五、实例详解
#if defined (STM32F10X_LD_VL) || (defined STM32F10X_MD_VL) || (defined STM32F10X_HD_VL)//如果定义了这些系统时钟将设为24M，如果没有定义则为72M
/* #define SYSCLK_FREQ_HSE HSE_VALUE */
#define SYSCLK_FREQ_24MHz 24000000
#else
/* #define SYSCLK_FREQ_HSE HSE_VALUE */
/* #define SYSCLK_FREQ_24MHz 24000000 */
/* #define SYSCLK_FREQ_36MHz 36000000 */
/* #define SYSCLK_FREQ_48MHz 48000000 */
/* #define SYSCLK_FREQ_56MHz 56000000 */
#define SYSCLK_FREQ_72MHz 72000000 //系统时钟默认值的定义
，如果没有定义外部高速时钟则用内部高速时钟，为8000000 /*只需修改以上几句就可以自动设置使用外部倍频作为系统时钟，如果以上宏都未定义则在下边把内部高速时钟作为系统时钟*/
#endif /*!< Uncomment the following line if you need to use external SRAM mounted
on STM3210E-EVAL board (STM32 High density and XL-density devices) or on
STM32100E-EVAL board (STM32 High-density value line devices) as data memory */
#if defined (STM32F10X_HD) || (defined STM32F10X_XL) || (defined STM32F10X_HD_VL)//内外部SRAM选择
/* #define DATA_IN_ExtSRAM */
#endif /*!< Uncomment the following line if you need to relocate your vector Table in
Internal SRAM. */
/* #define VECT_TAB_SRAM */
#define VECT_TAB_OFFSET 0x0 /*!< Vector Table base offset field. //向量表的基址偏移量
This value must be a multiple of 0x100. */
/*******************************************************************************
* Clock Definitions;以下为把系统时钟的定义值传给系统内核时钟变量,如果没有定义外部高速时钟则用内部高速时钟，为8M
*******************************************************************************/
#ifdef SYSCLK_FREQ_HSE
uint32_t SystemCoreClock = SYSCLK_FREQ_HSE; /*!< System Clock Frequency (Core Clock) */
#elif defined SYSCLK_FREQ_24MHz
uint32_t SystemCoreClock = SYSCLK_FREQ_24MHz; /*!< System Clock Frequency (Core Clock) */
#elif defined SYSCLK_FREQ_36MHz
uint32_t SystemCoreClock = SYSCLK_FREQ_36MHz; /*!< System Clock Frequency (Core Clock) */
#elif defined SYSCLK_FREQ_48MHz
uint32_t SystemCoreClock = SYSCLK_FREQ_48MHz; /*!< System Clock Frequency (Core Clock) */
#elif defined SYSCLK_FREQ_56MHz
uint32_t SystemCoreClock = SYSCLK_FREQ_56MHz; /*!< System Clock Frequency (Core Clock) */
#elif defined SYSCLK_FREQ_72MHz
uint32_t SystemCoreClock = SYSCLK_FREQ_72MHz; /*!< System Clock Frequency (Core Clock) */
#else /*!< HSI Selected as System Clock source */
uint32_t SystemCoreClock = HSI_VALUE; /*!< System Clock Frequency (Core Clock) 如果没有定义外部高速时钟则用内部高速时钟，为8000000*/
#endif __I uint8_t AHBPrescTable[16] = {0, 0, 0, 0, 0, 0, 0, 0, 1, 2, 3, 4, 6, 7, 8, 9};//AHB配方表
/**
* @}
*/ /** @addtogroup STM32F10x_System_Private_FunctionPrototypes
* @{
*/
/*********************************************************************************
以下为函数声明
*********************************************************************************/
static void SetSysClock(void); //设置系统时钟的函数声明
//以下为根据不同的系统时钟的定义来声明用到的相应的函数，为后面的函数调用做好准备
#ifdef SYSCLK_FREQ_HSE
static void SetSysClockToHSE(void);
#elif defined SYSCLK_FREQ_24MHz
static void SetSysClockTo24(void);
#elif defined SYSCLK_FREQ_36MHz
static void SetSysClockTo36(void);
#elif defined SYSCLK_FREQ_48MHz
static void SetSysClockTo48(void);
#elif defined SYSCLK_FREQ_56MHz
static void SetSysClockTo56(void);
#elif defined SYSCLK_FREQ_72MHz
static void SetSysClockTo72(void);
#endif #ifdef DATA_IN_ExtSRAM //外部SRAM选择后的初始化函数声明
static void SystemInit_ExtMemCtl(void);
#endif /* DATA_IN_ExtSRAM */ | 
