LED

一.启动文件：

.text
.global _start
_start:
            ldr     r0, =0x53000000     @ WATCHDOG寄存器地址
            mov     r1, #0x0                     
            str   r1, [r0]              @ 写入0，禁止WATCHDOG，否则CPU会不断重启
            ldr     sp, =1024*4         @ 设置堆栈，注意：不能大于4k, 因为现在可用的内存只有4K
                                        @ nand flash中的代码在复位后会移到内部ram中，此ram只有4K
            bl      main                @ 调用C程序中的main函数
halt_loop:
            b       halt_loop      

启动文件里面主要做了硬件方面的的初始化（关闭看门狗）以及软件相关的初始化（设置栈、设置main函数的返回地址并调用main函数、清理工作）。

c函数（main函数）调用之前，要先设置栈，即将栈指针指向某个内存。

通常启动文件硬件相关的任务位：

1.关看门狗

2.初始化时钟

3.初始化SDRAM

由于本次程序里没有用到始终以及SDRAM，所以没有这方面的功能。

二.main函数

#define GPFCON(*(volatile unsigned long *)0x56000050)    //volatile防止对程序进行优化
#define GPFDAT(*(volatile unsigned long *)0x56000054)
#define GPF4_out(1<<(4*2))
#define GPF5_out(1<<(5*2))
#define GPF6_out(1<<(6*2))
#define GPF7_out(1<<(7*2))
void  wait(volatile unsigned long dly)
{
for(; dly > 0; dly--);
}
int main(void)
{
unsigned long i = 0;
GPFCON = GPF4_out|GPF5_out|GPF6_out;// 将LED1-3对应的GPF4/5/6三个引脚设为输出
while(1){
wait(30000);
GPFDAT = (~(i<<4));// 根据i的值，点亮LED1-3
if(++i == 8)
i = 0;
}
return 0;
}

三.MAKEFILE

CFLAGS := -Wall -Wstrict-prototypes -g -fomit-frame-pointer -ffreestanding
all : crt0.S  leds.c
arm-linux-gcc $(CFLAGS) -c -o crt0.o crt0.S
arm-linux-gcc $(CFLAGS) -c -o leds.o leds.c
arm-linux-ld -Tleds.lds  crt0.o leds.o -o leds_elf
arm-linux-objcopy -O binary -S leds_elf leds.bin
arm-linux-objdump -D -m arm  leds_elf > leds.dis     //生成反汇编文件
clean:
rm -f   leds.dis leds.bin leds_elf *.o

四.反汇编文件：

leds_elf:     file format elf32-littlearm
Disassembly of section .text:
00000000 <_start>:
   0: e3a00453 mov r0, #1392508928; 0x53000000
   4: e3a01000 mov r1, #0; 0x0
   8: e5801000 str r1, [r0]
   c: e3a0da01 mov sp, #4096; 0x1000
  10: eb00000b bl 44 <main>
00000014 <halt_loop>:
  14: eafffffe b 14 <halt_loop>

00000018 <wait>:
  18: e24dd004 sub sp, sp, #4; 0x4
  1c: e58d0000 str r0, [sp]
  20: e59d3000 ldr r3, [sp]
  24: e3530000 cmp r3, #0; 0x0
  28: 0a000003 beq 3c <wait+0x24>
  2c: e59d3000 ldr r3, [sp]
  30: e2433001 sub r3, r3, #1; 0x1
  34: e58d3000 str r3, [sp]
  38: eafffff8 b 20 <wait+0x8>
  3c: e28dd004 add sp, sp, #4; 0x4
  40: e1a0f00e mov pc, lr

