STM32 system_stm32f10x.c file analysis

In the startup_stm32f10x_md.s file, a function called SystemInit is called. This function is actually defined in system_stm32f10x.c. It is designed to initialize the system clock, initialize the external SRAM, and set the interrupt vector table address.

void SystemInit (void)
{
  /* Enable internal high-speed clock */
  RCC->CR |= (uint32_t)0x00000001;

#ifndef STM32F10X_CL
  RCC->CFGR &= (uint32_t)0xF8FF0000;
#else
  RCC->CFGR &= (uint32_t)0xF0FF0000;
#endif
  
  /* Disable PLL, disable initial clock detection, disable external high-speed clock */
  RCC->CR &= (uint32_t)0xFEF6FFFF;

  /* External 1-25M oscillator is not bypassed */
  RCC->CR &= (uint32_t)0xFFFBFFFF;

  /* USB prescaler PLL is not divided, PLL multiplier is 2, HSE is not divided, HSI/2 is used as PLL frequency */
  RCC->CFGR &= (uint32_t)0xFF80FFFF;

/* Disable clock interrupt register */

#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

 /* Configure system clock */
  SetSysClock();

/*Interrupt vector offset address setting*/

#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 
}