linux usb簡介

參考書：《linux device drivers》、《usb 2.0規範》 《usb3.1規範》《usb白皮書》

 

以linux爲例來講明usb系統。

 

先看一下usb藍牙適配器的詳細信息：

$ lsusb | grep Cambridge
Bus 001 Device 006: ID 0a12:0001 Cambridge Silicon Radio, Ltd Bluetooth Dongle (HCI mode)
$ sudo lsusb -s 001:006 -v
[sudo] password for host: 

Bus 001 Device 006: ID 0a12:0001 Cambridge Silicon Radio, Ltd Bluetooth Dongle (HCI mode)
Device Descriptor:
  bLength                18
  bDescriptorType         1
  bcdUSB               2.00
  bDeviceClass          224 Wireless
  bDeviceSubClass         1 Radio Frequency
  bDeviceProtocol         1 Bluetooth
  bMaxPacketSize0        64
  idVendor           0x0a12 Cambridge Silicon Radio, Ltd
  idProduct          0x0001 Bluetooth Dongle (HCI mode)
  bcdDevice           88.91
  iManufacturer           0 
  iProduct                2 CSR8510 A10
  iSerial                 0 
  bNumConfigurations      1
  Configuration Descriptor:
    bLength                 9
    bDescriptorType         2
    wTotalLength          177
    bNumInterfaces          2
    bConfigurationValue     1
    iConfiguration          0 
    bmAttributes         0xe0
      Self Powered
      Remote Wakeup
    MaxPower              100mA
    Interface Descriptor:
      bLength                 9
      bDescriptorType         4
      bInterfaceNumber        0
      bAlternateSetting       0
      bNumEndpoints           3
      bInterfaceClass       224 Wireless
      bInterfaceSubClass      1 Radio Frequency
      bInterfaceProtocol      1 Bluetooth
      iInterface              0 
      Endpoint Descriptor:
        bLength                 7
        bDescriptorType         5
        bEndpointAddress     0x81  EP 1 IN
        bmAttributes            3
          Transfer Type            Interrupt
          Synch Type               None
          Usage Type               Data
        wMaxPacketSize     0x0010  1x 16 bytes
        bInterval               1
      Endpoint Descriptor:
        bLength                 7
        bDescriptorType         5
        bEndpointAddress     0x02  EP 2 OUT
        bmAttributes            2
          Transfer Type            Bulk
          Synch Type               None
          Usage Type               Data
        wMaxPacketSize     0x0040  1x 64 bytes
        bInterval               1
      Endpoint Descriptor:
        bLength                 7
        bDescriptorType         5
        bEndpointAddress     0x82  EP 2 IN
        bmAttributes            2
          Transfer Type            Bulk
          Synch Type               None
          Usage Type               Data
        wMaxPacketSize     0x0040  1x 64 bytes
        bInterval               1
    Interface Descriptor:
      bLength                 9
      bDescriptorType         4
      bInterfaceNumber        1
      bAlternateSetting       0
      bNumEndpoints           2
      bInterfaceClass       224 Wireless
      bInterfaceSubClass      1 Radio Frequency
      bInterfaceProtocol      1 Bluetooth
      iInterface              0 
      Endpoint Descriptor:
        bLength                 7
        bDescriptorType         5
        bEndpointAddress     0x03  EP 3 OUT
        bmAttributes            1
          Transfer Type            Isochronous
          Synch Type               None
          Usage Type               Data
        wMaxPacketSize     0x0000  1x 0 bytes
        bInterval               1
      Endpoint Descriptor:
        bLength                 7
        bDescriptorType         5
        bEndpointAddress     0x83  EP 3 IN
        bmAttributes            1
          Transfer Type            Isochronous
          Synch Type               None
          Usage Type               Data
        wMaxPacketSize     0x0000  1x 0 bytes
        bInterval               1
    Interface Descriptor:
      bLength                 9
      bDescriptorType         4
      bInterfaceNumber        1
      bAlternateSetting       1
      bNumEndpoints           2
      bInterfaceClass       224 Wireless
      bInterfaceSubClass      1 Radio Frequency
      bInterfaceProtocol      1 Bluetooth
      iInterface              0 
      Endpoint Descriptor:
        bLength                 7
        bDescriptorType         5
        bEndpointAddress     0x03  EP 3 OUT
        bmAttributes            1
          Transfer Type            Isochronous
          Synch Type               None
          Usage Type               Data
        wMaxPacketSize     0x0009  1x 9 bytes
        bInterval               1
      Endpoint Descriptor:
        bLength                 7
        bDescriptorType         5
        bEndpointAddress     0x83  EP 3 IN
        bmAttributes            1
          Transfer Type            Isochronous
          Synch Type               None