00000044 <main>:
  44: e52de004 str lr, [sp, #-4]!
  48: e24dd004 sub sp, sp, #4; 0x4
  4c: e3a03000 mov r3, #0; 0x0
  50: e58d3000 str r3, [sp]
  54: e3a03456 mov r3, #1442840576; 0x56000000
  58: e2833050 add r3, r3, #80; 0x50
  5c: e3a02c15 mov r2, #5376; 0x1500
  60: e5832000 str r2, [r3]
  64: e3a00c75 mov r0, #29952; 0x7500
  68: e2800030 add r0, r0, #48; 0x30
  6c: ebffffe9 bl 18 <wait>
  70: e3a02456 mov r2, #1442840576; 0x56000000
  74: e2822054 add r2, r2, #84; 0x54
  78: e59d3000 ldr r3, [sp]
  7c: e1a03203 mov r3, r3, lsl #4
  80: e1e03003 mvn r3, r3
  84: e5823000 str r3, [r2]
  88: e59d3000 ldr r3, [sp]
  8c: e2833001 add r3, r3, #1; 0x1
  90: e58d3000 str r3, [sp]
  94: e3530008 cmp r3, #8; 0x8
  98: 1afffff1 bne 64 <main+0x20>
  9c: e3a03000 mov r3, #0; 0x0
  a0: e58d3000 str r3, [sp]
  a4: eaffffee b 64 <main+0x20>
Disassembly of section .debug_line:

00000000 <.debug_line>:
   0: 00000032 andeq r0, r0, r2, lsr r0
   4: 001a0002 andeqs r0, sl, r2
   8: 01020000 tsteq r2, r0
   c: 000a0efb streqd r0, [sl], -fp
  10: 01010101 tsteq r1, r1, lsl #2
  14: 01000000 tsteq r0, r0
  18: 74726300 ldrvcbt r6, [r2], #-768
  1c: 00532e30 subeqs r2, r3, r0, lsr lr
  20: 00000000 andeq r0, r0, r0
  24: 00020500 andeq r0, r2, r0, lsl #10
  28: 17000000 strne r0, [r0, -r0]
  2c: 2d2d2c2c stccs 12, cr2, [sp, #-176]!
  30: 0002022d andeq r0, r2, sp, lsr #4
  34: 00380101 eoreqs r0, r8, r1, lsl #2
  38: 00020000 andeq r0, r2, r0
  3c: 0000001a andeq r0, r0, sl, lsl r0
  40: 0efb0102 cdpeq 1, 15, cr0, cr11, cr2, {0}
  44: 0101000a tsteq r1, sl
  48: 00000101 andeq r0, r0, r1, lsl #2
  4c: 6c000100 stfvss f0, [r0], {0}
  50: 2e736465 cdpcs 4, 7, cr6, cr3, cr5, {3}
  54: 00000063 andeq r0, r0, r3, rrx
  58: 05000000 streq r0, [r0]
  5c: 00001802 andeq r1, r0, r2, lsl #16
  60: 010a0300 tsteq sl, r0, lsl #6
  64: 484ad448 stmmida sl, {r3, r6, sl, ip, lr, pc}^
  68: b8648249 stmltda r4!, {r0, r3, r6, r9, pc}^
  6c: 0006029c muleq r6, ip, r2
  70: Address 0x70 is out of bounds.

Disassembly of section .debug_info:

