my copy function

pico_my_copy.s

.syntax unified      
.section .text
.thumb_func 
.global my_cpy
my_cpy:
    push {r4, lr}    @ push r4 and lr onto the stack
    movs r4, #0
loop:
    ldrb r3, [r1, r4] @ load byte from r1 + r4 into r3
    strb r3, [r0, r4] @ store byte from r3 into r0 + r4
    adds r4, r4, #1 @ increment r4
    cmp r4, r2     @ compare r4 with 10
    bne loop         @ branch to loop if r2 is not zero
    pop {r4, pc}     @ pop r4 and pc from the stack