UART

Introduction

AIO-3566JD4 supports  UART3, UART5(disabled by default, Serial port
and SPI multiplexing), RS232(UART9), and RS485(UART0). Each UART has a
256-byte FIFO buffer for data receiving and sending. Among them:

UART3, UART5 are TTL level interfaces, RS232 are RS232 level
interfaces, and RS485 are RS485 level interfaces.

each sub-channel has 256 BYTE FIFO, which can be programmed according
to user requirements.

has a subserial port to receive FIFO timeout interrupts.

supports start bit error detection.

The serial interface diagram of the AIO-3566JD4 development board is
as follows:

UART

RS232

RS485

DTS configuration

File "kernel/arch/arm64/boot/dts/rockchip/rk3566-firefly-aiojd4.dtsi"
has the definition of spi to uart related nodes:

   &uart0 {
       status = "okay";
   };

   &uart3 {
       pinctrl-0 = <&uart3m0_xfer>;
       status = "okay";
   };

   &uart9 {
       pinctrl-0 = <&uart9m1_xfer>;
       status = "okay";
   };

Debug method

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

   RS485：/dev/ttyS0
   RS232：/dev/ttyS9
   UART3：/dev/ttyS3

Users can send and receive data to the serial port of the development
board by using the USB to serial port adapter of different host
according to different interfaces. For example, the debugging steps of
RS485 are as follows:

(1) Connected hardware

Connect A, B and GND pins of development board RS485 with A, B and GND
pins of host serial port adapter (USB to 485 to serial port module)
respectively.

(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 9600
   C-Kermit> set flow-control none
   C-Kermit> connect

/dev/ttyUSB0 is the device file for USB to serial port adapter.

(3) Send data

The device file for RS485 is "/dev/ttyS0". Run the following commands
on the device:

   echo firefly RS485 test... > /dev/ttyS0

The serial terminal in the host can receive a string: "firefly RS485
test... "

(4) Receive data

First run the following commands on the device:

   cat /dev/ttyS0

Then enter a string at the host's serial terminal: "Firefly RS485
test...", the device side can see the same string.