00000000 <.debug_info>:
   0: 0000003d andeq r0, r0, sp, lsr r0
   4: 00000002 andeq r0, r0, r2
   8: 01040000 tsteq r4, r0
...
  14: 00000018 andeq r0, r0, r8, lsl r0
  18: 30747263 rsbccs r7, r4, r3, ror #4
  1c: 2f00532e swics 0x0000532e
  20: 6b726f77 blvs 1c9be04 <main+0x1c9bdc0>
  24: 7261682f rsbvc r6, r1, #3080192; 0x2f0000
  28: 72617764 rsbvc r7, r1, #26214400; 0x1900000
  2c: 656c2f65 strvsb r2, [ip, #-3941]!
  30: 47007364 strmi r7, [r0, -r4, ror #6]
  34: 4120554e teqmi r0, lr, asr #10
  38: 2e322053 mrccs 0, 1, r2, cr2, cr3, {2}
  3c: 01003531 tsteq r0, r1, lsr r5
  40: 0000ae80 andeq sl, r0, r0, lsl #29
  44: 14000200 strne r0, [r0], #-512
  48: 04000000 streq r0, [r0]
  4c: 00003601 andeq r3, r0, r1, lsl #12
  50: 0000a800 andeq sl, r0, r0, lsl #16
  54: 00001800 andeq r1, r0, r0, lsl #16
  58: 554e4700 strplb r4, [lr, #-1792]
  5c: 33204320 teqcc r0, #-2147483648; 0x80000000
  60: 352e342e strcc r3, [lr, #-1070]!
  64: 656c0100 strvsb r0, [ip, #-256]!
  68: 632e7364 teqvs lr, #-1879048191; 0x90000001
  6c: 6f772f00 swivs 0x00772f00
  70: 682f6b72 stmvsda pc!, {r1, r4, r5, r6, r8, r9, fp, sp, lr}
  74: 77647261 strvcb r7, [r4, -r1, ror #4]!
  78: 2f657261 swics 0x00657261
  7c: 7364656c cmnvc r4, #452984832; 0x1b000000
  80: 00670200 rsbeq r0, r7, r0, lsl #4
  84: 77010000 strvc r0, [r1, -r0]
  88: 00746961 rsbeqs r6, r4, r1, ror #18
  8c: 18010b01 stmneda r1, {r0, r8, r9, fp}
  90: 44000000 strmi r0, [r0]
  94: 01000000 tsteq r0, r0
  98: 6c64035d stcvsl 3, cr0, [r4], #-372
  9c: 0a010079 beq 40288 <main+0x40244>
  a0: 00000067 andeq r0, r0, r7, rrx
  a4: 00009102 andeq r9, r0, r2, lsl #2
  a8: 00006c04 andeq r6, r0, r4, lsl #24
  ac: 6f6c0500 swivs 0x006c0500
  b0: 7520676e strvc r6, [r0, #-1902]!
  b4: 6769736e strvsb r7, [r9, -lr, ror #6]!
  b8: 2064656e rsbcs r6, r4, lr, ror #10
  bc: 00746e69 rsbeqs r6, r4, r9, ror #28
  c0: aa060704 bge 181cd8 <main+0x181c94>
  c4: 01000000 tsteq r0, r0
  c8: 6e69616d powvsez f6, f1, #5.0
  cc: 01100100 tsteq r0, r0, lsl #2
  d0: 000000aa andeq r0, r0, sl, lsr #1
  d4: 00000044 andeq r0, r0, r4, asr #32
  d8: 000000a8 andeq r0, r0, r8, lsr #1
  dc: 69075d01 stmvsdb r7, {r0, r8, sl, fp, ip, lr}
  e0: 6c110100 ldfvss f0, [r1], {0}
  e4: 02000000 andeq r0, r0, #0; 0x0
  e8: 05000091 streq r0, [r0, #-145]
  ec: 00746e69 rsbeqs r6, r4, r9, ror #28
  f0: Address 0xf0 is out of bounds.

Disassembly of section .debug_abbrev:

