RTC Low Power Wakeup in STM32U385xx

[alxm]

Hello everyone,

I am working with NUCLEO-U385RG-Q board and using the RTC wake-up timer as the wake source for low-power modes. I noticed consistent differences between STOP2 and STOP3:

Issue

• The RTC wake-up interrupt works reliably in STOP2.

• The exact same configuration does not wake the system from STOP3.

Configuration

• LSE is running (32.768 kHz crystal).

• RTC is clocked from LSE.

• RTC wake-up timer is configured via HAL_RTCEx_SetWakeUpTimer_IT().

• No other wake sources are enabled.

Questions

1. Is the RTC wake-up timer officially supported as a wake source in STOP3?

2. Are there additional registers or power settings required for STOP3 to allow RTC wake-up events?

3. Does STOP3 disable any internal domains used by the wake-up timer?

4. Are there known limitations or errata regarding STOP3 + RTC WUT on STM32U-series devices that i may have overlooked?

Any hints or confirmations would be very helpful.
Thank you!