USB通信存儲(chǔ)測(cè)試中的應(yīng)用外文翻譯@中英文翻譯@外文文獻(xiàn)翻譯

英文翻譯 USB 的互連支持?jǐn)?shù)據(jù)在 USB 主機(jī)與 USB 設(shè)備之間的流動(dòng)。這一章主要講述為了簡化主機(jī)上的 客戶軟件 (Software client)與設(shè)備的功能部件 (function)之間的通信而必須的主機(jī)接口 (host interface)。在本章中所涉及的具體實(shí)現(xiàn)部份并不是必要的，這些實(shí)現(xiàn)部份是作為例子來闡述在響應(yīng) USB 設(shè)備請(qǐng)求時(shí)的主機(jī)系統(tǒng)的行為。只要 USB 設(shè)備并不感覺到主機(jī)行為的改變， USB 主機(jī)完全可以提供一個(gè)不同的軟件系統(tǒng)實(shí)現(xiàn)方法。 10.1 USB 主機(jī)概況 10.1.1 概論 圖 10-1 展示了 USB 通信模型之間基本的信息流與互連關(guān)系： 邏輯的信息流 實(shí)際的信息流 圖 10-1 通信模型層次關(guān)系圖 由圖 10-1 可見，主機(jī)與設(shè)備都被劃分成不同的層次。主機(jī)上垂直的箭頭是實(shí)際的信息流。設(shè)備上對(duì)應(yīng)的接口是基于不同實(shí)現(xiàn)的。在主機(jī)與設(shè)備之間的所有通信最終都是通過 USB 的電纜進(jìn)行，然而，在上層的水平層之間存在邏輯的 主機(jī) 設(shè)備信息流。主機(jī)上的客戶軟件和設(shè)備功能部件之間的通信是基于實(shí)際的應(yīng)用需求及設(shè)備所能提供的能力。 客戶軟件與功能部件之間的透明通信的要求，決定主機(jī)和設(shè)備下層部件的功客戶 USB 系統(tǒng) 主機(jī)控制器 功能部件 USB 設(shè)備 USB 總線接口 能以及它們的界面 (interface) 這一章從主機(jī)的角度來描述上述的通信模型，圖 10-2 描述了從主機(jī)角度看到的它與設(shè)備的連接。 主機(jī)在整個(gè) USB 系統(tǒng)中是唯一的，它包括如下幾個(gè)層次。 USB 總線接口 USB 系統(tǒng) (USB System) USB 客戶 (Client) 其中， USB 總線接 口處理電氣及協(xié)議層的互連 (詳見第 7 章及第 8 章 )。從互連的角度看， USB 設(shè)備和 USB 主機(jī)都提供類似的 USB 總線接口，如串行接口引擎(Serial Interface Engine SIE)。由于主機(jī)在 USB 系統(tǒng)中的特殊性， USB 主機(jī)上的總線接口還必須具備主機(jī)控制器的功能 (Host Controller)，主機(jī)控制器具有一個(gè)內(nèi)集成的集線器 (根集線器 )提供與 USB 電纜的連接。 USB 系統(tǒng) (USB System)使用主機(jī)控制器來管理主機(jī)與 USB 設(shè)備的數(shù)據(jù)傳輸。USB 系統(tǒng)與主機(jī)控制器之間的界面基于主機(jī)控制器的硬件特性 。 USB 系統(tǒng)層相對(duì)于主機(jī)控制器而言，處理的是以客戶觀點(diǎn)見到的數(shù)據(jù)傳輸及客戶與設(shè)備的交互。這包括附加的 USB 信息，比如協(xié)議頭 (Protocol Wrappers)。 USB 系統(tǒng)還必須管理 USB 的系統(tǒng)資源，以使得客戶的訪問成為可能。 通道組（到某一接口） IRPS 配置信息 客戶 （管理界面） USB 系統(tǒng)（管理通道） USB 驅(qū)動(dòng)器 主機(jī)軟件 標(biāo)準(zhǔn)通道（到缺省端口地址） 硬件定義 USB 電纜 通道，代表相應(yīng)層之間連接的抽象 圖 10-2 主機(jī)通信圖 USB 系統(tǒng)有三個(gè)主要組成部份 : 主機(jī)控制器驅(qū)動(dòng)（ Host Controller Driver） USB 驅(qū)動(dòng) (USB Driver) 主機(jī)軟件 (host software) 主機(jī)控制器驅(qū)動(dòng)的存在，方便地將各種不同的主機(jī)控制器實(shí)現(xiàn)映射到 USB系統(tǒng)，客戶可以不必知道設(shè)備到底接在哪個(gè)主機(jī)控制器上就能同設(shè)備進(jìn)行通信。USB 驅(qū)動(dòng)提供了基本的面向客戶的主機(jī)界面。在 HCD 與 USB 之間的接口稱為主機(jī)控制器驅(qū)動(dòng)接口 (Host Controller Driver Interface HCDI)。這層接口不能被客戶直接訪問，所以也不是由 USB 具體來完成的。一個(gè)典型的 HCDI 是由支撐各種不同主機(jī)控制器的 操作系統(tǒng)來定義的。 USBD 提供 I/O 請(qǐng)求包 (I/O Request Packets)形式的數(shù)據(jù)傳輸，以某一特定通道來傳輸數(shù)據(jù)。另外， USBD 為它的客戶提供一個(gè)容易被支配及配置的抽象的設(shè)備。作為這種抽象的一部份， USBD 擁有標(biāo)準(zhǔn)通道 (參見第 5 章及第 9 章 )對(duì)設(shè) 主機(jī)控制器 驅(qū)動(dòng) 硬件定義 USB 總線接口 主機(jī)控制器 SIE 備進(jìn)行一些標(biāo)準(zhǔn)的控制。這標(biāo)準(zhǔn)通道實(shí)現(xiàn)了 USBD 與抽象設(shè)備之間的邏輯通信。(見圖 10-2) 在有些操作系統(tǒng)中，提供了額外的非 USB 系統(tǒng)軟件以支持設(shè)備的配置及設(shè)備驅(qū)動(dòng)程序的加載。在這樣的操作系統(tǒng)中，設(shè)備驅(qū)動(dòng)程序應(yīng)使用提供的主機(jī)軟件接口而不是直 接訪問 USBDI。 客戶層描述的是直接與 USB 設(shè)備進(jìn)行交互所需要的軟件包。當(dāng)所有的設(shè)備都已連上系統(tǒng)時(shí)，這些客戶就可以直接通設(shè)備進(jìn)行通信。一個(gè)客戶不能直接訪問設(shè)備的硬件。 該言之，主機(jī)可提供如下的功能 檢測(cè) USB 設(shè)備的連接與斷開。 管理主機(jī)與設(shè)備之間的標(biāo)準(zhǔn)控制流。 