STM32CubeF1

/**
  @page TIM_TimeBase TIM example
  
  @verbatim
  ******************** (C) COPYRIGHT 2016 STMicroelectronics *******************
  * @file    Examples_LL/TIM/TIM_TimeBase/readme.txt 
  * @author  MCD Application Team
  * @brief   Description of the TIM_TimeBase 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

Configuration of the TIM peripheral to generate a timebase. This 
example is based on the STM32F1xx TIM LL API. The peripheral initialization 
uses LL unitary service functions for optimization purposes (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 get TIM2 counter clock at 10 KHz, the Prescaler is computed as following:
    Prescaler = (TIM2CLK / TIM2 counter clock) - 1
    Prescaler = (SystemCoreClock /10 KHz) - 1

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 72 MHz for STM32F1xx 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 PA.05
(connected to LED2 on board STM32F103RB-Nucleo) is toggled.

User 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 User 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/stm32f1xx_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/stm32f1xx_it.c          Interrupt handlers
  - TIM/TIM_TimeBase/Src/main.c                  Main program
  - TIM/TIM_TimeBase/Src/system_stm32f1xx.c      STM32F1xx system source file


@par Hardware and Software environment

  - This example runs on STM32F103xB devices.
    
  - This example has been tested with STM32F103RB-Nucleo 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


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