按键控制LED灯亮---我的第一个嵌入式程序

JZ2440开发板功能实现，通过按下3个开关键，控制3个LED灯的亮灭

.text
.global _start
_start:
    ldr r0,=0x53000000
    mov r1,#0x0
    str r1,[r0]

    ldr sp,=1024*4

    bl main
loop:
    b loop

#define GPFCON (*(volatile unsigned long*)0x56000050)
#define GPFDAT (*(volatile unsigned long*)0x56000054)

#define GPGCON (*(volatile unsigned long*)0x56000060)
#define GPGDAT (*(volatile unsigned long*)0x56000064)

/*LEDs*/
#define GPF4_OUT (1<<(2*4))
#define GPF5_OUT (1<<(2*5))
#define GPF6_OUT (1<<(2*6))

#define GPF4_MSK (3<<(2*4))
#define GPF5_MSK (3<<(2*5))
#define GPF6_MSK (3<<(2*6))

/*KEYs*/
#define GPF0_IN (0<<(2*0))
#define GPF2_IN (0<<(2*2))
#define GPG3_IN (0<<(2*3))

#define GPF0_MSK (3<<(2*0))
#define GPF2_MSK (3<<(2*2))
#define GPG3_MSK (3<<(2*3))

int main()
{
    unsigned long DAT;
    /*set LED1 LED2 LED4 for output*/
    GPFCON&=~(GPF4_MSK | GPF5_MSK | GPF6_MSK);
    GPFCON|=(GPF4_OUT | GPF5_OUT | GPF6_OUT);

    /*set KEY2 KEY3 for input*/
    GPFCON&=~(GPF0_MSK | GPF2_MSK);
    GPFCON|=(GPF0_IN | GPF2_IN);

    /*set KEY4 for input*/
    GPGCON&=~GPG3_MSK;
    GPGCON|=GPG3_IN;

    while(1)
    {
        DAT=GPFDAT;
        if(DAT & (1<<0))/*no press KEY2*/
            GPFDAT|=(1<<4);/*light down*/
        else
            GPFDAT&=~(1<<4);/*light on*/

        if(DAT & (1<<2))/*no press KEY3*/
            GPFDAT|=(1<<5);
        else
            GPFDAT&=~(1<<5);

        DAT=GPGDAT;
        if(DAT & (1<<3))/*no press KEY4*/
            GPFDAT|=(1<<6);
        else
            GPFDAT&=~(1<<6);
    }


    return 0;
}

leds_key.bin:crt0.S leds_key.c
    arm-linux-gcc -g -c -o crt0.o crt0.S
    arm-linux-gcc -g -c -o leds_key.o leds_key.c
    arm-linux-ld -Ttext 0x00000000 -g crt0.o leds_key.o -o leds_key_elf
    arm-linux-objcopy -O binary -S leds_key_elf leds_key.bin
clean:
    rm -f *.o leds_key_elf leds_key.bin