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1、USB3.01 Introduction1.1 MotivationThe original motivation for the Universal Serial Bus (USB) came from several considerations, two of the most important being: Ease-of-useThe lack of flexibility in reconfiguring the PC had been acknowledged as the Achilles heel toits further deployment. The combinat
2、ion of user-friendly graphical interfaces and the hardware and software mechanisms associated with new-generation bus architectures have made computers less confrontational and easier to reconfigure. However, from the end users point of view, the PCs I/O interfaces, such as serial/parallel ports, ke
3、yboard/mouse/joystickinterfaces, etc., did not have the attributes of plug-and-play. Port ExpansionThe addition of external peripherals continued to be constrained by port availability. The lackof a bidirectional, low-cost, low-to-mid speed peripheral bus held back the creative proliferation of peri
4、pherals such as storage devices, answering machines, scanners, PDAs,keyboards, and mice. Existing interconnects were optimized for one or two point products. Aseach new function or capability was added to the PC, a new interface had been defined toaddress this need.Initially, USB provided two speeds
5、 (12 Mb/s and 1.5 Mb/s) that peripherals could use. As PCs became increasingly powerful and able to process larger amounts of data, users needed to get more and more data into and out of their PCs. This led to the definition of the USB 2.0 specification in 2000 to provide a third transfer rate of 48
6、0 Mb/s while retaining backward compatibility. In 2005, with wireless technologies becoming more and more capable, Wireless USB was introduced to provide a new cable free capability to USB.USB is the most successful PC peripheral interconnect ever defined and it has migrated heavily into the CE and
7、Mobile segments. In 2006 alone over 2 billion USB devices were shipped and there are over 6 billion USB products in the installed base today. End users “know” what USB is. Product developers understand the infrastructure and interfaces necessary to build a successful product.USB has gone beyond just
8、 being a way to connect peripherals to PCs. Printers use USB tointerface directly to cameras. PDAs use USB connected keyboards and mice. The USB On-The-Go definition provides a way for two dual role capable devices to be connected and negotiate which one will operate as the “host.” USB, as a protoco
9、l, is also being picked up and used in many nontraditional applications such as industrial automation.Now, as technology innovation marches forward, new kinds of devices, media formats, and large inexpensive storage are converging. They require significantly more bus bandwidth to maintain the intera
10、ctive experience users have come to expect. HD Camcorders will have tens of gigabytes of storage that the user will want to move to their PC for editing, viewing, and archiving. Furthermore existing devices like still image cameras continue to evolve and are increasing their storage capacity to hold
11、 even more uncompressed images. Downloading hundreds or even thousands of 10 MB, or larger, raw images from a digital camera will be a time consuming process unless the transfer rate is increased. In addition, user applications demand a higher performance connection between the PC and these increasi
12、ngly sophisticated peripherals. USB 3.0 addresses this need by adding an even higher transfer rate to match these new usages and devices.Thus, USB (wired or wireless) continues to be the answer to connectivity for PC, ConsumerElectronics, and Mobile architectures. It is a fast, bidirectional, low-co
13、st, dynamically attachable interface that is consistent with the requirements of the PC platforms of today and tomorrow.1.2 Objective of the SpecificationThis document defines the next generation USB industry-standard, USB 3.0. The specification describes the protocol definition, types of transactio
14、ns, bus management, and the programming interface required to design and build systems and peripherals that are compliant with this specificationUSB 3.0s goal remains to enable devices from different vendors to interoperate in an openarchitecture, while maintaining and leveraging the existing USB in
15、frastructure (device drivers, software interfaces, etc.). The specification is intended as an enhancement to the PC architecture, spanning portable, business desktop, and home environments, as well as simple device-to-device communications. It is intended that the specification allow system OEMs and
16、 peripheral developers adequate room for product versatility and market differentiation without the burden of carrying obsolete interfaces or losing compatibility.1.3 Scope of the DocumentThe specification is primarily targeted at peripheral developers and platform/adapter developers, but provides v
