GRTC resets after sys_reboot() when using MCUboot (NCS v3.1.0)

[bzhou]

Description:

We're using GRTC on the nRF54L15 to implement RTC calendar functionality in our project. During development, we observed the following behavior:

• When MCUboot is used, calling sys_reboot(SYS_REBOOT_COLD) or sys_reboot(SYS_REBOOT_WARM) from the application causes GRTC to reset.

• When MCUboot is not used, GRTC remains unchanged across reboots.

This reset breaks our calendar logic, which depends on GRTC continuity. We're using NCS version v3.1.0 with sysbuild enabled.

Questions:

1. What part of MCUboot or its initialization flow causes grtc.SYSCOUNT to reset?

2. Is there a recommended way to preserve GRTC across reboots when using MCUboot?

Any insights or suggestions would be greatly appreciated!

[bzhou]

I've just tested this PR and confirmed it's working. Thank you.

[Vidar Berg]

Thank you for confirming.