Linux USB OTG
This page is using the default release RELEASE_SUMO_V1.0_DART-MX8M.
To view this page for a specific Variscite SoM and software release, please follow these steps:
- Visit variwiki.com
- Select your SoM
- Select the software release
Configuring the USB OTG port under Linux
By default, the USB OTG port is configured as OTG in the device tree, and a USB type-C receptacle is assembled on the DART-MX8M custom board.
To use it as host only or peripheral only you need to change the value of the dr_mode property under the USB node in the device tree.
dr_mode: One of "host", "peripheral" or "otg". Defaults to "otg"
For example:
Follow either the "Build the Linux kernel from source code" or "Customizing the Linux kernel" Wiki pages and edit the following device tree file:
arch/arm64/boot/dts/freescale/fsl-imx8mq-var-dart-common.dtsi
&usb_dwc3_0 {
status = "okay";
extcon = <&typec_ptn5150>;
- dr_mode = "otg";
+ dr_mode = "host";
};
If you build the kernel manually from source code, you should build only the device trees and copy them to your SD card or eMMC.
Note: You can read the current dr_mode value on a running target, by executing the following command:
# cat /sys/firmware/devicetree/base/usb@38100000/dwc3/dr_mode;
Using the USB OTG port under Linux
As host (default)
As peripheral
In order to use the board as a peripheral, an appropriate module needs to be loaded.
For example, there is an Ethernet gadget module called g_ether, a mass storage gadget called g_mass_storage, a serial gadget called g_serial, etc.
Examples
Connect a type-C plug to Standard-A plug cable between the board and a host PC, and run the following examples on the target board:
Mass Storage Device
The following uses the g_mass_storage module to expose the root partition on eMMC to a PC while booting from recovery SD card:
# umount /dev/mmcblk0p1 # modprobe g_mass_storage file=/dev/mmcblk0p1
The partition should be loaded on the PC as a mass storage device.
USB Debug Console
The following uses the g_serial module to spawn a new debug console over USB:
On target:
# echo g_serial > /etc/modules-load.d/g_serial.conf # Load g_serial module on boot # sudo systemctl enable getty@ttyGS0.service # Spawn a new tty session on ttyGS0 # reboot # Reboot to take effect
On Host:
$ minicom -D /dev/ttyACM0 # Launch minicom on Host computer to login to target tty console
Ethernet Device
The following uses the g_ether to establish an ethernet link with a host computer over USB.
First, connect a USB cable from a host computer to the USB OTG port of the target. Then run the following commands:
On the target:
Load the g_ether module, assigning the host mac address 02:00:00:00:00:01 Note: you may exclude the host_addr argument, it's used here because the host computer will rename usb0 to enx020000000001 # modprobe g_ether host_addr=02:00:00:00:00:01 Tell NetworkManager not to manage this interface (skip this step if NetworkManager is not running on the target) # nmcli dev set usb0 managed no Assign a static IP address of 192.168.10.2 # ip addr flush usb0; ip addr add 192.168.10.2/24 dev usb0; ip link set usb0 up
On the host computer:
Tell NetworkManager not to manage this interface (skip this step if NetworkManager is not running on the host) # nmcli dev set enx020000000001 managed no Assign a static IP address of 192.168.10.1 $ sudo ip addr flush enx020000000001; sudo ip addr add 192.168.10.1/24 dev enx020000000001; sudo ip link set enx020000000001 up
Ping the target from the host:
$ ping 192.168.10.2 -c 3 PING 192.168.10.2 (192.168.10.2) 56(84) bytes of data. 64 bytes from 192.168.10.2: icmp_seq=1 ttl=64 time=0.931 ms 64 bytes from 192.168.10.2: icmp_seq=2 ttl=64 time=0.822 ms 64 bytes from 192.168.10.2: icmp_seq=3 ttl=64 time=0.777 ms --- 192.168.10.2 ping statistics --- 3 packets transmitted, 3 received, 0% packet loss, time 2032ms rtt min/avg/max/mdev = 0.777/0.843/0.931/0.064 ms
As OTG
With OTG, the board can be either a host, or a peripheral.
In order to use it as a host and connect a peripheral (e.g. a USB flash drive) to it, either use a peripheral with type-C connector or use type-C to type-A adapter.
In order to use it as a peripheral and connect it to a PC, for example, a cable with a type-C plug on one end and a Standard-A plug on the other is needed.