管理主機(jī)與設(shè)備之間的數(shù)據(jù)流。 收集狀態(tài)及一些活動(dòng)的統(tǒng)計(jì)數(shù)字。 控制主機(jī)控制器與 USB 設(shè)備的電氣接口，包括提供有限的能源。 在下面的章節(jié)中，我們將較細(xì)的闡述 USBDI 所能提供的功能。對(duì)于特定的主機(jī)平臺(tái) 與操作系統(tǒng)下的實(shí)現(xiàn)接口請(qǐng)參照相關(guān)的操作系統(tǒng)手冊(cè)。 所有的集線器都通過狀態(tài)改變通道報(bào)告它的狀態(tài)的改變，其中包括設(shè)備的連上與斷開等。 USBD 的一類特殊客戶即：集線器驅(qū)動(dòng)器擁有這些狀態(tài)改變通道，接收這些狀態(tài)的改變。對(duì)于像設(shè)備連結(jié)這種狀態(tài)改變，集線器驅(qū)動(dòng)器將加載設(shè)備的驅(qū)動(dòng)程序。在有些系統(tǒng)中，這種集線器驅(qū)動(dòng)程序是操作系統(tǒng)提供的主機(jī)軟件的一部份，它用來管理設(shè)備。 10 1.2 控制機(jī)構(gòu) 控 制 信 號(hào) 可 通 過 帶 內(nèi) 信 號(hào) （ in-band-singling ） 及 帶 外 信 號(hào)(out-of-bard-signaling)兩種方式在主機(jī)與 設(shè)備之間傳輸。帶內(nèi)信號(hào)將控制信息及數(shù)據(jù)信息混在一起用同一通道傳輸，以至于主機(jī)根本就沒有覺察到。而外帶信號(hào)是通過單獨(dú)的通道進(jìn)行傳輸。 任何一個(gè)已連接的設(shè)備都有一個(gè)標(biāo)準(zhǔn)的信息通道，即標(biāo)準(zhǔn)通道。這個(gè)主機(jī)與設(shè)備之間的邏輯的連接用于傳輸 USB 的標(biāo)準(zhǔn)控制信息，比如對(duì)設(shè)備的配置信息等。這些標(biāo)準(zhǔn)通道為 USB 的設(shè)備提供了標(biāo)準(zhǔn)的接口，它也可以用來進(jìn)行基于特定設(shè)備而不同的通信，這些通信由擁有所有這些通道的 USBD 作媒介。 一些特定的設(shè)備可能允許使用額外的信息通道來傳輸特定設(shè)備的控制信息。這些額外的信息通道與標(biāo)準(zhǔn)通道使用同 樣的協(xié)議，但是傳遞的信息是基于特定的設(shè)備的，也不是由 USB 具體標(biāo)準(zhǔn)化的。 USBD 支持和它的客戶共享使用標(biāo)準(zhǔn)通道，它還提供給客戶與設(shè)備相連的其它控制通道的訪問。 10.1.3 數(shù)據(jù)流 主機(jī)控制器在主機(jī)與 USB 設(shè)備之間傳遞數(shù)據(jù)。這些數(shù)據(jù)被看作連續(xù)的字節(jié)流。 USB 支持 4 種形式的數(shù)據(jù)傳輸 控制傳輸。 同步傳輸。 中斷傳輸。 塊傳輸。 有關(guān)于傳輸方式的額外信息請(qǐng)參見第 5 章 每個(gè)設(shè)備具有一到多個(gè)界面以用于客戶與設(shè)備之間的數(shù)據(jù)傳輸。每個(gè)接口由一到多個(gè)在客戶及設(shè)備 端點(diǎn)之間獨(dú)立傳輸?shù)耐ǖ澜M成。 USBD 根據(jù)主機(jī)軟件的請(qǐng)求來初始化這些通道和接口。當(dāng)這些配置請(qǐng)求提出后，主機(jī)控制器將基于主機(jī)軟件所提供的參數(shù)來提供服務(wù)。 每個(gè)通道基于數(shù)據(jù)傳輸模式和請(qǐng)求的有如下幾個(gè)特性： 數(shù)據(jù)傳輸?shù)念l率。 數(shù)據(jù)是以恒定速率提供還是隨機(jī)出現(xiàn)的。 在數(shù)據(jù)傳輸前可延遲的時(shí)間。 在傳輸過程中數(shù)據(jù)的丟失是否是具有災(zāi)難性。 USB 設(shè)備的端口描述了與之相連接的通道的特性。 USB 設(shè)備端口的特性的具體描述可參照第 9 章。 10.1.4 收集狀態(tài)及活動(dòng)統(tǒng)計(jì)數(shù)據(jù) 作為普通的為所有主機(jī)與設(shè)備之間的控制流與數(shù)據(jù)流服務(wù)的 USB 系統(tǒng)與主機(jī)控制器，一直處于隨時(shí)接收狀態(tài)變化及活動(dòng)信息的狀態(tài)，以使軟件能及時(shí)接收并處理這些狀態(tài)的變化。這里并不具體講述需要被跟蹤的狀態(tài)信息及這些狀態(tài)信息的特殊的格式。 10.1.5 電氣接口因素 主機(jī)為連在集線器上的 USB 設(shè)備提供能量。一個(gè)集線器口所能提供的能量具體值在第七章有詳細(xì)說明。 10.2 主機(jī)控制器功能 在所有的實(shí)現(xiàn)中，主機(jī)控制器都必須提供基本相同的功能。主機(jī)控制器對(duì)主機(jī)及設(shè)備來講都必須滿足一定的要求。下面是主機(jī)控制器所 提供的功能的概況。每種功能在下面的小節(jié)中還有具體的說明。 1 狀態(tài)處理 (State Handling) 作為主機(jī)的一部份，主機(jī)控制器報(bào)告及管理它的狀態(tài)。 2 串行化與反串行化 對(duì)于從主機(jī)輸出的數(shù)據(jù)，主機(jī)控制器將協(xié)議及數(shù)據(jù)信息從它原始形狀轉(zhuǎn)換為字位流。而對(duì)于主機(jī)接收的數(shù)據(jù)主機(jī)控制器進(jìn)行反向操作。 3 幀產(chǎn)生 (Frame Generation) 主機(jī)控制器以每 1ms 為單位產(chǎn)生 SOF 標(biāo)志包。 4 數(shù)據(jù)處理 主機(jī)控制器處理從主機(jī)輸入輸出數(shù)據(jù)的請(qǐng)求。 5 協(xié)議引擎 主機(jī)控制器支持 USB 具 體規(guī)定的協(xié)議 6 傳輸差錯(cuò)控制 所有的主機(jī)控制器在發(fā)現(xiàn)和處理已定義的錯(cuò)誤時(shí)展現(xiàn)相似的行為。 7 遠(yuǎn)程喚醒 所有的主機(jī)控制器都應(yīng)具有將總線置于掛起狀態(tài)及在遠(yuǎn)程喚醒事件下重新啟動(dòng)的能力。 8 集線器 集線器提供了標(biāo)準(zhǔn)的將多個(gè) USB 設(shè)備連到主機(jī)控制器的功能。 