/**
  @page COMP_PulseWidthMeasurement COMP Pulse Width measurement example
  
  @verbatim
  ******************** (C) COPYRIGHT 2012 STMicroelectronics *******************
  * @file    COMP/COMP_PulseWidthMeasurement/readme.txt 
  * @author  MCD Application Team
  * @version V1.0.0
  * @date    18-June-2014
  * @brief   Description of the COMP COMP Pulse Width measurement 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 shows how to configure the COMP1 peripheral to measure pulse width.
  This method (measuring signal pulse using comparator is interesting when
  external signal doesn't respect the VIL and VIH levels).

  - COMP1 is configured as following:
     - Inverting input is internally connected to DAC output
     - Non Inverting input is connected to PA1
     - Output is internally connected to TIM2 Input Capture 4 (IC4)

  - DAC channel is used as a digital threshold for measurement, DAC output
    is internally connected to COMP2 inverting input. 
    DAC is configured in 12-bit right alignment. DAC output = VREF * DOR / 4095
                                                            = 3.3 * 868 / 4095
                                                            = 0.7V

    In this example, the pulse of an external signal of around 0.7V 
    (e.g. high level = 0.8V and low level = 0.6V) can be performed.

  - TIM2 counter is clocked by TIM2CLK = 32MHz, TIM2 channel 4 is configured in
    input capture mode.
    TIM2 counter is captured at each transition detection: rising or falling edges
    (each time COMP1 inverting input crosses DAC output)

  - External signal should be connected to PA1. 
    Pulse is computed in microsecond then displayed on the debugger in uwMeasuredPulse variable.
    Pulse duration shouldn't be higher than 65535 * TIM2CLK = 2.047 ms
    Pulse duration shouldn't be lower than TIM2 ISR processing time / TIM2CLK 
                                         ~ 110 (clock cycle) / 32 MHz = 3 us

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

If LED3 is toggling successively: This indicates that the system generates an error.

@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_PulseWidthMeasurement/Inc/stm32l0xx_hal_conf.h    HAL configuration file
  - COMP/COMP_PulseWidthMeasurement/Inc/stm32l0xx_it.h          DMA interrupt handlers header file
  - COMP/COMP_PulseWidthMeasurement/Inc/main.h                  Header for main.c module  
  - COMP/COMP_PulseWidthMeasurement/Src/stm32l0xx_it.c          DMA interrupt handlers
  - COMP/COMP_PulseWidthMeasurement/Src/main.c                  Main program
  - COMP/COMP_PulseWidthMeasurement/Src/stm32l0xx_hal_msp.c     HAL MSP file
  - COMP/COMP_PulseWidthMeasurement/Src/system_stm32l0xx.c      STM32L0xx system source file
         
@par Hardware and Software environment

  - This example runs on STM32L051xx, STM32L052xx, STM32L053xx STM32L062xx and 
    STM32L063xx device lines RevZ
    
  - This example has been tested with STM32L0538-DISCO RevB  board and can be
    easily tailored to any other supported device and development board.

  - STM32L0538-DISCO Set-up
    - Use LED3 connected to PB4 pin.
    - Connect an external signal to PA.01 pin.


@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>
 */

