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1 Configuring the USB1 port under Linux

By default, the USB1 port is configured as host in the device tree, and a USB type-A receptacle is assembled on the VAR-6ULCustomBoard.
To use it as peripheral (OTG is not supported in the VAR-6ULCustomBoard) you need to change the value of the dr_mode property under the usbotg1 node in the device tree, and assemble a USB Micro-AB receptacle at J23 on the bottom of the VAR-6ULCustomBoard.

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:
(in very old kernel releases where this file is not available, you should edit arch/arm/boot/dts/imx6ul-var-dart.dtsi instead)

 &usbotg1 {
-       dr_mode = "host";
+       dr_mode = "peripheral";
        status = "okay";

If you build the kernel manually from source code, you should build only the device trees and copy them to your SD card.

Note: You can read the current dr_mode value on a running target, by executing the following command:

# cat /sys/firmware/devicetree/base/soc/aips-bus@02100000/usb@02184000/dr_mode; echo

2 Using the USB1 port under Linux

2.1 As host (default)

USB host

2.2 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.

Example using the g_mass_storage module to expose the BOOT partition on our recovery SD card to a PC:
Connect a micro-B plug to Standard-A plug cable between the board and a PC, and run the following on the board:

# umount /dev/mmcblk0p1
# modprobe g_mass_storage file=/dev/mmcblk0p1

The partition should be loaded on the PC as a mass storage device.