熟悉RCC配置细节，系统运行不同的频率RCC配置不一样 RCC 用于配置系统运行频率，通过改变宏定义不同频率 LED交替闪烁的速度不一样，体现CPU运行速度快慢。-Familiar RCC configuration details, the system runs a different frequency is not the same RCC RCC configuration is used to configure the system operating frequency, different frequencies by changing the macro definition LED flashes alternately speed is not the same, reflecting the speed of CPU operation.