MLB_USIO_REG_FBYTE
max_count = readw(port->membase + MLB_USIO_REG_FBYTE) >> 8;
writew(0, port->membase + MLB_USIO_REG_FBYTE);
writew(BIT(12), port->membase + MLB_USIO_REG_FBYTE);
writew(0, port->membase + MLB_USIO_REG_FBYTE);
writew(BIT(12), port->membase + MLB_USIO_REG_FBYTE);
(readw(port->membase + MLB_USIO_REG_FBYTE) & 0xff);