To speed up my development, I’ll try using the dummy_hcd kernel module, which allows to emulate an OTG port connected to the computer.
dummy_hcd is missing on my GNU/Linux distribution (Linux Mint 17.3), so I had to build it myself:
apt-get source linux-image-`uname -r`
cd linux-lts-vivid-3.19.0
cp /boot/config-`uname -r` .config
cp /usr/src/linux-headers-`uname -r`/Module.symvers .
make menuconfig
# select → Device Drivers → USB support → USB Gadget Support → USB Peripheral Controller → Dummy HCD
make prepare
make scripts
make -j 4 M=drivers/usb/gadget
sudo cp drivers/usb/gadget/udc/dummy_hcd.ko /lib/modules/`uname -r`/kernel/drivers/usb/gadget/udc/
sudo depmod -aAdding the following line to /etc/fstab makes it easier to mount the gadget file system:
gadget /dev/gadget gadgetfs noauto,user,group 0 0
Creating a udev rule in /etc/udev/rules.d/99-gadgetfs.rules allows to automatically mount the gadget filesystem when dummy_hcd is loaded:
ACTION=="add", DEVPATH=="/module/dummy_hcd" SUBSYSTEM=="module" RUN+="/bin/mkdir /dev/gadget" RUN+="/bin/mount /dev/gadget"
ACTION=="remove", DEVPATH=="/module/dummy_hcd" SUBSYSTEM=="module" RUN+="/bin/umount /dev/gadget" RUN+="/bin/rmdir /dev/gadget"To apply this rule without rebooting:
sudo udevadm control --reload-rules
dummy_hcd can be loaded using modprobe:
sudo modprobe dummy_hcd
or automatically loaded at boot time adding this line to /etc/module:
dummy_hcd
The gadget can finally be controlled using the /dev/gadget/dummy_udc file.
Awesome work. Thanks for your time and effort.
Hi,
Any development work already done?
I got a S905 TV Box for < 30 Euro, which supports OTG.
Linux and some gadget experiments are running.
It seems that configs is the successor of gadgetfs.
There is an easier to use library: https://github.com/libusbgx/libusbgx
I will now start to develop a PS4 pad emulator.
Johns
Hi,
Yes, I did some preliminary work in the gadget branch of my serialusb project:
https://github.com/matlo/serialusb/tree/gadget
https://github.com/matlo/serialusb/tree/gadget/sw/lib/gasync/src/gadget/linux/gadget.c
configfs only allows to create devices that implement standard functions (e.g. an ethernet function, a serial function…). It does not provide full control, which is required for emulating devices with vendor-specific functions.
Thanks for the hints.
You may be right, but there is functionfs see linuxDocumentation/usb/functionfs.txt
Which should do what we want.
I have the problem on the device that the gadgetfs hangs after removing a device
.
functionfs and configfs seems to work better.
An example for ffs is in the linux kernel: tools/usb/ffs-test.c
Johns
I’m unsure if functionfs supports non blocking IO. I avoid threading as much as I can as it adds complexity and overhead. gadgetfs has non blocking IO through AIO.
Did you check if your gadgetfs issue is fixed in newer kernels?
Looks like AIO is also available for functionfs:
https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/tree/tools/usb/ffs-aio-example/simple/device_app/aio_simple.c
I knew that i can’t use poll/select with normal gadgetfs.
Nice to know that i can use AIO with poll and select.
I hoped that I can use normal IO and poll/select, will be the first test.
The boards that i have A20 with kernel 3.4.x and S905 with kernel 3.14.x use these custom kernels. Only these Kernels support all features.
But on all is mainline linux kernel running, with missing features.
I haven’t tested it yet.
Johns
Too bad linux 3.4.x didn’t support configs and linux 3-14.x didn’t support AIO with functionfs.
Johns
I sent you a mail to the address you provided when posting.
Got only an email from postmaster about this new post.