在Cygwin下使用GNU tools 开发contex-m4

使用的开发工具为YAGARTO最新版本：（29.04.2011更新）

Binutils-2.21

Newlib-1.19.0
GCC-4.6.0
GDB-7.2 

下面贴一下自己的代码，以备查阅。（代码不能实际运行，只是为了看生成的反汇编代码）

test.s

1. .text
2. .global _start
3. .code 16
4. .syntax unified
5. _start:
6. .word 0x20002000
7. .word reset
8. .type reset, function
9. reset:
10. ldr r0,=main
11. bx r0
12. .end

main.c

1. int main(void)
   
2. {
   
3.         float a=3.1415926,b=12.9873421,result;
   
4.         result=a*b*b;
   
5.         while(1);
   
6.         return 0;
   
7. }

Makefile

1. test.elf : test.s main.c
2. arm-none-eabi-gcc -c -gdwarf-2 -mcpu=cortex-m4 -mfloat-abi=hard -mthumb -o test.o test.s
3. arm-none-eabi-gcc -c -gdwarf-2 -mcpu=cortex-m4 -mthumb -mfloat-abi=hard -o main.o main.c
4. arm-none-eabi-ld -Ttext 0x0 test.o main.o -o test.elf
5. arm-none-eabi-objcopy -O binary -S test.elf test.bin
6. arm-none-eabi-objdump -D -m arm test.elf >_test.dis
7. dos2unix _test.dis
8. clean:
9. rm test.o main.o test.elf _test.dis test.bin

只有这3个文件，可以看到在Makefile中有"-mfloat-abi=hard"，这个可以用来生成FPU代码（cortex-m4带DSP运算单元）。

生成的反汇编代码如下：

1. test.elf: file format elf32-littlearm
4. Disassembly of section .text:
6. 00000000 :
7. 0: 20002000 andcs r2, r0, r0
8. 4: 00000009 andeq r0, r0, r9
10. 00000008 :
11. 8: 4800 ldr r0, [pc, #0] ; (c )
12. a: 4700 bx r0
13. c: 00000011 andeq r0, r0, r1, lsl r0
15. 00000010 :
16. 10: b480 push {r7}
17. 12: b085 sub sp, #20
18. 14: af00 add r7, sp, #0
19. 16: 4b08 ldr r3, [pc, #32] ; (38 )
20. 18: 60fb str r3, [r7, #12]
21. 1a: 4b08 ldr r3, [pc, #32] ; (3c )
22. 1c: 60bb str r3, [r7, #8]
23. 1e: ed97 7a03 vldr s14, [r7, #12]
24. 22: edd7 7a02 vldr s15, [r7, #8]
25. 26: ee67 7a27 vmul.f32 s15, s14, s15
26. 2a: ed97 7a02 vldr s14, [r7, #8]
27. 2e: ee67 7a87 vmul.f32 s15, s15, s14
28. 32: edc7 7a01 vstr s15, [r7, #4]
29. 36: e7fe b.n 36
30. 38: 40490fda ldrdmi r0, [r9], #-250 ; 0xffffff06
31. 3c: 414fcc27 cmpmi pc, r7, lsr #24

----------------------------------------------------------------------------------------------------------------------------------

生成软件浮点代码：

Makefile:

1. test.elf : test.s main.c
2. arm-none-eabi-gcc -c -gdwarf-2 -mcpu=cortex-m4 -mfloat-abi=soft -mthumb -o test.o test.s
3. arm-none-eabi-gcc -c -gdwarf-2 -mcpu=cortex-m4 -mthumb -mfloat-abi=soft -o main.o main.c
4. arm-none-eabi-gcc -Ttext 0x0 -mcpu=cortex-m4 -mfloat-abi=soft -mthumb -nostartfiles test.o main.o -o test.elf
5. arm-none-eabi-objcopy -O binary -S test.elf test.bin
6. arm-none-eabi-objdump -D -m arm test.elf >_test.dis
7. dos2unix _test.dis
8. clean:
9. rm test.o main.o test.elf _test.dis test.bin

生成结果如下：

1. 00000000 :
2. 0: 20002000 andcs r2, r0, r0
3. 4: 00000009 andeq r0, r0, r9
5. 00000008 :
6. 8: 4800 ldr r0, [pc, #0] ; (c )
7. a: 4700 bx r0
8. c: 00000011 andeq r0, r0, r1, lsl r0
10. 00000010 :
11. 10: b580 push {r7, lr}
12. 12: b084 sub sp, #16
13. 14: af00 add r7, sp, #0
14. 16: 4b08 ldr r3, [pc, #32] ; (38 )
15. 18: 60fb str r3, [r7, #12]
16. 1a: 4b08 ldr r3, [pc, #32] ; (3c )
17. 1c: 60bb str r3, [r7, #8]
18. 1e: 68f8 ldr r0, [r7, #12]
19. 20: 68b9 ldr r1, [r7, #8]
20. 22: f000 f80d bl 40
21. 26: 4603 mov r3, r0
22. 28: 4618 mov r0, r3
23. 2a: 68b9 ldr r1, [r7, #8]
24. 2c: f000 f808 bl 40
25. 30: 4603 mov r3, r0
26. 32: 607b str r3, [r7, #4]
27. 34: e7fe b.n 34
28. 36: bf00 nop
29. 38: 40490fda ldrdmi r0, [r9], #-250 ; 0xffffff06
30. 3c: 414fcc27 cmpmi pc, r7, lsr #24
32. 00000040 :
33. 40: f04f 0cff mov.w ip, #255 ; 0xff
34. 44: ea1c 52d0 ands.w r2, ip, r0, lsr #23
35. 48: bf1e ittt ne
36. 4a: ea1c 53d1 andsne.w r3, ip, r1, lsr #23
37. 4e: ea92 0f0c teqne r2, ip
38. 52: ea93 0f0c teqne r3, ip
39. 56: d06f beq.n 138
40. 58: 441a add r2, r3
41. 5a: ea80 0c01 eor.w ip, r0, r1
42. 5e: 0240 lsls r0, r0, #9
43. 60: bf18 it ne
44. ........(以下省略)