SysTick_Config()函数中选择外部和内部时钟的问题

enginezhong · 发表于 2015-12-8 21:44:17

在SysTick_Config()函数中，CTRL寄存器被配置为SysTick_CTRL_CLKSOURCE_Msk ，想了解一下，配置为SysTick_CTRL_CLKSOURCE_Msk表示的是选择外部还是内部时钟啊？
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 */
}