UART

Introduction

AIO-3562JQ supports UART, RS232 and RS485 interfaces

UART x 1

RS485 x 2

RS232 x 2

The UART is uart7, RS232 is converted from RK3562 uart8 and uart9,
RS485 is converted from uart5 and uart6.

The serial interface diagram of the AIO-3562JQ development board is as
follows:


DTS configuration

File "kernel/arch/arm64/boot/dts/rockchip/rk3562-firefly-aio-
3562jq.dtsi" has the definition of uart related nodes:

   /* RS485 */
   &uart5 {
       status = "okay";
       pinctrl-names = "default";
       pinctrl-0 = <&uart5m1_xfer>;
   };

   &uart6 {
       status = "okay";
       pinctrl-names = "default";
       pinctrl-0 = <&uart6m0_xfer>;
   };

   &uart7 {
       status = "okay";
       pinctrl-names = "default";
       pinctrl-0 = <&uart7m0_xfer>;
   };

   /* RS232 */
   &uart8 {
       status = "okay";
       pinctrl-names = "default";
       pinctrl-0 = <&uart8m0_xfer>;
   };

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

The nodes on the hardware interface corresponding to the software are:

   485A1/B1：   /dev/ttyS5
   485A2/B2：   /dev/ttyS6
   TX7/RX7：    /dev/ttyS7
   232TX1/RX1:  /dev/ttyS8
   232TX2/RX2:  /dev/ttyS9

Direction Control

RS485 needs additional GPIOs to control its direction(Send or
Receive). The last pin of GPIO extension chip PCA9555 controls
485A1/B1 direction, the penultimate pin controls 485A2/B2 direction.

First we need to check the PCA9555 GPIO pin index, run this command
and find out the index range is 496-511. This range may change because
of the modified kernel, please refer to the actual situation.

   root@firefly#: cat /sys/kernel/debug/gpio | grep 2-0021
   gpiochip5: GPIOs 496-511, parent: i2c/2-0021, 2-0021, can sleep:

So the last pin index is 511 and the penultimate pin index is 510.

Use /sys/class/gpio sub-system to operate GPIO:

   # export GPIO 511
   echo 511 > /sys/class/gpio/export

   # set the direction as output
   echo out > /sys/class/gpio/gpio511/direction

   # echo 1 means GPIO output logic 1 voltage, RS485 goes into send mode
   echo 1 > /sys/class/gpio/gpio511/value

   # echo 0 means GPIO output logic 0 voltage, RS485 gose into receive mode
   echo 0 > /sys/class/gpio/gpio511/value

   # operate another GPIO with the same way, just change the index.

You can also read/write files in codes to achieve the same purpose
instead of using shell.