STM32L4S5VIT6 STOP2 Mode Wake-Up Issue in Release

[Gohil]

Hello STM32 Community,

I'm working with the STM32L4S5VIT6 microcontroller and implementing low power functionality using STOP2 mode.

 Setup Summary:

• I use a GPIO button (external interrupt) to enter STOP2 mode on the first press.

• On the second press, I attempt to wake up the MCU and call low_power_off() to reinitialize peripherals and resume operation.

• I’m using MSI as the system clock (no PLL), and STOP2 mode is entered with HAL_PWREx_EnterSTOP2Mode(PWR_STOPENTRY_WFI);.

Behavior in Debug Mode:

• Everything works as expected:

  • First button press → enters STOP2 via low_power_on().

  • Second press → wakes up and executes low_power_off() successfully.

 Problem in Release Mode:

• First button press → MCU enters STOP2 mode.

• Second button press does not wake up the MCU as expected.

• It seems the EXTI interrupt is not firing in release mode, or the wakeup source isn't triggering properly.

 What I've Checked:

• EXTI configuration seems correct.

• Wakeup pin is properly pulled up, and configured for falling edge.

• SystemClock_Config() runs correctly on wakeup and reinitializes MSI.

• __HAL_PWR_CLEAR_FLAG(PWR_FLAG_WU); and __HAL_GPIO_EXTI_CLEAR_IT() are used before STOP2.

• Wakeup_Button_Init() is called both before entering STOP2 and after wakeup.

Please review my attached main.c code (which includes low_power_on() and low_power_off() logic).
Is there anything I might be missing or doing incorrectly that's causing this issue in Release Mode only?

Any suggestions to improve reliability or correctness of wakeup logic are very welcome.

Thank you!

[Sarra.S]

Hello @Gohil, 

Could you check the compiler optimizations, as the issue might be related to how the code is optimized in release mode compared to debug mode.

Check this related thread