STM32WL55JC1 Not Waking from Standby via RTC Alarm A

[pavan1]

Hi,

I'm facing an issue with waking the STM32WL55JC1 from Standby mode using RTC Alarm A.

Setup:

• Using LSE as RTC clock source

• RTC and Alarm A are initialized correctly

• Alarm A interrupt works when not entering standby

• Wake-up via RTC Wakeup Timer works fine (standby + timer = success)

Issue:

When I:

1. Clear RTC time and date

2. Set Alarm A to trigger a few seconds ahead

3. Enter Standby mode

4. Wait for wake-up

→ The system does not wake up from Alarm A.

However, if I skip Standby mode, Alarm A fires the interrupt as expected.

Observation:

• RTC Alarm A interrupt is configured and enabled.

• EXTI and NVIC settings are correct.

• I suspect the Alarm A wakeup source isn’t properly enabled or EXTI line isn’t configured before entering standby.
  
  
  

  Request:

  Could you confirm the correct sequence or any missing configuration required for:

  • Enabling Alarm A as a wakeup source from standby

  • Ensuring EXTI line 17 is correctly set before standby

  Let me know if additional register dumps or code snippets are needed.

  Thanks,

  
  
  
  

  Edited by ST Moderator to add the right labels

[Sarra.S]

Hello @pavan1, 

The correct sequence is: 

• Configure EXTI 17 to be sensitive to rising edges and enable it in interrupt mode.
• Enable the RTC Alarm A interrupt (ALRAIE in RTC_CR) 
• Clear the ALRAF flag before entering Standby.
• Make sure the RTC clock source (LSE/LSI) is stable and active.

Hope that helps!