LPC1788系统时钟初始化

LPC1788系统时钟初始化

#ifndef __SYS_H_

#define __SYS_H_

#include "common.h"

#define SystemCoreClock  120000000  //cpu时钟频率,计算时有用

#define ApbClock        120000000   //120M

#define EmcClock        60000000    //60M

#define UsbClock        48000000    //48M

void SystemInit(void);//系统时钟初始化,启动代码调用

#endif

#include "sys.h"

#define XTAL_FREQ   12000000

#define LPC_PBOOST  *((volatile unsigned long  *)(0X400FC1B0))

void SystemInit(void)

{

    LPC_SC->SCS       = 0x00000021;//osc晶振使能,地址线不移位模式

    while ((LPC_SC->SCS & (1<<6)) == 0);/* 等待osc晶振准备好    */

    LPC_SC->CLKSRCSEL = 0x00000001;    /*选择osc为系统输入时钟*/

    LPC_PBOOST |= (3<<0);   //打开功耗提升,可以提升到120MHZ

//    PLL0 Configuration (Main PLL)

//      PLL0 Configuration Register (PLL0CFG)

//         PLL out clock = (F_cco / (2 * P))

//         F_cco = (F_in * M * 2 * P)

//         F_in  must be in the range of 1 MHz to 25 MHz

//         PLL out clock must be in the range of 9.75 MHz to 160 MHz

//         F_cco   156-320M

//      MSEL: PLL Multiplier Selection 0-4bit m

//         M Value

//       PSEL: PLL Divider Selection 5-6bit p

//         P Value

//         1

//         2

//         4

//         8

    LPC_SC->PLL0CFG   = 0x00000009;//选择倍频系数 P = 1 M = 10 FCCO = FIN*P*M*2=240M PLL_OUT = FCCO/(2*P)=120M

    LPC_SC->PLL0CON   = 0x01;             /* PLL0 使能 */

    LPC_SC->PLL0FEED  = 0xAA;

    LPC_SC->PLL0FEED  = 0x55;

    while (!(LPC_SC->PLL0STAT & (1<<10)));/* 等待PLL锁定 */

    LPC_SC->PLL1CFG   = 0x00000023; //选择倍频系数 m = 4 p = 2 fcco = fin*2*p*m = 192m pllout = 192/2*p = 48M

    LPC_SC->PLL1CON   = 0x01;             /* PLL1 使能    */

    LPC_SC->PLL1FEED  = 0xAA;

    LPC_SC->PLL1FEED  = 0x55;

    while (!(LPC_SC->PLL1STAT & (1<<10)));  /* 等待PLL1 锁定 */

    LPC_SC->CCLKSEL   = (1<<0)|(1<<8);      /* pll0为主时钟,分频数为1 */

    LPC_SC->USBCLKSEL = (1<<0)|(2<<8);      /* pll1为cpu主时钟 */

    LPC_SC->EMCCLKSEL = (1<<0);             /* EMC 为系统是时钟的一半  */

    LPC_SC->PCLKSEL   = (1<<0);             /* 外设时钟分频数为1,120M */

    LPC_SC->PCONP     = 0x00;               /* 可以关闭的外设全部被关闭 */

    LPC_SC->CLKOUTCFG &= ~(1<<8);           /* 停止时钟输出    */

  LPC_SC->FLASHCFG  = (5<<12)|0x03A;//6个cpu flash访问时钟,最安全的设置,120M时候可用

#ifdef  __RAM_MODE__//设置中断向量表的位置,一般不改

  SCB->VTOR  = 0x10000000 & 0x3FFFFF80;

#else

  SCB->VTOR  = 0x00000000 & 0x3FFFFF80;

#endif

}

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