17、aluable information for platform operating system/ BIOS/ device driver, adapter IHVs/ISVs, and system OEMs. This specification can be used for developing new products and associated software.Product developers using this specification are expected to know and understand the USB 2.0Specification. Spe
18、cifically, USB 3.0 devices must implement device framework commands and descriptors as defined in the USB 2.0 Specification.1.4 USB Product ComplianceAdopters of the USB 3.0 specification have signed the USB 3.0 Adopters Agreement, whichprovides them access to a reasonable and nondiscriminatory (RAN
19、DZ) license from the Promoters and other Adopters to certain intellectual property contained in products that are compliant with the USB 3.0 specification. Adopters can demonstrate compliance with the specification through the testing program as defined by the USB Implementers Forum. Products that d
20、emonstrate compliance with the specification will be granted certain rights to use the USB Implementers Forum logos as defined in the logo license.1.5 Document OrganizationChapters 1 through 4 provide an overview for all readers, while Chapters 5 through 11 contain detailed technical information def
21、ining USB 3.0.Readers should contact operating system vendors for operating system bindings specific toUSB 3.0.1.6 Design GoalsUSB 3.0 is the next evolutionary step for wired USB. The goal is that end users view it as the same as USB 2.0, just faster. Several key design areas to meet this goal are l
22、isted below: Preserve the USB model of smart host and simple device. Leverage the existing USB infrastructure. There are a vast number of USB products in use today. A large part of their success can be traced to the existence of stable software interfaces, easily developed software device drivers, a
23、nd a number of generic standard device class drivers (HID, mass storage, audio, etc.). SuperSpeed USB devices are designed to keep this software infrastructure intact so that developers of peripherals can continue to use the same interfaces and leverage all of their existing development work. Signif
24、icantly improve power management. Reduce the active power when sending data and reduce idle power by providing a richer set of power management mechanisms to allow devices to drive the bus into lower power states. Ease of use has always been and remains a key design goal for all varieties of USB. Pr
25、eserve the investment. There are a large number of PCs in use that support only USB 2.0. There are a larger number of USB 2.0 peripherals in use. Retaining backward compatibility at the Type-A connector to allow SuperSpeed devices to be used, albeit at a lower speed, with USB 2.0 PCs and allow high
26、speed devices with their existing cables to be connected to the USB 3.0 SuperSpeed Type-A connectors.1.7 Related DocumentsUniversal Serial Bus Specification, Revision 2.0USB On-the-Go Supplement to the USB 2.0 Specification, Revision 1.3Universal Serial Bus Micro-USB Cables and Connectors Specificat
27、ion, Revision 1.01EIA-364-1000.01: Environmental Test Methodology for Assessing the Performance of ElectricalConnectors and Sockets Used in Business Office ApplicationsUSB 3.0 Connectors and Cable Assemblies Compliance DocumentUSB SuperSpeed Electrical Test Methodology white paperUSB 3.0 Jitter Budg
28、eting white paperINCITS TR-35-2004, INCITS Technical Report for Information Technology Fibre Channel Methodologies for Jitter and Signal Quality Specification (FC-MJSQ)USB 3.0 Architectural OverviewThis chapter presents an overview of Universal Serial Bus 3.0 architecture and key concepts. USB 3.0 i
29、s similar to earlier versions of USB in that it is a cable bus supporting data exchange between a host computer and a wide range of simultaneously accessible peripherals. The attached peripherals share bandwidth through a host-scheduled protocol. The bus allows peripherals to be attached, configured
30、, used, and detached while the host and other peripherals are in operation.USB 3.0 utilizes a dual-bus architecture that provides backward compatibility with USB 2.0. It provides for simultaneous operation of SuperSpeed and non-SuperSpeed (USB 2.0 speeds)information exchanges. This chapter is organi
31、zed into two focus areas. The first focuses onarchitecture and concepts related to elements which span the dual buses. The second focuses on SuperSpeed specific architecture and concepts.Later chapters describe the various components and specific requirements of SuperSpeed USB in greater detail. The
32、 reader is expected to have a fundamental understanding of the architectural concepts of USB 2.0. Refer to the Universal Serial Bus Specification, Revision 2.0 for complete details.3.1 USB 3.0 System DescriptionUSB 3.0 is a physical SuperSpeed bus combined in parallel with a physical USB 2.0 bus (se
33、eFigure 3-1). It has similar architectural components as USB 2.0, namely: USB 3.0 interconnect USB 3.0 devices USB 3.0 hostThe USB 3.0 interconnect is the manner inwhich USB 3.0 and USB 2.0 devicesconnect to and communicate with theUSB 3.0 host. The USB 3.0 interconnectinherits core architectural el
