stm32 article--system initialization

Following the program execution flow, main is the program entry, where various initializations are performed.

1. Clock configuration

      First is RCC_Configuration(), which performs basic clock initialization. STM32 has multiple clock sources: (1) HSI is enabled by default when powered on, and has low precision; (2) HSE external high-speed clock, which is generally used by the system clock and multiplied by PLL; (3) LSE external low-speed clock, which is generally used for RTC; (4) LSI internal low-speed clock, which has low precision and is generally used for IWDGCLK;

void RCC_Configuration(void)

{

  RCC_DeInit(); //Reset RCC to default value

  RCC_HSEConfig(RCC_HSE_ON); //Turn on the HSE clock as the clock source for the PLL

  HSEStartUpStatus = RCC_WaitForHSEStartUp(); //Get HSE clock status

  if(HSEStartUpStatus == SUCCESS) //If HSE starts successfully

  {

    FLASH_PrefetchBufferCmd(FLASH_PrefetchBuffer_Enable); // Enable FLASH prefetch function

    RCC_HCLKConfig(RCC_SYSCLK_Div1);   //配置HCLK,PCLK2,PCLK1,PLL

    RCC_PCLK2Config(RCC_HCLK_Div1); 

    RCC_PCLK1Config(RCC_HCLK_Div1);

    RCC_SYSCLKConfig(RCC_SYSCLKSource_HSE);

    while(RCC_GetSYSCLKSource() != 0x04) // Check whether HSE is used as system clock after frequency multiplication

    {

    }

  }

 }

   In this way, the clock is initialized. First reset the RCC, then configure each clock source, get the status and wait for success. If we want to use a certain function or pin, we need to turn on the relevant clock source.

2. Interrupt vector setting

void NVIC_Configuration(void)

{

#ifdef  VECT_TAB_RAM  

  /* Set the Vector Table base location at 0x20000000 */ 

  NVIC_SetVectorTable(NVIC_VectTab_RAM, 0x0); 

#else  /* VECT_TAB_FLASH  */

  /* Set the Vector Table base location at 0x08000000 */ 

  NVIC_SetVectorTable(NVIC_VectTab_FLASH, 0x0);   

#endif

}

NVIC_SetVectorTable sets the position and offset of the vector table

NVIC_ VectTab Description

NVIC_VectTab_FLASH vector table is located in FLASH

NVIC_VectTab_RAM The vector table is located in RAM and is used to set the priority of various interrupts, the address of the vector table, etc.