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STM32系统Tick定时器的初始化和配置

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1.首先确定SystemCoreClock系统时钟

?系统时钟需要根据具体的系统时钟配置来确定,这里采用SystemCoreClock = 72MHZ来说明。至于系统时钟的计算和配置,后面单独介绍说明一下吧。


2.?配置SysTick定时器

SysTick_Config(SystemCoreClock/OS_TICKS_PER_SEC);//初始化并使能SysTick定时器

假设我们想配置SysTick定时器中断间隔周期为1ms,即每间隔1ms定时中断来一次。


可定义一个宏定义


#define OS_TICKS_PER_SEC 1000 /* Set the number of ticks in one second

即每1S SysTick定时器中断触发1000次,下面就需要计算一个每次中断触发间隔多少个时钟周期了。


SystemCoreClock?时钟频率是70000000Hz(72Mhz),那边一个时钟周期T=1/F?= 1/72000000(S),? 1(S)/T=F=72000000,即1S有72000000个时钟周期


(这里说的可能比较绕,方便部分群体理解吧~~)


下面来说一下SysTick_Config的入参,入参的定义可以见下面代码,@param ? ticks ? number of ticks between two interrupts? ?即SysTick每两次中断的间隔时间->间隔多少个ticks系统时钟周期数量,?可由SystemCoreClock /OS_TICKS_PER_SEC计算得到。至于SysTick_Config接口内部实现可见下面代码注释。??


上述说明如有不正确的地方,望指正~


/**
* @brief Initialize and start the SysTick counter and its interrupt.
*
* @param ticks number of ticks between two interrupts
* @return 1 = failed, 0 = successful
*
* Initialise the system tick timer and its interrupt and start the
* system tick timer / counter in free running mode to generate
* periodical interrupts.
*/
static __INLINE uint32_t SysTick_Config(uint32_t ticks)
{
if (ticks > SysTick_LOAD_RELOAD_Msk) return (1); /* Reload value impossible */

SysTick->LOAD = (ticks & SysTick_LOAD_RELOAD_Msk) - 1; /* set reload register */
NVIC_SetPriority (SysTick_IRQn, (1<<__NVIC_PRIO_BITS) - 1); /* set Priority for Cortex-M0 System Interrupts */
SysTick->VAL = 0; /* Load the SysTick Counter Value */
SysTick->CTRL = SysTick_CTRL_CLKSOURCE_Msk |
SysTick_CTRL_TICKINT_Msk |
SysTick_CTRL_ENABLE_Msk; /* Enable SysTick IRQ and SysTick Timer */
return (0); /* Function successful */
}

?


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