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                    README-usb-dev-mode
                      Linux for Tegra
                      USB Device Mode =======================================================================

The USB device mode configuration script configures the Tegra USB flashing port to act as a USB device and implement various protocols. The script allows a USB host system to interact with the Tegra device using a USB cable. The following implemented protocols can be used at the same time:

  • Ethernet: allows system login using SSH and high-bandwidth file copying using SFTP.
  • UART/Serial: allows system login using a terminal application.
  • USB Mass Storage: Similar in concept to a USB memory stick.

Using Ethernet Protocol ———————————————————————- Linux for Tegra implements two types of Ethernet devices to support various operating systems running on the USB host machine. It is safe to ignore system errors for missing drivers for an RNDIS or an NCM device. If your system supports both devices, either device can be used. However, do not configure both devices at the same time.

Linux for Tegra assigns a link-local IPv6 address of fe80::1 to the USB Ethernet device(s). You should not have to configure your host machine in order to use an IPv6 link-local address. If you connect multiple Jetson devices to the same host machine, each Jetson device uses the same IPv6 link-local address. You may still connect to any connected Jetson device, however, since use of IPv6 link-local addresses also requires specifying which network interface to connect over, and there is a unique interface for each Jetson.

Linux for Tegra assigns a static IPv4 address of 192.168.55.1 to Jetson, and runs a DHCP server to automatically assign an IPv4 address of 192.168.55.100 to your host machine. This provides point-to-point connectivity. If a Jetson device experiences very high CPU or disk IO load, this DHCP server may fail to respond in a timely manner to requests from the host machine. This may cause IPv4 connections to drop. If this problem occurs, configure your host machine to use a static IPv4 address of 192.168.55.100 with netmask 255.255.255.0 and no gateway or DNS servers.

Linux for Tegra configures a very low priority default IPv4 route on the USB Ethernet device(s), and configures Google’s public DNS server (8.8.8.8) as the fallback DNS server for use when no other network connection is available. This allows your host machine to act as an Intranet or Internet gateway for Jetson.

If you connect multiple Jetson devices to the same host machine, each Jetson device uses the same IPv4 address. This prevents IPv4-based communication with all but one Jetson device, since your host operating system determines which Jetson device it communicates with. To solve this, edit the Jetson-based script that sets up the network and assign a unique network address to each Jetson device. IPv6-based communication works with any number of Jetson devices without modifying the aforementioned script.

Once the Ethernet device is configured, use SSH to connect to the Jetson device.

SSH is natively available on Linux and Macintosh operating systems. Connect using IPv6 with the following command:

ssh nvidia@fe80::1%usb0

Connect using IPv4 with the following command:

ssh [email protected]

On Windows, use the PuTTY application.

Ethernet on Linux

Two USB Ethernet devices are created and the required drivers are automatically activated. These devices are typically named usb0 and usb1, depending on how your Linux distribution is configured, and what other hardware is attached to the system. To avoid the potential for interference between the two USB Ethernet devices, it is best, but not strictly required, to use your host’s network configuration tool (e.g. Network Manager), to disable one of the two USB Ethernet interfaces implemented by the Jetson device.

View available Ethernet devices with the following command:

/sbin/ifconfig -a

Knowledge of the Ethernet device name is required in order to use IPv6 link-local addresses.

Use the following procedure to configure your host as a gateway for Jetson.

  1. Enable IP forwarding with your host’s configuration tools, or by running the following command as root: 
    echo 1 > /proc/sys/net/ipv4/ip_forward

    If your host system is connected to multiple networks at the same time, please consider any security implications of this configuration change.

    Depending on your Linux distribution, you may be able to make this change permanent by editing /etc/sysctl.conf.

  2. Enable Network Address Translation (NAT) using your host’s configuration tools to do this, or by running the following command as root: 
    iptables -t nat -A POSTROUTING -o eth0 -j SNAT --to 192.168.1.100

    where: eth0 is the name of your host’s upstream Ethernet interface. 192.168.1.100 is your host’s IP address on that interface.

Depending on your Linux distribution, you may have to run this command every time your host is rebooted.

Ethernet on Windows

An RNDIS USB Ethernet device is created, and the required driver is automatically installed. You can safely ignore the message that the NCM device is unknown. Depending on the Windows version you have, you might need to disable the NCM device.

