毕业设计论文 外文文献翻译 计算机专业 嵌入式 Linux 应用概述 中英文对照.docx

毕业设计论文 外文文献翻译 计算机专业 嵌入式 Linux 应用概述 中英文对照.docx

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毕业设计论文外文文献翻译计算机专业嵌入式Linux应用概述中英文对照

毕业设计外文资料翻译

（译文）

题目名称：

EmbeddedLinuxapplications:

Anoverview

学院：

计算机科学技术

专业年级：

计算机科学与技术07级

学生姓名：

xx

班级学号：

1班16号

指导教师：

xx

二○一一年四月十日

译文题目：

EmbeddedLinuxapplications:

Anoverview

原文题目：

嵌入式Linux应用：

概述

原文出处：

Internetsource:

忽略:

//

-works/cn/linux/embed/embl/overview/index.html

EmbeddedLinuxapplications:

Anoverview

Linuxnowspansthespectrumofcomputingapplications,includingIBM'stinyLinuxwristwatch,hand-helddevices（PDAsandcellphones）,Internetappliances,thinclients,firewalls,industrialrobotics,telephonyinfrastructureequipment,andevencluster-basedsupercomputers.Let'stakealookatwhatLinuxhastoofferasanembeddedsystem,andwhyit'sthemostattractiveoptioncurrentlyavailable.

One.Emergenceofembeddedsystems

Thecomputersusedtocontrolequipment,otherwiseknownasembeddedsystems,havebeenaroundforaboutaslongascomputersthemselves.Theywerefirstusedbackinthelate1960sincommunicationstocontrolelectromechanicaltelephoneswitches.Asthecomputerindustryhasmovedtowardeversmallersystemsoverthepastdecadeorso,embeddedsystemshavemovedalongwithit,providingmorecapabilitiesforthesetinymachines.Increasingly,theseembeddedsystemsneedtobeconnectedtosomesortofnetwork,andthusrequireanetworkingstack,whichincreasesthecomplexitylevelandrequiresmorememoryandinterfaces,aswellas,youguessedit,theservicesofanoperatingsystem.

Off-the-shelfoperatingsystemsforembeddedsystemsbegantoappearinthelate1970s,andtodayseveraldozenviableoptionsareavailable.Outofthese,afewmajorplayershaveemerged,suchasVxWorks,pSOS,Neculeus,andWindowsCE.

Two.Advantages/disadvantagesofusingLinuxforyourembeddedsystem

AlthoughmostLinuxsystemsrunonPCplatforms,Linuxcanalsobeareliableworkhorseforembeddedsystems.Thepopular"back-to-basics"approachofLinux,whichmakesiteasierandmoreflexibletoinstallandadministerthanUNIX,isanaddedadvantageforUNIXguruswhoalreadyappreciatetheoperatingsystembecauseithasmanyofthesamecommandsandprogramminginterfacesastraditionalUNIX.

Thetypicalshrink-wrappedLinuxsystemhasbeenpackagedtorunonaPC,withaharddiskandtonsofmemory,muchofwhichisnotneededonanembeddedsystem.AfullyfeaturedLinuxkernelrequiresabout1MBofmemory.However,theLinuxmicro-kernelactuallyconsumesverylittleofthismemory,only100KonaPentiumCPU,includingvirtualmemoryandallcoreoperatingsystemfunctions.Withthenetworkingstackandbasicutilities,acompleteLinuxsystemrunsquitenicelyin500KofmemoryonanIntel386microprocessor,withan8-bitbus（SX）.Becausethememoryrequiredisoftendictatedbytheapplicationsneeded,suchasaWebserverorSNMPagent,aLinuxsystemcanactuallybeadaptedtoworkwithaslittleas256KBROMand512KBRAM.Soit'salightweightoperatingsystemtobringtotheembeddedmarket.

AnotherbenefitofusinganopensourceoperatingsystemlikeEmbeddedLinuxoveratraditionalreal-timeoperatingsystem（RTOS）,isthattheLinuxdevelopmentcommunitytendstosupportnewIPandotherprotocolsfasterthanRTOSvendorsdo.Forexample,moredevicedrivers,suchasnetworkinterfacecard（NIC）driversandparallelandserialportdrivers,areavailableforLinuxthanforcommercialoperatingsystems.

ThecoreLinuxoperatingsystemitselfhasafairlysimplemicro-kernelarchitecture.Networkingandfilesystemsarelayeredontopofthemicro-kernelinmodularfashion.Driversandotherfeaturescanbeeithercompiledinoraddedtothekernelatrun-timeasloadablemodules.Thisprovidesahighlymodularbuilding-blockapproachtoconstructingacustomembeddablesystem,whichtypicallyusesacombinationofcustomdriversandapplicationprogramstoprovidetheaddedfunctionality.

Anembeddedsystemalsooftenrequiresgenericcapabilities,which,inordertoavoidre-inventingthewheel,arebuiltwithoff-the-shelfprogramsanddrivers,manyofwhichareavailableforcommonperipheralsandapplications.Linuxcanrunonmostmicroprocessorswithawiderangeofperipheralsandhasareadyinventoryofoff-the-shelfapplications.

Linuxisalsowell-suitedforembeddedInternetdevices,becauseofitssupportofmultiprocessorsystems,whichlendsitscalability.Thiscapabilitygivesadesignertheoptionofrunningareal-timeapplicationonadualprocessorsystem,increasingtotalprocessingpower.SoyoucanrunaLinuxsystemononeprocessorwhilerunningaGUI,forexample,simultaneouslyonanotherprocessor.