34、ements fromUSB 2.0, although several are augmented toaccommodate the dual bus architecture.The baseline structural topology is the sameas USB 2.0. It consists of a tiered startopology with a single host at tier 1 andhubs at lower tiers to provide busconnectivity to devices.The USB 3.0 connection mod
35、elaccommodates backwards and forwardcompatibility for connecting USB 3.0 orUSB 2.0 devices into a USB 3.0 bus.Similarly, USB 3.0 devices can be attachedto a USB 2.0 bus. The mechanical andelectrical backward/forwards compatibility for USB 3.0 is accomplished via a composite cable and associated conn
36、ector assemblies that form the dual-bus architecture. USB 3.0 devices accomplish backward compatibility by including both SuperSpeed and non-SuperSpeed bus interfaces. USB 3.0 hosts also include both SuperSpeed and non-SuperSpeed bus interfaces, which are essentially parallel buses that may be activ
37、e simultaneously.The USB 3.0 connection model allows for the discovery and configuration of USB devices at the highest signaling speed supported by the device, the highest signaling speed supported by all hubs between the host and device, and the current host capability and configuration.USB 3.0 hub
38、s are a specific class of USB device whose purpose is to provide additional connection points to the bus beyond those provided by the host. In this specification, non-hub devices are referred to as peripheral devices in order to differentiate them from hub devices. In addition, in USB 2.0 the term “
39、function” was sometimes used interchangeably with device. In this specification a function is a logical entity within a device, see Figure 3-3.The architectural implications of SuperSpeed on hosts and devices are described in detail inSection 3.2.3.1.1 USB 3.0 Physical InterfaceThe physical interfac
40、e of USB 3.0 is comprised of USB 2.0 electrical (Chapter 7 of the USB 2.0 specification), mechanical (Chapter 5), and SuperSpeed physical (Chapter 6) specifications for the buses. The SuperSpeed physical layer is described in Section 3.2.1.3.1.1.1 USB 3.0 MechanicalThe mechanical specifications for
41、USB 3.0 cables and connector assemblies are provided inChapter 5. All USB devices have an upstream connection. Hosts and hubs (defined below) have one or more downstream connections. Upstream and downstream connectors are not mechanically interchangeable, thus eliminating illegal loopback connection
42、s at hubs.USB 3.0 cables have eight primary conductors: three twisted signal pairs for USB data paths and a power pair. Figure 3-2 illustrates the basic signal arrangement for the USB 3.0 cable. In addition to the twisted signal pair for USB 2.0 data path, two twisted signal pairs are used to provid
43、e the SuperSpeed data path, one for the transmit path and one for the receive path.3-2. USB 3.0 CableUSB 3.0 Architectural Overview3-3USB 3.0 receptacles (both upstream and downstream) are backward compatible with USB 2.0connector plugs. USB 3.0 cables and plugs are not intended to be compatible wit
44、h USB 2.0upstream receptacles. As an aid to users, USB 3.0 mandates standard coloring for plastic portions of USB 3.0 plugs and receptacles.Electrical (insertion loss, return loss, crosstalk, etc.) performance for USB 3.0 is defined withregard to raw cables, mated connectors, and mated cable assembl
45、ies, with compliance requirements using industry test specifications established for the latter two categories. Similarly, mechanical (insertion/extraction forces, durability, etc.) and environmental (temperature life, mixed flowinggas, etc.) requirements are defined and compliance established via r
46、ecognized industry test specifications.3.1.2 USB 3.0 PowerThe specification covers two aspects of power: Power distribution over the USB deals with the issues of how USB devices consume power provided by the downstream ports to which they are connected. USB 3.0 power distribution is similar to USB 2
47、.0, with increased supply budgets for devices operating at SuperSpeed. Power management deals with how hosts, devices, hubs, and the USB system software interact to provide power efficient operation of the bus. The power management of the USB 2.0 bus portion is unchanged. The use model for power man
48、agement of the SuperSpeed bus isdescribed in Appendix C.3.1.3 USB 3.0 System ConfigurationUSB 3.0 supports USB devices (all speeds) attaching and detaching from the USB 3.0 at any time. Consequently, system software must accommodate dynamic changes in the physical bus topology. The architectural ele
49、ments for the discovery of attachment and removal of devices on USB 3.0 are identical to those in USB 2.0. There are enhancements provided to manage the specifics of the SuperSpeed bus for configuration and power management.The independent, dual-bus architecture allows for activation of each of the buses independently and provides fo