MBOX4
out_ptr = sbus_readw(qpti->qregs + MBOX4);
sbus_writew(in_ptr, qpti->qregs + MBOX4);
case 5: sbus_writew(param[4], qpti->qregs + MBOX4);
case 5: param[4] = sbus_readw(qpti->qregs + MBOX4);
sbus_writew(in_ptr, qpti->qregs + MBOX4);