CHAPTER 5 Input1.ppt

《CHAPTER 5 Input1.ppt》由会员上传分享，免费在线阅读，更多相关内容在教育资源-天天文库。

1、CHAPTER5InputWhatIsInput?IntroductionInputgenerallyplacesgreateremphasisondependability&cost.Inputmustalsoplanforexpandabilityanddiversityofdevices.PerformanceplaysasmallroleforI/Osystems.2DiversityofInput/OutputsystemsThreecharacteristicsareusefulinorganizingthewidevarietyofI/Osystems.Behavi

2、or:Input(readonce),Output(writeonly)orstoragePartner:EitherHumanoramachineattheendoftheI/Odevice.Datarate:Thepeakrateatwhichthedatacanbetransferredbetweenthei/odevicesandmainmemoryorprocessor.Ex:Akeyboard,i/pdeviceusedbyahumanwithdatarateabout10bytespersecond.3AtypicalcollectionofI/Odevices4T

3、ypicalI/Odevices5InterfacingI/OdevicestoprocessormemoryandoperatingsystemsGivingCommandstoi/odevicesBasicallytwotechniquesareusedtoaddressthedevices.1.Memory-mappedI/O:Ani/oschemeinwhichportionsofaddressspaceareassignedtoi/odevices.Ex:Simpleprinterhas2i/odeviceregisters.Statusregister:Itconta

4、insdonebitanderrorbit.Dataregister:Thedatatobeprintedisputintothisregister.62.Alternativemethodistousededicatedi/oinstructionsintheprocessor.Thesespecifyboththedeviceno.andcommandword.Theprocessorcommunicatesviaasetofwiresnormallyincludedasapartofi/obus.Commandscanbetransmittedoverdatalinesin

5、thebus.Ex:IntelIA32,IBM370.7Communicatingwiththeprocessor.Polling:Theprocessofperiodicallycheckingthestatusofthei/odevicestodeterminetheneedtoservicethedevices.Disadvantage:Wasteofprocessortime.InterruptDriveni/oSystems:Itemploysi/ointerruptstoindicatetheprocessorthatani/odeviceneedsattention

6、.Asystemcanuseeithervectorinterruptsoranexceptioncauseregister.11/5/20088ComputerArchitecture&DesignThestatusregisterdetermineswhocaninterruptthecomputer.Amorerefinedblockingofinterruptsisavailableintheinterruptmaskfield.Thereisabitinthemaskcorrespondingeachbitinthependinginterruptfieldofcaus

7、eregister.9TransferringthedatabetweenadeviceandmemoryPollingandi/ointerruptsarethebasicmethodsforimplementingdatatransfer.DirectMemoryAccess:Amechanismthatprovidesadrivercontrollertheabilitytotransferthedatadirectlytoorfrommemorywithoutinvolv