/**
  @page TIM_TimeBase TIM example
  
  @verbatim
  ******************** (C) COPYRIGHT 2017 STMicroelectronics *******************
  * @file    Examples_LL/TIM/TIM_TimeBase/readme.txt 
  * @author  MCD Application Team
  * @brief   Description of the TIM_TimeBase 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
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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 the TIM peripheral to generate a time base; 
Example using the STM32F2xx TIM LL API, 
peripheral initialization done using LL unitary services functions
for optimization purpose (performance and size).

    In this example TIM2 input clock (TIM2CLK)  is set to APB1 clock (PCLK1),
    since APB1 prescaler is equal to 1.
      TIM2CLK = PCLK1
      PCLK1 = HCLK
      => TIM2CLK = HCLK = SystemCoreClock

To set the TIM2 counter clock frequency to 10 KHz, the pre-scaler (PSC) is calculated as follows:
PSC = (TIM2CLK / TIM2 counter clock) - 1
PSC = (SystemCoreClock /10 KHz) - 1

SystemCoreClock is set to 120 MHz for STM32F2xx Devices.

The auto-reload (ARR) is calculated to get a time base period of 100ms,
meaning that initial time base frequency is 10 Hz.
ARR = (TIM2 counter clock / time base frequency) - 1
ARR = (TIM2 counter clock / 10) - 1

Update interrupts are enabled. Within the update interrupt service routine pin PB.0
(connected to LED1 on board NUCLEO-F207ZG) is toggled.

Key push-button can be used to modify the time base period from 100 ms
to 1 s in 100 ms steps. To do so, every time Key push-button is pressed, the
autoreload register (ARR) is updated. In up-counting update event is generated 
at each counter overflow (when the counter reaches the auto-reload value). 

Finally the time base frequency is calculated as follows:
time base frequency = TIM2 counter clock /((PSC + 1)*(ARR + 1)*(RCR + 1))

@par Directory contents 

  - TIM/TIM_TimeBase/Inc/stm32f2xx_it.h          Interrupt handlers header file
  - TIM/TIM_TimeBase/Inc/main.h                  Header for main.c module
  - TIM/TIM_TimeBase/Inc/stm32_assert.h          Template file to include assert_failed function
  - TIM/TIM_TimeBase/Src/stm32f2xx_it.c          Interrupt handlers
  - TIM/TIM_TimeBase/Src/main.c                  Main program
  - TIM/TIM_TimeBase/Src/system_stm32f2xx.c      STM32F2xx system source file


@par Hardware and Software environment

  - This example runs on STM32F207xx devices.
    
  - This example has been tested with NUCLEO-F207ZG 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>
 */
