do_fine_delay:
                MOV     A,R7            ; Get input parameter
                clr     c
                subb    a,#xxx          ; xxx= overhead cycles
                jnc     luvverly        ; may need to check OV as well ??? just trying to be fast
                lcall   Crash           ; whatever your coding error catcher is called
luvverly:
                CPL     A               ; Take two's compliment
                INC     A
                MOV     DPTR,#NOPS      ; Point DPTR at the NOP table
                JMP     @A+DPTR         ; Jump into table