RDA_UART_RXTX_BUFFER
val = rda_uart_read(port, RDA_UART_RXTX_BUFFER);
rda_uart_write(port, port->x_char, RDA_UART_RXTX_BUFFER);
rda_uart_write(port, ch, RDA_UART_RXTX_BUFFER);
val = rda_uart_read(port, RDA_UART_RXTX_BUFFER);
rda_uart_write(port, ch, RDA_UART_RXTX_BUFFER);