you are right, this is one of those that work beatifully till a change of buffer size.

With the loopcount fixed, I would do this

$IF ((LOW LOOPCOUNT) = 0)
mov r6,#(HIGH LOOPCOUNT)
$ELSE
mov r6,#((HIGH LOOPCOUNT) +1)
$ENDIF
mov r7, #LOW LOOPCOUNT

I stand corrected,

Erik