linux系統路徑：/sys/bus/usb/devices
1-0:1.0 2-1.1:1.0 2-1.5:1.0 2-1.5:1.4 3-0:1.0 usb3
2-0:1.0 2-1.1:1.1 2-1.5:1.1 2-1.6 4-0:1.0 usb4
2-1 2-1.1:1.2 2-1.5:1.2 2-1.6:1.0 usb1
2-1.1 2-1.5 2-1.5:1.3 2-1:1.0 usb2
A. 其中usb1、usb2、usb3、usb4表示MCU上接了4條USB總線，即4個USB主機控制器（4個RootHub）；
B. 2-1 2號總線的1號端口(物理端口，真實的USB口)設備，即Root Hub
C. 2-1.1 2-1爲RootHub，".1"表示RootHub的1號端口設備連接了一個Hub
D. 2-1.1:1.0 2-1爲RootHub，".1"表示RootHub的1號端口設備連接了一個Hub，":1"表示1號配置，".0"表示接口號，1個接口即表示一種功能
E. 2-1.1:1.1 2-1爲RootHub，".1"表示RootHub的1號端口設備連接了一個Hub，":1"表示1號配置，".1"表示接口號，1個接口即表示一種功能
USB設備報文枚舉過程分析：
[10196.531727] ehci_irq: highspeed device disconnect
[10196.536973] ehci_irq: highspeed device connect
//1-1 RootHub 1號總線1號端口
[10196.541713] usb 1-1: USB disconnect, device number 2
[10196.543288] ehci_irq: highspeed device disconnect
[17227.295188] ehci_irq: highspeed device connect
//2-1 RootHub 2號總線1號端口
[17227.530065] usb 2-1: new high-speed USB device number 2 using sunxi-ehci
[17227.681173] usb 2-1: New USB device found, idVendor=0424, idProduct=2517
[17227.688561] usb 2-1: New USB device strings: Mfr=0, Product=0, SerialNumber=0
//2-1:1.0 RootHub 2號總線1號端口，1號配置，0號接口
[17227.699690] hub 2-1:1.0: USB hub found
[17227.704257] hub 2-1:1.0: 7 ports detected
//2-1.1 RootHub爲2-1，在RootHub 1號端口上級聯了hub，並且使用級聯hub的1號端口
[17227.990506] usb 2-1.1: new full-speed USB device number 3 using sunxi-ehci
[17228.090313] usb 2-1.1: device descriptor read/64, error -32
[17228.280520] usb 2-1.1: device descriptor read/64, error -32
[17228.470637] usb 2-1.1: new full-speed USB device number 4 using sunxi-ehci
[17228.570508] usb 2-1.1: device descriptor read/64, error -32
[17228.760635] usb 2-1.1: device descriptor read/64, error -32
[17228.950494] usb 2-1.1: new full-speed USB device number 5 using sunxi-ehci
[17229.370289] usb 2-1.1: device not accepting address 5, error -32
//2-1.6 RootHub爲2-1，在RootHub 1號端口上級聯了hub，並且使用級聯hub的6號端口
[17229.490500] usb 2-1.6: new high-speed USB device number 7 using sunxi-ehci
[17229.622282] usb 2-1.6: New USB device found, idVendor=0b95, idProduct=772b
[17229.629862] usb 2-1.6: New USB device strings: Mfr=1, Product=2, SerialNumber=3
[17229.638246] usb 2-1.6: Product: AX88772B
[17229.642696] usb 2-1.6: Manufacturer: ASIX Elec. Corp.
[17229.648246] usb 2-1.6: SerialNumber: 000001
[17229.976571] asix 2-1.6:1.0 eth1: register 'asix' at usb-sunxi-ehci-1.6, ASIX AX88772B USB 2.0 Ethernet, 00:0e:c6:87:72:01
[17230.220645] usb 2-1.1: new full-speed USB device number 8 using sunxi-ehci
[17230.352509] usb 2-1.1: config 1 has an invalid descriptor of length 0, skipping remainder of the config
[17230.364405] usb 2-1.1: New USB device found, idVendor=0483, idProduct=5740
[17230.372160] usb 2-1.1: New USB device strings: Mfr=1, Product=2, SerialNumber=3
[17230.380321] usb 2-1.1: Product: Composite HID CDC
[17230.385501] usb 2-1.1: Manufacturer: STMicroelectronics
[17230.391462] usb 2-1.1: SerialNumber: 395B35563137
[17230.405648] hid-generic 0003:0483:5740.0001: hiddev0,hidraw0: USB HID v1.11 Device [STMicroelectronics Composite HID CDC] on usb-sunxi-ehci-1.1/input0
[17230.425804] cdc_acm 2-1.1:1.1: This device cannot do calls on its own. It is not a modem.
[17230.443286] cdc_acm 2-1.1:1.1: ttyACM0: USB ACM device
[17236.810364] usb 2-1.4: new high-speed USB device number 9 using sunxi-ehci
[17236.950567] usb 2-1.4: New USB device found, idVendor=3763, idProduct=3c93
[17236.958148] usb 2-1.4: New USB device strings: Mfr=1, Product=2, SerialNumber=0
[17236.966518] usb 2-1.4: Product: Android
[17236.970879] usb 2-1.4: Manufacturer: Android
//2-1.4:1.0 RootHub爲2-1，在RootHub 1號端口上級聯了hub，並且使用級聯hub的4號端口，1號配置，0號端口
[17236.978885] option 2-1.4:1.0: GSM modem (1-port) converter detected
[17236.988588] usb 2-1.4: GSM modem (1-port) converter now attached to ttyUSB0
//2-1.4:1.0 RootHub爲2-1，在RootHub 1號端口上級聯了hub，並且使用級聯hub的4號端口，1號配置，1號端口
[17236.997837] option 2-1.4:1.1: GSM modem (1-port) converter detected
[17237.007254] usb 2-1.4: GSM modem (1-port) converter now attached to ttyUSB1
//2-1.4:1.0 RootHub爲2-1，在RootHub 1號端口上級聯了hub，並且使用級聯hub的4號端口，1號配置，2號端口
[17237.016753] option 2-1.4:1.2: GSM modem (1-port) converter detected
[17237.026222] usb 2-1.4: GSM modem (1-port) converter now attached to ttyUSB2
//2-1.4:1.0 RootHub爲2-1，在RootHub 1號端口上級聯了hub，並且使用級聯hub的4號端口，1號配置，3號端口
[17237.042223] cdc_ether 2-1.4:1.3 usb0: register 'cdc_ether' at usb-sunxi-ehci-1.4, CDC Ethernet Device, 9e:08:f0:10:ff:04