USB 协议 (二) 术语

extensible-host-controler-interface-usb-xhci.pdf
Universal Serial Bus 3.0 Specification.pdf

xHCI
	eXtensible Host Controller Interface (xHCI) 
	可扩展的 主机 控制器 接口
	describes the register-level host controller interface for Universal Serial Bus (0) Revision 2.0 and above

Root Hub
	A (tier 1) Root Hub is always presented by the xHC. Refer to section 4.19 for more information.
	xHC始终提供（第1层）根集线器。有关更多信息，请参阅第4.19节。
Root Hub Port
	The downstream port on a Root Hub.
	根集线器上的下游端口。

Default Control Endpoint
	The Default Control Endpoint always exists once a USB
	device is powered, in order to provide access to the device's
	configuration, status, and control information. The Default
	Control Endpoint is always endpoint number '0'.
	一旦USB设备通电，默认控制端点始终存在，以便提供对设备配置、状态和控制信息的访问。
	默认控制端点始终为端点编号“0”。

Device Context Base Address Array
	The Device Context Base Address Array contains 256
	entries and supports up to 255 USB devices or hubs, where
	each element in the array is a 64-bit pointer to the base
	address of a Device Context. Entry 0 is reserved.
	设备上下文基址数组包含256个条目(数组)，最多支持255个USB设备或集线器.每个设备有一个数组,(每个数组成员存储了不同上下文的基址)
	其中数组中的每个元素是一个64位指针，指向设备上下文的基址
	条目0已保留。 // 条目0 ??
	
Device Context
	A Device Context is a data structure that describes an
	individual USB device attached to the host controller. A
	Device Context is organized as an array of up to 32 context
	data structures, consisting of 1 Slot Context and up to 31
	Endpoint Context data structures.
	
	设备上下文是描述连接到主机控制器的单个USB设备的数据结构。
	
	设备上下文组织为多达32个上下文数据结构的数组，由1个插槽上下文和多达31个端点上下文数据结构组成。
	
	中间的每个数组最多有32个成员.每个成员指向的结构体 为 32 个字节(该32个字节为 context data structure)

Dequeue Pointer
	The Dequeue Pointer is a pointer into a TRB Ring. It
	references the next TRB in a TRB Ring to be processed by
	the consumer of TRB Ring work items. The Dequeue
	Pointer for Transfer and Command Rings is NOT defined as
	a physical xHC register. A facsimile of this pointer is
	maintained internally by the xHC and system software to
	manage a respective ring.
	
	出列指针是指向TRB环的指针。
	它引用TRB环中要由TRB环工作项的使用者处理的下一个TRB。
	传输环和命令环的出列指针未定义为物理xHC寄存器。
	xHC和系统软件在内部维护该指针的传真，以管理相应的环。

Enqueue Pointer
	The Enqueue Pointer is a pointer into a TRB Ring. It
	references the next TRB location available to producer for
	scheduling work items to the Ring. The Enqueue Pointer is
	NOT defined as a physical xHC register. A facsimile of this
	pointer is maintained internally by the xHC and system
	software to manage a respective ring.

	排队指针是指向TRB环的指针。
	它引用生产者可用于将工作项调度到环的下一个TRB位置。
	排队指针未定义为物理xHC寄存器。
	xHC和系统软件在内部维护该指针的传真，以管理相应的环。


Transfer Request Block(TRB)
	A TRB is a small, flexible data structure in memory that
	defines the characteristics of a single DMA operation
	executed by the xHC.

Transfer Ring
	A Transfer Ring is a TRB Ring associated with an Endpoint
	Context. Each Transfer Ring describes the scheduled work
	items for a single USB Endpoint.
Transfer Type
	Determines the characteristics of the data flow between a
	software client and its function. Four standard transfer
	types are defined: control, interrupt, bulk, and isochronous.

TRB Ring
	A TRB Ring is defined by three parameters: 
		a pointer to the TRB Ring data structure base address, 
		and Enqueue Pointers that define the “active” TRBs in the ring
		and Dequeue Pointers that define the “active” TRBs in the ring.

TBR 种类
	Event Data TRB
		A Normal Transfer TRB with its Event Data (ED) flag equal to ‘1’. Refer to section 4.11.5.2.
	Isoch TRB
		An Isochronous Transfer Request Block that is always the
		first TRB of an Isoch TD. They are only found on the
		Transfer Rings associated with Isoch Endpoints. Refer to
		section 4.11.2.3.

	Link TRB
		A Transfer Request Block that is always the last TRB of a
		TRB Ring Segment. Link TRBs are used to form large, non-
		contiguous Transfer Rings that cross Page boundaries.
		Refer to section 4.11.5.1.
	Normal TRB
		A Normal Transfer Request Block that is used on transfer
		Rings to define a single contiguous buffer for a data
		transfer. Normal TRBs may be “chained” to support
		scatter/gather or buffer concatenation operations. Refer to
		section 4.11.2.1.
	Setup Stage TRB
		A Setup Stage Transfer Request Block that is always the
		first TRB of a Setup Stage TD. They are only found on the
		Transfer Rings associated with Control Endpoints. Refer to
		section 4.11.2.2.