9 主機(jī)系統(tǒng)接口 主機(jī)控制器在主機(jī)系統(tǒng)控制器之間建立一個(gè)高速的數(shù)據(jù)通道。 下面的各節(jié)將對(duì)上面提到的各功能進(jìn)行詳細(xì)的討論。 10.2.1 狀態(tài)處理 主機(jī)控制器具有一系列 USB 系統(tǒng)管理的狀態(tài)。另外，主機(jī)控制器為 下面兩個(gè)與 USB 有關(guān)的部份提供接口。 狀態(tài)改變傳播 根集線器 根集線器提供與其它 USB 設(shè)備一樣的標(biāo)準(zhǔn)狀態(tài)給集線器驅(qū)動(dòng)器。有關(guān) USB狀態(tài)與其它之間的相互關(guān)系的詳細(xì)討論請(qǐng)參照第 7 章。 主機(jī)控制器的總的狀態(tài)與根集線器及總體的 USB 密不可分。任何一個(gè)對(duì)設(shè)備來說可見的狀態(tài)的改變都應(yīng)反映設(shè)備狀態(tài)的相應(yīng)改變。從而保證主機(jī)控制器與設(shè)備之間的狀態(tài)是一致的。 USB 設(shè)備通過使用恢復(fù)信號(hào)請(qǐng)求喚醒，使設(shè)備回利已配置的狀態(tài)。主機(jī)控制器本身也可以通過同樣的方法產(chǎn)生一個(gè)恢復(fù)事件。主機(jī)控制器通過 使用該實(shí)現(xiàn)系統(tǒng)的某種機(jī)制來通知主機(jī)的其它部份已產(chǎn)生了一個(gè)恢復(fù)事件。 10.2.2 串行化與反串行化 通過物理上的傳輸是以字位流的形式出現(xiàn)的。不管是作為主機(jī)的一部份，還是作為設(shè)備的一部份，串行接口引擎 (STE)處理 USB 傳輸過程中的串行化與文串行化工作。在主機(jī)上，串行接口引擎是主機(jī)控制器的一部份。 The basic flow and interrelationships of the USB communications model are shown in Figure 10-1 Figure 10-1. Interlayer Communications Model The host and the device are divided into the distinct layers depicted in Figure 10-1. Vertical arrows indicate the actual communication on the host. The corresponding interfaces on the device are implementation-specific. All communications between the host and device ultimately occur on the physical USB wire. However, there are logical host-device interfaces between each horizontal layer. These communications, between client software resident on the host and the function provided by the device, are typified by a contract based on the needs of the application currently using the device and the capabilities provided by the device. This client-function interaction creates the requirements for all of the underlying layers and their interfaces. Universal Serial Bus Specification Revision 1.1 208 This chapter describes this model from the point of view of the host and its layers. Figure 10-2 describes, based on the overall view introduced in Chapter 5, the hosts view of its communication with the device. Figure 10-2. Host Communications Universal Serial Bus Specification Revision 1.1 209 There is only one host for each USB. The major layers of a host consist of the following: _ USB bus interface _ USB System _ Client. The USB bus interface handles interactions for the electrical and protocol layers (refer to Chapter 7 and Chapter 8). From the interconnect point of view, a similar USB bus interface is provided by both the USB device and the host, as exemplified by the Serial Interface Engine (SIE). On the host, however, the USB bus interface has additional responsibilities due to the unique role of the host on the USB and is implemented as the Host Controller. The Host Controller has an integrated root hub providing attachment points to the USB wire. The USB System uses the Host Controller to manage data transfers between the host and USB devices. The interface between the USB System and the Host Controller is