stm32 學習筆記 systick定時器

systick其實本為移植操作系統提供滴答時鐘的方便。

前兩天再次接觸STM32，使用了V3.5的庫，突然發現繁瑣的Systick用法被簡化成一句話。

即：

void SysTick_Configuration(void)
{
if (SysTick_Config(SystemCoreClock / 1000000))//72, 1us per tick
{
/* Capture error */
while (1);
}
}

而Systick_Config函數已經取代了之前所有的設置過程。

systick.c文件也被簡除，該函數直接歸在了內核文件core_cm3.h里面。

/* ################################## SysTick function ############################################ */

#if (!defined (__Vendor_SysTickConfig)) || (__Vendor_SysTickConfig == 0)

/**
* @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 */
}

#endif

優點是設置相當簡化，

缺點是控制不如以前靈活了，一旦開啟，確實沒有庫函數方便地重載或禁用。