          Usage Type               Data
        wMaxPacketSize     0x0009  1x 9 bytes
        bInterval               1
    Interface Descriptor:
      bLength                 9
      bDescriptorType         4
      bInterfaceNumber        1
      bAlternateSetting       2
      bNumEndpoints           2
      bInterfaceClass       224 Wireless
      bInterfaceSubClass      1 Radio Frequency
      bInterfaceProtocol      1 Bluetooth
      iInterface              0 
      Endpoint Descriptor:
        bLength                 7
        bDescriptorType         5
        bEndpointAddress     0x03  EP 3 OUT
        bmAttributes            1
          Transfer Type            Isochronous
          Synch Type               None
          Usage Type               Data
        wMaxPacketSize     0x0011  1x 17 bytes
        bInterval               1
      Endpoint Descriptor:
        bLength                 7
        bDescriptorType         5
        bEndpointAddress     0x83  EP 3 IN
        bmAttributes            1
          Transfer Type            Isochronous
          Synch Type               None
          Usage Type               Data
        wMaxPacketSize     0x0011  1x 17 bytes
        bInterval               1
    Interface Descriptor:
      bLength                 9
      bDescriptorType         4
      bInterfaceNumber        1
      bAlternateSetting       3
      bNumEndpoints           2
      bInterfaceClass       224 Wireless
      bInterfaceSubClass      1 Radio Frequency
      bInterfaceProtocol      1 Bluetooth
      iInterface              0 
      Endpoint Descriptor:
        bLength                 7
        bDescriptorType         5
        bEndpointAddress     0x03  EP 3 OUT
        bmAttributes            1
          Transfer Type            Isochronous
          Synch Type               None
          Usage Type               Data
        wMaxPacketSize     0x0019  1x 25 bytes
        bInterval               1
      Endpoint Descriptor:
        bLength                 7
        bDescriptorType         5
        bEndpointAddress     0x83  EP 3 IN
        bmAttributes            1
          Transfer Type            Isochronous
          Synch Type               None
          Usage Type               Data
        wMaxPacketSize     0x0019  1x 25 bytes
        bInterval               1
    Interface Descriptor:
      bLength                 9
      bDescriptorType         4
      bInterfaceNumber        1
      bAlternateSetting       4
      bNumEndpoints           2
      bInterfaceClass       224 Wireless
      bInterfaceSubClass      1 Radio Frequency
      bInterfaceProtocol      1 Bluetooth
      iInterface              0 
      Endpoint Descriptor:
        bLength                 7
        bDescriptorType         5
        bEndpointAddress     0x03  EP 3 OUT
        bmAttributes            1
          Transfer Type            Isochronous
          Synch Type               None
          Usage Type               Data
        wMaxPacketSize     0x0021  1x 33 bytes
        bInterval               1
      Endpoint Descriptor:
        bLength                 7
        bDescriptorType         5
        bEndpointAddress     0x83  EP 3 IN
        bmAttributes            1
          Transfer Type            Isochronous
          Synch Type               None
          Usage Type               Data
        wMaxPacketSize     0x0021  1x 33 bytes
        bInterval               1
    Interface Descriptor:
      bLength                 9
      bDescriptorType         4
      bInterfaceNumber        1
      bAlternateSetting       5
      bNumEndpoints           2
      bInterfaceClass       224 Wireless
      bInterfaceSubClass      1 Radio Frequency
      bInterfaceProtocol      1 Bluetooth
      iInterface              0 
      Endpoint Descriptor:
        bLength                 7
        bDescriptorType         5
        bEndpointAddress     0x03  EP 3 OUT
        bmAttributes            1
          Transfer Type            Isochronous
          Synch Type               None
          Usage Type               Data
        wMaxPacketSize     0x0031  1x 49 bytes
        bInterval               1
      Endpoint Descriptor:
        bLength                 7
        bDescriptorType         5
        bEndpointAddress     0x83  EP 3 IN
        bmAttributes            1
          Transfer Type            Isochronous
          Synch Type               None
          Usage Type               Data
        wMaxPacketSize     0x0031  1x 49 bytes
        bInterval               1
Device Status:     0x0001
  Self Powered

根據《linux device drivers》中的說明，一個設備能夠有一個或者多個configuration（一般只有一個）,

一個configuration能夠有一個或者多個interface,一個interface中能夠有一個或者多個endpoint.

