How to reach indexed values in an array on a Cortex-M3 with assembly?

Question

On the Cortex-M3 I wanted to set the first two values of the array to 0 and 1, so I did the following:

main    MOV R4, #0

array   DCD 4,7,6,8
        LDR R1, =array ; R1 = base address of array

        STR R4, [R1, R4, LSL #2]
        ADD R4, R4, #1
        STR R4, [R1, R4, LSL #2]

        END

Apparently the STR instruction does not what I wanted it to do. What's wrong with that? In the "The Cortex-M3 Instruction Set" manual it says:

STR R0, [R1, R2, LSL #2] ; Stores R0 to an address equal to sum of R1
; and four times R2.

Disassembly looks like that:

0x00000000 0200      DCW      0x0200
0x00000002 2000      DCW      0x2000
0x00000004 0009      DCW      0x0009
0x00000006 0000      DCW      0x0000
0x00000008 F04F0400  MOV      r4,#0x00
0x0000000C 0004      DCW      0x0004
0x0000000E 0000      DCW      0x0000
0x00000010 0007      DCW      0x0007
0x00000012 0000      DCW      0x0000
0x00000014 0006      DCW      0x0006
0x00000016 0000      DCW      0x0000
0x00000018 0008      DCW      0x0008
0x0000001A 0000      DCW      0x0000
0x0000001C 4903      LDR      r1,[pc,#12]  ; @0x0000002C
0x0000001E F8414024  STR      r4,[r1,r4,LSL #2]
0x00000022 F1040401  ADD      r4,r4,#0x01
0x00000026 F8414024  STR      r4,[r1,r4,LSL #2]
0x0000002A 0000      DCW      0x0000
0x0000002C 000C      DCW      0x000C
0x0000002E 0000      DCW      0x0000

Answer 1

As Michael explained the instruction array DCD 4,7,6,8 has to be after the AREA d, DATA directive - otherwise the array will be placed in read-only code area and can thus not be overwritten.

Answer 2

PRESERVE8 THUMB AREA RESET, DATA, READONLY EXPORT __Vectors __Vectors DCD 0x20001000 ;stack pointerenter code here value when initilized

        DCD Reset_Handler ;reset vector

        ALIGN


;AREA DATA

MAXP DCD MAX Min DCD MIN

N DCD 12 NUM1 DCD 3,-7,2,-2,10,20,30,15,32,8,64,66 POINTER DCD NUM1

AREA MYRAM, DATA, READWRITE

MAX DCD 0 MIN DCD 0

AREA MYCODE,CODE, READONLY
ENTRY
EXPORT Reset_Handler

Reset_Handler

Main LDR R1 , = POINTER ;Load Pointer in R1 LDR R2 ,[R1] ;get address of array from pointer LDR R3 , = MAX ;Load MAX pointer in R3 LDR R6, [R3] ;Get address of MAX from MAX pointer LDR R7 , = N ;Load counter Adress in R5 LDR R0,[R7] ;Load Value of Counter from counter address which is in R5 LDR R8, = MIN ;Load MIN pointer in R8 Address LDR R5, [R8] ;Load MIN value from MIN pointer LOOP LDR R4 , [R2],#4 ;Loading value from array and updating(increment) the address of pointer CMP R4, R6 ;Compare R6 value with R3 IT GT ;If greater then exectue next instruction MOVGT R6,R4 ;if Array value greater than than value in R6 then move R6 value in R3 CMP R4, R5 ;compare R6 with R0 the minimum value IT LT ;if value is less than the minimum value then execute nex instruction MOVLT R5,R4 ;updat value of minimum number in R0

SUB R0,R0,#1       ;Decrement counter by one in every loop itration 
CMP R0, #0          ;Compare remaining counter value with zero
BNE LOOP            ;if value is not zero then jump to loop 

STR R5, [R8]         ;if counter become zero then store Min value at address MIN 
STR R6, [R3]         ;Store MAX value at address MAX

END

Answer 3

PRESERVE8
                THUMB
                AREA RESET, DATA, READONLY
                EXPORT __Vectors
__Vectors
                DCD 0x20001000   ;stack pointer value when initilized
                
                DCD Reset_Handler ;reset vector
                    
                ALIGN
                

        ;AREA DATA

MAXP    DCD MAX
Min     DCD MIN

N       DCD 12
NUM1    DCD 3,-7,2,-2,10,20,30,15,32,8,64,66
POINTER DCD NUM1
    
        AREA MYRAM, DATA, READWRITE
MAX     DCD 0   
MIN     DCD 0   
    
        AREA MYCODE,CODE, READONLY
        ENTRY
        EXPORT Reset_Handler

Reset_Handler   

Main
        LDR R1 , = POINTER  ;Load Pointer in R1
        LDR R2 ,[R1]        ;get address of array from pointer
        LDR R3 , = MAX     ;Load MAX pointer in R3
        LDR R6, [R3]        ;Get address of MAX from MAX pointer 
        LDR R7 , = N        ;Load counter Adress in R5
        LDR R0,[R7]         ;Load Value of Counter from counter address which is in R5
        LDR R8, = MIN       ;Load MIN pointer in R8 Address
        LDR R5, [R8]        ;Load MIN value from MIN pointer   
LOOP    
        LDR R4 , [R2],#4    ;Loading value from array and updating(increment) the address of pointer    
        CMP R4, R6          ;Compare R6 value with R3
        IT GT               ;If greater then exectue next instruction
        MOVGT R6,R4         ;if Array value greater than than value in R6 then move R6 value in R3
        CMP R4, R5          ;compare R6 with R0 the minimum value 
        IT LT               ;if value is less than the minimum value then execute nex instruction 
        MOVLT R5,R4         ;updat value of minimum number in R0 
        
        SUB R0,R0,#1       ;Decrement counter by one in every loop itration 
        CMP R0, #0          ;Compare remaining counter value with zero
        BNE LOOP            ;if value is not zero then jump to loop 
        
        STR R5, [R8]         ;if counter become zero then store Min value at address MIN 
        STR R6, [R3]         ;Store MAX value at address MAX
        
    END