Connect to the Dev Board Mini's serial console

Although we recommend that you access the shell terminal with MDT, some situations require direct connection with the serial console. So this page shows you how to do that with the Dev Board Mini.

You'll need the following items:

  • Coral Dev Board Mini
  • Linux, Windows 10, or macOS computer
  • USB-to-TTL serial cable (it must support 3.3 V logic levels, such as this one by Adafruit)
  • 2 A / 5 V USB-C power supply
Note: If you're on Linux or Mac and your board is fully booted, you can instead open the serial console using the USB OTG port.
Figure 1. The ground and UART pins connected to 40-pin header

Connect with Linux

You can connect to the Dev Board Mini's serial console from Linux as follows:

  1. First make sure your Linux user account is in the plugdev and dialout system groups by running this command:

    sudo usermod -aG plugdev,dialout <username>

    Then reboot your computer for the new groups to take effect.

  2. Connect the USB-to-TTL serial cable to your computer and the board, as shown in figure 1:

    • Pin 6 is ground
    • Pin 8 is UART TX
    • Pin 10 is UART RX

    Warning: Do not connect the power wire (if provided). Doing so allows power to flow between the USB power and your computer, which degrades the USB power supply's ability to power the board, and can potentially damage to your hardware.

  3. Connect the board to power using the USB power port, and firmly press the power button to boot the board.

  4. Determine the USB-to-TTL cable's device name by running this command on your Linux computer:

    dmesg | grep ttyUSB

    You should see results such as this:

    [ 6437.706335] usb 2-13.1: cp210x converter now attached to ttyUSB0

    If you don't see anything like this, double-check your USB cable is connected.

  5. Then connect with this command (using the name of the device listed in the previous step):

    screen /dev/ttyUSB0 115200

    Help! If screen prints Cannot access line '/dev/ttyUSB0', then your Linux user account is not in the plugdev and/or dialout system group. Ask your system admin to add your account to both groups, and then restart your computer for it to take effect.

    If you see [screen is terminating], it might also be due to the system groups, or there's something else wrong with screen—ensure all screen sessions are closed (type screen -ls to see open sessions), unplug the USB cable from the Dev Board, and then try again.

  6. If the screen terminal is blank, press Enter and then you should see the login prompt appear.

    The default username and password are both "mendel".

When you're done, kill the screen session by pressing CTRL+A, K, and then Y to confirm.

Connect with Windows

You can connect to the Dev Board Mini's serial console from a Windows 10 computer as follows:

  1. Connect the USB-to-TTL serial cable to your computer and the board, as shown in figure 1:

    • Pin 6 is ground
    • Pin 8 is UART TX
    • Pin 10 is UART RX

    Warning: Do not connect the power wire (if provided). Doing so allows power to flow between the USB power and your computer, which degrades the USB power supply's ability to power the board, and can potentially damage to your hardware.

  2. Connect the board to power using the USB power port, and firmly press the power button to boot the board.

  3. On your Windows computer, open Device Manager and find the cable's COM port.

    Within a minute of connecting the USB cable, Windows should automatically install the necessary driver. So if you expand Ports (COM & LPT), you should see a device corresponding to your serial cable (for example, "Silicon Labs CP210x USB to UART Bridge" or "Prolific USB-to-Serial Comm Port").

    Take note of the COM port for the serial cable (such as "COM3"). You'll use it in the next step.

    If Windows cannot identify the USB cable, it should instead be listed under Other devices. Right-click on the device and select Update driver to find the appropriate device driver.

  4. Open PuTTY or another serial console app and start a serial console connection with the above COM port, using a baud rate of 115200. For example, if using PuTTY:

    1. Select Session in the left pane.

    2. For the Connection type, select Serial.

    3. Enter the COM port ("COM3") for Serial line, and enter "115200" for Speed.

    4. Then click Open.

  5. If the screen terminal is blank, press Enter and then you should see the login prompt appear.

    The default username and password are both "mendel".

Connect with macOS

You can connect to the Dev Board Mini's serial console from a macOS computer as follows:

  1. Connect the USB-to-TTL serial cable to your computer and the board, as shown in figure 1:

    • Pin 6 is ground
    • Pin 8 is UART TX
    • Pin 10 is UART RX

    Warning: Do not connect the power wire (if provided). Doing so allows power to flow between the USB power and your computer, which degrades the USB power supply's ability to power the board, and can potentially damage to your hardware.

  2. Connect the board to power using the USB power port, and firmly press the power button to boot the board.

  3. Determine the USB-to-TTL cable's device name by running this command from your Mac terminal:

    ls /dev/cu*

    You should see a device with the name usbserial (such as /dev/cu.usbserial-0001). If not, you might need to install a driver provided by the cable manufacturer.

    You'll use this usbserial device name in the next step. However, if you've already installed a driver for the chipset in your serial cable (such as the CP210x VCP driver required for the Dev Board), then you should use a different device name that appears (such as cu.SLAB_USBtoUART for CP210x devices/cables).

  4. Connect to the serial console using screen and a baud rate of 115200. For example:

    screen /dev/cu.usbserial-0001 115200

    Your device name might be different, but the baud rate is always 115200.

  5. If the screen terminal is blank, press Enter and then you should see the login prompt appear.

    The default username and password are both "mendel".

When you're done, kill the screen session by pressing CTRL+A, K, and then Y to confirm.

Connect over USB OTG

You can also connect to the serial console without the USB-to-TTL cable, but only if your host computer is Linux or Mac, and your board is fully booted up.

Note: The USB OTG port provides serial console access only when Mendel is booted up. As such, this approach does not provide access to the kernel boot logs or the u-boot command prompt. If you want those things or your board fails to boot Mendel, you must use the USB-to-TTL cable as described above.
Figure 2. The USB data line can open the serial console

To connect to the serial console using the USB OTG port, follow these steps:

  1. Make sure your board is fully booted up.

  2. Connect a USB cable from your computer to the board's OTG port, and then run the following command in a terminal:

    • On Linux: 

      ls /dev/ttyACM*

    • On Mac: 

      ls /dev/cu.usbmodem*

  3. Connect to the device shown using a serial console program such as screen as follows:

    screen /dev/ttyACM0 115200

  4. If the screen terminal is blank, press Enter and then you should see the login prompt.

    The default username and password are both "mendel".

When you're done, kill the screen session by pressing CTRL+A, K, and then Y to confirm.

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