USB Networking with Gumstix Overos

Last Updated on Saturday, 27 November 2010 20:55

The OTG USB port on the Overo expansion boards support USB networking. To enable this, the OTG port needs to be configured as a USB peripheral or gadget. The default kernels from Gumstix have the OTG port configured to act as a USB host.

This comes from a how-to I posted in the USB section of the Gumstix Users Wiki.

The procedure for changing the configuration requires rebuilding your kernel, so you should first be comfortable with setting up a build environment and building images for your Overo.

The following steps assume you are using a recent snapshot of the gumstix-oe git tree and are going to use kernel version 2.6.31 or greater.

The gumstix recipes for these kernels has a variable that allows you to specify how you want the OTG usb port configured.

Gumstix Overos use the linux-omap3 kernels by default. You can check which kernel version you'll be working with like this:

$ cd ${OVEROTOP}
$ bitbake --show-versions | grep linux-omap3
linux-omap3                        0:2.6.34-r81

So the recipe file in this case would be ${OVEROTOP}/org.openembedded.dev/recipes/linux/linux-omap3_2.6.34.bb. You'll see a line in there

MUSB_MODE ?= "host"

There are three valid values for MUSB_MODE: "host", "peripheral" or "otg".

You could change the MUSB_MODE assignment directly in the recipe, but a better way to do this is to modify your local.conf file and add a MUSB_MODE variable.

The ?= assignment means "host" will be assigned to MUSB_MODE only if it does not already have a value which it will if you give it one in local.conf.

The local.conf file is found here ${OVEROTOP}/build/conf/local.conf

Add the line

MUSB_MODE = "peripheral"

or

MUSB_MODE = "otg"  

depending on your preference.

Now rebuild your kernel.

$ cd ${OVEROTOP}
$ bitbake -c clean virtual/kernel
$ bitbake virtual/kernel

And then rebuild your rootfs since the drivers available in /lib/modules will have changed.

$ bitbake omap3-console-image    

Change omap3-console-image to whatever image you use.

Once you have booted the new system, you still need to load the g_ether driver since it was built as a module.

You can add g_ether to /etc/modules if you always want it to load at boot.

root@overo# modbprobe g_ether
g_ether gadget: using random self ethernet address
g_ether gadget: using random host ethernet address
usb0: MAC d6:2c:8f:d9:51:32
usb0: HOST MAC f2:99:dc:4c:cb:7a
g_ether gadget: Ethernet Gadget, version: Memorial Day 2008
g_ether gadget: g_ether ready

root@overo:~# ifconfig -a
lo      Link encap:Local Loopback
        inet addr:127.0.0.1  Mask:255.0.0.0
        inet6 addr: ::1/128 Scope:Host
        UP LOOPBACK RUNNING  MTU:16436  Metric:1
        RX packets:0 errors:0 dropped:0 overruns:0 frame:0
        TX packets:0 errors:0 dropped:0 overruns:0 carrier:0
        collisions:0 txqueuelen:0
        RX bytes:0 (0.0 b)  TX bytes:0 (0.0 b)

usb0    Link encap:Ethernet  HWaddr D6:2C:8F:D9:51:32
        BROADCAST MULTICAST  MTU:1500  Metric:1
        RX packets:0 errors:0 dropped:0 overruns:0 frame:0
        TX packets:0 errors:0 dropped:0 overruns:0 carrier:0
        collisions:0 txqueuelen:1000
        RX bytes:0 (0.0 b)  TX bytes:0 (0.0 b)

Configure the usb0 interface the way you would any other.

For example

root@overo:~# ifconfig usb0 192.168.20.2 netmask 255.255.255.0

If you then plug the usb OTG cable into a host computer ready for usb networking you'll get a console message

g_ether gadget: high speed config #1: CDC Ethernet (ECM)

The rest is all standard Linux networking.