什么是FCLK，ICLK ？

      关于什么是Function clock 和 什么是 Interface clock，TI的TRM手册里面有详细的说明：

3.5.3.1.1

To be operational, a module requires a functional clock(s); to communicate with other modules, it requires an interface clock. For example, the functional clock of a general-purpose timer (GPTIMER) must be active for it to run, but its interface clock can be turned off.

A module can use one or more optional functional clocks. Because an optional functional clock is used only for specific features of the module, it can be shut down without stopping the module activity (for example, 54 MHz for the DSS power domain and 96 MHz for the CAM power domain).