[嵌入式]STM32F103系统时钟设置

概述

实际使用STM32F103单片机时，第一步就是配置系统的工作时钟。我们时常需要选择使用外部时钟源和内部时钟源，这里我们以F103为例子，提供两个函数参考，供大家实际开发中使用配置系统时钟。

实例

废话不多说，直接上代码。

#include "dri_sysclk.h"

static void SetSystemClk(eSelectClkSrc _ClkSrc);

T_SysClk_Device g_tSysClk_Dev = {
	.SysClkConfig = SetSystemClk
};


static void SetSysClockTo64(void)
{
	__IO ErrorStatus HSIStartUpStatus = 0;

	/* SYSCLK, HCLK, PCLK2 and PCLK1 configuration -----------------------------*/   
	/* RCC system reset(for debug purpose) */
	RCC_DeInit();

	/* Enable HSI */
	RCC_HSICmd(ENABLE);

	/* Wait till HSI is ready */
	if((RCC->CR & RCC_CR_HSIRDY) == RCC_CR_HSIRDY)
		HSIStartUpStatus = SUCCESS;
	else
		HSIStartUpStatus = ERROR;

	if(HSIStartUpStatus == SUCCESS)
	{
		/* Enable Prefetch Buffer */
		FLASH_PrefetchBufferCmd(FLASH_PrefetchBuffer_Enable);

		/* Flash 2 wait state */
		FLASH_SetLatency(FLASH_Latency_2);

		/* HCLK = SYSCLK */
		RCC_HCLKConfig(RCC_SYSCLK_Div1); 

		/* PCLK2 = HCLK */
		RCC_PCLK2Config(RCC_HCLK_Div1); 

		/* PCLK1 = HCLK/2 */
		RCC_PCLK1Config(RCC_HCLK_Div2);

		/* PLLCLK = 8MHz / 2 * 16 = 64 MHz */
		RCC_PLLConfig(RCC_PLLSource_HSI_Div2, RCC_PLLMul_16);

		/* Enable PLL */ 
		RCC_PLLCmd(ENABLE);

		/* Wait till PLL is ready */
		while (RCC_GetFlagStatus(RCC_FLAG_PLLRDY) == RESET)
		{
		}

		/* Select PLL as system clock source */
		RCC_SYSCLKConfig(RCC_SYSCLKSource_PLLCLK);

		/* Wait till PLL is used as system clock source */
		while(RCC_GetSYSCLKSource() != 0x08)
		{
		}
	}
	else
	{ /* If HSI fails to start-up, the application will have wrong clock configuration.
	   User can add here some code to deal with this error */    

		/* Go to infinite loop */
		while (1)
		{
		}
	}
}

static void SetSysClockTo72(void)
{
	__IO ErrorStatus HSEStartUpStatus = ERROR;

	/* SYSCLK, HCLK, PCLK2 and PCLK1 configuration -----------------------------*/   
	/* RCC system reset(for debug purpose) */
	RCC_DeInit();

	/* Enable HSE */
	RCC_HSEConfig(RCC_HSE_ON);

	/* Wait till HSE is ready */
	HSEStartUpStatus = RCC_WaitForHSEStartUp();

	if (HSEStartUpStatus == SUCCESS)
	{
		/* Enable Prefetch Buffer */
		FLASH_PrefetchBufferCmd(FLASH_PrefetchBuffer_Enable);

		/* Flash 2 wait state */
		FLASH_SetLatency(FLASH_Latency_2);

		/* HCLK = SYSCLK */
		RCC_HCLKConfig(RCC_SYSCLK_Div1); 

		/* PCLK2 = HCLK */
		RCC_PCLK2Config(RCC_HCLK_Div1); 

		/* PCLK1 = HCLK/2 */
		RCC_PCLK1Config(RCC_HCLK_Div2);

		/* PLLCLK = 8MHz * 9 = 72 MHz */
		RCC_PLLConfig(RCC_PLLSource_HSE_Div1, RCC_PLLMul_9);

		/* Enable PLL */ 
		RCC_PLLCmd(ENABLE);

		/* Wait till PLL is ready */
		while (RCC_GetFlagStatus(RCC_FLAG_PLLRDY) == RESET)
		{
		}

		/* Select PLL as system clock source */
		RCC_SYSCLKConfig(RCC_SYSCLKSource_PLLCLK);

		/* Wait till PLL is used as system clock source */
		while(RCC_GetSYSCLKSource() != 0x08)
		{
		}
	}
	else
	{ /* If HSE fails to start-up, the application will have wrong clock configuration.
	   User can add here some code to deal with this error */    

		/* Go to infinite loop */
		while (1)
		{
		}
	}
}

static void SetSystemClk(eSelectClkSrc _ClkSrc)
{
	switch(_ClkSrc)
	{
		case USE_HSE_FOR_CLKSRC:
			SetSysClockTo72();
		break;

		case USE_HSI_FOR_CLKSRC:
			SetSysClockTo64();
			
		break;

		default:
		break;
	}

	/* Enable Clock Security System(CSS): this will generate an NMI exception
	when HSE or HSI clock fails */
	RCC_ClockSecuritySystemCmd(ENABLE);
}

结论

通过上述配置，我们就可以成功配置系统时钟。