通用串行总线20规范 英文翻译.docx

通用串行总线20规范 英文翻译.docx

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通用串行总线20规范英文翻译

UniversalSerialBusSpecificationRevision2.0

Introduction

1.1Motivation

TheoriginalmotivationfortheUniversalSerialBus（USB）camefromthreeinterrelatedconsiderations:

•ConnectionofthePCtothetelephone

Itiswellunderstoodthatthemergeofcomputingandcommunicationwillbethebasisforthenext

generationofproductivityapplications.Themovementofmachine-orientedandhuman-orienteddatatypesfromonelocationorenvironmenttoanotherdependsonubiquitousandcheapconnectivity.Unfortunately,thecomputingandcommunicationindustrieshaveevolvedindependently.TheUSBprovidesaubiquitouslinkthatcanbeusedacrossawiderangeofPC-to-telephoneinterconnects.

•Ease-of-use

ThelackofflexibilityinreconfiguringthePChasbeenacknowledgedastheAchilles’heeltoits

furtherdeployment.Thecombinationofuser-friendlygraphicalinterfacesandthehardwareand

softwaremechanismsassociatedwithnew-generationbusarchitectureshavemadecomputersless

confrontationalandeasiertoreconfigure.However,fromtheenduser’spointofview,thePC’sI/Ointerfaces,suchasserial/parallelports,keyboard/mouse/joystickinterfaces,etc.,donothavetheattributesofplug-and-play.

•Portexpansion

Theadditionofexternalperipheralscontinuestobeconstrainedbyportavailability.Thelackofabidirectional,low-cost,low-to-midspeedperipheralbushasheldbackthecreativeproliferationof

peripheralssuchastelephone/fax/modemadapters,answeringmachines,scanners,PDA’s,keyboards,mice,etc.Existinginterconnectsareoptimizedforoneortwopointproducts.AseachnewfunctionorcapabilityisaddedtothePC,anewinterfacehasbeendefinedtoaddressthisneed.

ThemorerecentmotivationforUSB2.0stemsfromthefactthatPCshaveincreasinglyhigherperformanceandarecapableofprocessingvastamountsofdata.Atthesametime,PCperipheralshaveaddedmoreperformanceandfunctionality.UserapplicationssuchasdigitalimagingdemandahighperformanceconnectionbetweenthePCandtheseincreasinglysophisticatedperipherals.USB2.0addressesthisneedbyaddingathirdtransferrateof480Mb/stothe12Mb/sand1.5Mb/soriginallydefinedforUSB.USB2.0isanaturalevolutionofUSB,deliveringthedesiredbandwidthincreasewhilepreservingtheoriginalmotivationsforUSBandmaintainingfullcompatibilitywithexistingperipherals.Thus,USBcontinuestobetheanswertoconnectivityforthePCarchitecture.Itisafast,bi-directional,isochronous,low-cost,dynamicallyattachableserialinterfacethatisconsistentwiththerequirementsofthePCplatformoftodayandtomorrow.

1.2ObjectiveoftheSpecification

Thisdocumentdefinesanindustry-standardUSB.Thespecificationdescribesthebusattributes,theprotocoldefinition,typesoftransactions,busmanagement,andtheprogramminginterfacerequiredtodesignandbuildsystemsandperipheralsthatarecompliantwiththisstandard.

Thegoalistoenablesuchdevicesfromdifferentvendorstointeroperateinanopenarchitecture.ThespecificationisintendedasanenhancementtothePCarchitecture,spanningportable,businessdesktop,andhomeenvironments.ItisintendedthatthespecificationallowsystemOEMsandperipheraldevelopersadequateroomforproductversatilityandmarketdifferentiationwithouttheburdenofcarryingobsoleteinterfacesorlosingcompatibility.

1.3ScopeoftheDocument

ThespecificationisprimarilytargetedtoperipheraldevelopersandsystemOEMs,butprovidesvaluableinformationforplatformoperatingsystem/BIOS/devicedriver,adapterIHVs/ISVs,andplatform/adaptercontrollervendors.Thisspecificationcanbeusedfordevelopingnewproductsandassociatedsoftware.

1.4USBProductCompliance

AdoptersoftheUSB2.0specificationhavesignedtheUSB2.0AdoptersAgreement,whichprovidesthemaccesstoareciprocalroyalty-freelicensefromthePromotersandotherAdopterstocertainintellectualpropertycontainedinproductsthatarecompliantwiththeUSB2.0specification.AdopterscandemonstratecompliancewiththespecificationthroughthetestingprogramasdefinedbytheUSBImplementersForum.ProductsthatdemonstratecompliancewiththespecificationwillbegrantedcertainrightstousetheUSBImplementersForumlogoasdefinedinthelogolicense.

1.5DocumentOrganization

Chapters1through5provideanoverviewforallreaders,whileChapters6through11containdetailedtechnicalinformationdefiningtheUSB.

•PeripheralimplementersshouldparticularlyreadChapters5through11.

•USBHostControllerimplementersshouldparticularlyreadChapters5through8,10,and11.

•USBdevicedriverimplementersshouldparticularlyreadChapters5,9,and10.

ThisdocumentiscomplementedandreferencedbytheUniversalSerialBusDeviceClassSpecifications.Deviceclassspecificationsexistforawidevarietyofdevices.PleasecontacttheUSBImplementersForumforfurtherdetails.

