Can't activate a USB HID Device on BeagleBoneBlack - usb

Question

Background:
I'm trying to figure out how to use ConfigFS to set up an HID device on BeagleBoneBlack.
I found the following example (www.isticktoit.net/?p=1383) on the web and tried it. The sample runs on a Raspberry Pi Zero. However, the sample does not work on my BBB. The following is the script that I wrote and which is executed as root. The script attempts to define a keyboard hid device.
#!/bin/bash
cd /sys/kernel/config/usb_gadget/
modprobe libcomposite
modprobe usb_f_hid
mkdir -p isticktoit
cd isticktoit
echo 0x1d6b > idVendor # Linux Foundation
echo 0x0104 > idProduct # Multifunction Composite Gadget
echo 0x0100 > bcdDevice # v1.0.0
echo 0x0200 > bcdUSB # USB2
mkdir -p strings/0x409
echo "fedcba9876543210" > strings/0x409/serialnumber
echo "Tobias Girstmair" > strings/0x409/manufacturer
echo "iSticktoit.net USB Device" > strings/0x409/product
mkdir -p configs/c.1/strings/0x409
echo "Config 1: ECM network" > configs/c.1/strings/0x409/configuration
echo 250 > configs/c.1/MaxPower
# Add functions here
pwd
mkdir -p functions/hid.xyz
echo 1 > functions/hid.xyz/protocol
echo 1 > functions/hid.xyz/subclass
echo 8 > functions/hid.xyz/report_length
echo -ne \\x05\\x01\\x09\\x06\\xa1\\x01\\x05\\x07\\x19\\xe0\\x29\\xe7\\x15\\x00\\x25\\x01\\x75\\x01\\x95\\x08\\x81\\x02\\x95\\x01\\x75\\x08\\x81\\x03\\x95\\x05\\x75\\x01\\x05\\x08\\x19\\x01\\x29\\x05\\x91\\x02\\x95\\x01\\x75\\x03\\x91\\x03\\x95\\x06\\x75\\x08\\x15\\x00\\x25\\x65\\x05\\x07\\x19\\x00\\x29\\x65\\x81\\x00\\xc0 > functions/hid.xyz/report_desc
ln -s functions/hid.xyz configs/c.1/
# End functions
ls /sys/class/udc > UDC
The error that I get is "ls: write error: Devicew or resource busy".
I am running Debian Jessie - Linux version 4.4.9-ti-r25
I did an lsmod and libcomposite and usb_f_hid are loaded.
The usb device controller, musb-hdrc-0.auto, is loaded.
Questions:
How can I tell which device is busy?
Where can I find the USB configfs defect bug list for BBB.
Is there a logging file and enabling parameter that would give me a clue as to what is happening?
Thanks for any help
David Glaser

Answer 1

The problem you are likely having with the beaglebone black is the cdc_acm driver. It is difficult to remove (well, not really now that I KNOW how to do it) if you don't know how because the steps aren't just laid out to find anywhere yet. I found this: https://media.defcon.org/DEF%20CON%2023/DEF%20CON%2023%20presentations/DEFCON-23-Phil-Polstra-One-device-to-Pwn-them-all.pdf
which led me to the following solution
#!/usr/bin/env bash
function checkModule(){
MODULE="$1"
if lsmod | grep "$MODULE" &> /dev/null ; then
echo "$MODULE" found.
return 0
else
echo "$MODULE" not found.
return 1
fi
}
if which 'systemctl' | grep "systemctl" &> /dev/null ; then
systemctl stop serial-getty#ttyGS0.service >/dev/null
fi
if checkModule "g_serial" == 0; then
modprobe -r g_serial
fi
if checkModule "usb_f_acm" == 0; then
modprobe -r usb_f_acm
fi
if ! checkModule "libcomposite" == 0; then
modprobe libcomposite
fi
basically, it stops the serial-getty service which allows you to remove the g_serial device and then this allows you to remove usb_f_acm. This in turn removes the libcomposite device, which you actually want to keep. Once this is done, you can likely do all the things you needed to do. I got a nice HID keyboard working this way (well, okay I guess its a KeygleBone Black now)... It is pretty dirt simple once you understand ALL of the pieces, but I'm having a little trouble tearing my device back down. I might not need to eventually, but I'd like to be able to do that and it seems that certain directories cannot be removed (namely the "strings" directories that I've created). This means I can't really fully tear down the device, but maybe I only need to:
echo "" > /sys/kernel/config/usb_gadget/my_gadget/UDC
to actually tear it down. I haven't worked that part out yet. There are also some C libraries, but I've got a bunch of python scripts that I want to use and I don't yet have python wrappers for those. But that probably isn't too much work.
I didn't want to forget to mention, that I tried to throw the above script into rc.local so the beaglebone black I am using would be "HID ready" on boot. There are probably better locations and methods to do this, but I just wanted to use rc.local because the above is a script, rc.local is a script, it should run on boot... But it doesn't... You have to make sure to make rc.local runable ( chmod 755 /etc/rc.local ) as well as modifying the default shell it wants to run (well, it always runs bash, but its method for running bash is the "POSIX" method, and that doesn't seem to work, so you have to force it to run bash in non-POSIX mode with:
#!/usr/bin/bash
Again, there are probably other better methods (I was lazy here and, well, I'm just old school), especially if your device is going to be an IoT device or anything linked to the net, so you might want to consider something else if you need this script to run on boot.
I did stupidly leave out one thing: I made sure the beaglebone black doesn't present its usual "disk" portion as well. I would put the details here, but frankly, those I'd have to track back down. I basically googled around for how to disable the beaglebone black disk. It isn't hard and amounted to me moving some file to another name so it doesn't find the "USB disk" configuration on boot. You can also change a line in the uboot config somewhere I believe, but I didn't really want to do that.
Found the file: /var/local/bb_usb_mass_storage.img
Well, it might be bbg_usb_mass_storage.img if it is a beaglebone green, but I just moved this file so it wouldn't present the mass storage device. That should allow you to do what you want.