally generated by the NFC module to “wake-on-field”
4. A reset

When the system wakes up from System OFF mode, it gets reset. For more details, see Reset behavior.

One or more RAM sections can be retained in System OFF mode depending on the settings in the RAM[n].POWER registers.

RAM[n].POWER are retained registers, see Reset behavior. Note that these registers are usually overwritten by the startup code provided with the nRF application examples.

Before entering System OFF mode, the user must make sure that all on-going EasyDMA transactions have been completed. This is usually accomplished by making sure that the EasyDMA enabled peripheral is not active when entering System OFF".

EDIT: ALMOST All peripherals are reset after a wakeup from SYSTEM OFF.

best regards

Jared

[cpeng]

Thanks for your reply Jared. So it does shut off Radio, timer and SRAM during system off is that correct?

Also what state does the GPIO output pin will be left when the chip goes to system off?

Does it leave them to be 1s?

Does it leave them to be 0s?

Does it leave them to tri-state?

[Jared]

Hi,

I would like to edit my previous answer. Almost all peripherals are reset after a SYSTEM OFF (All except for GPIO, NFC and LPCOMP). The GPIO peripheral will retain its state through SYSTEM OFF and a wake-up. The state that it's in depends on the configuration before you execute a SYSTEM OFF.

RAM can be retained in SYSTEM OFF, but the default behavior is to not use RAM retention. 

Sorry for the misunderstanding.

Jared