系统定时器SysTick

STM32的系统时钟函数

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 */
}

ticks表示的是重装载寄存器中的值，系统时钟的重装载寄存器是24位的

系统定时器的时钟选择有2中：AHB,AHB/8