usb-descriptor

usb descriptor

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更新記錄

item	note
20161027	第一版

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目錄

• USB Descriptors
  • Device Descriptor
  • Device Descriptor s
  • Configuration Descriptors
  • Interface Descriptors
  • Endpoint Descriptors
• Device Classes
• 參考

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USB Descriptors

usb descriptors如下：

• Device Descriptors
• Configuration Descriptors
• Interface Descriptors
• Endpoint Descriptors

Device Descriptor

• CH341

  Device Descriptor:
   | bDescriptorType : 1
   | bNumConfigurations : 1
   |---------------------------------------
             |                                                                
             Configuration Descriptor:
                  | bDescriptorType : 2
                  | bNumInterfaces : 1
                  |
                  |----------------------------
                         |
                         Interface Descriptor:
                                | bDescriptorType : 4
                                | bNumEndpoints : 3 
                                |
                                |-----------------------------------------------------------------------------------------------------------------
                                      |                                               |                                                         |
                                      Endpoint Descriptor:                Endpoint Descriptor:                          Endpoint Descriptor:                          
                                          | bDescriptorType : 5

每個descriptor都會填入自已的type如下

Device Descriptor s

Device Descriptors

說明

item	note
bDescriptorType (1)	固定為1
bcdUSB (1.10)	identify the device as a USB 1.0, USB 1.1 or USB 2.0 compliant device
bDeviceClass	Class Code (Assigned by USB Org)
	defines the device type
bMaxPacketSize0	端點0所支持最大數據長度

• bDeviceClass
  If equal to 0xFF, the class code is vendor specified. (表示由厂商自定义设备类型)
  If equal to Zero, each interface specifies it’s own class code (表示由接口描述符来指定)
  0x01~0xfe，表示为USB-IF定义的设备类，例如0x03为HID设备，0x09为HUB设备
  ex. USB Mouse is a Human Interface Device (HID) , 0x03

• bMaxPacketSize0
  端點0所支持最大數據長度
  low speed : 8byte
  high speed : 8, 16,32, 64byte
  full speed : 64byte

Configuration Descriptors

Configuration Descriptors

說明

• wTotalLength
  為1個Configure內部的資料(即下例資料總合)

  - Configure
    - Interface 0
       |- EP1
       |- EP2
    - Interface 1
       |- EP1
       |- EP2

• bMaxPower
  1個單位表示2mA，USB最大輸出500mA，此值最大為250

Interface Descriptors

Interface Descriptors

說明

item	note
bInterfaceNumber	由0開始，表示第幾個interface (indicates the index of the interface descriptor.)
bAlternateSetting	預設為0，由host來設定configuration生成新的EP
bNumEndpoints	表示此interface裡下生成多少EP,以ch341為例有3個(EP2 IN,EP2 OUT, EP1 IN)

Endpoint Descriptors

• Endpoint descriptors are used to describe endpoints other than endpoint zero.

• USB中規定，端點0沒有端點描述符，其餘端點必順包含端點描述符

Endpoint Descriptor

說明

item	1	2	3
bEndpointAddress	0x82 EP 2 IN	0x02 EP 2 OUT	0x81 EP 1 IN
bmAttributes	2	2	3
Transfer Type	Bulk	Bulk	Interrupt
Synch Type	Nonoe	None	None
Usage Type	Data	Data	Data
wMaxPacketSize	0x0020 1x 32 bytes	0x0020 1x 32 bytes	0x0008 1x 8 bytes
bInterval	0	0	1

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Device Classes

Communication Device Class (CDC)

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參考

• AlternateSetting