UART

Introduction

AIO-1126BQ38 supports UART3 and UART5 interfaces. UART3 is used as
RS485, and UART5 is used as RS232.

DTS Configuration

File path: "kernel-6.1/arch/arm64/boot/dts/rockchip/rv1126b-firefly-
aio-1126bq38.dts"

   #ifdef FF_UART3
   &uart3 {
           pinctrl-0 = <&uart3m1_xfer_pins>;
           status = "okay";
   };
   #endif

   #ifdef FF_UART5
   &uart5 {
           pinctrl-0 = <&uart5m1_xfer_pins>;
           status = "okay";
   };
   #endif

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

   UART3:  /dev/ttyS3	RS485
   UART5:  /dev/ttyS5	RS232

Send And Receive Verification

Users can use different host USB-to-serial adapters to send and
receive data to and from the development board's serial port,
depending on the interface. For example, the debugging steps for UART5
are as follows:

(1) Development board sends, host receives

   # Host terminal executes first:
   # /dev/ttyUSB0 is the node for the host serial port adapter; modify it according to your actual setup. Set the baud rate to 115200.
   stty -F /dev/ttyUSB0 115200 cs8 -cstopb -parenb -icanon -echo
   cat /dev/ttyUSB0

   # Development board debug serial port terminal executes:
   # /dev/ttyS5 is the UART5 node. The baud rate is set to 115200.
   stty -F /dev/ttyS5 115200 cs8 -cstopb -parenb -icanon -echo
   echo "firefly UART5 test..." > /dev/ttyS5

The host terminal can receive the string "firefly UART5 test..."

(2) Host sends, development board receives

   # Development board debug serial port terminal executes first:
   # /dev/ttyS5 is the UART5 node. The baud rate is set to 115200.
   stty -F /dev/ttyS5 115200 cs8 -cstopb -parenb -icanon -echo
   cat /dev/ttyS5

   # Host terminal execution:
   # /dev/ttyUSB0 is the node for the host serial port adapter; modify it according to your actual setup. Set the baud rate to 115200.
   stty -F /dev/ttyUSB0 115200 cs8 -cstopb -parenb -icanon -echo
   echo "firefly UART5 test..." > /dev/ttyUSB0

The development board debugging serial port terminal can receive the
string "firefly UART5 test..."

RS485

GPIO0_B0 is used as an RS485 control pin for transmitting and
receiving. Pulling this pin high enables transmitting, and pulling it
low enables receiving. Users can operate it through the
"/sys/class/gpio" subsystem.

Below is the configuration of GPIO0_B0 for output:

   echo 8 > /sys/class/gpio/export
   echo out > /sys/class/gpio/gpio8/direction

Pulling GPIO0_B0 high, RS485 transmitting: echo 1 >
/sys/class/gpio/gpio8/value

Pulling GPIO0_B0 low, RS485 receiving: echo 0 >
/sys/class/gpio/gpio8/value