UART

This guide will show you how to use the UART channels on the phyCORE-i.MX8X development kit Carrier Board.

../_images/pcm-065_uart.png

Note

Please note that the PCB version 1491.1 has a different location for the X59 header. In more recent revisions of the carrier board (1491.2) the header was relocated to be closer to the center of the board.

../_images/pcm-065_uart-x59-1491-2-header-correction.jpg

The UART channels correspond to the following connectors and system paths.

UART Channels

Hardware Interface

Connector

Sysfs Path

UART0

X51 (Micro USB)

/dev/ttyLP0

UART1

X99 (DB9 - RS232)

/dev/ttyLP1

UART2

X59 (General Purpose Header)

/dev/ttyLP2

Note

All of the UART interfaces have muxing options available. Please refer to our Booting Essentials page for more information.

The FTDI device connected to UART0 also provides access to the M40_UART0 through the same connector (not supported in i.MX8X ALPHA1 release). The connector X99 allows for the use of UART1 a General Purpose (GP) UART (ttyLP1), which is translated to RS-232 levels. Note this UART is muxed with BT functionality. The connector X59 allows for the use of UART2 a General Purpose (GP) UART (ttyLP2). Note this UART is muxed with the CAN interface and an overlay must be applied in U-Boot.

Requirements

Hardware Setup

UART0 (Debug)

  • This is the default communication interface with the development kit.

../_images/pcm-065_uart0.png

UART1

  • Connect the RS-232 to USB adapter cable between the Host PC and X99.

    ../_images/pcm-065_uart1.png

UART2

Note

This is not a standard UART and requires the use of female to female jumper wires.

Additionally, UART2 is muxed with the CAN interface through Switch S6 on the carrier board.

  • Change S6 to UART2

    ../_images/pcm-065_uart2.png

  • Using female to female jumper wires, connect between the pins of connector X59 and the RS-232 to USB adapter cable using the table and images below. Connect the other end of the RS-232 cable to your host PC.

TTL Cable and X59 Header Signals

GND

Black Connecter

Pin 9 (X59)

TXD

Orange Connecter

Pin 6 (X59)

RXD

Yellow Connecter

Pin 5 (X59)
../_images/pcm-065_uart2_x59-pin-out.png ../_images/pcm-065_uart2-x59-ttl.png

  • With the default console (UART0) connected, power on the kit and stop in U-Boot.

  • Apply the device tree overlay that enables the UART2 interface. Then boot into Linux.

    Target (U-boot)
    setenv overlay_files phytec-imx8qxp-uart2.dtbo
boot

UART1 & UART2 Communication

  • Open a terminal on your host PC, choose the COM port associated with the UART channel and make sure it has the following port settings.

    COM Port Settings

    Baud Rate

    115200

    Data

    8-bit

    Parity

    none

    Stop Bit

    1

    Flow Control

    none

  • In Linux setup which UART channel you would like to use (/dev/ttyLP1 or /dev/ttyLP2) and then echo a test message through the UART channel to your other opened terminal.

    Target (Linux)
    stty -F /dev/ttyLP1 115200
echo 'Testing GP UART!' > /dev/ttyLP1
Expected Output
Testing GP UART!

  • Now set up your default UART0 channel to listen for data from the UART channel you are using (/dev/ttyLP1 or /dev/ttyLP2).

    Target (Linux)
    cat /dev/ttyLP1

  • Type something into your secondary UART console and hit enter.

    UART1 or UART2 Console Input
    Testing!
    Expected Output
    Testing!

  • Use Ctrl+C to stop UART0 from listening for new data.

Enabling UART1 or UART2 as an Additional Serial Console

  • From the default UART channel (UART0), use system control to enable and start the desired UART channel (/dev/ttyLP1 or /dev/ttyLP2).

    Note

    Note that this setting will persist between boots but will not affect the default console in U-Boot and Linux.

  • Enable your desired UART channel in system control.

    Target (Linux)
    systemctl enable [email protected]
    Expected Output
    Created symlink /etc/systemd/system/getty.target.wants/[email protected] -> /lib/systemd/system/[email protected].

  • Start the service for the UART channel.

    Target (Linux)
    systemctl start [email protected]

  • You should now see the login prompt on the console linked to your desired UART channel. Type “root” to login.

    UART1 or UART2 Console Output
    imx8x-phycore-kit login:

  • Test the console input/output using the echo command.

    Target (Linux)
    echo "hello from ttyLP0" > /dev/ttyLP1
    UART1 or UART2 Console Output
    hello from ttyLP0
    UART1 or UART2 Console Input
    echo "hello from ttyLP1" > /dev/ttyLP0
    Expected Output (Linux)
    hello from ttyLP1

  • Use the following commands to disable the new serial console.

    Target (UART1 Linux Console)
    systemctl stop [email protected]
systemctl disable [email protected]