Delay of about 20.5 milliseconds

The code below gives a delay of about 20 milliseconds.

;
; AssemblerApplication2.asm
;
; Created: 10/05/2018 10:05:11 AM
; Author : peterb
;


; Replace with your application code
start:
    clr r16
ldi r18,$ff
loop: dec r18
nop
nop
brne loop
dec r16
brne loop
 stop:   rjmp stop