STM32 system_stm32f10x.c文件分析

startup_stm32f10x_md.s文件中，调用了一个叫SystemInit的函数，该函数其实在system_stm32f10x.c中定义，旨在初始化系统时钟、初始化外部SRAM、设置中断向量表地址。

void SystemInit (void)
{
  /* 使能内部高速时钟 */
  RCC->CR |= (uint32_t)0x00000001;

#ifndef STM32F10X_CL
  RCC->CFGR &= (uint32_t)0xF8FF0000;
#else
  RCC->CFGR &= (uint32_t)0xF0FF0000;
#endif
  
  /* 禁用PLL、禁用始时钟检测、禁用外部高速时钟 */
  RCC->CR &= (uint32_t)0xFEF6FFFF;

  /* 外部1-25M振荡器未被绕过 */
  RCC->CR &= (uint32_t)0xFFFBFFFF;

  /* USB预分频器PLL未分频、PLL倍频2、HSE未被分频、HSI/2作为PLL频率 */
  RCC->CFGR &= (uint32_t)0xFF80FFFF;

/* 禁用时钟中断寄存器 */

#ifdef STM32F10X_CL
  RCC->CR &= (uint32_t)0xEBFFFFFF;

  RCC->CIR = 0x00FF0000;

  RCC->CFGR2 = 0x00000000;
#elif defined (STM32F10X_LD_VL) || defined (STM32F10X_MD_VL) || (defined STM32F10X_HD_VL)
  RCC->CIR = 0x009F0000;

  /* Reset CFGR2 register */
  RCC->CFGR2 = 0x00000000;      
#else
  RCC->CIR = 0x009F0000;
#endif /* STM32F10X_CL */
    

/* 设置外部SRAM */
#if defined (STM32F10X_HD) || (defined STM32F10X_XL) || (defined STM32F10X_HD_VL)
  #ifdef DATA_IN_ExtSRAM
    SystemInit_ExtMemCtl(); 
  #endif /* DATA_IN_ExtSRAM */
#endif

 /* 配置系统时钟 */
  SetSysClock();

/*中断向量偏移地址设置 */

#ifdef VECT_TAB_SRAM
  SCB->VTOR = SRAM_BASE | VECT_TAB_OFFSET; /* Vector Table Relocation in Internal SRAM. */
#else
  SCB->VTOR = FLASH_BASE | VECT_TAB_OFFSET; /* Vector Table Relocation in Internal FLASH. */
#endif 
}