1、SDK代码中有以下描述，通过SysCtlClockGet()函数获得系统时钟，但是我没找到这个函数声明或原型，请问这个函数在哪个文件中？
//! The peripheral clock is the same as the processor clock. The frequency of
//! the system clock is the value returned by SysCtlClockGet(), or it can be
//! explicitly hard coded if it is constant and known (to save the
//! code/execution overhead of a call to SysCtlClockGet()).
2、UtilsDelay函数介绍说每个循环花费3个时钟周期，按照80MHz时钟算，延时一秒是不是应该用UtilsDelay(80000000/3)？为什么和一秒时间差异很大？
//*****************************************************************************
//
//! Provides a small delay.
//!
//! \param ulCount is the number of delay loop iterations to perform.
//!
//! This function provides a means of generating a constant length delay. It
//! is written in assembly to keep the delay consistent across tool chains,
//! avoiding the need to tune the delay based on the tool chain in use.
//!
//! The loop takes 3 cycles/loop.
//!
//! \return None.
//
//*****************************************************************************
UtilsDelay(unsigned long ulCount)
