Device 侧 gadget zero
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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