To configure your host as a gateway for Jetson:

  1. Click Control Panel -> Network and Internet -> Network Connections.

  2. Edit the “Remote NDIS Compatible Device” interface and configure “Property”.

  3. Ensure that the IP address is 192.168.55.100. If Windows always gives you another IP address, for example, 192.168.137, you might need to configure a static IP address.

  4. Click Control Panel -> Network and Internet -> Network Connections.

  5. Edit the interface of your public interface and configure “Property”.

  6. On the Sharing tab, enable the “Allow other network users to connect through this computer’s internet connection” option.

  7. In the “Home networking connection” menu, select the RNDIS interface.

Ethernet on Mac

An NCM USB Ethernet device is created, and the required driver is automatically activated. Since the Mac operating system does not support the RNDIS device, the device is not activated by default.

Changing the IPv4 Address

Edit /opt/nvidia/l4t-usb-device-mode/nv-l4t-usb-device-mode-config.sh on Jetson to change the IPv4 network parameters. The following variables must be changed, and must maintain consistent values:

  • net_ip
  • net_mask
  • net_net
  • net_dhcp_start
  • net_dhcp_end

Using the Serial Port ———————————————————————- Linux for Tegra implements a single USB serial port, and presents a login prompt on the port. You may log into the system and run shell commands over this port.

Any standard serial terminal application may be used with the port. For example:

  • Screen (Linux/Mac)
  • Picocom (Linux)
  • Tera Term (Windows)
  • HyperTerminal (Windows)

Since this is an emulated serial port, any baud rate will work. The port must be configured for 8N1 (8-bits per character, no stop bit, 1 parity bit).

Serial Port on Linux

Linux creates a device such as /dev/ttyACM0 for the serial port. To locate the exact name:

  1. Launch a shell prompt.
  2. Run the command: ls /dev.
  3. Search for “ACM”.

Serial Port on Windows

Windows creates a standard COM port device for the serial port.

On systems using an operating system prior to Windows 10, you must manually install the driver for the serial port. To install the driver:

  1. Open Device Manager.
  2. Locate the “CDC Serial” device.
  3. Right-click the device and select “update Driver Software”.
  4. Select to Browse for the driver software.
  5. Set the path to the USB disk drive that is implemented by your Linux for Tegra device.

Windows will locate the required .inf file and install the relevant drivers for the serial port.

Serial Port on Mac

Mac OS creates a device such as /dev/tty.usbmodem1232 for the serial port. To locate the exact name:

  1. Launch a shell prompt.
  2. Run the command: ls /dev.
  3. Search for “tty.usbmodem”.

Using USB Mass Storage ———————————————————————- Linux for Tegra implements a USB Mass Storage device, known as a USB disk or USB memory stick, that is natively supported by all operating systems. The USB disk automatically appears in the graphical filesystem browser such as:

  • Linux desktop
  • Windows Explorer
  • Mac Finder

On Linux or Mac, you can manually mount the disk from the command line, just like a USB storage device.

The USB storage device is read-only and contains various driver files and Linux for Tegra documentation.

Disabling USB Device Mode Temporarily ———————————————————————-

To disable USB device mode temporarily:

  1. On the Linux for Tegra system, launch a shell prompt.
  2. Log in as root.
  3. Execute the command: service nv-l4t-usb-device-mode stop

To re-enable USB device mode:

  1. On the Linux for Tegra system, launch a shell prompt.
  2. Log in as root.
  3. Execute the command: service nv-l4t-usb-device-mode start

USB device mode will be re-enabled automatically the next time the system is rebooted.

Disabling USB Device Mode Permanently ———————————————————————- To disable USB device mode permanently:

  1. On the Linux for Tegra system, launch a shell prompt.
  2. Log in as root.
  3. Execute the commands: service nv-l4t-usb-device-mode stop systemctl disable nv-l4t-usb-device-mode.service

This is equivalent to deleting the following files:

/etc/systemd/system/nv-l4t-usb-device-mode.service /etc/systemd/system/multi-user.target.wants/nv-l4t-usb-device-mode.service

To re-enable USB device mode, execute the commands:

systemctl enable /opt/nvidia/l4t-usb-device-mode/nv-l4t-usb-device-mode.service service nv-l4t-usb-device-mode start