Peripheral Control functions
[PWR Exported Functions]

 ===============================================================================
                 ##### Peripheral Control functions #####
 ===============================================================================
 
     [..]
     *** PVD configuration ***
    =========================
    [..]
      (+) The PVD is used to monitor the VDD power supply by comparing it to a
          threshold selected by the PVD Level (PLS[2:0] bits in PWR_CR2 register).

      (+) PVDO flag is available to indicate if VDD/VDDA is higher or lower
          than the PVD threshold. This event is internally connected to the EXTI
          line16 and can generate an interrupt if enabled. This is done through
          __HAL_PVD_EXTI_ENABLE_IT() macro.
      (+) The PVD is stopped in Standby mode.
 
    
    *** WakeUp pin configuration ***
    ================================
    [..]
      (+) WakeUp pins are used to wakeup the system from Standby mode or Shutdown mode. 
          The polarity of these pins can be set to configure event detection on high 
          level (rising edge) or low level (falling edge).


   
    *** Low Power modes configuration ***
    =====================================
    [..]
      The devices feature 8 low-power modes:
      (+) Low-power Run mode: core and peripherals are running, regulator in low power mode.
      (+) Sleep mode: Cortex-M4 core stopped, peripherals kept running, regulator in normal mode.
      (+) Low-power Sleep mode: Cortex-M4 core stopped, peripherals kept running, regulator in low power mode.      
      (+) Stop 1 mode: all clocks are stopped except LSI and LSE, regulator in normal or low power mode.
      (+) Stop 2 mode: all clocks are stopped except LSI and LSE, regulator in low power mode, reduced set of waking up IPs compared to Stop 1 mode.      
      (+) Standby mode with SRAM2: all clocks are stopped except LSI and LSE, SRAM2 content preserved, regulator in low power mode. 
      (+) Standby mode without SRAM2: all clocks are stopped except LSI and LSE, regulator off.
      (+) Shutdown mode: all clocks are stopped except LSE, regulator off.       


   *** Low-power run mode ***
   ==========================
    [..]
      (+) Entry: (from main run mode)
        (++) set LPR bit with HAL_PWREx_EnableLowPowerRunMode() API after having decreased the system clock below 2 MHz. 
     
      (+) Exit:
        (++) clear LPR bit then wait for REGLP bit to be reset with HAL_PWREx_DisableLowPowerRunMode() API. Only
             then can the system clock frequency be increased above 2 MHz.


   *** Sleep mode / Low-power sleep mode ***
   =========================================
    [..]
      (+) Entry:                                                         
          The Sleep mode / Low-power Sleep mode is entered thru HAL_PWR_EnterSLEEPMode() API
          in specifying whether or not the regulator is forced to low-power mode and if exit is interrupt or event-triggered. 
          (++) PWR_MAINREGULATOR_ON: Sleep mode (regulator in main mode).              
          (++) PWR_LOWPOWERREGULATOR_ON: Low-power sleep (regulator in low power mode).
          In the latter case, the system clock frequency must have been decreased below 2 MHz beforehand.           
          (++) PWR_SLEEPENTRY_WFI: enter SLEEP mode with WFI instruction
          (++) PWR_SLEEPENTRY_WFE: enter SLEEP mode with WFE instruction
     
      (+) WFI Exit:
        (++) Any peripheral interrupt acknowledged by the nested vectored interrupt
             controller (NVIC) or any wake-up event.
             
      (+) WFE Exit:
        (++) Any wake-up event such as an EXTI line configured in event mode.             
             
         [..] When exiting the Low-power sleep mode by issuing an interrupt or a wakeup event, 
             the MCU is in Low-power Run mode. 

