当使用C编程点亮LED时, 发现如下语句会影响运行结果:
unsigned long mGPBconValue = 0x00014400; (main函数14行)
mGPBconValue 从未被使用,只是加入一个赋值语句而已.
- 屏蔽该语句,运行结果正常 (LED被正常点亮)
- 启用该语句,运行结果错误
哪位大侠指点一下....难道和函数堆栈有关系?
simon@lionteeth:~/work/studycdrom/hardware/led_on_c$ cat -n led_on_c2.c
1 #define pGPBCON (volatile unsigned long*)(0x56000010)
2 #define GPIO_OUTPUT 0x01
3 #define pGPBDATA (volatile unsigned long*)(0x56000014)
4 #define GET_GPIOCON_OUTPUTBITS(x) (GPIO_OUTPUT << (2*x))
5
6 /* Let me light LED1, LED3, LED4
7 LED1: GPB5
8 LED3: GPB7
9 LED4: GPB8
10 */
11 int main()
12 {
13
14 //unsigned long mGPBconValue = 0x00014400;
15
16 //mGPBconValue |= GET_GPIOCON_OUTPUTBITS(5);
17 //mGPBconValue |= GET_GPIOCON_OUTPUTBITS(7);
18 //mGPBconValue |= GET_GPIOCON_OUTPUTBITS(8);
19
20 //*pGPBCON = mGPBconValue;
21 //*pGPBCON = 0x00015400;
22 //*pGPBCON = 0x00015400;
23 //*pGPBCON = 0x00015000;
24 *pGPBCON = GET_GPIOCON_OUTPUTBITS(5) |
25 GET_GPIOCON_OUTPUTBITS(6) |
26 GET_GPIOCON_OUTPUTBITS(7) |
27 GET_GPIOCON_OUTPUTBITS(8);
28
29 *pGPBDATA = 0;
30
31 while(1);
32 return 0;
33 }
simon@lionteeth:~/work/studycdrom/hardware/led_on_c$ cat simoncrt.S
.text
.global _start
_start:
mov sp, #1024*4
bl main
loop:
b loop
simon@lionteeth:~/work/studycdrom/hardware/led_on_c$ make clean;make
rm -f led_on_c2.dis led_on_c2.bin led_on_c2_elf *.o
arm-linux-gcc -g -c -o simoncrt.o simoncrt.S
arm-linux-gcc -g -c -o led_on_c2.o led_on_c2.c
arm-linux-ld -Ttext 0x0000000 -g simoncrt.o led_on_c2.o -o led_on_c2_elf
arm-linux-objcopy -O binary -S led_on_c2_elf led_on_c2.bin
arm-linux-objdump -D -m arm led_on_c2_elf > led_on_c2.dis
