Setting REGOUT0 in merged.hex

[mondalaci]

@benedekkupper Please see this Nordic thread: https://devzone.nordicsemi.com/f/nordic-q-a/116490/setting-regout0-in-merged-hex/511242

Can you help with this? The suggested approach is not the cleanest, and the build fails when I try to use it. The cleanest Zephyr-native approach is preferred if implemented in a reasonable timeframe.

[benedekkupper]

I need more context than what's in the thread. To me it seems you want to perform a write to a memory mapped register. Main questions to be answered:

• at what point in time should this register write occur? As soon as MCUBoot / zephyr OS in general boots up, e.g. in the reset handler? The approach you are discussing in the thread doesn't make much sense to me, I'd rather patch a small task into the zephyr boot process that performs this write.
• is this something applicable for all 3 boards, on all boots?

[mondalaci]

The register should be set declaratively in the hex file. To my knowledge, this way, no write would occur during execution.

This should be applied to the dongle. Without this change, the dongle's LEDs are very dim, and its reset button doesn't work.

[benedekkupper]

Hmm it indeed seems that this register is non-volatile:
https://devzone.nordicsemi.com/f/nordic-q-a/28562/nrf52840-regulator-configuration
https://devzone.nordicsemi.com/f/nordic-q-a/93532/is-it-possible-to-configure-regout0-at-programming-time-with-the-nrf-connect-sdk

This is the zephyr way to do it: https://github.com/nrfconnect/sdk-zephyr/blob/89bad3f2d60239a2e3503d7d79e4f92eeba0a5ba/boards/nordic/nrf52840dongle/board.c#L21

I will send a MR tomorrow.

[benedekkupper]

Do I need to implement a backport of the change to 2.6.1, or is it enough to have it on 2.8.0?

[mondalaci]

2.8.0 is enough if we can merge its PR in a week or two.

[benedekkupper]

Merged in #353