Introduction

This repository contains some test code to demonstrate how to use the proposed patch for the Linux Kernel to implement mmap for USB Gadget FunctionFS.

Setting up your USB Gadget device

To setup USB Gadget FunctionFS on your device you need to do some configuration.

An example shell script is included here at script/usb_gadget_mk.sh.

The assumption here is, that neither ConfigFS nor FunctionFS are already mounted. The script will create the directories

• /config to mount ConfigFS
• /usbfunc to mount FunctionFS

If ConfigFS or FunctionFS is already mounted on your device you need to modify the script (and subsequently the test application).

Compiling C sources

Compiling the test application for your USB Gadget device

Assumptions:

• Your USB Gadget device is running a Linux Kernel with the proposed patch
• You have a cross compiler to create ELF files for the USB Gadget device
• You have libaio available for your USB Gadget device

Here is an example how to compile the application for your USB Gadget device. In this example the targeted device has an SMP Cortex-A53 cluster. The device is running Linux with "musl libc".

The GCC cross compiler used here is called aarch64-linux-musl-gcc

SYSROOT=/home/rohloff/linux_gadget/sysroot

aarch64-linux-musl-gcc --sysroot=${SYSROOT} -mcpu=cortex-a53 -O2 -o usb_ffs_tst src/usb_ffs_tst.c -laio
aarch64-linux-musl-strip usb_ffs_tst

You very likely need to modify the source code to:

• Use the right directories for ConfigFS and FunctionFS (see definitions of CFGFS_DIR and FFS_DIR)
• Point to the right USB Device Controller (see definition of g_udc_name[])

Now you have to copy the usb_ffs_tst ELF file to your USB gadget device.

Compiling the test application for your PC

This application is intended to talk to the USB Gadget device via USB.

Example compilation:

gcc -Wall -Og -fno-inline -o usb_pc_tst pc/usb_pc_tst.c

Running the test

Start test application on your USB Gadget device.

Once the script to create the USB function has run, you have to start the usb_ffs_tst application on your Gadget Device.

Make sure you have modified the source code to fit to your ConfigFS, FunctionFS and USB Device Controller.

Connect your USB Gadget device to the PC

After connecting your USB Gadget device to the PC, the device should be listed by lsusb.

Example:

rohloff@mypc:~/linux_gadget$ lsusb
<...>
Bus 002 Device 009: ID 1209:0005 Generic pid.codes Test PID
<...>

The usb_gadget_mk.sh script configures the USB Gadget to use Vendor ID 1209 and Product ID 0005.

Run the test application on the PC

Use the bus and device numbers listed by lsusb as shown above.

Example run:

rohloff@mybc:~/linux_gadget$ ./usb_pc_tst /dev/bus/usb/002/008 echo
checkUsbDevice : Device is using SuperSpeed
scanEndpointDescriptors : Found bulk IN  endpoint 0x81
scanEndpointDescriptors : Found bulk OUT endpoint 0x01
Started write of 4 bytes to OUT EP
Finished write of 4 bytes to OUT EP
Running ECHO test
Transfering 4096 x 131056 bytes
Total time in usecs        : 1320378
Echo test successful, transferred 536805376 bytes
bytes per second: 406554317

Depending on the setup of your Linux PC you might need to run the usb_pc_tst application as root; alternatively it might be possible to add your user to the usb group to make sure you have access to your USB Gadget device.