UART

Introduction

In order to facilitate user development, roc-3399-pc-plus introduces
two channels such as UART0 and UART4 (reuse with SPI1) on the double-
row extension interface of the board.

UART0 and UART4 are TTL level interfaces.

UART0 UART4 maximum support baud rate 691200.

Each subchannel has a 256-byte FIFO that can receive/send
independently. FIFO interrupt can be programmed to trigger according
to user needs

With a sub-serial port to receive FIFO timeout interrupt

Support initial bit error detection

DTS

In the case of UART0 configuration, the device tree opens UART0 nodes
by default.

   &uart4 {              
       status = "okay";
   };

Debug method

After the serial port is configured, the corresponding nodes of the
hardware interface on the software are:

   UART0：/dev/ttyS0

(1) The connection of hardware

Connect the TX of UART0 with the RX port and the RX and TX of the USB
adapter.

(2) Open the serial terminal of the host

Open kermit at the terminal and set the baud rate:

   $ sudo kermit
   C-Kermit> set line /dev/ttyUSB0
   C-Kermit> set speed 115200
   C-Kermit> set flow-control none
   C-Kermit> connect

The /dev/ttyUSB0 is the device file for the USB adapter

(3) Send data

The device file for UART0 is /dev/ttys0.Run the following commands on
the device:

   echo firefly test... > /dev/ttyS0

The serial terminal in the host receives the string "firefly test..."

(4) Receive data

First run the following command on the device:

   cat /dev/ttyS0

Then enter the string "firefly test...", the device side will see the
same string.