/**
  @page COMP_PWMSignalControl COMP Pulse Width measurement example
  
  @verbatim
  ******************** (C) COPYRIGHT 2014 STMicroelectronics *******************
  * @file    COMP/COMP_PWMSignalControl/readme.txt
  * @author  MCD Application Team
  * @version $VERSION$
  * @date    $DATE$
  * @brief   Description of the COMP PWM Signal Control 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
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  * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  *
  ******************************************************************************
  @endverbatim

@par Example Description 

This example shows how to configure COMP2 peripheral to automatically hold
TIM2 PWM output on safe state (low level) as soon as comparator output is set
at high level.

  - COMP2 is configured as following:
     - Inverting input is internally connected to VREFINT = 1.22V
     - Non Inverting input is connected to pin PB.05
     - Output is internally connected to TIM2 TIM_CHANNEL_2 OCRef clear input.

  - TIM2 counter is used for PWM signal generation.
     - Timer frequency is set to 1kHz, PWM duty cycle 25%. Frequency can be tuned using defined label "TIMER_FREQUENCY_HZ" (unit: Hz).
     - TIM2 channel TIM_CHANNEL_2 is configured in PWM output mode, connected to pin PB.03.


Board settings:
  - STM32L152RE-Nucleo Rev C Set-up
      @note This example run in stand alone mode.
    - Set voltage level on pin PB.05 (comparator input): above or below Vrefint (1.22V).
      Note: to avoid the need of a power supply, possibility to connect a wire between this pin to a pin of the board: Vdda pin (3.3V) or ground pin (0V).
    - Watch waveform on pin PB.03 (timer PWM output) with an oscilloscope, or watch average value mith a multimeter (Vdda=3.3v and duty cycle 25% should give a=n average voltage of 0.825V)

Expected results:
If voltage on comparator input is lower than Vrefint (1.22V), then timer PWM output if running normally.
If voltage on comparator input is higher than Vrefint (1.22V), then timer PWM output if forced to 0V.

STM32L152RE-Nucleo Rev C board's LED is be used to monitor the program execution status:
 - Error: In case of error, LED2 is toggling at a frequency of 1Hz.
 

@note To have a precise value of the pulse, HSI as a source of clock system should be 
calibrated or use an external clock.


@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 

  - COMP/COMP_PWMSignalControl/Inc/stm32l1xx_hal_conf.h    HAL configuration file
  - COMP/COMP_PWMSignalControl/Inc/stm32l1xx_it.h          COMP interrupt handlers header file
  - COMP/COMP_PWMSignalControl/Inc/main.h                  Header for main.c module
  - COMP/COMP_PWMSignalControl/Src/stm32l1xx_it.c          COMP interrupt handlers
  - COMP/COMP_PWMSignalControl/Src/main.c                  Main program
  - COMP/COMP_PWMSignalControl/Src/stm32l1xx_hal_msp.c     HAL MSP file 
  - COMP/COMP_PWMSignalControl/Src/system_stm32l1xx.c      STM32L1xx system source file


@par Hardware and Software environment 

  - This example runs on STM32L1xx devices.

  - This example has been tested with STM32L152RE-Nucleo Rev C 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>
 */