/**
  @page RTC_Calendar RTC Calendar Example
  
  @verbatim
  ******************** (C) COPYRIGHT 2017 STMicroelectronics *******************
  * @file    RTC/RTC_Calendar/readme.txt 
  * @author  MCD Application Team
  * @brief   Description of the RTC Calendar example.
  ******************************************************************************
  *
  * Redistribution and use in source and binary forms, with or without modification,
  * are permitted provided that the following conditions are met:
  *   1. Redistributions of source code must retain the above copyright notice,
  *      this list of conditions and the following disclaimer.
  *   2. Redistributions in binary form must reproduce the above copyright notice,
  *      this list of conditions and the following disclaimer in the documentation
  *      and/or other materials provided with the distribution.
  *   3. Neither the name of STMicroelectronics nor the names of its contributors
  *      may be used to endorse or promote products derived from this software
  *      without specific prior written permission.
  *
  * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
  * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
  * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
  * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
  * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
  * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
  * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  *
  ******************************************************************************
  @endverbatim

@par Example Description 

This example guides you through the different configuration steps by mean of HAL API 
to ensure Calendar configuration using the RTC peripheral.  

At the beginning of the main program the HAL_Init() function is called to reset 
all the peripherals, initialize the Flash interface and the systick.
Then the SystemClock_Config() function is used to configure the system
clock (SYSCLK) to run at 120 MHz.

The RTC peripheral configuration is ensured by the HAL_RTC_Init() function.
This later is calling the HAL_RTC_MspInit()function which core is implementing
the configuration of the needed RTC resources according to the used hardware (CLOCK, 
PWR, RTC clock source and BackUp). You may update this function to change RTC configuration.

LSE oscillator clock is used as RTC clock source. 

HAL_RTC_SetTime()and HAL_RTC_SetDate() functions are then called to initialize the 
time and the date.

A key value is written in backup data register 1 to indicate if the RTC is already configured.  
The program behaves as follows:

1. After startup the program checks the backup data register 1 value:
    - BKP_DR1 value not correct: (RTC_BKP_DR1 value is not correct or has not yet
      been programmed when the program is executed for the first time) the RTC is
      configured.
    
    - BKP_DR1 value correct: this means that the RTC is configured and the time
      and date are displayed on Debugger.
2. When a reset (except power on reset) occurs the BKP domain is not reset and the RTC 
   configuration is not lost. LED1 is ON.
   
3. When power on reset occurs:
    - The BKP domain is reset and the RTC configuration is lost.
    Note: During first debugger re-run, the power on reset already occurred just before 
    (at switch ON) then RTC configuration is not lost and LED3 is ON.

LED1 is turned ON when the RTC configuration is done correctly.

The current time and date are updated and displayed on the debugger in aShowTime 
and aShowDate variables.

@note Care must be taken when using HAL_Delay(), this function provides accurate delay (in milliseconds)
      based on variable incremented in SysTick ISR. This implies that if HAL_Delay() is called from
      a peripheral ISR process, then the SysTick interrupt must have higher priority (numerically lower)
      than the peripheral interrupt. Otherwise the caller ISR process will be blocked.
      To change the SysTick interrupt priority you have to use HAL_NVIC_SetPriority() function.
      
@note The application need to ensure that the SysTick time base is always set to 1 millisecond
      to have correct HAL operation.

@par Directory contents 

  - RTC/RTC_Calendar/Inc/stm32f2xx_hal_conf.h    HAL configuration file
  - RTC/RTC_Calendar/Inc/stm32f2xx_it.h          Interrupt handlers header file
  - RTC/RTC_Calendar/Inc/main.h                  Header for main.c module  
  - RTC/RTC_Calendar/Src/stm32f2xx_it.c          Interrupt handlers
  - RTC/RTC_Calendar/Src/main.c                  Main program
  - RTC/RTC_Calendar/Src/stm32f2xx_hal_msp.c     HAL MSP module
  - RTC/RTC_Calendar/Src/system_stm32f2xx.c      STM32F2xx system source file

@par Hardware and Software environment

  - This example runs on STM32F207xG Devices.
  - This example has been tested with STMicroelectronics NUCLEO-207ZG Rev.B
    board and can be easily tailored to any other supported device and 
    development board. 

@par How to use it ? 

In order to make the program work, you must do the following :
 - Open your preferred toolchain 
 - Rebuild all files and load your image into target memory
 - Run the example

 * <h3><center>&copy; COPYRIGHT STMicroelectronics</center></h3>
 */
