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);