dependent on the hardware definition of the Host Controller. The USB System, in concert with the Host Controller, performs the translation between the clients view of data transfers and the USB transactions appearing on the interconnect. This includes the addition of any USB feature support such as protocol wrappers. The USB System is also responsible for managing USB resources, such as bandwidth and bus power, so that client access to the USB is possible. The USB System has three basic components: _ Host Controller Driver _ USB Driver _ Host Software. The Host Controller Driver (HCD) exists to more easily map the various Host Controller implementations into the USB System, such that a client can interact with its device without knowing to which Host Controller the device is connected. The USB Driver (USBD) provides the basic host interface (USBDI) for clients to USB devices. The interface between the HCD and the USBD is known as the Host Controller Driver Interface (HCDI). This interface is never available directly to clients and thus is not defined by the USB Specification. A particular HCDI is, however, defined by each operating system that supports various Host Controller implementations. The USBD provides data transfer mechanisms in the form of I/O Request Packets (IRPs), which consist of a request to transport data across a specific pipe. In addition to providing data transfer mechanisms, the USBD is responsible for presenting to its clients an abstraction of a USB device that can be manipulated for configuration and state management. As part of this abstraction, the USBD owns the default pipe (see Chapter 5 and Chapter 9) through which all USB devices are accessed for the purposes of standard USB control. This default pipe represents a logical communication between the USBD and the abstraction of a USB device as shown in Figure 10-2. In some operating systems, additional non-USB System Software is available that provides configuration and loading mechanisms to device drivers. In such operating systems, the device driver shall use the provided interfaces instead of directly accessing the USBDI mechanisms. The client layer describes all the software entities that are responsible for directly interacting with USB devices. When each device is attached to the system, these clients might interact directly with the peripheral hardware. The shared characteristics of the USB place USB System Software between the client and its device； that is, a client cannot directly access the devices hardware. Universal Serial Bus Specification Revision 1.1 210 Overall, the host layers provide the following capabilities: _ Detecting the attachment and removal of USB devices _ Managing USB standard control flow between the host and USB devices _ Managing data flow between the host and USB devices _ Collecting status and activity statistics _ Controlling the electrical interface