Question

2. a)Write the ARM ALP conditional code snippet for the following statements written in C-language. Assume R1 to Rn as06 variables Let R1, R2, R3 contain the starting addresses of arrays X, Y and Z respectively Use Register R4 for variable i. Display appropriate messages. While (i+10) else Z[i] XiYi; b)i Write a program to display a message "This is an examination Question" on the screen using 06 a function sub program Note the following Address of the string to be passed as a register parameter to the function. Display one character at a time. Use appropriate interrupt number to display a character Write the equivalent code snippet to display the above message using a single instruction in the subroutine by calling appropriate routine

Answer 1

Assuming we have a C code like this :

void fillZ() {
    int x[10];
    int y[10];
    int z[10];
    int i=0;
    while(i++<=10){
        if(x[i]==y[i])
            z[i]=x[i]*y[i];
        else
            z[i]=x[i]+y[i];
    }  
}

Then the ARM gcc 8.2 (WinCE) code for the above will be below :

fillZ():
        str     fp, [sp, #-4]!
        add     fp, sp, #0
        sub     sp, sp, #124
        mov     r3, #0
        str     r3, [fp, #-4]
.L5:
        ldr     r3, [fp, #-4] //start while(i++<=10){
        add     r2, r3, #1
        str     r2, [fp, #-4]
        cmp     r3, #10
        movle   r3, #1
        movgt   r3, #0
        and     r3, r3, #255
        cmp     r3, #0
        beq     .L6                //end while(i++<=10){
        ldr     r3, [fp, #-4]        //start if(x[i]==y[i])
        lsl     r3, r3, #2
        add     r3, fp, r3
        ldr     r2, [r3, #-44]
        ldr     r3, [fp, #-4]
        lsl     r3, r3, #2
        add     r3, fp, r3
        ldr     r3, [r3, #-84]
        cmp     r2, r3
        bne     .L3                //end if(x[i]==y[i])
        ldr     r3, [fp, #-4] //start z[i]=x[i]*y[i];
        lsl     r3, r3, #2
        add     r3, fp, r3
        ldr     r1, [r3, #-44]
        ldr     r3, [fp, #-4]
        lsl     r3, r3, #2
        add     r3, fp, r3
        ldr     r3, [r3, #-84]
        mul     r2, r3, r1
        ldr     r3, [fp, #-4]
        lsl     r3, r3, #2
        add     r3, fp, r3
        str     r2, [r3, #-124]
        b       .L5            //end z[i]=x[i]*y[i];
.L3:
        ldr     r3, [fp, #-4] //start else z[i]=x[i]+y[i];
        lsl     r3, r3, #2
        add     r3, fp, r3
        ldr     r2, [r3, #-44]
        ldr     r3, [fp, #-4]
        lsl     r3, r3, #2
        add     r3, fp, r3
        ldr     r3, [r3, #-84]
        add     r2, r2, r3
        ldr     r3, [fp, #-4]
        lsl     r3, r3, #2
        add     r3, fp, r3
        str     r2, [r3, #-124] //end else z[i]=x[i]+y[i];
        b       .L5                 
.L6:
        nop
        add     sp, fp, #0
        ldr     fp, [sp], #4
        mov     pc, lr

Please note, the comments(//) are used for understanding purpose.