系统初始化SystemInit(): ，还有系统滴答初始化，变量SystemCoreClock variable:的设置
* @file system_stm32f10x.c * @author MCD Application Team * @version V3.5.0 * @date 11-March-2011 * @brief CMSIS Cortex-M3 Device Peripheral Access Layer System Source File. * * 1. This file provides two functions and one global variable to be called from * user application: * ...