General Purpose Registers

RE: General Purpose Registers

Gmrck — Sat, 06 Dec 2025 22:12:14 GMT

Hi, Bjorn,

Working with nrf52840DK latest revision here, nrfConnect SDK 3.0. When I try to use

nrf_power_gpregret_ext_get or nrf_power_gpregret2_get functions I am getting the build waring

warning: implicit declaration of function 'nrf_power_gpregret_ext_get'; did you mean 'nrf_power_gpregret_get'

which ends up with the build failure.

Then, looking at the documentation here https://docs.nordicsemi.com/bundle/ncs-2.4.1/page/nrfx/drivers/power/hal.html
I am confused with the NOTE next to the nrf_power_gpregret2_get function description:
This register is not available in all MCUs.
while a similar NOTE for nrf_power_gpregret2_set says:
This register is not available in the nRF51 MCU family.

Is there a legal way to write into the gpregret2 register on nrf52840DK preferably with using these functions?

RE: General Purpose Registers

Alemons — Wed, 30 Aug 2017 13:20:48 GMT

Ok Bjørn, thank you for the answer.

RE: General Purpose Registers

bjorn-spockeli — Wed, 30 Aug 2017 08:48:11 GMT

Hi Alemons,

Yes, the General Purpose Retained Registers(GPREGRET and GPREGRET2 ) can be freely used by the application to store flags etc.

However, if you plan on adding DFU support to your product, then you should be aware that GPREGRET register is used by to signal the device to enter bootloader mode. (The application writes a specific value to the GPREGRET register and performs a soft-reset. Upon a reset the device will pass execution to the bootloader first, which then checks the value of the GPREGRET register to determine if the device should stay in bootloader mode or pass execution to the application.

In short, any flags stored in GPREGRET will be overwritten during a DFU.