上面的藍牙適配器有1個configuration,這個configuration有7個interface,每一個interface有2個或者3個endpoint.

在linux驅動中usb設備驅動與interface相對應。

 

usb之間最基本的通訊是經過endpoint完成的，endpoint之間只能向一個方向發送數據（主機到設備(即OUT endpoint)或者設備到主機(即IN endpoint))。

endpoint傳輸數據能夠是下面四種類型之一：

(1) control endpoint: 用於存取usb設備的不通部分，能夠配置設備、向設備發命令或者獲取設備狀態信息。

(2)interrupt endpoint: 主機向設備請求數據量較少時使用，例如鍵盤和鼠標

(3)bulk endpoint:用於大量數據傳送。 若是傳送數據過大，則可能分紅多個塊傳送

(4)isochronous endpoint:能夠傳送大量數據，一般用於能處理數據丟失以及固定速率傳送數據的設備。

 

usb數據傳輸實際是經過packet來進行傳輸的，每一個packet由SYNC(1個字節）、PID(1個字節）、CONTENT（不一樣PID可能有不一樣長度）和CRC(不一樣PID可能有不一樣長度）

詳細的packet定義能夠查看usb規範。

 

interface用於處理一種類型的usb鏈接，例如鼠標或者鍵盤等。前面的藍牙適配器有多個interface,能夠用來支持多個藍牙設備。

interface還可能有alternate setting,　能夠用來選擇不一樣的interface參數值。

 

查看pci設備信息：

$ lspci
00:00.0 Host bridge: Intel Corporation 82G33/G31/P35/P31 Express DRAM Controller (rev 10)
00:02.0 VGA compatible controller: Intel Corporation 82G33/G31 Express Integrated Graphics Controller (rev 10)
00:1b.0 Audio device: Intel Corporation NM10/ICH7 Family High Definition Audio Controller (rev 01)
00:1c.0 PCI bridge: Intel Corporation NM10/ICH7 Family PCI Express Port 1 (rev 01)
00:1c.1 PCI bridge: Intel Corporation NM10/ICH7 Family PCI Express Port 2 (rev 01)
00:1c.2 PCI bridge: Intel Corporation NM10/ICH7 Family PCI Express Port 3 (rev 01)
00:1c.3 PCI bridge: Intel Corporation NM10/ICH7 Family PCI Express Port 4 (rev 01)
00:1d.0 USB controller: Intel Corporation NM10/ICH7 Family USB UHCI Controller #1 (rev 01)
00:1d.1 USB controller: Intel Corporation NM10/ICH7 Family USB UHCI Controller #2 (rev 01)
00:1d.2 USB controller: Intel Corporation NM10/ICH7 Family USB UHCI Controller #3 (rev 01)
00:1d.3 USB controller: Intel Corporation NM10/ICH7 Family USB UHCI Controller #4 (rev 01)
00:1d.7 USB controller: Intel Corporation NM10/ICH7 Family USB2 EHCI Controller (rev 01)
00:1e.0 PCI bridge: Intel Corporation 82801 PCI Bridge (rev e1)
00:1f.0 ISA bridge: Intel Corporation 82801GB/GR (ICH7 Family) LPC Interface Bridge (rev 01)
00:1f.1 IDE interface: Intel Corporation 82801G (ICH7 Family) IDE Controller (rev 01)
00:1f.2 IDE interface: Intel Corporation NM10/ICH7 Family SATA Controller [IDE mode] (rev 01)
00:1f.3 SMBus: Intel Corporation NM10/ICH7 Family SMBus Controller (rev 01)
04:00.0 Ethernet controller: Realtek Semiconductor Co., Ltd. RTL8101E/RTL8102E PCI Express Fast Ethernet controller (rev 02)

安裝tree:

