在锁相环时钟频率切换过程中，只有当锁相环稳定后CPU才会切换到新的PLL设置。因此在设置完PLLCR后需要等待PLL稳定。PLL的切换时间大约等于131072个输入时钟周期。 -The PLL clock frequency switching process only when the phase-locked loop stable CPU will switch to the new PLL settings. After setting PLLCR need to wait for t