IEVENT_BSY
sc->sc_imask |= IEVENT_RXF | IEVENT_BSY;
if (ievent & IEVENT_BSY) {
sc->sc_imask &= ~IEVENT_BSY;
imask |= IEVENT_BSY;
sc->sc_imask |= IEVENT_RXF | IEVENT_BSY | IEVENT_RXC;