nRF54L15-DK does not wake up from GRTC after sys_poweroff()

[AllWhy]

Hi everyone,

I'm using the nRF54L15-DK and trying to implement a simple low-power cycle where the board:

1. Measures sensor values
2. Sends them via CoAP over OpenThread
3. Enters system off
4. Wakes up after a fixed delay using the GRTC timer

Setup:

• Board Version: 0.9.1 (2024.44)
• NRF Connect (VS Code)
• Toolchain: 2.9.0
• SDK: 2.9.0
• Build type: secure

After calling z_nrf_grtc_wakeup_prepare() followed by sys_poweroff(), the board enters system off correctly. I also see current dropping to around 1.2 µA, which looks good — but the board never wakes up again, even after the defined timeout.

I’ve pieced the code together from various SDK samples (so I know it might not be perfect), but I can't figure out what’s missing or incorrect with the GRTC configuration.

For simplicity, I’ve uploaded the complete project to GitHub:

https://github.com/wyssalan/nrf_grtc_wakeup/

In the attached image, you can see the program output before it gets stuck. After the "Retunr to main Program" log, it already goes into deepsleep.

Thanks in advance,

Alan