CR_MTX
if ((cr & CR_MTX) && (sr & SR_RXAK)) {
cr = sc->sc_enable_mask | CR_MTX | CR_MSTA;
I2C_WRITE(I2CCR, sc->sc_enable_mask | CR_MTX | CR_MSTA);
KASSERT(cr & CR_MTX);
cr &= ~CR_MTX; /* clear transmit flags */