TX_FIFO_INTS
vt8500_port->ier &= ~TX_FIFO_INTS;
vt8500_port->ier &= ~TX_FIFO_INTS;
vt8500_port->ier |= TX_FIFO_INTS;
if (isr & TX_FIFO_INTS)
vt8500_port->ier = RX_FIFO_INTS | TX_FIFO_INTS;