gadgetconfig 0.0.3

gadgetconfig creates and controls Gadget USB Devices and integrates Gadget with systemd

Gadget Config

Stuart Lynne

Sun Mar 01 13:36:16 PST 2020

This package contains tools for configuring Gadget USB Devices and integrating with systemd.

It relies on the Gadget ConfigFS module libcomposite to create and manage Gadget USB Devices.

Gadget USB Device Overview

The Gadget USB Device implementation has three layers when using the new libcomposite driver:

• Function Drivers, e.g. usb_f_acm, usb_f_ecm, usb_f_eem
• LibComposite, for selecting and configuring the device to use the Function Drivers
• UDC, to connect the Function Drivers to the underlying USB Device Controller hardware

The libcomposite implementation allows the USB Device configuration to be specified ad hoc and changed as needed.

A USB Device definition contains:

• idVendor, idProduct, bcdDevice and other attributes
• one of more configurations
• a list of functions that configurations may use
• strings describing the device

Each configuration contains:

• attributes
• list of functions to be used
• strings describing the configuration

Systemd Integration

A gadget.service file is installed which will use the following to start and stop the gadget service:

/usr/lib/gadgetservice/gadget.start
/usr/lib/gadgetservice/gadget.stop

These rely on a default Gadget Device Definition file being present in:

/etc/gadgetservice/default.json

The service should auto-start when the system is rebooted. The systemctl command can also be used;

systemctl start gadget
systemctl stop gadget

See below for more information on Gadget Device Definition files.

Gadget USB Device Lifecycle

The gadgetconfig program uses USB Device definitions stored in JSON files.

Gadget Libcomposite:

• Create: gadgetconfig --create gadget-definition.json
• Enable: gadgetconfig --enable configuration_name
• Disable: gadgetconfig --disable
• Destroy: gadgetconfig --destroy

Gadget UDC:

• Disconnect: gadgetconfig --soft_connect disconnect
• Connect: gadgetconfig --soft_connect connect

            +-------------------+
            |     No Gadget     |
            +-------------------+
                  |       ^             
                  |       |
               Create   Destroy
                  |       |
                  v       |
            +-------------------+
            | Distabled Gadget  |<---
            +-------------------+   |
                  |                 | 
                  |                 |
                Enable           Disable
                  |                 |
                  v                 |
            +-------------------+   |
            | Configured Gadget |---|
   Gadget   +-------------------+                                    
     - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
   UDC      +-------------------+  Disconnect   +-------------------+ 
            | Attached Gadget   |-------------->| Detached Gadget   |
            |                   |<------------- |                   |
            +-------------------+   Connect     +-------------------+
     - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
   Hardware                                                           

N.B.

1. Multiple Gadget USB Device Definitions can be created and co-exist.
2. Only a single Gadget USB Device can be enabled at one time.
3. Attempting to enable a Gadget USB Device will fail another Gadget Device is enabled.
4. When enabled a device defaults to attached.
5. An enabled Gadget Device cannot be removed.
6. Each of multiple Gadget Devices must be separately removed.

Gadget USB Device Definition File

Gadget USB Device Definition Files are JSON files that contain all of the information to define one or more USB Device's along with their attributes, strings, os descriptors, functions and configurations.

There is a close correspondence between the JSON definition file and the resulting Gadget ConfigFS information.

N.B.

• multiple USB Device Definitions can be present and can be configured into the GadgetFS
• multiple USB Device Functions can be specified (from the list of Gadget Functions available)
• multiple USB Device Configurations can be specified, each with a different set of the available USB Device Functions
• within a configuration the array of configuration function definitions are used to create the symlinks pointing to the defined functions by the creation process.
• some entries in ConfigFS functions display Gadget generated data, notably acm port_num and ecm ifname are automatically created and not set from the definition file
• the os_desc entry rules are specific and designed to support Windows, see the RNDIS example for more information
• multiple languages can have strings by specifying separate LANG identifiers for each, for both the USB Device Definition and each USB Device Configuration

Example

This defines a composite USB Device called belcarra containing two ACM and one ECM functions. There is one configuration called "Belcarra Composite CDC 2xACM+ECM.1" which will be the default configuration presented to the host during enumeration.

