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.
- 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/divided by the PLL factors.
(*) HSI_VALUE is a constant defined in stm32f4xx.h file (default value 16 MHz) but the real value may vary depending on the variations in voltage and temperature.
(**) HSE_VALUE is a constant defined in stm32f4xx.h file (default value 25 MHz), 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.
- Return values
Definition at line 286 of file system_stm32f4xx.c.