sudo apt-get install tree

查看sysfs中全部usb設備文件：

$ tree /sys/bus/usb/devices/
/sys/bus/usb/devices/
├── 1-0:1.0 -> ../../../devices/pci0000:00/0000:00:1d.7/usb1/1-0:1.0
├── 1-1 -> ../../../devices/pci0000:00/0000:00:1d.7/usb1/1-1
├── 1-1:1.0 -> ../../../devices/pci0000:00/0000:00:1d.7/usb1/1-1/1-1:1.0
├── 1-1.2 -> ../../../devices/pci0000:00/0000:00:1d.7/usb1/1-1/1-1.2
├── 1-1.2:1.0 -> ../../../devices/pci0000:00/0000:00:1d.7/usb1/1-1/1-1.2/1-1.2:1.0
├── 1-1.2:1.1 -> ../../../devices/pci0000:00/0000:00:1d.7/usb1/1-1/1-1.2/1-1.2:1.1
├── 1-1.3 -> ../../../devices/pci0000:00/0000:00:1d.7/usb1/1-1/1-1.3
├── 1-1.3:1.0 -> ../../../devices/pci0000:00/0000:00:1d.7/usb1/1-1/1-1.3/1-1.3:1.0
├── 1-1.3:1.1 -> ../../../devices/pci0000:00/0000:00:1d.7/usb1/1-1/1-1.3/1-1.3:1.1
├── 1-4 -> ../../../devices/pci0000:00/0000:00:1d.7/usb1/1-4
├── 1-4:1.0 -> ../../../devices/pci0000:00/0000:00:1d.7/usb1/1-4/1-4:1.0
├── 2-0:1.0 -> ../../../devices/pci0000:00/0000:00:1d.0/usb2/2-0:1.0
├── 2-2 -> ../../../devices/pci0000:00/0000:00:1d.0/usb2/2-2
├── 2-2:1.0 -> ../../../devices/pci0000:00/0000:00:1d.0/usb2/2-2/2-2:1.0
├── 3-0:1.0 -> ../../../devices/pci0000:00/0000:00:1d.1/usb3/3-0:1.0
├── 3-1 -> ../../../devices/pci0000:00/0000:00:1d.1/usb3/3-1
├── 3-1:1.0 -> ../../../devices/pci0000:00/0000:00:1d.1/usb3/3-1/3-1:1.0
├── 4-0:1.0 -> ../../../devices/pci0000:00/0000:00:1d.2/usb4/4-0:1.0
├── 5-0:1.0 -> ../../../devices/pci0000:00/0000:00:1d.3/usb5/5-0:1.0
├── usb1 -> ../../../devices/pci0000:00/0000:00:1d.7/usb1
├── usb2 -> ../../../devices/pci0000:00/0000:00:1d.0/usb2
├── usb3 -> ../../../devices/pci0000:00/0000:00:1d.1/usb3
├── usb4 -> ../../../devices/pci0000:00/0000:00:1d.2/usb4
└── usb5 -> ../../../devices/pci0000:00/0000:00:1d.3/usb5

本機藍牙適配器鏈接到usb集線器，usb集線器鏈接到pc的一個usb口上。而且usb集線器還鏈接了其餘的一些設備。

從上面的輸出能夠推測，1-1開頭部分應該是usb集線器上鍊接的設備。

/sys/devices/pci0000\:00/0000\:00\:1d.7/usb1應該對應host controller設備，1-1對應struct usb_device.

1-1.2表示藍牙適配器所在hub口，1-1.2:1.0和1-1.2:1.1可能分別表示藍牙適配器的接口。

　

查看這兩個接口的endpoint：

$ ls -d /sys/devices/pci0000\:00/0000\:00\:1d.7/usb1/1-1/1-1.2/1-1.2\:1.0/ep*
/sys/devices/pci0000:00/0000:00:1d.7/usb1/1-1/1-1.2/1-1.2:1.0/ep_02  /sys/devices/pci0000:00/0000:00:1d.7/usb1/1-1/1-1.2/1-1.2:1.0/ep_82
/sys/devices/pci0000:00/0000:00:1d.7/usb1/1-1/1-1.2/1-1.2:1.0/ep_81

$ ls -d /sys/devices/pci0000\:00/0000\:00\:1d.7/usb1/1-1/1-1.2/1-1.2\:1.1/ep*
/sys/devices/pci0000:00/0000:00:1d.7/usb1/1-1/1-1.2/1-1.2:1.1/ep_03  /sys/devices/pci0000:00/0000:00:1d.7/usb1/1-1/1-1.2/1-1.2:1.1/ep_83

1-1.2:1.0下有三個endpoint,對應與lsusb輸出信息中的第一個interface中的3個endpoint.

1-1.2:1.1下有兩個endpoint,對應於lsusb輸出信息中的其餘interface中的2個endpoint。

可是lsusb中總共有7個interface,最後6個interface只用一個interface就能表示，彷佛看起來很奇怪。

仔細看上面的輸出信息能夠知道,最後6個interface確實是一個interface，只是使用了alterate setting,其bAlternateSetting的值分別是0-5，其它組成部分的值如出一轍。