/**
* @brief This function configures the source of the time base.
* The time source is configured to have 1ms time base with a dedicated
* Tick interrupt priority.
* @note This function is called automatically at the beginning of program after
* reset by HAL_Init() or at any time when clock is reconfigured by HAL_RCC_ClockConfig().
* @note In the default implementation, SysTick timer is the source of time base.
* It is used to generate interrupts at regular time intervals.
* Care must be taken if HAL_Delay() is called from a peripheral ISR process,
* The SysTick interrupt must have higher priority (numerically lower)
* than the peripheral interrupt. Otherwise the caller ISR process will be blocked.
* The function is declared as __weak to be overwritten in case of other
* implementation in user file.
* @param TickPriority Tick interrupt priority.
* @retval HAL status
*/
__weak HAL_StatusTypeDef HAL_InitTick(uint32_t TickPriority)
{
/* Configure the SysTick to have interrupt in 1ms time basis*/
if (HAL_SYSTICK_Config(SystemCoreClock / (1000U / uwTickFreq)) > 0U)
{
return HAL_ERROR;
}
/* Configure the SysTick IRQ priority */
if (TickPriority < (1UL << __NVIC_PRIO_BITS))
{
HAL_NVIC_SetPriority(SysTick_IRQn, TickPriority, 0U);
uwTickPrio = TickPriority;
}
else
{
return HAL_ERROR;
}
/* Return function status */
return HAL_OK;
}
函数里面有一句注释： /* Configure the SysTick to have interrupt in 1ms time basis*/，翻译过来就是，将 SysTick 配置为 1ms 中断。也就是说，经过此函数，SysTick 定时器被初始化为 1ms 的时基单元，即每毫秒进入一次 Systick 中断。
/**
* @brief This function handles System tick timer.
*/
void SysTick_Handler(void)
{
/* USER CODE BEGIN SysTick_IRQn 0 */
/* USER CODE END SysTick_IRQn 0 */
HAL_IncTick();
/* USER CODE BEGIN SysTick_IRQn 1 */
/* USER CODE END SysTick_IRQn 1 */
}
里面只有一个 HAL_IncTick() 函数，我们右键转跳到该函数可以看到该函数的定义。
/**
* @brief This function is called to increment a global variable "uwTick"
* used as application time base.
* @note In the default implementation, this variable is incremented each 1ms
* in SysTick ISR.
* @note This function is declared as __weak to be overwritten in case of other
* implementations in user file.
* @retval None
*/
__weak void HAL_IncTick(void)
{
uwTick += uwTickFreq;
}
每毫秒 uwTick 加一，用于计算 Systick 产生的节拍数。
在 HAL_IncTick 函数的下方有一个 HAL_GetTick(void) 函数，主要用于获取当前节拍，如果内核正常运行，则 uwTick 的值即为已经经过的 ms 数。
/**
* @brief This function provides minimum delay (in milliseconds) based
* on variable incremented.
* @note In the default implementation , SysTick timer is the source of time base.
* It is used to generate interrupts at regular time intervals where uwTick
* is incremented.
* @note This function is declared as __weak to be overwritten in case of other
* implementations in user file.
* @param Delay specifies the delay time length, in milliseconds.
* @retval None
*/
__weak void HAL_Delay(uint32_t Delay)
{
uint32_t tickstart = HAL_GetTick();
uint32_t wait = Delay;
/* Add a freq to guarantee minimum wait */
if (wait < HAL_MAX_DELAY)
{
wait += (uint32_t)(uwTickFreq);
}
while ((HAL_GetTick() - tickstart) < wait)
{
}
}
