當(dāng)HSI被用于作為PLL時鐘的輸入時，系統(tǒng)時鐘能得到的最大頻率是64MHZ。

STM3210X_RCC.H頭文件，主要是對RCC相關(guān)的寄存器進行了一個重新的定義命名以及對.c文件中的函數(shù)進行申明。

可以從參考手冊的6.3 RCC寄存器描述了解到。更加詳細的內(nèi)容

/******************** (C) COPYRIGHT 2008 STMicroelectronics ********************
* File Name : stm32f10x_rcc.h
* Author : MCD Application Team
* Version : V2.0.2
* Date : 07/11/2008
* Description : This file contains all the functions prototypes for the
* RCC firmware library.
********************************************************************************
* THE PRESENT FIRMWARE WHICH IS FOR GUIDANCE ONLY AIMS AT PROVIDING CUSTOMERS
* WITH CODING INFORMATION REGARDING THEIR PRODUCTS IN ORDER FOR THEM TO SAVE TIME.
* AS A RESULT, STMICROELECTRONICS SHALL NOT BE HELD LIABLE FOR ANY DIRECT,
* INDIRECT OR CONSEQUENTIAL DAMAGES WITH RESPECT TO ANY CLAIMS ARISING FROM THE
* CONTENT OF SUCH FIRMWARE AND/OR THE USE MADE BY CUSTOMERS OF THE CODING
* INFORMATION CONTAINED HEREIN IN CONNECTION WITH THEIR PRODUCTS.
*******************************************************************************/

/* Define to prevent recursive inclusion -------------------------------------*/
#ifndef __STM32F10x_RCC_H
#define __STM32F10x_RCC_H

/* Includes ------------------------------------------------------------------*/
#include "stm32f10x_map.h"

/* Exported types ------------------------------------------------------------*/
typedef struct
{
u32 SYSCLK_Frequency;
u32 HCLK_Frequency;
u32 PCLK1_Frequency;
u32 PCLK2_Frequency;
u32 ADCCLK_Frequency;
}RCC_ClocksTypeDef; //定義結(jié)構(gòu)體

/* Exported constants --------------------------------------------------------*/
/* HSE configuration */
/********RCC_CR時鐘控制寄存器***********
第16位：HSE ON 外部高速時鐘使能
0：HSE振蕩器關(guān)閉
1：HSE振蕩器開啟

第18位：HSEBYP 外部高速時鐘旁路
0：外部4-16MHZ振蕩器沒有旁路
1：外部4-16MHZ外部晶體振蕩器被旁路
***************END**********************/
#define RCC_HSE_OFF ((u32)0x00000000)
#define RCC_HSE_ON ((u32)0x00010000)
#define RCC_HSE_Bypass ((u32)0x00040000)

#define IS_RCC_HSE(HSE) (((HSE) == RCC_HSE_OFF) || ((HSE) == RCC_HSE_ON) ||
((HSE) == RCC_HSE_Bypass))

/* PLL entry clock source */
/********RCC_CFGR時鐘配置寄存器***********
第16位：PLLSRC PLL輸入時鐘源
0：HSI振蕩器時鐘經(jīng)2分頻后作為PLL輸入時鐘
1：HSE時鐘作為PLL輸入時鐘

第17位：PLLXTPRE HSE分頻器作為PLL輸入
0：HSE 不分頻
1：HSE 2分頻
***************END**********************/
#define RCC_PLLSource_HSI_Div2 ((u32)0x00000000)
#define RCC_PLLSource_HSE_Div1 ((u32)0x00010000)
#define RCC_PLLSource_HSE_Div2 ((u32)0x00030000)

#define IS_RCC_PLL_SOURCE(SOURCE) (((SOURCE) == RCC_PLLSource_HSI_Div2) ||
((SOURCE) == RCC_PLLSource_HSE_Div1) ||
((SOURCE) == RCC_PLLSource_HSE_Div2))

/* PLL multiplication factor */
/********RCC_CFGR時鐘配置寄存器***********
第21：18位：PLLMUL PLL倍頻系數(shù)
由軟件設(shè)置來確定PLL倍頻系數(shù)，只有在PLL關(guān)閉的情況下才能被寫入
注意：PLL的輸出頻率不能超過72MHZ
***************END**********************/
#define RCC_PLLMul_2 ((u32)0x00000000)
#define RCC_PLLMul_3 ((u32)0x00040000)
#define RCC_PLLMul_4 ((u32)0x00080000)
#define RCC_PLLMul_5 ((u32)0x000C0000)
#define RCC_PLLMul_6 ((u32)0x00100000)
#define RCC_PLLMul_7 ((u32)0x00140000)
#define RCC_PLLMul_8 ((u32)0x00180000)
#define RCC_PLLMul_9 ((u32)0x001C0000)
#define RCC_PLLMul_10 ((u32)0x00200000)
#define RCC_PLLMul_11 ((u32)0x00240000)
#define RCC_PLLMul_12 ((u32)0x00280000)
#define RCC_PLLMul_13 ((u32)0x002C0000)
#define RCC_PLLMul_14 ((u32)0x00300000)
#define RCC_PLLMul_15 ((u32)0x00340000)
#define RCC_PLLMul_16 ((u32)0x00380000)

#define IS_RCC_PLL_MUL(MUL) (((MUL) == RCC_PLLMul_2) || ((MUL) == RCC_PLLMul_3) ||
((MUL) == RCC_PLLMul_4) || ((MUL) == RCC_PLLMul_5) ||
((MUL) == RCC_PLLMul_6) || ((MUL) == RCC_PLLMul_7) ||
((MUL) == RCC_PLLMul_8) || ((MUL) == RCC_PLLMul_9) ||
((MUL) == RCC_PLLMul_10) || ((MUL) == RCC_PLLMul_11) ||
((MUL) == RCC_PLLMul_12) || ((MUL) == RCC_PLLMul_13) ||
((MUL) == RCC_PLLMul_14) || ((MUL) == RCC_PLLMul_15) ||
((MUL) == RCC_PLLMul_16))

/* System clock source */
/********RCC_CFGR時鐘配置寄存器***********
第1:0位：SW[1:0] 系統(tǒng)時鐘切換
00：HSI作為系統(tǒng)時鐘
01：HSE作為系統(tǒng)時鐘
10：PLL輸出作為系統(tǒng)時鐘
***************END**********************/
#define RCC_SYSCLKSource_HSI ((u32)0x00000000)
#define RCC_SYSCLKSource_HSE ((u32)0x00000001)
#define RCC_SYSCLKSource_PLLCLK ((u32)0x00000002)

#