.db video_start 0xF37F
.db msg "Hello, world!", 0

load r1, [msg] ; Because the lod* instructions can't load an address
               ; from anything but a register, this becomes laa r1, [msg]

;Routine: string_length
;In: String address in r1
;Out: Length in R2

string_length:
loadb r3, [r1] ; Load the byte from the address in R1, into R3
load r2, 0 ; String length
cmp r3, 0 ; Is R3 a null byte?
je end
inc r2

start:
    inc r1 ; next char
    loadb r3, [r1] ; Load the next character byte into R3
    cmp r3, 0 ; Null byte?
    je end
    inc r2 ; Nope, increment the length counter
    jmp start

end:
ret