between the Host Controller and USB devices, including the provision of a limited amount of power. The following sections describe these responsibilities and the requirements placed on the USBDI in greater detail. The actual interfaces used for a specific combination of host platform and operating system are described in the appropriate operating system environment guide. All hubs (see Chapter 11) report internal status changes and their port change status via the status change pipe. This includes a notification of when a USB device is attached to or removed from one of their ports. A USBD client generically known as the hub driver receives these notifications as owner of the hubs Status Change pipe. For device attachments, the hub driver then initiates the device configuration process. In some systems, this hub driver is a part of the host software provided by the operating system for managing devices. 10.1.2 Control Mechanisms Control information may be passed between the host and a USB device using in-band or out-of-band signaling. In-band signaling mixes control information with data in a pipe outside the awareness of the host. Out-of-band signaling places control information in a separate pipe. There is a message pipe called the default pipe for each attached USB device. This logical association between a host and a USB device is used for USB standard control flow such as device enumeration and configuration. The default pipe provides a standard interface to all USB devices. The default pipe may also be used for device-specific communications, as mediated by the USBD, which owns the default pipes of all of the USB devices. A particular USB device may allow the use of additional message pipes to transfer device-specific control information. These pipes use the same communications protocol as the default pipe, but the information transferred is specific to the USB device and is not standardized by the USB Specification. The USBD supports the sharing of the default pipe, which it owns and uses, with its clients. It also provides access to any other control pipes associated with the device. 10.1.3 Data Flow The Host Controller is responsible for transferring streams of data between the host and USB devices. These data transfers are treated as a continuous stream of bytes. The USB supports four basic types of data transfers: _ Control transfers _ Isochronous transfers _ Interrupt transfers _ Bulk transfers. For additional information on transfer types, refer to Chapter 5. Each device presents one or more interfaces that a client may use to communicate with the device. Each interface is composed of zero or more pipes that individually transfer data between the client and a particular endpoint on the device. The USBD establishes interfaces and pipes at the explicit request of the Host Software. The Host Controller provides service based on parameters provided by