First program in ARM assembly - unable to write to file

[fatalaccidents]

Hello all,

Let me first state that this is my first program written in ARM, so please excuse that it might seem a bit chaotic. Also, I want to state that this is a homework assignment for an assembly class. I am supposed to read in an input file, only print out ascii chars space, A-Z, and a-z (toUpper as A-Z) as well as Carriage Return Line Feeds and a CRLF as the 1A (EOF char). Going through the debugger it seems to be working as intended, but it isn't writing to the outfile :( If anyone can point out the error to me I would be very grateful. I know there is a lot of optimization that can be done to make the code smaller, but none of that matters really if I can't get the file to write. Thank you very much for your time.

;----------------------------------
; Software Interrupt values
;----------------------------------
         .equ SWI_Open,  0x66     ;Open  a file
         .equ SWI_Close, 0x68     ;Close a file
         .equ SWI_PrStr, 0x69     ;Write a null-ending string
         .equ SWI_RdStr, 0x6a     ;Read a string and terminate with null char
         .equ SWI_Exit,  0x11     ;Stop execution
;----------------------------------

         .global   _start
         .text

_start:
         ldr  r0, =InFileName     ;r0 points to the file name
         ldr  r1, =0              ;r1 = 0 specifies the file is input
         swi  SWI_Open            ;open the file ... r0 will be the file handle
         ldr  r1, =InFileHandle   ;r1 points to handle location
         str  r0, [r1]            ;store the file handle

         ldr  r0, =OutFileHandle  ;r0 points to the output file handle
         ldr  r1, =1
         swi  SWI_Open
         ldr  r1, =OutFileHandle
         str  r0, [r1]

_read:        
         ldr  r0, =InFileHandle
         ldr  r0, [r0]
         ldr  r1, =InString
         ldr  r2, =80
         swi  SWI_RdStr

         ldr  r0, =InString       ;r0 points to the input  string
         ldr  r1, =OutString      ;r1 points to the output string
_loop:                            ;
         ldrb r2, [r0], #1        ;get the next input byte
                                  ; then increment the input pointer
         b    _testZ
_cap:
         sub  r2,r2,#32           ; subtract 32 to make it uppercase ascii
_testZ:
         cmp  r2,#90               ;see if it is above ascii "Z"
         bgt  _cap
_testA:
         cmp  r2,#65               ; see if it is above ascii "A"
         bgt  _store               ; if it is > "A" and <="Z" it must be A-Z
_testch:
         cmp  r2,#32              ;it is a space 
         beq  _store
_testeof:
         cmp  r2,#26               ;eof character - go to write
         beq  _write
_testeol:
         cmp  r2,#0                ; eol character
         bne  _loop
_store: 
         strb r2,[r1],#1            ; store the byte and inc pointer by 1
         cmp  r2,#0                 ; if it's the end of the line fall through to write
         bne  _loop
_write:   
         ldr  r0, =OutFileHandle
         ldr  r0, [r0]
         ldr  r1, =OutString 
         swi  SWI_PrStr           ;write the null terminated string  
         ldr  r1, =CRLF
         swi  SWI_PrStr
         cmp  r2,#0x1A
         bne  _read 
_exit:                            
         ldr  r0, =InFileHandle   ;r0 points to the input  file handle
         ldr  r0, [r0]            ;r0 has the input file handle
         swi  SWI_Close           ;close the file
                                  ;
         ldr  r0, =OutFileHandle  ;r0 points to the output file handle
         ldr  r0, [r0]            ;r0 has the output file handle
         swi  SWI_Close           ;close the file
                                  ;
         swi  SWI_Exit            ;terminate the program

         .data
;----------------------------------
InFileHandle:  .skip 4            ;4 byte field to hold the input  file handle
OutFileHandle: .skip 4            ;4 byte field to hold the output file handle
                                  ;
InFileName:    .asciz "KEY.IN"   ;Input  file name, null terminated

InString:      .skip 128          ;reserve a 128 byte string for input
OutString:     .skip 128          ;reserve a 128 byte string for output
                                  ;
CRLF:          .byte 13, 10, 0    ;CR LF
                                  ;
OutFileName:   .asciz "FILE.OUT"  ;Output file name, null terminated
;----------------------------------
         .end

[turboscrew]

Are you sure your output string is null-terminated?

You seem to be using armsim?

[fatalaccidents]

Yes, I'm using armsim. I'm not sure how to tell if it is being null terminated for sure or not. Could that be the problem here? Is there any way that I could check to be for sure?

[fatalaccidents]

Line 21 should be OutFileName and not Handle. That being said if anyone sees any ways to make the code better I would gladly take your advice. Thanks turbo for the response.

[turboscrew]

Line 21 should be OutFileName and not Handle.

Escaped my eyes too. Good that you noticed it.

The string is null-terminated if you add null at the end of it.

    _testeof:
             cmp  r2,#26               ;eof character - go to write
             beq  _write
    _testeol:
             cmp  r2,#0                ; eol character
             bne  _loop
    _store: 
             strb r2,[r1],#1            ; store the byte and inc pointer by 1
             cmp  r2,#0                 ; if it's the end of the line fall through to write
             bne  _loop
    _write:  
             ; if EOF, you come here without storing NUL
             ; at the end of output string. If there was a NUL, you would have
             ; come here before encountering EOF.
             ldr  r0, =OutFileHandle

[Rajan_7]

Yes.... You are right that line 21 should be OutFileName and not Handle.