STM32WLE Standby Mode Pull Up/Down Registers - PWR_PUCRx vs GPIOx_PUPDR

[RLind.3]

Hi there,

I am trying to set PU/PD resistors that will stay set while my STM32WLE is in Standby mode. Am I correct in saying that I need to use the PWR_PUCRx registers to keep the PU/PD resistors active while in Standby? If so, is there anything else that could catch me out? Eg, do I need to reset the GPIOx_PUPDR registers? Can I use the PWR_PUCRx registers while in Run mode, or should I only use the GPIOx_PUPDR registers while running?

A brief explanation of PWR_PUCRx vs GPIOx_PUPDR would be greatly appreciated. 😊

Thanks,

Rebecca

[KDJEM.1]

Hi @RLind.3​ ,

In Standby mode, for STM32WLE, you need the PWR_PUCRx registers to keep the PU resistors active and the PWR_PDCRx registers to keep the PD resistors active. There should be no constraints if you use PWR_PUCRx  or PWR_PDCRx registers in run mode. However their main purpose is to allow pull-up or pull down while being in a low power mode (GPIO clock disabled). 

We can add that, the GPIOx_PUPDR is only one register for pull-up/pull-down resistors while you have PWR_PUCR (Power pull-up control register) dedicated for pull-up resistors and PWR_PDCR (Power pull-down control register) dedicated for pull-up resistors. Also, please note that the I/O pull-up and pull-down configurations defined in the PWR_PUCRx and PWR_PDCRx registers are applied only when APC bit is set in PWR control register 3. 

Does this answer your question?

Kaouthar

[Piranha]

> low power mode (GPIO clock disabled)

Those two are unrelated and the "explanation" in parentheses is confusing.

[RLind.3]

Hi @KDJEM.1​ ,

Thanks for your reply and explanation.

I have been doing some tests with the STM32WLE and I have found some unexpected behaviours:

• When I use only the GPIOx_PUPDR register and enter standby, the PU/PD resistors are kept - checking the voltages with a multimeter shows they are pulled high/low as set in GPIOx_PUPDR.
• When I set the APC bit and use the PWR_PUCRx/PWR_PDCRx registers, there is an additional 2mA drawn when I enter standby. I disabled all GPIOx_PUPDR resistors before using the PWR_PUCRx/PWR_PDCRx ones. I have checked my PU/PD configuration and it is equivalent to the GPIOx_PUPDR one I used previously.

The C1SBF in PWR_EXTSCR is set when I wake from Standby so I believe I am entering it correctly. I clear C1SBF each time the MCU wakes up.

Do you have any clues as to these behaviours?

Thanks,

Rebecca

[Piranha]

> there is an additional 2mA drawn when I enter standby

When entering low-power mode, set DBGMCU_CR to zero and disconnect the debugger physically.

> When I use only the GPIOx_PUPDR register and enter standby, the PU/PD resistors are kept

Show the code, which enters the low-power mode and configures wake-up features.

[RLind.3]

Hi @Piranha​ ,

Thank you for your advice. I have set DBGMCU_CR to zero and that has fixed the problem of excessive current.

Here is my standby_begin() function:

void standby_begin(void)
{
    // Keep SRAM2
    PWR->CR3 |= PWR_CR3_RRS;
 
    // Enable WKUP1 pin PA0
    PWR->CR3 |= PWR_CR3_EWUP1;
    PWR->CR4 &= ~PWR_CR4_WP1; // Rising edge
 
    // Set SLEEPDEEP bit
    SCB->SCR |= SCB_SCR_SLEEPDEEP_Msk;
 
    // Set to enter standby
    PWR->CR1 &= ~PWR_CR1_LPMS;
    PWR->CR1 |= PWR_LOWPOWERMODE_STANDBY;
 
    // Change to periodic sampling of VDD
    PWR->CR3 |= PWR_CR3_ULPEN;
 
    // Wait for radio to finish (if not under reset)
    if (!(RCC->CSR & RCC_CSR_RFRST))
    {
        while((PWR->SR2 & PWR_SR2_RFBUSYMS) && (PWR->SR2 & PWR_SR2_RFBUSYS));
 
        // Shutdown radio
        RCC->CSR |= RCC_CSR_RFRST;
    }
 
    // Clear wake up flags
    PWR->SCR |= 0x4907; // Clear all flags
 
    // Set all GPIO to input
    GPIOA->MODER = 0x00;
    GPIOB->MODER = 0x00;
    GPIOC->MODER = 0x00;
 
    // Set all GPIO to pull down except LEDs, ADC input, SWDIO, OSC32, WKUP1
    GPIOA->PUPDR = 0xA556AAA4; // 1010 0101 0101 1010 1010 1010 1010 0100
    GPIOB->PUPDR = 0xAAA95AAA; // 1010 1010 1010 1001 0101 1010 1010 1010
    GPIOC->PUPDR = 0x0AAAAAAA;
 
        // Use PWR PU/PD instead of GPIOx
//      PWR->PDCRA = 0xC3F4; // 1100 0011 1111 0100
//      PWR->PDCRB = 0x1035; // 0001 0000 0011 0101
//      PWR->PDCRC = 0x3FFF; // 0011 1111 1111 1111
//      PWR->PUCRA = 0x3C0A; // 0011 1100 0000 1010
//      PWR->PUCRB = 0x01C0; // 0000 0001 1100 0000
//      PWR->PUCRC = 0x0000;
//
//      GPIOA->PUPDR = 0x00;
//      GPIOB->PUPDR = 0x00;
//      GPIOC->PUPDR = 0x00;
//      PWR->CR3 |= PWR_CR3_APC;
 
    // Disable debugging in LP modes
    DBGMCU->CR = 0;
 
    // Disable RTC alarm interrupt
    NVIC_DisableIRQ(RTC_Alarm_IRQn);
    NVIC_ClearPendingIRQ(RTC_Alarm_IRQn);
 
    // Disable radio interrupt
    NVIC_DisableIRQ(SUBGHZ_Radio_IRQn);
    NVIC_ClearPendingIRQ(SUBGHZ_Radio_IRQn);
 
    // Disable ADC interrupt
    NVIC_DisableIRQ(ADC_IRQn);
    NVIC_ClearPendingIRQ(ADC_IRQn);
 
    // Disable TIM1 interrupt
    NVIC_DisableIRQ(TIM1_CC_IRQn);
    NVIC_ClearPendingIRQ(TIM1_CC_IRQn);
 
   // Disable low power timer interrupts
    NVIC_DisableIRQ(LPTIM1_IRQn);
    NVIC_ClearPendingIRQ(LPTIM1_IRQn);
    NVIC_DisableIRQ(LPTIM2_IRQn);
    NVIC_ClearPendingIRQ(LPTIM2_IRQn);
    NVIC_DisableIRQ(LPTIM3_IRQn);
    NVIC_ClearPendingIRQ(LPTIM3_IRQn);
 
    // Disable SysTick and interrupt
    SysTick->CTRL &= ~(SysTick_CTRL_TICKINT_Msk | SysTick_CTRL_ENABLE_Msk);
    NVIC_ClearPendingIRQ(SysTick_IRQn);
 
    watchdog_kick();
 
     // Check low power regulator is ready
     while((PWR->SR2 & PWR_SR2_REGLPS) == 0);
 
    // Enter standby
    __WFI();
}

Please let me know if you need any other code or information.

Thanks,

Rebecca