VAR-SOM-MX7 USB OTG

VAR-SOM-MX7 - USB OTG

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-MX7CustomBoard.
To use it as OTG or peripheral 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 J27 on the bottom of the VAR-MX7CustomBoard.
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/arm/boot/dts/imx7d-var-som.dtsi

 &usbotg1 {
        vbus-supply = <&reg_usb_otg1_vbus>;
-       dr_mode = "host";
+       dr_mode = "otg";
        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@30800000/usb@30b10000/dr_mode; echo

Using the USB1 port under Linux

As host (default)

USB host

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-A 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.

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 mouse) to it, an OTG cable is needed (a cable with a micro-A plug on one end and a Standard-A receptacle on the other).
In order to use it as a peripheral and connect it to a PC, for example, a cable with a micro-A plug on one end and a Standard-A plug on the other is needed.