[嵌入式]STM32F103时钟配置

sysclock.h文件：

#ifndef __SYSCLOCK_H
#define __SYSCLOCK_H

#include "stm32f10x.h"

#define HSE_READY_OVERTIMR (uint32_t)0xFFF

void My_HSE_SetSysClock(void);

#endif

sysyclock.c文件：

#include "sysclock.h"

/**
 * 简介：外部高速晶振配置为系统时钟
 */
void My_HSE_SetSysClock(void)
{
	uint32_t delay_time = 0;
	uint32_t tmpreg = 0;
	uint8_t status = 0;
	
	/* 使能HSE时钟 */
	RCC->CR |= (uint32_t)0x00010000;
	
	/* 等待HSE时钟就绪 */
	do
	{
		tmpreg = RCC->CR & (uint32_t)0x00020000;
		delay_time++;
	}
    while((delay_time != HSE_READY_OVERTIMR) && (tmpreg == 0));
	
	/* 再次判断HSE是否就绪 */	
	if((RCC->CR & (uint32_t)0x00020000) != 0) status = 0x01;
	else status = 0;
	
	if(status == 0x01)
	{
		/* Enable Prefetch Buffer */
		FLASH->ACR |= FLASH_ACR_PRFTBE;

		/* Flash 2 wait state */
		FLASH->ACR &= (uint32_t)((uint32_t)~FLASH_ACR_LATENCY);
		FLASH->ACR |= (uint32_t)FLASH_ACR_LATENCY_2; 
		
		/* HCLK = SYSCLK */
		RCC->CFGR |= (uint32_t)0x00000000;
		
		/* HAPB1 = HCLK/2 */
		RCC->CFGR |= (uint32_t)0x00000400;
		
		/* HAPB2 = HCLK */
		RCC->CFGR |= (uint32_t)0x00000000;
		
		/* 配置PLL HSE时钟作为PLL输入时钟 HSE不分频 PLL 9倍频输出 */
		RCC->CFGR &= ~(((uint32_t)0x01)<<16) | (((uint32_t)0x01)<<17) | (((uint32_t)0x0F)<<18);
		RCC->CFGR |= (((uint32_t)0x01)<<16) | (((uint32_t)0x00)<<17) | (((uint32_t)0x07)<<18);
		
		/* 使能PLL时钟 */
		RCC->CR |= ((uint32_t)0x01)<<24; 
		
		while((RCC->CR & 0x02000000) == 0)
		{
		}
		
		/* 选择PLL作为系统时钟 */
		RCC->CFGR &= ~(uint32_t)0x03;
		RCC->CFGR |= (uint32_t)0x02;
		
		while((RCC->CFGR & 0x0000000C) != 0x08)
		{
		}
	}
	else 
	{
		/* 外部时钟未就绪 可添加代码在此处用于指示 */
	}	
}