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Processor sometimes ignoring WFI instruction

Adrian over 8 years ago

Hello everyone,

I have a problem with WFI instruction and deep sleep mode.
Normally everything work correct, but sometimes processor ignore instruction WFI and continue work.

I use ARM Cortex-M0+ (exactly STM32L051), and below is my sleep procedure:

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    __ASM volatile ("cpsid i" : : : "memory");
    // if WKUP pins are already high, the WUF bit will be set
    PWR->CSR |= PWR_CSR_EWUP2;
    PWR->CR |=  PWR_CR_CWUF |               // clear the WUF flag after 2 clock cycles
                PWR_CR_CSBF |               // clear StandBy flag
                PWR_CR_ULP;                 // V_{REFINT} is off in low-power mode
    PWR->CR |=  PWR_CR_LPSDSR |             //
                PWR_CR_PDDS;                // Enter Standby mode when the CPU enters deepsleep
    SCB->SCR |= SCB_SCR_SLEEPDEEP_Msk;      // low-power mode = stop mode
    __WFI();                                // enter low-power mode
    while(1)
    {
        uprintf("Interrupt loop");
    }
XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX

	__ASM volatile ("cpsid i" : : : "memory");

	// if WKUP pins are already high, the WUF bit will be set
	PWR->CSR |= PWR_CSR_EWUP2;

	PWR->CR |=	PWR_CR_CWUF	|				// clear the WUF flag after 2 clock cycles
		    	PWR_CR_CSBF	|				// clear StandBy flag
		    	PWR_CR_ULP;					// V_{REFINT} is off in low-power mode
	PWR->CR |=	PWR_CR_LPSDSR |				//
		    	PWR_CR_PDDS;				// Enter Standby mode when the CPU enters deepsleep

	SCB->SCR |= SCB_SCR_SLEEPDEEP_Msk;		// low-power mode = stop mode

	__WFI();								// enter low-power mode
	while(1)
	{
		uprintf("Interrupt loop");
	}

I haven't found information on the conditions that must be met before use WFI in deep sleep mode.

Processor sometimes ignoring WFI instruction

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