ARM Flow Control Instructions

Examples

Example 1

    PRESERVE8
    THUMB
    AREA  RESET, DATA, READONLY
    EXPORT __Vectors
__Vectors
    DCD 0x20001000
    DCD Reset_Handler
    ALIGN
string1 DCB "Hello world!",0
    AREA MYCODE, CODE, READONLY
    ENTRY
    EXPORT Reset_Handler
Reset_Handler
    LDR R0, = string1 ; Load the address of string1 into the register R0
    MOV R1, #0 ; Initialize the counter counting the length of string1
loopCount
    LDRB R2, [R0] ; Load the character from the address R0 contains
    CMP R2, #0
    BEQ countDone   ; If it is zero...remember null terminated...
                    ; You are done with the string. The length is in R1.
    ADD R0, #1 ; Otherwise, increment index to the next character
    ADD R1, #1 ; increment the counter for length
    B loopCount
countDone
STOP
    B STOP
    END

Example 2

    PRESERVE8
    THUMB
    AREA  RESET, DATA, READONLY
    EXPORT __Vectors
__Vectors
    DCD 0x20001000
    DCD Reset_Handler
    ALIGN
SUMP DCD SUM
N DCD 5
    AREA MYDATA, DATA, READWRITE
SUM DCD 0
    AREA MYCODE, CODE, READONLY
    ENTRY
    EXPORT Reset_Handler
Reset_Handler
    LDR R1, N ;Load count into R1
    MOV R0, #0 ;Clear accumulator R0
LOOP
    ADD R0, R0, R1 ;Add number into R0
    SUBS R1, R1, #1 ;Decrement loop counter R1
    BGT LOOP ;Branch back if not done
    LDR R3, SUMP ;Load address of SUM to R3
    STR R0, [R3] ;Store SUM
    LDR R4, [R3]
STOP
    B STOP
    END

Lab Work

Write an ARM Assembly progrom to count the number of vowels/non-vowels in a string.

Note: The string should be stored in the memory and the program should read the string from the memory. "ARM Assembly language", 0

Criteria

1. Use R1 to hold the address of the string.
2. Use R2 to be the counter for the number of vowels.
3. Use R3 to be the counter for the number of non-vowels.