多年的開發STM32，遇到一些簡單的需要計時的任務，比如延時等，最方便的是其提供的systick。

systick其實本為移植作業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函式已經取代了之前所有的設定過程。

systick.c檔案也被簡除，該函式直接歸在了核心檔案core_cm3.h裡面。

/* ##################################    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

優點是設定相當簡化，

缺點是控制不如以前靈活了，一旦開啟，確實沒有庫函式方便地過載或禁用。