UART

Introduction

AIO-3588JD4 has one RS232 interfaces and one RS485 interface

The serial interface diagram of the AIO-3588JD4 development board is
as follows:


DTS configuration

The RS232 interface of the development board is extended by the main
control UART1, and the RS485 interface is extended by the main control
UART6.

File path "kernel/arch/arm64/boot/dts/rockchip/aio-3588jd4.dtsi"

   /* RS485 */
   &uart6{
           pinctrl-0 = <&uart6m1_xfer>;
           status = "okay";
   };

   /* RS232 */
   &uart1{
           pinctrl-0 = <&uart1m1_xfer>;
           status = "okay";
   };

After configuring the serial port, the nodes on the software
corresponding to the hardware interface are:

   RS232:   /dev/ttyS1
   RS485：  /dev/ttyS6

Send and receive verification

Users can use different host's USB-to-serial adapters to send and
receive data to the serial port of the development board according to
different interfaces. For example, the debugging steps of RS485 are as
follows(AIO-3588JD4 RS485 is half-duplex and requires gpio to control
transmission and reception):

(1) Development board sends, host receives

   # The host terminal executes first:
   # /dev/ttyUSB0 is the node of the host serial adapter, modify it according to the actual situation
   cat /dev/ttyUSB0

   # The development board debugs the serial port terminal and executes:
   # /dev/ttyS1 is the RS485 node
   echo "firefly RS485 test..." > /dev/ttyS1

The host terminal will receive the string "firefly RS485 test..."

(2) Host sends, development board receives

   echo 34 > /sys/class/gpio/export
   echo out > /sys/class/gpio/gpio34/direction

   # To debug the serial terminal on the development board, execute first:
   # /dev/ttyS1 is the RS485 node
   echo 0 > /sys/class/gpio/gpio34/value
   busybox  stty -echo -F /dev/ttyS1       # turn off echo
   cat /dev/ttyS1

   # The host terminal executes:
   # /dev/ttyUSB0 is the node of the host serial adapter, modify it according to the actual situation
   echo 1 > /sys/class/gpio/gpio34/value
   echo "firefly RS485 test..." > /dev/ttyUSB0

The development board debugs the serial terminal to receive the string
"firefly RS485 test..."