ARM Architecture and Programming Notes

1. Sorting

1. AREA TEXT,CODE,READWRITE    

2.     ENTRY    

3.     MOV R0,#100 ;Number of loops    

4.     MOV R1,#0 ; Initialize data    

5. LOOP    

6.     ADD R1,R1,R0; add the data to get the final data    

7.     SUBS R0,R0,#1; loop data R0 minus 1    

8.     CMP R0,#0 ; Compare R0 with 0 to see if the loop is finished    

9.     BNE LOOP ; Determine whether the loop is finished, if accepted, proceed to the following steps      

10.     LDR R2,=RESULT    

11.     STR R1,[R2]    

12. RESULT    

13.     DCD 0    

14. STOP    

15.     B STOP   

16.     ; Arrangement algorithm: first compare all the data with the first one, and finally take out the smallest data and put it in the first memory unit    

17.     ;Then start comparing from the second memory unit and put the second smallest data into the second memory unit.    

18.     ; By this inference, the ten data can be arranged.    

19.     AREA TEXT,CODE,READWRITE    

20.     ENTRY    

21.     LDR R0,=DATA; Get the starting address of DATA data    

22.     MOV R1,R0        

23.     MOV R5,#9; The number of loops at the beginning is 10, so it should start from 9    

24.     MOV R6,R5    

25. COMPARE    

26.     ADD R0,R0,#4; The address stored in R0 + 4 is represented as the address of the next number to be compared      

27.     SUB R6,R6,#1 ; Loop once and subtract 1    

28.     LDR R2,[R1]; Take the data in the register and compare the size    

29.     LDR R3,[R0]    

30.     CMP R3,R2    

31.     MOVCC R7,R2; If the value of the following address is smaller than the previous one, swap their data    

32.     MOVCC R2,R3    

33.     MOVCC R3,R7    

34.     STR R2,[R1] ; store data in the corresponding memory unit    

35.     STR R3,[R0]    

36.     CMP R6,#0 ; Check if each cycle ends    

37.     BNE COMPARE    

38.     ADD R1,R1,#4; After each loop, the initial memory address is moved back one unit.    

39.     MOV R0,R1 ; Reinitialize the address stored in the register in the previous loop    

40.     SUB R5,R5,#1; After each loop, the number of times in the following loops will be reduced by 1    

41.     MOV R6,R5    

42.     CMP R5,#0 ; Check if all loops are finished    

43.     BNE COMPARE    

44. DATA    

45.     DCD 9,4,6,7,8,1,3,2,0,5    

46. STOP    

47.     B STOP   

C language code:

1. #include     

2. extern void strcopy(char *d, const char *s);    

3. int main()    

4. {    

5.     const char *srcstr="abcdefghi";    

6.     char dststr[]="ighfedcba";      

7.     strcopy(dststr,srcstr);    

8.     return 0;    

9. }     

ARM assembly code:

1. STACK_TOPEQU 0x40002000    

2.     PRESERVE8    

3.     AREA SCopy, CODE, READONLY    

4.     EXPORT START    

5.     EXPORT strcopy    

6.     import main    

7.     ENTRY    

8. START    

9.     LDR R13,=STACK_TOP    

10.     B main    

11. strcopy                    

12.     LDRB r2, [r1], #1    

13.     STRB r2, [r0], #1    

14.     CMP r2, #0            

15.     BNE strcopy            

16.     MOV pc,lr          

17.     END   

1. stack_top equ0x40002000  

2. PRESERVE8  

3. export copy  

4. AREA copy,CODE,READONLY  

5. import copystr  

6. export start  

7. ENTRY  

8. start  

9. ldr r13,=stack_top  

10. ldr r0,=src  

11. ldr r1,=dst  

12. BL copystr  

13. src      

14. dcb "abcdefghij"  

15. dst  

16. dcb "helloworld"  

17. end  

1. //C program  

2. #include   

3. void copystr(char *d,char *s)  

4. {  

5. while((*d++=*s++)!='');  

6. }