/**
  @page RTC_LSI RTC prescaler adjustment with LSI Measurements example
  
  @verbatim
  ******************** (C) COPYRIGHT 2012 STMicroelectronics *******************
  * @file    RTC/RTC_LSI/readme.txt 
  * @author  MCD Application Team
  * @version V1.1.1
  * @date    13-April-2012
  * @brief   Description of the RTC prescaler adjustment with LSI Measurements example.
  ******************************************************************************
  *
  * Licensed under MCD-ST Liberty SW License Agreement V2, (the "License");
  * You may not use this file except in compliance with the License.
  * You may obtain a copy of the License at:
  *
  *        http://www.st.com/software_license_agreement_liberty_v2
  *
  * Unless required by applicable law or agreed to in writing, software 
  * distributed under the License is distributed on an "AS IS" BASIS, 
  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  * See the License for the specific language governing permissions and
  * limitations under the License.
  *
  ******************************************************************************
   @endverbatim

@par Example Description 

This example demonstrates and explains how to use the LSI clock source auto
calibration to get a precise RTC clock. 
As an application example, it demonstrates how to configure the TIM10 timer
internally connected to LSI clock output, in order to adjust the RTC prescaler. 

The Low Speed Internal (LSI) clock is used as RTC clock source.
After reset, the RTC prescaler (asynchronous and synchronous) is set with the 
default LSI frequency (37KHz). 
The RTC WakeUp is configured to generate an interrupt each 1s. The WakeUp counter
is clocked by the RTC CK_SPRE signal (1Hz) and its counter is set to 0x0.
LED1 is toggled inside the RTC WakeUp interrupt each 1s.

The inaccuracy of the LSI clock causes the RTC WakeUp Interrupt to be inaccurate.
The RTC CK_SPRE signal can be monitored by LED1 which is toggled into the RTC 
Wakeup interrupt service routine.

The program waits until Key Push button is pressed to begin the auto calibration 
procedure:
 - Configure the TIM10 to remap internally the TIM10 Channel 1 Input Capture to 
   the LSI clock output.
 - Enable the TIM10 Input Capture interrupt: after one cycle of LSI clock, the
   period value is stored in a variable and compared to the HCLK clock to get
   its real value.
 - The RTC prescaler is adjusted with this LSI frequency value so that the RTC
   CK_SPRE value become more accurate.
 - When calibration is done LED2 is turned ON to indicate the end of this operation.

@par Directory contents 

  - RTC/RTC_LSI/stm32l1xx_conf.h    Library Configuration file
  - RTC/RTC_LSI/stm32l1xx_it.c      Interrupt handlers
  - RTC/RTC_LSI/stm32l1xx_it.h      Interrupt handlers header file
  - RTC/RTC_LSI/main.c              Main program
  - RTC/RTC_LSI/system_stm32l1xx.c  STM32L1xx system source file
  
@note The "system_stm32l1xx.c" is generated by an automatic clock configuration 
      system and can be easily customized to your own configuration. 
      To select different clock setup, use the "STM32L1xx_Clock_Configuration_V1.1.0.xls" 
      provided with the AN3309 package available on <a href="http://www.st.com/internet/mcu/family/141.jsp">  ST Microcontrollers </a>
         
@par Hardware and Software environment

  - This example runs on STM32L1xx Ultra Low Power High-, Medium-Density and Medium-Density Plus Devices.
  
  - This example has been tested with STMicroelectronics STM32L152D-EVAL (STM32L1xx 
    Ultra Low Power High-Density) and STM32L152-EVAL (STM32L1xx Ultra Low 
    Power Medium-Density) evaluation board and can be easily tailored to any 
    other supported device and development board.

  - STM32L152-EVAL Set-up
    - Use LED1 and LED2 leds connected respectively to PD.00 and PD.01 pins
    - Use the Key push button connected to PA.00 pin


  - STM32L152D-EVAL Set-up
    - Use LED1 and LED2 leds connected respectively to PD.03 and PD.07 pins
    - Use the Key push button connected to PA.00 pin

@par How to use it ? 

In order to make the program work, you must do the following :
 - Copy all source files from this example folder to the template folder under
   Project\STM32L1xx_StdPeriph_Templates
 - Open your preferred toolchain 
 - Rebuild all files and load your image into target memory
 - Run the example

@note
- Ultra Low Power Medium-density devices are STM32L151xx and STM32L152xx 
  microcontrollers where the Flash memory density ranges between 64 and 128 Kbytes.
- Ultra Low Power Medium-density Plus devices are STM32L151xx, STM32L152xx and 
  STM32L162xx microcontrollers where the Flash memory density is 256 Kbytes.
- Ultra Low Power High-density devices are STM32L151xx, STM32L152xx and STM32L162xx 
  microcontrollers where the Flash memory density is 384 Kbytes.
    
 * <h3><center>&copy; COPYRIGHT STMicroelectronics</center></h3>
 */