   *** Stop 1 and Stop 2 modes ***
   ===============================
    [..]
      (+) Entry:                                                 
          The Stop 1 or Stop 2 modes are entered thru the following API's:
          (++) HAL_PWR_EnterSTOPMode() [for legacy porting reasons] or HAL_PWREx_EnterSTOP1Mode() for mode 1
          (++) HAL_PWREx_EnterSTOP2Mode for mode 2.  
      (+) Regulator setting (applicable to Stop 1 mode only):
          (++) PWR_MAINREGULATOR_ON
          (++) PWR_LOWPOWERREGULATOR_ON
      (+) Exit (interrupt or event-triggered, specified when entering STOP mode):
          (++) PWR_STOPENTRY_WFI: enter Stop mode with WFI instruction
          (++) PWR_STOPENTRY_WFE: enter Stop mode with WFE instruction
          
      (+) WFI Exit:
          (++) Any EXTI Line (Internal or External) configured in Interrupt mode.
          (++) Some specific communication peripherals (USART, LPUART, I2C) interrupts 
               when programmed in wakeup mode. 
      (+) WFE Exit:  
          (++) Any EXTI Line (Internal or External) configured in Event mode.
       
       [..]                      
          When exiting Stop 1 mode, the MCU is either in Run mode or in Low-power Run mode
          depending on the LPR bit setting. 
          When exiting Stop 2 mode, the MCU is in Run mode. 

   *** Standby mode ***
   ====================
     [..]
      The Standby mode offers two options: 
      (+) option a) all clocks off except LSI and LSE, RRS bit set (keeps voltage regulator in low power mode).
        SRAM and registers contents are lost except for the SRAM2 content, the RTC registers, RTC backup registers 
        and Standby circuitry.      
      (+) option b) all clocks off except LSI and LSE, RRS bit cleared (voltage regulator then disabled).
        SRAM and register contents are lost except for the RTC registers, RTC backup registers 
        and Standby circuitry.

      (++) Entry:                                    
          (+++) The Standby mode is entered thru HAL_PWR_EnterSTANDBYMode() API. 
           SRAM1 and register contents are lost except for registers in the Backup domain and 
           Standby circuitry. SRAM2 content can be preserved if the bit RRS is set in PWR_CR3 register. 
           To enable this feature, the user can resort to HAL_PWREx_EnableSRAM2ContentRetention() API 
           to set RRS bit.   
          
      (++) Exit:
          (+++) WKUP pin rising edge, RTC alarm or wakeup, tamper event, time-stamp event, 
               external reset in NRST pin, IWDG reset.
                
      [..]    After waking up from Standby mode, program execution restarts in the same way as after a Reset.
          

    *** Shutdown mode ***
   ======================
     [..]
      In Shutdown mode, 
        voltage regulator is disabled, all clocks are off except LSE, RRS bit is cleared.
        SRAM and registers contents are lost except for backup domain registers.

      (+) Entry:                                    
          The Shutdown mode is entered thru HAL_PWREx_EnterSHUTDOWNMode() API.
          
      (+) Exit:
          (++) WKUP pin rising edge, RTC alarm or wakeup, tamper event, time-stamp event, 
               external reset in NRST pin.
               
         [..] After waking up from Shutdown mode, program execution restarts in the same way as after a Reset.


   *** Auto-wakeup (AWU) from low-power mode ***
   =============================================
    [..]
      The MCU can be woken up from low-power mode by an RTC Alarm event, an RTC
      Wakeup event, a tamper event or a time-stamp event, without depending on
      an external interrupt (Auto-wakeup mode).

      (+) RTC auto-wakeup (AWU) from the Stop, Standby and Shutdown modes
  

        (++) To wake up from the Stop mode with an RTC alarm event, it is necessary to
             configure the RTC to generate the RTC alarm using the HAL_RTC_SetAlarm_IT() function.

        (++) To wake up from the Stop mode with an RTC Tamper or time stamp event, it
             is necessary to configure the RTC to detect the tamper or time stamp event using the
             HAL_RTCEx_SetTimeStamp_IT() or HAL_RTCEx_SetTamper_IT() functions.

        (++) To wake up from the Stop mode with an RTC WakeUp event, it is necessary to
              configure the RTC to generate the RTC WakeUp event using the HAL_RTCEx_SetWakeUpTimer_IT() function.