Low Power modes configuration functions
[PWR_Private_Functions]

 ===============================================================================
              ##### Low Power modes configuration functions #####
  ==============================================================================

    [..] The devices feature three low-power modes:
    (+) Sleep mode: Cortex-M4 core stopped, peripherals kept running.
    (+) Stop mode: all clocks are stopped, regulator running, regulator in low power mode
    (+) Standby mode: VCORE domain powered off

  *** Sleep mode *** 
  ==================
  [..] 
    (+) Entry:
        (++) The Sleep mode is entered by executing the WFE() or WFI() instructions.
    (+) Exit:
        (++) Any peripheral interrupt acknowledged by the nested vectored interrupt 
             controller (NVIC) can wake up the device from Sleep mode.

  *** Stop mode *** 
  =================
  [..] In Stop mode, all clocks in the VCORE domain are stopped, the PLL, the HSI,
       and the HSE RC oscillators are disabled. Internal SRAM and register 
       contents are preserved.
       The voltage regulator can be configured either in normal or low-power mode.

    (+) Entry:
        (++) The Stop mode is entered using the PWR_EnterSTOPMode(PWR_Regulator_LowPower,) 
             function with regulator in LowPower or with Regulator ON.
    (+) Exit:
        (++) Any EXTI Line (Internal or External) configured in Interrupt/Event mode
             or any internal IPs (I2C or UASRT) wakeup event.

  *** Standby mode *** 
  ====================
  [..] The Standby mode allows to achieve the lowest power consumption. It is based 
       on the Cortex-M4 deepsleep mode, with the voltage regulator disabled. 
       The VCORE domain is consequently powered off. The PLL, the HSI, and the HSE 
       oscillator are also switched off. SRAM and register 
       contents are lost except for the Backup domain (RTC registers, RTC backup 
       registers and Standby circuitry).
   
  [..] The voltage regulator is OFF.

    (+) Entry:
        (++) The Standby mode is entered using the PWR_EnterSTANDBYMode() function.
    (+) Exit:
        (++) WKUP pin rising edge, RTC alarm (Alarm A and Alarm B), RTC wakeup,
             tamper event, time-stamp event, external reset in NRST pin, IWDG reset.

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

    (+) RTC auto-wakeup (AWU) from the Stop mode
        (++) To wake up from the Stop mode with an RTC alarm event, it is necessary to:
             (+++) Configure the EXTI Line 17 to be sensitive to rising edges (Interrupt 
                   or Event modes) using the EXTI_Init() function.
             (+++) Enable the RTC Alarm Interrupt using the RTC_ITConfig() function
             (+++) Configure the RTC to generate the RTC alarm using the RTC_SetAlarm() 
                   and RTC_AlarmCmd() functions.
        (++) To wake up from the Stop mode with an RTC Tamper or time stamp event, it 
             is necessary to:
             (+++) Configure the EXTI Line 19 to be sensitive to rising edges (Interrupt 
                   or Event modes) using the EXTI_Init() function.
             (+++) Enable the RTC Tamper or time stamp Interrupt using the RTC_ITConfig() 
                   function.
             (+++) Configure the RTC to detect the tamper or time stamp event using the
                   RTC_TimeStampConfig(), RTC_TamperTriggerConfig() and RTC_TamperCmd()
                   functions.

    (+) RTC auto-wakeup (AWU) from the Standby mode
        (++) To wake up from the Standby mode with an RTC alarm event, it is necessary to:
             (+++) Enable the RTC Alarm Interrupt using the RTC_ITConfig() function.
             (+++) Configure the RTC to generate the RTC alarm using the RTC_SetAlarm() 
                   and RTC_AlarmCmd() functions.
        (++) To wake up from the Standby mode with an RTC Tamper or time stamp event, it 
             is necessary to:
             (+++) Enable the RTC Tamper or time stamp Interrupt using the RTC_ITConfig() 
                   function.
             (+++) Configure the RTC to detect the tamper or time stamp event using the
                   RTC_TimeStampConfig(), RTC_TamperTriggerConfig() and RTC_TamperCmd()
                   functions.

    (+) Comparator auto-wakeup (AWU) from the Stop mode
        (++) To wake up from the Stop mode with a comparator wakeup event, it is necessary to:
             (+++) Configure the correspondent comparator EXTI Line to be sensitive to 
                   the selected edges (falling, rising or falling and rising) 
                   (Interrupt or Event modes) using the EXTI_Init() function.
             (+++) Configure the comparator to generate the event.