STM32 use Timer instead of Systick

@par Example Description 

This example describes how to customize the HAL time base using a general purpose timer instead of Systick as main source of time base.

In this example the used timer is TIM6.

Time base duration is kept unchanged: 1ms  since PPP_TIMEOUT_VALUEs are defined and handled in milliseconds basis.

The example brings, in user file, a new implementation of the following HAL weak functions:
HAL_InitTick()
HAL_SuspendTick()
HAL_ResumeTick()

This implementation will overwrite native implementation in stm32f7xx_hal.c and so user functions will be invoked instead when called.

The following time base functions are kept as implemented natively:
HAL_IncTick()
HAL_Delay()

When user pushes the Tamper push-button, the Tick increment is suspended if it is already enabled, else it will be resumed.
In an infinite loop, LED1 toggles spaced out over 1s delay.

@note Care must be taken when using HAL_Delay(), this function provides accurate delay (in milliseconds)
      based on variable incremented in TIM6 ISR. This implies that if HAL_Delay() is called from
      a peripheral ISR process, then the TIM6 interrupt must have higher priority (numerically lower)
      than the peripheral interrupt. Otherwise the caller ISR process will be blocked.
      To change the TIM6 interrupt priority you have to use HAL_NVIC_SetPriority() function.

@note The application needs to ensure that the TIM6 time base is always set to 1 millisecond
      to have correct HAL operation.

@par Keywords

System, General purpose Timer, Time base, HAL

@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”



uint32_t uwIncrementState = 0;
/* Private function prototypes -----------------------------------------------*/
static void SystemClock_Config(void);
static void CPU_CACHE_Enable(void);


/* Private functions ---------------------------------------------------------*/

/**
  * @brief  Main program
  * @param  None
  * @retval None
  */
int main(void)
{
 /* This sample code shows how to configure The HAL time base source base with a
    dedicated  Tick interrupt priority.
    A general purpose timer (TIM6) is used instead of Systick as source of time base. 
    Time base duration is fixed to 1ms since PPP_TIMEOUT_VALUEs are defined and
    handled in milliseconds basis.
    */

  /* Enable the CPU Cache */
  CPU_CACHE_Enable();


  /* STM32F7xx HAL library initialization:
       - Configure the Flash prefetch
       - Configure timer (TIM6) to generate an interrupt each 1 msec
       - Set NVIC Group Priority to 4
       - Low Level Initialization
     */
  HAL_Init();
 
  /* Configure the system clock to 216 MHz */
  SystemClock_Config();
 
  /* Configure LED1 */
  BSP_LED_Init(LED1); 
 
  /* Configure Tamper push-button */
  BSP_PB_Init(BUTTON_KEY, BUTTON_MODE_EXTI);

  /* Insert a Delay of 1000 ms and toggle LED2, in an infinite loop */ 
  while (1)
  {
    /* Insert a 1s delay */
    HAL_Delay(1000);
   
    /* Toggle LED1 */
    BSP_LED_Toggle(LED1);
  }
}

/**
  * @brief EXTI line detection callback.
  * @param GPIO_Pin: Specifies the pins connected EXTI line
  * @retval None
  */
void HAL_GPIO_EXTI_Callback(uint16_t GPIO_Pin)
{
  if(GPIO_Pin == KEY_BUTTON_PIN)
  {
    if (uwIncrementState == 0)
    {
      /* Suspend tick increment */
      HAL_SuspendTick();
     
      /* Change the Push button state */
      uwIncrementState = 1;
    }
    else
    {
      /* Resume tick increment */
      HAL_ResumeTick();
     
      /* Change the Push button state */
      uwIncrementState = 0;
    }
  } 
}

/**
  * @brief  System Clock Configuration
  *         The system Clock is configured as follow :
  *            System Clock source            = PLL (HSE)
  *            SYSCLK(Hz)                     = 216000000
  *            HCLK(Hz)                       = 216000000
  *            AHB Prescaler                  = 1
  *            APB1 Prescaler                 = 4
  *            APB2 Prescaler                 = 2
  *            HSE Frequency(Hz)              = 25000000
  *            PLL_M                          = 25
  *            PLL_N                          = 432
  *            PLL_P                          = 2
  *            PLL_Q                          = 9
  *            VDD(V)                         = 3.3
  *            Main regulator output voltage  = Scale1 mode
  *            Flash Latency(WS)              = 7
  * @param  None
  * @retval None
  */
static void SystemClock_Config(void)
{
  RCC_ClkInitTypeDef RCC_ClkInitStruct;
  RCC_OscInitTypeDef RCC_OscInitStruct;
  HAL_StatusTypeDef  ret = HAL_OK;
 
  /* Enable Power Control clock */
  __HAL_RCC_PWR_CLK_ENABLE();
 
  /* The voltage scaling allows optimizing the power consumption when the device is
     clocked below the maximum system frequency, to update the voltage scaling value
     regarding system frequency refer to product datasheet.  */
  __HAL_PWR_VOLTAGESCALING_CONFIG(PWR_REGULATOR_VOLTAGE_SCALE1);

  /* Enable HSE Oscillator and activate PLL with HSE as source */
  RCC_OscInitStruct.OscillatorType = RCC_OSCILLATORTYPE_HSE;
  RCC_OscInitStruct.HSEState = RCC_HSE_ON;
  RCC_OscInitStruct.PLL.PLLState = RCC_PLL_ON;
  RCC_OscInitStruct.PLL.PLLSource = RCC_PLLSOURCE_HSE;
  RCC_OscInitStruct.PLL.PLLM = 25;
  RCC_OscInitStruct.PLL.PLLN = 432; 
  RCC_OscInitStruct.PLL.PLLP = RCC_PLLP_DIV2;
  RCC_OscInitStruct.PLL.PLLQ = 9;
 
  ret = HAL_RCC_OscConfig(&RCC_OscInitStruct);
  if(ret != HAL_OK)
  {
    while(1) { ; }
  }
 
  /* Activate the OverDrive to reach the 216 MHz Frequency */
  ret = HAL_PWREx_EnableOverDrive();
  if(ret != HAL_OK)
  {
    while(1) { ; }
  }
 
  /* Select PLL as system clock source and configure the HCLK, PCLK1 and PCLK2 clocks dividers */
  RCC_ClkInitStruct.ClockType = (RCC_CLOCKTYPE_SYSCLK | RCC_CLOCKTYPE_HCLK | RCC_CLOCKTYPE_PCLK1 | RCC_CLOCKTYPE_PCLK2);
  RCC_ClkInitStruct.SYSCLKSource = RCC_SYSCLKSOURCE_PLLCLK;
  RCC_ClkInitStruct.AHBCLKDivider = RCC_SYSCLK_DIV1;
  RCC_ClkInitStruct.APB1CLKDivider = RCC_HCLK_DIV4; 
  RCC_ClkInitStruct.APB2CLKDivider = RCC_HCLK_DIV2;
 
  ret = HAL_RCC_ClockConfig(&RCC_ClkInitStruct, FLASH_LATENCY_7);
  if(ret != HAL_OK)
  {
    while(1) { ; }
  }
}
/**
* @brief  CPU L1-Cache enable.
* @param  None
* @retval None
*/
static void CPU_CACHE_Enable(void)
{
  /* Enable I-Cache */
  SCB_EnableICache();

  /* Enable D-Cache */
  SCB_EnableDCache();
}