ReadersarealsorequestedtocontactoperatingsystemvendorsforoperatingsystembindingsspecifictotheUSB.

Background

ThischapterpresentsabriefdescriptionofthebackgroundoftheUniversalSerialBus（USB）,includingdesigngoals,featuresofthebus,andexistingtechnologies.

2.1GoalsfortheUniversalSerialBus

TheUSBisspecifiedtobeanindustry-standardextensiontothePCarchitecturewithafocusonPCperipheralsthatenableconsumerandbusinessapplications.ThefollowingcriteriawereappliedindefiningthearchitecturefortheUSB:

•Ease-of-useforPCperipheralexpansion

•Low-costsolutionthatsupportstransferratesupto480Mb/s

•Fullsupportforreal-timedataforvoice,audio,andvideo

•Protocolflexibilityformixed-modeisochronousdatatransfersandasynchronousmessaging

•Integrationincommoditydevicetechnology

•ComprehensionofvariousPCconfigurationsandformfactors

•Provisionofastandardinterfacecapableofquickdiffusionintoproduct

•EnablingnewclassesofdevicesthataugmentthePC’scapability

•FullbackwardcompatibilityofUSB2.0fordevicesbuilttopreviousversionsofthespecification

2.2TaxonomyofApplicationSpace

Figure2-1describesataxonomyfortherangeofdatatrafficworkloadsthatcanbeservicedoveraUSB.Ascanbeseen,a480Mb/sbuscomprehendsthehigh-speed,full-speed,andlow-speeddataranges.Typically,high-speedandfull-speeddatatypesmaybeisochronous,whilelow-speeddatacomesfrominteractivedevices.TheUSBisprimarilyaPCbusbutcanbereadilyappliedtootherhost-centriccomputingdevices.ThesoftwarearchitectureallowsforfutureextensionoftheUSBbyprovidingsupportformultipleUSBHostControllers.

Figure2-1.ApplicationSpaceTaxonomy

2.3FeatureList

TheUSBSpecificationprovidesaselectionofattributesthatcanachievemultipleprice/performanceintegrationpointsandcanenablefunctionsthatallowdifferentiationatthesystemandcomponentlevel.

Featuresarecategorizedbythefollowingbenefits:

Easytouseforenduser

•Singlemodelforcablingandconnectors

•Electricaldetailsisolatedfromenduser（e.g.,busterminations）

•Self-identifyingperipherals,automaticmappingoffunctiontodriverandconfiguration

•Dynamicallyattachableandreconfigurableperipherals

Widerangeofworkloadsandapplications

•Suitablefordevicebandwidthsrangingfromafewkb/stoseveralhundredMb/s

•Supportsisochronousaswellasasynchronoustransfertypesoverthesamesetofwires

•Supportsconcurrentoperationofmanydevices（multipleconnections）

•Supportsupto127physicaldevices

•Supportstransferofmultipledataandmessagestreamsbetweenthehostanddevices

•Allowscompounddevices（i.e.,peripheralscomposedofmanyfunctions）

•Lowerprotocoloverhead,resultinginhighbusutilization

Isochronousbandwidth

•Guaranteedbandwidthandlowlatenciesappropriatefortelephony,audio,video,etc.

Flexibility

•Supportsawiderangeofpacketsizes,whichallowsarangeofdevicebufferingoptions

•Allowsawiderangeofdevicedataratesbyaccommodatingpacketbuffersizeandlatencies

•Flowcontrolforbufferhandlingisbuiltintotheprotocol

Robustness

•Errorhandling/faultrecoverymechanismisbuiltintotheprotocol

•Dynamicinsertionandremovalofdevicesisidentifiedinuser-perceivedreal-time

•Supportsidentificationoffaultydevices

SynergywithPCindustry

•Protocolissimpletoimplementandintegrate

•ConsistentwiththePCplug-and-playarchitecture

•Leveragesexistingoperatingsysteminterfaces

Low-costimplementation

•Low-costsubchannelat1.5Mb/s

•Optimizedforintegrationinperipheralandhosthardware

•Suitablefordevelopmentoflow-costperipherals

•Low-costcablesandconnectors

•Usescommoditytechnologies

Upgradepath

•ArchitectureupgradeabletosupportmultipleUSBHostControllersinasystem

ArchitecturalOverview

ThischapterpresentsanoverviewoftheUniversalSerialBus（USB）architectureandkeyconcepts.TheUSBisacablebusthatsupportsdataexchangebetweenahostcomputerandawiderangeofsimultaneouslyaccessibleperipherals.TheattachedperipheralsshareUSBbandwidththroughahostscheduled,token-basedprotocol.Thebusallowsperipheralstobeattached,configured,used,anddetachedwhilethehostandotherperipheralsareinoperation.

LaterchaptersdescribethevariouscomponentsoftheUSBingreaterdetail.

3.1USBSystemDescription

AUSBsystemisdescribedbythreedefinitionalareas:

•USBinterconnect

•USBdevices

•USBhost

TheUSBinterconnectisthemannerinwhichUSBdevicesareconnectedtoandcommunicatewiththehost.Thisincludesthefollowing:

•BusTopology:

Connectionmodelbetwe