/**
  @page LPTIM_PWMExternalClock LPTIM PWM External clock example
  
  @verbatim
  ******************************************************************************
  * @file    LPTIM/LPTIM_PWMExternalClock/readme.txt 
  * @author  MCD Application Team
  * @brief   Description of the LPTIM PWM with an External clock example.
  ******************************************************************************
  * @attention
  *
  * Copyright (c) 2016 STMicroelectronics.
  * All rights reserved.
  *
  * This software is licensed under terms that can be found in the LICENSE file
  * in the root directory of this software component.
  * If no LICENSE file comes with this software, it is provided AS-IS.
  *
  ******************************************************************************
  @endverbatim

@par Example Description 

How to configure and use, through the HAL LPTIM API, the LPTIM peripheral using an external counter clock, 
to generate a PWM signal at the lowest power consumption.

The Autorelaod equal to 99 so the output frequency (OutputFrequency) will
be equal to the external counter clock (InputFrequency) divided by (99+1).

  OutputFrequency = InputFrequency / (Autoreload + 1)
                  = InputFrequency / 100

Pulse value equal to 49 and the duty cycle (DutyCycle) is computed as follow:

  DutyCycle = 1 - [(PulseValue + 1)/ (Autoreload + 1)]
  DutyCycle = 50%

To minimize the power consumption, after starting generating the PWM signal,
the MCU enters in STOP mode. Note that GPIOs are configured in Low Speed to
lower the consumption.

Wkup/Tamper push-button pin (PC.13)is configured as input with external interrupt (EXTI_Line10-15),
falling edge. When Wkup/Tamper push-button is pressed, wakeup event is generated and PWM signal
generation is stopped.

@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 Keywords

Timer, Low Power, PWM, Stop mode, Interrupt, External Clock, Output, Duty Cycle

@Note If the user code size exceeds the DTCM-RAM size or starts from internal cacheable memories (SRAM1 and SRAM2),that is shared between several processors,
      then it is highly recommended to enable the CPU cache and maintain its coherence at application level.
      The address and the size of cacheable buffers (shared between CPU and other masters)  must be properly updated to be aligned to cache line size (32 bytes).

@Note It is recommended to enable the cache and maintain its coherence, but depending on the use case
      It is also possible to configure the MPU as "Write through", to guarantee the write access coherence.
      In that case, the MPU must be configured as Cacheable/Bufferable/Not Shareable.
      Even though the user must manage the cache coherence for read accesses.
      Please refer to the AN4838 “Managing memory protection unit (MPU) in STM32 MCUs”
      Please refer to the AN4839 “Level 1 cache on STM32F7 Series”

@par Directory contents  

  - LPTIM/LPTIM_PWMExternalClock/Inc/stm32f7xx_hal_conf.h    HAL configuration file
  - LPTIM/LPTIM_PWMExternalClock/Inc/stm32f7xx_it.h          Interrupt handlers header file
  - LPTIM/LPTIM_PWMExternalClock/Inc/main.h                  Header for main.c module  
  - LPTIM/LPTIM_PWMExternalClock/Src/stm32f7xx_it.c          Interrupt handlers
  - LPTIM/LPTIM_PWMExternalClock/Src/main.c                  Main program
  - LPTIM/LPTIM_PWMExternalClock/Src/stm32f7xx_hal_msp.c     HAL MSP module
  - LPTIM/LPTIM_PWMExternalClock/Src/system_stm32f7xx.c      STM32F7xx system source file


@par Hardware and Software environment

  - This example runs on STM32F769xx/STM32F779xx/STM32F777xx/STM32F767xx devices.
    
  - This example has been tested with STMicroelectronics STM32F769I-EVAL
    board and can be easily tailored to any other supported device
    and development board.      

  - Connect an external square clock signal(GBF) to PD.12.
  - Connect PD.13 to an oscilloscope to monitor the LPTIM output waveform.

@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 


 */