系统时钟学习笔记

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12m晶振----->pll------>cpu

 

Mux多路选择器

Div分频器

示例代码如下：

汇编实现

.globlclock_init

 

clock_init:

 

/*1.设置LOCK_TIME*/

ldrr0,=0x7E00F000/*APLL_LOCK*/

ldrr1,=0x0000FFFF

strr1,[r0]

 

strr1,[r0,#4] /*MPLL_LOCK*/

strr1,[r0,#8] /*EPLL_LOCK*/

 

#defineOTHERS 0x7e00f900

@setasyncmode/*当CPU时钟!=HCLK时，要设为异步模式*/

ldrr0,=OTHERS

ldrr1,[r0]

bicr1,#0xc0

strr1,[r0]

 

loop1: /*等待，直到CPU进入异步模式*/

ldrr0,=OTHERS

ldrr1,[r0]

andr1,#0xf00

cmpr1,#0

bneloop1

 

/*SYNC667*/

/*MISC_CON[19]=0*/

 

#defineARM_RATIO0/*ARMCLK=DOUTAPLL/(ARM_RATIO+1)*/

#defineHCLKX2_RATIO1/*HCLKX2=HCLKX2IN/(HCLKX2_RATIO+1)*/

#defineHCLK_RATIO1/*HCLK=HCLKX2/(HCLK_RATIO+1)*/

#definePCLK_RATIO3/*PCLK=HCLKX2/(PCLK_RATIO+1)*/

#defineMPLL_RATIO0/*DOUTMPLL=MOUTMPLL/(MPLL_RATIO+1)*/

ldrr0,=0x7E00F020/*CLK_DIV0*/

ldrr1,=(ARM_RATIO)|(MPLL_RATIO<<4)|(HCLK_RATIO<<8)|(HCLKX2_RATIO<<9)|(PCLK_RATIO<<12)

strr1,[r0]

 

/*2.配置时钟*/

/*2.1配置APLL*/

/*2.1.1设置APLL

*2.1.2MUXAPLL

*2.1.3SYNC667

*2.1.4DIVAPLL

*/

#defineAPLL_CON_VAL((1<<31)|(266<<16)|(3<<8)|(1))

ldrr0,=0x7E00F00C

ldrr1,=APLL_CON_VAL

strr1,[r0] /*APLL_CON,FOUTAPL=MDIV*Fin/(PDIV*2^SDIV)=266*12/(3*2^1)=532MHz*/

 

/*2.2配置MPLL*/

/*2.2.1设置MPLL

*2.2.2MUXMPLL

*2.2.3SYNCMUX

*2.2.4SYNC667

*2.2.5HCLKX2_RATIO

*2.2.6PCLK_RATIO

*/

#defineMPLL_CON_VAL((1<<31)|(266<<16)|(3<<8)|(1))

ldrr0,=0x7E00F010

ldrr1,=MPLL_CON_VAL

strr1,[r0] /*MPLL_CON,FOUTMPL=MDIV*Fin/(PDIV*2^SDIV)=266*12/(3*2^1)=532MHz*/

 

/*3.选择PLL的输出作为时钟源*/

ldrr0,=0x7E00F01C

ldrr1,=0x03

strr1,[r0]

 

movpc,lr

 

 

 

C实现

#defineAPLL_LOCK(*((volatileunsignedlong*)0x7E00F000))

#defineMPLL_LOCK(*((volatileunsignedlong*)0x7E00F004))

#defineEPLL_LOCK(*((volatileunsignedlong*)0x7E00F008))

 

#defineOTHERS (*((volatileunsignedlong*)0x7E00F900))

 

#defineCLK_DIV0(*((volatileunsignedlong*)0x7E00F020))

 

#defineARM_RATIO 0

#defineHCLKX2_RATIO 4

#defineHCLK_RATIO 0

#definePCLK_RATIO 1

#defineMPLL_RATIO 0

 

#defineAPLL_CON(*((volatileunsignedlong*)0x7E00F00C))

#defineAPLL_CON_VAL((1<<31)|(250<<16)|(3<<8)|(1))

 

#defineMPLL_CON(*((volatileunsignedlong*)0x7E00F010))

#defineMPLL_CON_VAL((1<<31)|(250<<16)|(3<<8)|(1))

 

#defineCLK_SRC(*((volatileunsignedlong*)0x7E00F01C))

 

voidclock_init(void){

APLL_LOCK=0XFFFF;

MPLL_LOCK=0XFFFF;

EPLL_LOCK=0XFFFF;

 

/*当CPU时钟!=HCLK时，要设为异步模式*/

OTHERS&=~0XC0;

while((OTHERS&0XF00)!=0);

 

CLK_DIV0=(ARM_RATIO)|(MPLL_RATIO<<4)|(HCLK_RATIO<<8)|(HCLKX2_RATIO<<9)|(PCLK_RATIO<<12);

APLL_CON=APLL_CON_VAL;/*500MHZ*/

MPLL_CON=MPLL_CON_VAL;/*500MHZ*/

 

CLK_SRC=0X03;

}