STM32F10x_System_Exported_Functions

Functions
void	SystemInit (void)
	Setup the microcontroller system Initialize the Embedded Flash Interface, the PLL and update the SystemCoreClock variable. More...
void	SystemCoreClockUpdate (void)
	Update SystemCoreClock variable according to Clock Register Values. The SystemCoreClock variable contains the core clock (HCLK), it can be used by the user application to setup the SysTick timer or configure other parameters. More...

Detailed Description

Function Documentation

SystemCoreClockUpdate()

void SystemCoreClockUpdate

(

void

)

Update SystemCoreClock variable according to Clock Register Values. The SystemCoreClock variable contains the core clock (HCLK), it can be used by the user application to setup the SysTick timer or configure other parameters.

Note

Each time the core clock (HCLK) changes, this function must be called to update SystemCoreClock variable value. Otherwise, any configuration based on this variable will be incorrect.

- The system frequency computed by this function is not the real frequency in the chip. It is calculated based on the predefined constant and the selected clock source:

• If SYSCLK source is HSI, SystemCoreClock will contain the HSI_VALUE(*)
• If SYSCLK source is HSE, SystemCoreClock will contain the HSE_VALUE(**)
• If SYSCLK source is PLL, SystemCoreClock will contain the HSE_VALUE(**) or HSI_VALUE(*) multiplied by the PLL factors.

(*) HSI_VALUE is a constant defined in stm32f1xx.h file (default value 8 MHz) but the real value may vary depending on the variations in voltage and temperature.

(**) HSE_VALUE is a constant defined in stm32f1xx.h file (default value 8 MHz or 25 MHz, depending on the product used), user has to ensure that HSE_VALUE is same as the real frequency of the crystal used. Otherwise, this function may have wrong result.

• The result of this function could be not correct when using fractional value for HSE crystal.

  Parameters

  None

  Return values

  None

< Default value of the Internal oscillator in Hz. This value can be provided and adapted by the user application.

< Default value of the External oscillator in Hz. This value can be provided and adapted by the user application.

< Default value of the Internal oscillator in Hz. This value can be provided and adapted by the user application.

< Default value of the External oscillator in Hz. This value can be provided and adapted by the user application.

< Default value of the External oscillator in Hz. This value can be provided and adapted by the user application.

< Default value of the Internal oscillator in Hz. This value can be provided and adapted by the user application.

Definition at line 225 of file system_stm32f1xx.c.

{
  uint32_t tmp = 0U, pllmull = 0U, pllsource = 0U;
 
#if defined(STM32F105xC) || defined(STM32F107xC)
  uint32_t prediv1source = 0U, prediv1factor = 0U, prediv2factor = 0U, pll2mull = 0U;
#endif /* STM32F105xC */
 
#if defined(STM32F100xB) || defined(STM32F100xE)
  uint32_t prediv1factor = 0U;
#endif /* STM32F100xB or STM32F100xE */
    
  /* Get SYSCLK source -------------------------------------------------------*/
  tmp = RCC->CFGR & RCC_CFGR_SWS;
  
  switch (tmp)
  {
    case 0x00U:  /* HSI used as system clock */
      SystemCoreClock = HSI_VALUE;
      break;
    case 0x04U:  /* HSE used as system clock */
      SystemCoreClock = HSE_VALUE;
      break;
    case 0x08U:  /* PLL used as system clock */
 
      /* Get PLL clock source and multiplication factor ----------------------*/
      pllmull = RCC->CFGR & RCC_CFGR_PLLMULL;
      pllsource = RCC->CFGR & RCC_CFGR_PLLSRC;
      
#if !defined(STM32F105xC) && !defined(STM32F107xC)      
      pllmull = ( pllmull >> 18U) + 2U;
      
      if (pllsource == 0x00U)
      {
        /* HSI oscillator clock divided by 2 selected as PLL clock entry */
        SystemCoreClock = (HSI_VALUE >> 1U) * pllmull;
      }
      else
      {
 #if defined(STM32F100xB) || defined(STM32F100xE)
       prediv1factor = (RCC->CFGR2 & RCC_CFGR2_PREDIV1) + 1U;
       /* HSE oscillator clock selected as PREDIV1 clock entry */
       SystemCoreClock = (HSE_VALUE / prediv1factor) * pllmull; 
 #else
        /* HSE selected as PLL clock entry */
        if ((RCC->CFGR & RCC_CFGR_PLLXTPRE) != (uint32_t)RESET)
        {/* HSE oscillator clock divided by 2 */
          SystemCoreClock = (HSE_VALUE >> 1U) * pllmull;
        }
        else
        {
          SystemCoreClock = HSE_VALUE * pllmull;
        }
 #endif
      }
#else
      pllmull = pllmull >> 18U;
      
      if (pllmull != 0x0DU)
      {
         pllmull += 2U;
      }
      else
      { /* PLL multiplication factor = PLL input clock * 6.5 */
        pllmull = 13U / 2U; 
      }
            
      if (pllsource == 0x00U)
      {
        /* HSI oscillator clock divided by 2 selected as PLL clock entry */
        SystemCoreClock = (HSI_VALUE >> 1U) * pllmull;
      }
      else
      {/* PREDIV1 selected as PLL clock entry */
        
        /* Get PREDIV1 clock source and division factor */
        prediv1source = RCC->CFGR2 & RCC_CFGR2_PREDIV1SRC;
        prediv1factor = (RCC->CFGR2 & RCC_CFGR2_PREDIV1) + 1U;
        
        if (prediv1source == 0U)
        { 
          /* HSE oscillator clock selected as PREDIV1 clock entry */
          SystemCoreClock = (HSE_VALUE / prediv1factor) * pllmull;          
        }
        else
        {/* PLL2 clock selected as PREDIV1 clock entry */
          
          /* Get PREDIV2 division factor and PLL2 multiplication factor */
          prediv2factor = ((RCC->CFGR2 & RCC_CFGR2_PREDIV2) >> 4U) + 1U;
          pll2mull = ((RCC->CFGR2 & RCC_CFGR2_PLL2MUL) >> 8U) + 2U; 
          SystemCoreClock = (((HSE_VALUE / prediv2factor) * pll2mull) / prediv1factor) * pllmull;                         
        }
      }
#endif /* STM32F105xC */ 
      break;
 
    default:
      SystemCoreClock = HSI_VALUE;
      break;
  }
  
  /* Compute HCLK clock frequency ----------------*/
  /* Get HCLK prescaler */
  tmp = AHBPrescTable[((RCC->CFGR & RCC_CFGR_HPRE) >> 4U)];
  /* HCLK clock frequency */
  SystemCoreClock >>= tmp;  
}

SystemInit()

void SystemInit

(

void

)

Setup the microcontroller system Initialize the Embedded Flash Interface, the PLL and update the SystemCoreClock variable.

Note

This function should be used only after reset.

Parameters

None

Return values

None

Definition at line 176 of file system_stm32f1xx.c.

{
#if defined(STM32F100xE) || defined(STM32F101xE) || defined(STM32F101xG) || defined(STM32F103xE) || defined(STM32F103xG)
  #ifdef DATA_IN_ExtSRAM
    SystemInit_ExtMemCtl(); 
  #endif /* DATA_IN_ExtSRAM */
#endif 
 
  /* Configure the Vector Table location -------------------------------------*/
#if defined(USER_VECT_TAB_ADDRESS)
  SCB->VTOR = VECT_TAB_BASE_ADDRESS | VECT_TAB_OFFSET; /* Vector Table Relocation in Internal SRAM. */
#endif /* USER_VECT_TAB_ADDRESS */
}