the Host Software when the configuration request is made. Universal Serial Bus Specification Revision 1.1 211 A pipe has several characteristics based on the delivery requirements of the data to be transferred. Examples of these characteristics include the following: _ the rate at which data needs to be transferred _ whether data is provided at a steady rate or sporadically _ how long data may be delayed before delivery _ whether the loss of data being transferred is catastrophic. A USB device endpoint describes the characteristics required for a specific pipe. Endpoints are described as part of a USB devices characterization information. For additional details, refer to Chapter 9. 10.1.4 Collecting Status and Activity Statistics As a common communicant for all control and data transfers between the host and USB devices, the USB System and the Host Controller are well-positioned to track status and activity information. Such information is provided upon request to the Host Software, allowing that software to manage status and activity information. This specification does not identify any specific information that should be tracked or require any particular format for reporting activity and status information. 10.1.5 Electrical Interface Considerations The host provides power to USB devices attached to the root hub. The amount of power provided by a port is specified in Chapter 7. 10.2 Host Controller Requirements In all implementations, Host Controllers perform the same basic duties with regard to the USB and its attached devices. These basic duties are described below. The Host Controller has requirements from both the host and the USB. The following is a brief overview of the functionality provided. Each capability is discussed in detail in subsequent sections. State Handling As a component of the host, the Host Controller reports and manages its states. Serializer/Deserializer For data transmitted from the host, the Host Controller converts protocol and data information from its native format to a bit stream transmitted on the USB. For data being received into the host, the reverse operation is performed. Frame Generation The Host Controller produces SOF tokens at a period of 1ms. Data Processing The Host Controller processes requests for data transmission to and from the host. Protocol Engine The Host Controller supports the protocol specified by the USB. Transmission Error Handling All Host Controllers exhibit the same behavior when detecting and reacting to the defined error categories. Remote Wakeup All host controlers must have the ability to place the bus into the Suspended state and to respond to bus wakeup events. Root Hub The root hub provides standard hub function to link the Host Controller to one or more USB ports. Universal Serial Bus Specification Revision 1.1 212 Host System Interface Provides a high-speed data path between the Host Controller