system_stm32f4xx.c File Reference

CMSIS Cortex-M4 Device Peripheral Access Layer System Source File. More...

#include "stm32f4xx.h"

Macros
#define	HSE_VALUE   ((uint32_t)25000000)
#define	HSI_VALUE   ((uint32_t)16000000)

Functions
void	SystemInit (void)
	Setup the microcontroller system Initialize the FPU setting, vector table location and External memory configuration. 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...

Variables
uint32_t	SystemCoreClock = 16000000
const uint8_t	AHBPrescTable [16] = {0, 0, 0, 0, 0, 0, 0, 0, 1, 2, 3, 4, 6, 7, 8, 9}
const uint8_t	APBPrescTable [8] = {0, 0, 0, 0, 1, 2, 3, 4}

Detailed Description

CMSIS Cortex-M4 Device Peripheral Access Layer System Source File.

Author

MCD Application Team

This file provides two functions and one global variable to be called from user application:

• SystemInit(): This function is called at startup just after reset and before branch to main program. This call is made inside the "startup_stm32f4xx.s" file.
• SystemCoreClock variable: Contains the core clock (HCLK), it can be used by the user application to setup the SysTick timer or configure other parameters.
• SystemCoreClockUpdate(): Updates the variable SystemCoreClock and must be called whenever the core clock is changed during program execution.

Attention

© Copyright (c) 2017 STMicroelectronics. All rights reserved.

This software component is licensed by ST under BSD 3-Clause license, the "License"; You may not use this file except in compliance with the License. You may obtain a copy of the License at: opensource.org/licenses/BSD-3-Clause

Macro Definition Documentation

HSE_VALUE

#define HSE_VALUE   ((uint32_t)25000000)

@ CMSIS @ stm32f4xx_system @ STM32F4xx_System_Private_Includes Default value of the External oscillator in Hz

HSI_VALUE

#define HSI_VALUE   ((uint32_t)16000000)

Value of the Internal oscillator in Hz

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/divided by the PLL factors.

(*) HSI_VALUE is a constant defined in stm32f4xx_hal_conf.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_hal_conf.h file (its value depends on the application requirements), 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.

SystemInit()

void SystemInit

(

void

)

Setup the microcontroller system Initialize the FPU setting, vector table location and External memory configuration.

@ STM32F4xx_System_Private_Functions

Variable Documentation

SystemCoreClock

uint32_t SystemCoreClock = 16000000

@ STM32F4xx_System_Private_Variables