/**

* @說明配置STM32F407的時(shí)鐘系統(tǒng)

* @參數(shù)無

* @返回?zé)o

* @說明 void Clock_Config(void)按如下表格配置時(shí)鐘

*

*==================================================================

* Supported STM32F4xx device revision | Rev A

*-----------------------------------------------------------------------------

* System Clock source | PLL (HSE)

*-----------------------------------------------------------------------------

* SYSCLK(Hz) | 168000000

*-----------------------------------------------------------------------------

* HCLK(Hz) | 168000000

*-----------------------------------------------------------------------------

* AHB Prescaler | 1

*-----------------------------------------------------------------------------

* APB1 Prescaler | 4

*-----------------------------------------------------------------------------

* APB2 Prescaler | 2

*-----------------------------------------------------------------------------

* HSE Frequency(Hz) | 8000000

*-----------------------------------------------------------------------------

* PLL_M |8

*-----------------------------------------------------------------------------

* PLL_N | 336

*-----------------------------------------------------------------------------

* PLL_P | 2

*-----------------------------------------------------------------------------

* PLL_Q |7

*===================================================================

*/

void Clock_Config(void){

ErrorStatus State;

uint32_t PLL_M;

uint32_t PLL_N;

uint32_t PLL_P;

uint32_t PLL_Q;

/*配置前將所有RCC重置為初始值*/

RCC_DeInit();

/*這里選擇 外部晶振（HSE）作為 時(shí)鐘源，因此首先打開外部晶振*/

RCC_HSEConfig(RCC_HSE_ON);

/*等待外部晶振進(jìn)入穩(wěn)定狀態(tài)*/

while( RCC_WaitForHSEStartUp() != SUCCESS );

/*

**我們要選擇PLL時(shí)鐘作為系統(tǒng)時(shí)鐘，因此這里先要對(duì)PLL時(shí)鐘進(jìn)行配置

*/

/*選擇外部晶振作為PLL的時(shí)鐘源*/

/* 到這一步為止，已有HSE_VALUE = 8 MHz.

PLL_VCO input clock = (HSE_VALUE or HSI_VALUE / PLL_M)，

根據(jù)文檔，這個(gè)值被建議在1~2MHz，因此我們令PLL_M = 8，

即PLL_VCO input clock = 1MHz */

PLL_M = 8;

/* 到這一步為止，已有PLL_VCO input clock = 1 MHz.

PLL_VCO output clock = (PLL_VCO input clock) * PLL_N,

這個(gè)值要用來計(jì)算系統(tǒng)時(shí)鐘，我們 令PLL_N = 336,

即PLL_VCO output clock = 336 MHz.*/

PLL_N = 336;

/* 到這一步為止，已有PLL_VCO output clock = 336 MHz.

System Clock = (PLL_VCO output clock)/PLL_P ,

因?yàn)槲覀円猄ystemClock = 168 Mhz，因此令PLL_P = 2.

*/

PLL_P = 2;

/*這個(gè)系數(shù)用來配置SD卡讀寫，USB等功能，暫時(shí)不用，根據(jù)文檔，暫時(shí)先設(shè)為7*/

PLL_Q = 7;

/* 配置PLL并將其使能，獲得168Mhz的System Clock時(shí)鐘*/

RCC_PLLConfig(RCC_PLLSource_HSE, PLL_M, PLL_N, PLL_P, PLL_Q);

RCC_PLLCmd(ENABLE);

/*到了這一步，我們已經(jīng)配置好了PLL時(shí)鐘。下面我們配置Syetem Clock*/

/*選擇PLL時(shí)鐘作為系統(tǒng)時(shí)鐘源*/

RCC_SYSCLKConfig(RCC_SYSCLKSource_PLLCLK);