Raspberry Zero USB gadget with ethernet and and mass storage

Per default the Raspberry Zero runs in host mode as any other member of the Raspberry family. A OTG cable is connected to to inner USB port and it controls USB devices like webcams or Usb sticks for excample.

The Zero can be setup to run as an USB device. Then it may provide some services to a connected host. In this case ethernet over USB and a mass storage.

Setup with configfs

• In /boot/config.txt append dtoverlay=dwc2

• In /etc/modules append

dwc2
libcomposite

Clone the repository with

/var $ git clone https://github.com/r09491/zgadget.git

In the storage directory create the FAT image to be mounted as a loop file

/var/zgadget $ mkdir storage
/var/zgadget $ cd storage
/var/zgadget/storage $ sudo dd bs=1M if=/dev/zero of=/piusb.bin count=4096
/var/zgadget/storage $ sudo mkdosfs zgadget.img -F 32 -I
/var/zgadget/storage $

In the /etc/fstab append:

/var/zgadget/storage/zgadget.img /media/zgadget vfat loop,users,umask=000,noauto 0 2

Create the directory /media/zgadget for mounting:

/var/zgadget/storage $ sudo mkdir /media/zgadget

Usage

Create configuration tree and start sync server.

/var/zgadget/storage $ cd /var/zgadget/scripts
/var/zgadget/scripts $ sudo ./start_sync_storage.py

The configuration tree should look as follows:

/sys/kernel/config/usb_gadget/
└── g1
    ├── bcdDevice
    ├── bcdUSB
    ├── bDeviceClass
    ├── bDeviceProtocol
    ├── bDeviceSubClass
    ├── bMaxPacketSize0
    ├── configs
    │   └── c.1
    │       ├── bmAttributes
    │       ├── ecm.usb0 -> ../../../../usb_gadget/g1/functions/ecm.usb0
    │       ├── mass_storage.usb0 -> ../../../../usb_gadget/g1/functions/mass_storage.usb0
    │       ├── MaxPower
    │       └── strings
    │           └── 0x409
    │               └── configuration
    ├── functions
    │   ├── ecm.usb0
    │   │   ├── dev_addr
    │   │   ├── host_addr
    │   │   ├── ifname
    │   │   └── qmult
    │   └── mass_storage.usb0
    │       ├── lun.0
    │       │   ├── cdrom
    │       │   ├── file
    │       │   ├── inquiry_string
    │       │   ├── nofua
    │       │   ├── removable
    │       │   └── ro
    │       └── stall
    ├── idProduct
    ├── idVendor
    ├── os_desc
    │   ├── b_vendor_code
    │   ├── qw_sign
    │   └── use
    ├── strings
    │   └── 0x409
    │       ├── manufacturer
    │       ├── product
    │       └── serialnumber
    └── UDC

14 directories, 29 files

Connect the Raspberry Zero with a Linux Machine

• A USB disk is mounted and available for Linux file managment

• A random IP address is generated for the Zero (Avahi). In my case: 169.254.158.207/16

On the host side a port may be setup with: sudo ip a add 169.254.158.207/16 dev enx486f73745043

This allows to connect the host to Zero: '''ssh 169.254.158.207'''

Cleanup if you are done

var/zgadget/scripts $ sudo ./stop_sync_storage.py

Automate the process by adding zgadget_sync_watchdog.service to /etc/systemd/system

[Unit]
Description=USB gadget storage sync watchdog

[Service]
Type=simple
ExecStart=/var/zgadget/scripts/start_sync_storage.py
ExecStop=/var/zgadget/scripts/stop_sync_storage.py
KillMode=process

Restart=always

[Install]
WantedBy=multi-user.target

Activate the service

sudo systemctl daemon-reload
sudo systemctl enable zgadget_sync_watchdog.service
sudo systemctl start zgadget_sync_watchdog.service