TheonedisadvantagetorunningLinuxonanembeddedsystemisthattheLinuxarchitectureprovidesreal-timeperformancethroughtheadditionofreal-timesoftwaremodulesthatruninthekernelspace,theportionoftheoperatingsystemthatimplementstheschedulingpolicy,hardware-interruptsexceptionsandprogramexecution.Sincethesereal-timesoftwaremodulesruninthekernelspace,acodeerrorcanimpacttheentiresystem'sreliabilitybycrashingtheoperatingsystem,whichcanbeaveryseriousvulnerabilityforreal-timeapplications.

Anoff-the-shelfRTOS,ontheotherhand,isdesignedfromthegroundupforreal-timeperformance,andprovidesreliabilitythroughallocatingcertainprocessesahigherprioritythanotherswhenlaunchedbyauserasopposedtobysystem-levelprocesses.Processesareidentifiedbytheoperatingsystemasprogramsthatexecuteinmemoryorontheharddrive.TheyareassignedaprocessIDoranumericalidentifiersothattheoperatingsystemmaykeeptrackoftheprogramscurrentlyexecutingandoftheirassociatedprioritylevels.Suchanapproachensuresahigherreliability（predictability）withtheRTOStimethanLinuxiscapableofproviding.Butall-in-all,it'sstillamoreeconomicalchoice.

Three.DifferenttypesofEmbeddedLinuxsystems

TherearealreadymanyexamplesofEmbeddedLinuxsystems;it'ssafetosaythatsomeformofLinuxcanrunonjustaboutanycomputerthatexecutescode.TheELKS（EmbeddableLinuxKernelSubset）project,forexample,planstoputLinuxontoaPalmPilot.Hereareacoupleofthemorewell-knownsmallfootprintEmbeddedLinuxversions:

ETLinux--acompleteLinuxdistributiondesignedtorunonsmallindustrialcomputers,especiallyPC/104modules.

LEM--asmall（<8MB）multi-user,networkedLinuxversionthatrunson386s.

LOAF--"LinuxOnAFloppy"distributionthatrunson386s.

uClinux--LinuxforsystemswithoutMMUs.CurrentlysupportsMotorola68K,MCF5206,andMCF5207ColdFiremicroprocessors.

uLinux--tinyLinuxdistributionthatrunson386s.

ThinLinux--aminimizedLinuxdistributionfordedicatedcameraservers,X-10controllers,MP3players,andothersuchembeddedapplications.

Softwareandhardwarerequirements

Severaluser-interfacetoolsandprogramsenhancetheversatilityoftheLinuxbasickernel.It'shelpfultolookatLinuxasacontinuuminthiscontext,rangingfromastripped-downmicro-kernelwithmemorymanagement,taskswitchingandtimerservicestoafull-blownserversupportingacompleterangeoffilesystemandnetworkservices.

AminimalEmbeddedLinuxsystemneedsjustthreeessentialelements:

∙Abootutility

∙TheLinuxmicro-kernel,composedofmemorymanagement,processmanagementandtimingservices

∙Aninitializationprocess

Todoinganythingusefulwhileremainingminimal,youalsoneedtoadd:

∙Driversforhardware

∙Oneormoreapplicationprocessestoprovidetheneededfunctionality

Asadditionalrequirementsbecomenecessary,youmightalsowant:

∙Afilesystem（perhapsinROMorRAM）

∙TCP/IPnetworkstack

∙Adiskforstoringsemi-transientdataandswapcapability

∙A32-bitinternalCPU（requiredbyallcompleteLinuxsystems）

Four.Hardwareplatformoptions

Choosingthebesthardwarecanbecomplexbecauseofinternalcompanypolitics,prejudices,legaciesofotherprojects,alackofcompleteoraccurateinformation,andcost,whichshouldtakeintoaccountthetotalproductcostsandnotjusttheCPUitself.Sometimesafast,inexpensiveCPUcanbecomeexpensiveoncebuslogicandthedelaysnecessarytomakeitworkwithotherperipheralsareconsidered.TocalculatethenecessaryspeedofaCPUforanygivenproject,startwitharealisticviewofhowfasttheCPUneedstoruntoaccomplishagiventaskandtripleit.Also,determinehowfastthebusneedstorun.Iftherearesecondarybuses,suchasaPCIbus,considerthemalso.Aslowbus（thatis,onethatissaturatedwithDMAtraffic）cansignificantlyslowdownafastCPU.HerearesomeofthebesthardwaresolutionsforEmbeddedLinuxapplications.

BrightStarEngineering:

BrightStarEngineering'sipEngine-1isacredit-cardsizedsingle-boardcomputerwithEmbeddedLinuxsupport.ItutilizesaPowerPC-basedCPUandprovidesanarrayofon-boardperipherals,includingEthernet,LCD/VideoController,USB,SerialI/O,anda16Kgateuser-configurableFPGA.BSE'sEmbeddedLinuxconfigurationallowsLinuxtobebootedfromtheipEngine'son-board4MBflashmemory.

Calibri:

CalibriTM-133isaready-to-use,compact,multipurposenetworkappliancethatusesEmbeddedLinuxasitsoperatingsystem.Itoffersahighlyefficientandlow-costsolutiontofirewall,VPN,androutingdemands.

EmbeddedPlanet:

EmbeddedPlanethascreatedaPostPC-eracomputerthatcomesloadedwithMontaVista'sHardHatLinux.PoweredbyaPowerPC-basedcomputingengineandmatchingI/Ocard,LinuxPlanetcomesinacolorfultranslucentcasewithatouchscreenandaccesstodigitalandanalogI/O.

Eurotech:

EurotechprovidesembeddedPCSBCandsponsorsET-Linux,acomp