Device 侧 gadget zero

28 May 2024

Read time: 6 minute(s)

提供测试需要的 Device 设备有很多种方式，例如可用使用专门的测试 Device 里面烧录专有的测试 Firmware。节约成本的方式还是使用 Linux gadget 功能来动态模拟 USB Device 设备。针对 USB 测试，Linux 专门提供了 gadget zero 设备。

Device 创建

gadget zero 的核心是创建一个 Composite Device ，其包含了两个 Configuration ，其中一个 Configuration 0 包含 SourceSink Function/Interface ，另一个 Configuration 1 包含 Loopback Function/Interface 。某一时刻只能选择使用一个 Configuration ，通常情况下使用 Configuration 0 即 SourceSink 的功能。

gadget zero Device 由两种方式创建：

1、通过 zero_driver 创建，只要把对应驱动文件 drivers\usb\gadget\legacy\zero.c 编译进内核即可。

2、通过 functionfs 动态创建，这种方式更灵活，实例命令如下：

mount -t configfs none /sys/kernel/config
cd /sys/kernel/config/usb_gadget

mkdir g2
cd g2

echo "0x04e8" > idVendor
echo "0x2d01" > idProduct

mkdir configs/c.1
mkdir configs/c.2
mkdir functions/Loopback.0
mkdir functions/SourceSink.0

mkdir strings/0x409
mkdir configs/c.1/strings/0x409
mkdir configs/c.2/strings/0x409

echo "0x0525" > idVendor
echo "0xa4a0" > idProduct

echo "0123456789" > strings/0x409/serialnumber
echo "Samsung Inc." > strings/0x409/manufacturer
echo "Bar Gadget" > strings/0x409/product

echo "Conf 1" > configs/c.1/strings/0x409/configuration
echo "Conf 2" > configs/c.2/strings/0x409/configuration
echo 120 > configs/c.1/MaxPower

// SourceSink：驱动 set configuration 会选取 第一个 configuration
ln -s functions/Loopback.0 configs/c.2
ln -s functions/SourceSink.0 configs/c.1

echo 4100000.udc-controller > UDC

整个过程就是创建了一个 Vendor ID = 0x0525 、

Product ID =
                    0xa4a0

的 Composite Device ，在 Host 侧可以查看这个设备：

$ lsusb -s 1:3
Bus 001 Device 003: ID 0525:a4a0 Netchip Technology, Inc. Linux-USB "Gadget Zero"

$ lsusb -v -s 1:3

Bus 001 Device 003: ID 0525:a4a0 Netchip Technology, Inc. Linux-USB "Gadget Zero"
Couldn't open device, some information will be missing
Device Descriptor:
bLength                18
bDescriptorType         1
bcdUSB               2.00
bDeviceClass            0
bDeviceSubClass         0
bDeviceProtocol         0
bMaxPacketSize0        64
idVendor           0x0525 Netchip Technology, Inc.
idProduct          0xa4a0 Linux-USB "Gadget Zero"
bcdDevice            5.10
iManufacturer           1
iProduct                2
iSerial                 3
bNumConfigurations      2
Configuration Descriptor:
    bLength                 9
    bDescriptorType         2
    wTotalLength       0x0045
    bNumInterfaces          1
    bConfigurationValue     1
    iConfiguration          4
    bmAttributes         0x80
    (Bus Powered)
    MaxPower              120mA
    Interface Descriptor:
    bLength                 9
    bDescriptorType         4
    bInterfaceNumber        0
    bAlternateSetting       0
    bNumEndpoints           2
    bInterfaceClass       255 Vendor Specific Class
    bInterfaceSubClass      0
    bInterfaceProtocol      0
    iInterface              0
    Endpoint Descriptor:
        bLength                 7
        bDescriptorType         5
        bEndpointAddress     0x81  EP 1 IN
        bmAttributes            2
        Transfer Type            Bulk
        Synch Type               None
        Usage Type               Data
        wMaxPacketSize     0x0200  1x 512 bytes
        bInterval               0
    Endpoint Descriptor:
        bLength                 7
        bDescriptorType         5
        bEndpointAddress     0x01  EP 1 OUT
        bmAttributes            2
        Transfer Type            Bulk
        Synch Type               None
        Usage Type               Data
        wMaxPacketSize     0x0200  1x 512 bytes
        bInterval               0
    Interface Descriptor:
    bLength                 9
    bDescriptorType         4
    bInterfaceNumber        0
    bAlternateSetting       1
    bNumEndpoints           4
    bInterfaceClass       255 Vendor Specific Class
    bInterfaceSubClass      0
    bInterfaceProtocol      0
    iInterface              0
    Endpoint Descriptor:
        bLength                 7
        bDescriptorType         5
        bEndpointAddress     0x81  EP 1 IN
        bmAttributes            2
        Transfer Type            Bulk
        Synch Type               None
        Usage Type               Data
        wMaxPacketSize     0x0200  1x 512 bytes
        bInterval               0
    Endpoint Descriptor:
        bLength                 7
        bDescriptorType         5
        bEndpointAddress     0x01  EP 1 OUT
        bmAttributes            2
        Transfer Type            Bulk
        Synch Type               None
        Usage Type               Data
        wMaxPacketSize     0x0200  1x 512 bytes
        bInterval               0
    Endpoint Descriptor:
        bLength                 7
        bDescriptorType         5
        bEndpointAddress     0x82  EP 2 IN
        bmAttributes            1
        Transfer Type            Isochronous
        Synch Type               None
        Usage Type               Data
        wMaxPacketSize     0x0400  1x 1024 bytes
        bInterval               4
    Endpoint Descriptor:
        bLength                 7
        bDescriptorType         5
        bEndpointAddress     0x02  EP 2 OUT
        bmAttributes            1
        Transfer Type            Isochronous
        Synch Type               None
        Usage Type               Data
        wMaxPacketSize     0x0400  1x 1024 bytes
        bInterval               4
Configuration Descriptor:
    bLength                 9
    bDescriptorType         2
    wTotalLength       0x0020
    bNumInterfaces          1
    bConfigurationValue     2
    iConfiguration          5
    bmAttributes         0x80
    (Bus Powered)
    MaxPower                2mA
    Interface Descriptor:
    bLength                 9
    bDescriptorType         4
    bInterfaceNumber        0
    bAlternateSetting       0
    bNumEndpoints           2
    bInterfaceClass       255 Vendor Specific Class
    bInterfaceSubClass      0
    bInterfaceProtocol      0
    iInterface              6
    Endpoint Descriptor:
        bLength                 7
        bDescriptorType         5
        bEndpointAddress     0x81  EP 1 IN
        bmAttributes            2
        Transfer Type            Bulk
        Synch Type               None
        Usage Type               Data
        wMaxPacketSize     0x0200  1x 512 bytes
        bInterval               0
    Endpoint Descriptor:
        bLength                 7
        bDescriptorType         5
        bEndpointAddress     0x01  EP 1 OUT
        bmAttributes            2
        Transfer Type            Bulk
        Synch Type               None
        Usage Type               Data
        wMaxPacketSize     0x0200  1x 512 bytes
        bInterval               0