00000000 <.debug_abbrev>:
   0: 10001101 andne r1, r0, r1, lsl #2
   4: 12011106 andne r1, r1, #-2147483647; 0x80000001
   8: 1b080301 blne 200c14 <main+0x200bd0>
   c: 13082508 tstne r8, #33554432; 0x2000000
  10: 00000005 andeq r0, r0, r5
  14: 10011101 andne r1, r1, r1, lsl #2
  18: 11011206 tstne r1, r6, lsl #4
  1c: 13082501 tstne r8, #4194304; 0x400000
  20: 1b08030b blne 200c54 <main+0x200c10>
  24: 02000008 andeq r0, r0, #8; 0x8
  28: 1301012e tstne r1, #-2147483637; 0x8000000b
  2c: 08030c3f stmeqda r3, {r0, r1, r2, r3, r4, r5, sl, fp}
  30: 0b3b0b3a bleq ec2d20 <main+0xec2cdc>
  34: 01110c27 tsteq r1, r7, lsr #24
  38: 0a400112 beq 1000488 <main+0x1000444>
  3c: 05030000 streq r0, [r3]
  40: 3a080300 bcc 200c48 <main+0x200c04>
  44: 490b3b0b stmmidb fp, {r0, r1, r3, r8, r9, fp, ip, sp}
  48: 000a0213 andeq r0, sl, r3, lsl r2
  4c: 00350400 eoreqs r0, r5, r0, lsl #8
  50: 00001349 andeq r1, r0, r9, asr #6
  54: 03002405 tsteq r0, #83886080; 0x5000000
  58: 3e0b0b08 fmacdcc d0, d11, d8
  5c: 0600000b streq r0, [r0], -fp
  60: 1301012e tstne r1, #-2147483637; 0x8000000b
  64: 08030c3f stmeqda r3, {r0, r1, r2, r3, r4, r5, sl, fp}
  68: 0b3b0b3a bleq ec2d58 <main+0xec2d14>
  6c: 13490c27 cmpne r9, #9984; 0x2700
  70: 01120111 tsteq r2, r1, lsl r1
  74: 00000a40 andeq r0, r0, r0, asr #20
  78: 03003407 tsteq r0, #117440512; 0x7000000
  7c: 3b0b3a08 blcc 2ce8a4 <main+0x2ce860>
  80: 0213490b andeqs r4, r3, #180224; 0x2c000
  84: 0000000a andeq r0, r0, sl
Disassembly of section .debug_aranges:

00000000 <.debug_aranges>:
   0: 0000001c andeq r0, r0, ip, lsl r0
   4: 00000002 andeq r0, r0, r2
   8: 00040000 andeq r0, r4, r0
...
  14: 00000018 andeq r0, r0, r8, lsl r0
...
  20: 0000001c andeq r0, r0, ip, lsl r0
  24: 00410002 subeq r0, r1, r2
  28: 00040000 andeq r0, r4, r0
  2c: 00000000 andeq r0, r0, r0
  30: 00000018 andeq r0, r0, r8, lsl r0
  34: 00000090 muleq r0, r0, r0
...
Disassembly of section .debug_frame:

00000000 <.debug_frame>:
   0: 0000000c andeq r0, r0, ip
   4: ffffffff swinv 0x00ffffff
   8: 7c010001 stcvc 0, cr0, [r1], {1}
   c: 000d0c0e andeq r0, sp, lr, lsl #24
  10: 00000010 andeq r0, r0, r0, lsl r0
  14: 00000000 andeq r0, r0, r0
  18: 00000018 andeq r0, r0, r8, lsl r0
  1c: 0000002c andeq r0, r0, ip, lsr #32
  20: 00040e44 andeq r0, r4, r4, asr #28
  24: 00000014 andeq r0, r0, r4, lsl r0
  28: 00000000 andeq r0, r0, r0
  2c: 00000044 andeq r0, r0, r4, asr #32
  30: 00000064 andeq r0, r0, r4, rrx
  34: 44040e44 strmi r0, [r4], #-3652
  38: 018e080e orreq r0, lr, lr, lsl #16
Disassembly of section .debug_pubnames:

00000000 <.debug_pubnames>:
   0: 00000020 andeq r0, r0, r0, lsr #32
   4: 00410002 subeq r0, r1, r2
   8: 00b20000 adceqs r0, r2, r0
   c: 00400000 subeq r0, r0, r0
  10: 61770000 cmnvs r7, r0
  14: 81007469 tsthi r0, r9, ror #8
  18: 6d000000 stcvs 0, cr0, [r0]
  1c: 006e6961 rsbeq r6, lr, r1, ror #18
  20: 00000000 andeq r0, r0, r0
Disassembly of section .comment:

00000000 <.comment>:
   0: 43434700 cmpmi r3, #0; 0x0
   4: 4728203a undefined
   8: 2029554e eorcs r5, r9, lr, asr #10
   c: 2e342e33 mrccs 14, 1, r2, cr4, cr3, {1}
  10: Address 0x10 is out of bounds.