.text

.globl _start

_start:

ldr r0, =0x70000000

orr r0, r0, #0x13

mcr p15, 0, r0, c15, c2, 4

ldr r0, =0x7e004000

mov r1, #0

str r1, [r0]

bl clock_init

ldr sp, =8*1024

bl xxxx

b .

start.S 文件，调用完时钟初始化函数后调用跑马灯程序。

.globl clock_init

clock_init:

ldr r0, =0x7E00F000

ldr r1, =0x0000FFFF

str r1, [r0]

str r1, [r0, #4]

str r1, [r0, #8]

#define OTHERS0x7e00f900

ldr r0, =OTHERS

ldr r1, [r0]

bic r1, r1, #0xc0

str r1, [r0]

loop1:

ldr r0, =OTHERS

ldr r1, [r0]

and r1, r1, #0xf00

cmp r1, #0

bne loop1

#define ARM_RATIO 0 /* ARMCLK = DOUTAPLL / (ARM_RATIO + 1) */

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

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

#define PCLK_RATIO 3 /* PCLK = HCLKX2 / (PCLK_RATIO + 1) */

#define MPLL_RATIO 0 /* DOUTMPLL = MOUTMPLL / (MPLL_RATIO + 1) */

ldr r0, =0x7E00F020 /* CLK_DIV0 */

ldr r1, =(ARM_RATIO) | (MPLL_RATIO << 4) | (HCLK_RATIO << 8) | (HCLKX2_RATIO << 9) | (PCLK_RATIO << 12)

str r1, [r0]

#define APLL_CON_VAL ((1<<31) | (266 << 16) | (3 << 8) | (1))

ldr r0, =0x7E00F00C

ldr r1, =APLL_CON_VAL

str r1, [r0]

/*

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

*/

#define MPLL_CON_VAL ((1<<31) | (266 << 16) | (3 << 8) | (1))

ldr r0, =0x7E00F010

ldr r1, =MPLL_CON_VAL

str r1, [r0]

/*

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

*/

ldr r0, =0x7E00F01C

ldr r1, =0x03

str r1, [r0]

mov pc, lr

clock.S：时钟初始化。

all:start.o clock.o led.o

arm-linux-ld -Ttext 0 -o led.elf start.o clock.o led.o

arm-linux-objcopy -O binary led.elf led.bin

arm-linux-objdump -D led.elf > led.dis

cp led.bin /tftpboot/led.bin

%.o:%.S

arm-linux-gcc -c $< -o $@

%.o:%.c

arm-linux-gcc -c -o $@ $<

clean:

rm -rf *.o *.elf *.dis *.bin /tftpboot/*.bin

Makefile:在跑马灯的基础上添加clock.o

void delay ()

{

int i;

for (i = 0; i < 100000; i++)

;

}

int xxxx (void)

{

volatile unsigned long *gpmcon = (volatile unsigned long *)0x7f008820;volatile unsigned long *gpmdat = (volatile unsigned long *)0x7f008824;

int i;

for (i = 1; i <= 4; i++){

if (1 == i){

*gpmcon &= ~0xffff;

*gpmcon |= 0x1;

}else if (2 == i){

*gpmcon &= ~0xffff;

*gpmcon |= 0x10;

}else if (3 == i){

*gpmcon &= ~0xffff;

*gpmcon |= 0x100;

}else if (4 == i){

*gpmcon &= ~0xffff;

*gpmcon |= 0x1000;

i = 0;

}

*gpmdat = 0;

delay();

}

return 0;

}

led.c：同上一章一样。

结果：初始化时钟后，跑马灯速度明显快于不初始化时钟的跑马灯程序。