UART

Introduction

Face-RK3399 is equipped with three extended serial ports: UART1, UART2, RS485. Each UART has a 256 byte FIFO buffer for data reception and transmission:

• UART1 and UART2 is TTL interface, RS485 is RS485 interface.

• Uart1 and UART2 supports a maximum baud rate of 691200. RS485 is generally only supported below 115200 under the influence of communication media.

• Each sub channel has an independent 256 byte FIFO, and the interrupt of FIFO can be programmed according to the user’s requirements.

• With sub serial port to receive FIFO timeout interrupt.

• Support start bit error detection.

• The RS485 port can be reused as the Wiegand protocol port

The nodes on the software corresponding to the device interface are respectively:

RS485: /dev/ttyS4
UART2: /dev/ttyS0
UART1: /dev/ttyS3

The serial of Face-RK3399 is as follow:

The following is the RS485 connection diagram. VCC and GND can be provided through USB.

RS485 Debugging

DTS configuration

The definition of uart to RS485 node in kernel/arch/arm64/boot/dts/rockchip/rk3399.dtsi:

uart4: serial@ff370000 {
        compatible = "rockchip,rk3399-uart", "snps,dw-apb-uart";
        reg = <0x0 0xff370000 0x0 0x100>;
        clocks = <&pmucru SCLK_UART4_PMU>, <&pmucru PCLK_UART4_PMU>;
        clock-names = "baudclk", "apb_pclk";
        interrupts = <GIC_SPI 102 IRQ_TYPE_LEVEL_HIGH 0>;
        reg-shift = <2>;
        reg-io-width = <4>;
        pinctrl-names = "default";
        pinctrl-0 = <&uart4_xfer>;
        status = "disabled";
};

Enabled this node in kernel/arch/arm64/boot/dts/rockchip/rk3399-firefly-face.dtsi:

&uart4 {
-    status = "disable";
+    status = "okay";
};

Connection

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

1. Run the following command on the PC to receive data:

   cat /dev/ttyUSB1
   

2. Run the following command on the PC to send data:

   echo 1 > /sys/devices/platform/wiegand-gpio/mode_switch # Switch to  RS485 interface function
   echo firefly RS485 test... > /dev/ttyS4
   

Then you can receive the same string Firefly RS485 test... at the other end of the serial connection.

V2 UART

Serial interface has changed in Face-RK3399 V2.

The nodes on the software corresponding to the device interface are respectively:

RS485: /dev/ttyS4
UART: /dev/ttyS0
RS232: /dev/ttyS3

One of the TTL serial ports becomes RS232:

Note: UART (/dev/ttys0) and Bluetooth interface are reused, and only one of them can be used at the same time