MTTYF_STOP
SET(mp->mp_flags, MTTYF_STOP);
if( !ISSET(mtty->mp_flags, MTTYF_STOP) ) {
if( mtty->mp_txc == 0 || ISSET(mtty->mp_flags, MTTYF_STOP) ) {
CLR(mtty->mp_flags, MTTYF_STOP);