STM32U585 - Wakeup reason detection when exiting shutdown

[DHečk.1]

Hi,

Im trying to get WUP reason after the MCU exited the shutdown. I'm using pushbutton connected to PC5 pin to wake up the MCU. I cannot get the WUP flag to behave correctly. Sometimes it is present, sometimes not. This feature is part of bigger project where I use WUP by two alarms and pushbutton. I have no problem detecting that the WUP happend due to alarmA or alarmB, but I'm struggling with the pushbutton.

Here is code snippet from test app where I am debugging behaviour of WUP:

	__HAL_RCC_GPIOC_CLK_ENABLE();
 
	HAL_UART_Transmit(&hlpuart1, "Hello\r\n", 7, 300);
 
	if(PWR->WUSR & PWR_WUSR_WUF5)
	{
		PWR->WUSCR &= PWR_WUSCR_CWUF5;	//clear flag
		HAL_UART_Transmit(&hlpuart1, "Button WUP!\r\n", 13, 300);
	}
 
	char buff[32]="";
	sprintf(buff, "WUSR:%08X, CSR:%08X\r\n",PWR->WUSR,RCC->CSR);
	HAL_UART_Transmit(&hlpuart1, buff, strlen(buff), 300);
 
	HAL_PWR_DisableWakeUpPin(PWR_WAKEUP_PIN5);
	__HAL_PWR_CLEAR_FLAG(PWR_WAKEUP_FLAG5);
	HAL_PWR_EnableWakeUpPin(PWR_WAKEUP_PIN5_HIGH_0);
	HAL_PWREx_EnterSHUTDOWNMode();

If I attach the debugger everything starts to work just fine. Is there something I am doing wrong ? Are the registers reseted upon exiting shutdown ?

[Sarra.S]

Hello @David He�?ko​ and welcome to the Community 😊,

The Wake up flag WUF5 is cleared by writing 1 in the CWUF5 bit of PWR_WUSCR,

to do so, this is the right instruction : PWR->WUSCR |= PWR_WUSCR_CWUF5;

Thank you!

Sarra.

[DHečk.1]

Hi @Sarra.S​ , thank you for quick response. I've tried this fix and it unfortunately does not seems to help.

[Sarra.S]

Hello again @David He�?ko​,

I am not sure if the if statement is even being executed

if(PWR->WUSR & PWR_WUSR_WUF5)

{

PWR->WUSCR &= PWR_WUSCR_CWUF5; //clear flag

HAL_UART_Transmit(&hlpuart1, "Button WUP!\r\n", 13, 300);

}

To make sure, is the "Button WUP!" string being displayed ?

[Piranha]

No, the correct code is:

PWR->WUSCR = PWR_WUSCR_CWUF5;

Take a note that it doesn't use an OR instruction and is not a RMW (Read-Modify-Write) operation.