RXBUSY
sdd->state &= ~RXBUSY;
if (!(sdd->state & RXBUSY))
sdd->state |= RXBUSY;
sdd->state &= ~RXBUSY;
sdd->state &= ~RXBUSY;
(sdd->state & RXBUSY) ? 'f' : 'p',
if (xfer->rx_buf && (sdd->state & RXBUSY)) {