This is sample file:

{
    # Gadget Device Definition File
    # 2020-03-03
    "Default": {
        # USB Device Descriptor Fields
        "idVendor": "0x3923",
        "idProduct": "0x762f",
        "bcdDevice": "0x0001",
        "bDeviceClass": "0x00",
        "bDeviceSubClass": "0x00",
        "bDeviceProtocol": "0x00",
        "bcdUSB": "0x0200",
        "bMaxPacketSize0": "0x40",
        # USB Device Strings
        "strings": {
            "0x409": {
                "manufacturer": "Belcarra Test",
                "product": "Raspberry Pi 4 Model B Rev 1.1",
                "serialnumber": "1000000044142478"
            }
        },
        # Gadget Functions list: see /sys/module/usb_f*,
        # E.g.: usb_f_acm, usb_f_ecm, usb_f_eem, usb_f_hid, usb_f_mass_storage
        #       usb_f_midi, usb_f_ncm, usb_f_obex, usb_f_rndis, usb_f_serial
        # Use: The function name (without prefix) is used with instantion name, e.g. eem.usb0 or acm.GS0
        "functions": {
            "eem.usb0": {
                "dev_addr": "4e:28:20:f0:35:ab",
                "host_addr": "b6:fe:ea:86:2a:50",
                "qmult": "5"
            }
        },
        # Gadget Configurations list
        "configs": {
            "Belcarra EEM.1": {
                # Configuration Descriptor
                # bmAttributes: bit 5 support remote wakeup
                # bmAttributes: bit 6 self-powered
                # bmAttributes: bit 7 bus-powered
                # MaxPower: Power requirements in two-milliampere units, only valid of bit 7 is set
                "bmAttributes": "0x80",
                "eem.usb0": "eem.usb0",
                "MaxPower": "2",
                "strings": {
                    # USB Device Configuration Strings
                    "0x409": {
                        "configuration": "CDC EEM"
                    }
                },
                "functions": [
                    {
                        "name": "eem.usb0",
                        "function": "eem.usb0"
                    }
                ]
            }
        },
        # Microsoft OS Descriptors Support
        # C.f. https://docs.microsoft.com/en-us/previous-versions/gg463179(v=msdn.10)
        "os_desc": {
            "b_vendor_code": "0x00",
            "qw_sign": "",
            "use": "0"
        }
    }
}

We can view the generated Gadget ConfigFS using sysfstree_raspian:

# gadgetconfig --create belcarra-2acm+ecm.json
# sysfstree_raspbian --gadget
[/sys/kernel/config/usb_gadget]
└──[belcarra]
    ├──bcdDevice: 0x0001
    ├──bcdUSB: 0x0200
    ├──bDeviceClass: 0x00
    ├──bDeviceProtocol: 0x00
    ├──bDeviceSubClass: 0x00
    ├──bMaxPacketSize0: 0x40
    ├──[configs]
    │   └──[Belcarra Composite CDC 2xACM+ECM.1]
    │       ├──acm.GS0 -> /sys/kernel/config/usb_gadget/belcarra/functions/acm.usb0
    │       ├──acm.GS1 -> /sys/kernel/config/usb_gadget/belcarra/functions/acm.usb1
    │       ├──bmAttributes: 0x80
    │       ├──ecm.usb0 -> /sys/kernel/config/usb_gadget/belcarra/functions/ecm.usb0
    │       ├──MaxPower: 2
    │       └──[strings]
    │           └──[0x409]
    │               ├──configuration: CDC 2xACM+ECM
    ├──[functions]
    │   ├──[acm.usb0]
    │   │   ├──port_num: 0
    │   ├──[acm.usb1]
    │   │   ├──port_num: 1
    │   └──[ecm.usb0]
    │       ├──dev_addr: 4e:28:20:f0:35:ab
    │       ├──host_addr: b6:fe:ea:86:2a:50
    │       ├──ifname: usb0
    │       ├──qmult: 5
    ├──idProduct: 0xd031
    ├──idVendor: 0x15ec
    ├──[os_desc]
    │   ├──b_vendor_code: 0x00
    │   ├──qw_sign:
    │   ├──use: 0
    ├──[strings]
    │   └──[0x409]
    │       ├──manufacturer: Belcarra Technologies
    │       ├──product: Composite CDC 2xACM+ECM
    │       ├──serialnumber: 0123456789
    ├──UDC: fe980000.usb

Running Tests

gadgetconfig currently only has doctests.

Run tests with nose::

nosetests --with-doctest src/gadgetconfig

Run tests with doctest::

python -m doctest -v src/gadgetconfig/__init__.py

Author

[e-mail] Copyright (c) 2020 Belcarra Technologies (2005) Corp.