Wake up from Standby by RTC AlarmA in STM32U575

Joaam · ‎2025-09-15

Hi!

I’m currently building an application where I need to periodically wake up my NUCLEO-U575ZI-Q from Standby mode using RTC alarms. I’m aware of the Wake-Up Timers, but I’ve been specifically asked to use alarms. This will be integrated into a FreeRTOS system, but for now I’m trying to get it working in a plain project. I’m using IAR 9.50.1 as the IDE.

I’ve tried everything, but nothing works. I’ve cleared all the required flags, set the others, but I still can’t get it to wake up from an alarm. I’ve been able to wake the MCU using the user button and another wake-up pin, but not via alarms.

This is the code I’m currently working with: main.c

And this is an auxiliary rtc.c file used to initialize the RTC: rtc.c

All the important flags seem to be set correctly. For example, in RTC_SR: ALRAF/ALRBF/WUTF/TSF/TSOVF/ITSF/SSRUF = 0. In RTC_CR: ALRAIE = 1 and ALRAE = 1. In RCC_BDCR: RTCEN = 1.
In PWR, all WUFx flags are clear.

I’m also attaching the current values of the RTC, RCC, and PWR registers for reference.

What can I do? Why isn’t it working?

Gyessine · ‎2025-10-23

Hello, @Joaam
Apologies for the delay.
You can refer to this WIKI or this firmware example and base your project on it.
I attempted to replicate your case from my end, but I did not encounter this issue.

BR
Gyessine

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