/**
  @page IWDG_Example IWDG_Example
  
  @verbatim
  ******************** (C) COPYRIGHT 2012 STMicroelectronics *******************
  * @file    IWDG/IWDG_Example/readme.txt 
  * @author  MCD Application Team
  * @version V1.1.1
  * @date    13-April-2012
  * @brief   Description of the IWDG 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 shows how to update at regular period the IWDG reload counter and 
how to simulate a software fault generating an MCU IWDG reset on expiry of a 
programmed time period.

The IWDG timeout is set to 250 ms (the timeout may varies due to LSI frequency 
dispersion).

First, the TIM5 timer is configured to measure the LSI frequency as the 
LSI is internally connected to TIM5 CH4, in order to adjust the IWDG clock.

The LSI measurement using the TIM5 is described below:
 - Configure the TIM5 to remap internally the TIM5 CH4 Input Capture to the LSI
   clock output.
 - Enable the TIM5 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. 

Then, the IWDG reload counter is configured to obtain 250 ms according to the 
measured LSI frequency.

The IWDG reload counter is refreshed each 240 ms in the main program infinite loop 
to prevent a IWDG reset.
LED2 is also toggled each 240 ms indicating that the program is running.

An EXTI Line is connected to a GPIO pin, and configured to generate an interrupt
on the rising edge of the signal.

The EXTI Line is used to simulate a software failure: once the EXTI Line event 
occurs, by pressing the Key push-button, the corresponding interrupt is served.
In the ISR, a write to invalid address generates a Hardfault exception containing
an infinite loop and preventing to return to main program (the IWDG reload counter 
is not refreshed).
As a result, when the IWDG counter reaches 00h, the IWDG reset occurs.
If the IWDG reset is generated, after the system resumes from reset, LED1 turns on.

If the EXTI Line event does not occur, the IWDG counter is indefinitely refreshed
in the main program infinite loop, and there is no IWDG reset.

In this example the system clock is set to 32 MHz on Ultra Low Power High- and
Medium-Density Devices.

@par Directory contents 

  - IWDG_Example/system_stm32l1xx.c   STM32L1xx system clock configuration file 
  - IWDG_Example/stm32l1xx_conf.h     Library Configuration file
  - IWDG_Example/stm32l1xx_it.c       Interrupt handlers
  - IWDG_Example/stm32l1xx_it.h       Header for stm32l1xx_it.c
  - IWDG_Example/main.c               Main program

@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 LD1 and LD2 leds connected respectively to PD.00 and PD.01 pins
    - Use the KEY push button connected to PA.00 pin (EXTI Line0).

  - STM32L152D-EVAL Set-up
    - Use LD1 and LD2 leds connected respectively to PD.03 and PD.07 pins
    - Use the KEY push button connected to PA.00 pin (EXTI Line0).
      
    
@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>
 */


