Question

How can I print out a 2D array in ARM assembly?
I’m trying to take each row and then turn it into a null terminated string but it only prints out the first number. How can I move to the next number?

I was told this:To print the array it’s best to write a subroutine that loops through the array printing it one element at a time. printf only takes one argument and as in assembly language an array is just a load of numbers printf will only print the first one. Alternately you could write a subroutine that makes the board into a null terminated string. In either case the subroutine can both print the board and format it nicely.

But I only understand how to do it this way:

    AREA    Countdown, CODE, READONLY
IMPORT  main
IMPORT  getkey
IMPORT  sendchar
IMPORT  printf
EXPORT  start

start

    LDR R3, = teststr
    LDR R4, = array
wh1     LDRB R0, [R4]
    CMP R0, #0
    BEQ stop
    ADD R0, R0, #0X30
    STRB R0, [R3]
    ADD R3, R3, #1
    ADD R4, R4, #1  
    B wh1



stop B stop

AREA    Strings, DATA, READWRITE


teststr DCB "",0


array DCD 6, 3, 8, 2, 5, 2, 9, 1
     DCD 3, 7, 2, 8, 5, 7, 2, 6
     DCD 2, 4, 7, 4, 2, 6, 7, 4
     DCD 1, 9, 3, 2, 9, 5, 6, 8
     DCD 7, 5, 3, 7, 5, 8, 2, 1




END                 

Answer 1

Your program has several problems associated with it. One is that you’re not reserving space for the destination string, so you will be writing on unallocated memory. The other is that you’re not outputting a newline character.

ROW_LENGTH equ 8

start

    ldr r3, = teststr
    ldr r4, = array
    mov r2, #ROW_LENGTH-1   ; numbers displayed per row
wh1 ldrb r0, [r4],#1
    orrs r0,r0,#0x30  ; add '0' to our digit
    bmi  end_of_data  ; end of source data
    strb r0,[r3],#1
    subs r2,r2,#1
    moveq r1,#0xd ; carriage return
    streqb r1,[r3],#1
    moveq r1,#0xa ; line feed
    streqb r1,[r3],#1
    moveq r2,#ROW_LENGTH-1  ; reset row counter
    b wh1
end_of_data mov r0,#0   ; store string terminator
    strb r0,[r3]
    ; your return address in LR will no longer be preserved after the call to printf
    ; so you need to push/pop it to return to the caller
    ldr r0,=teststr   ; print the output
    bl  printf

teststr DCB "                                                                      ",0


array DCD 6, 3, 8, 2, 5, 2, 9, 1
     DCD 3, 7, 2, 8, 5, 7, 2, 6
     DCD 2, 4, 7, 4, 2, 6, 7, 4
     DCD 1, 9, 3, 2, 9, 5, 6, 8
     DCD 7, 5, 3, 7, 5, 8, 2, 1
     DCD -1       ; array terminator