Input Output Organization.pdf

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1、SFTW230:SystemsandNetworksIComputerOrganizationTopicscovered:Chapter4.Input/OutputOrganizationDr.WUWen,FST,UMOutlineßAccessingI/OdevicesßTransferringdatabetweenI/OdeviceandprocessorßStandardI/Ointerfaces14.1AccessingI/Odevices(From:wiki)•MultipleI/Odevicesmaybeconnectedtoth

2、eprocessorandthememoryviaabus.•Busconsistsofthreesetsoflinestocarryaddress,dataandcontrolsignals.•EachI/Odeviceisassignedauniqueaddress.•ToaccessanI/Odevice,theprocessorplacestheaddressontheaddresslines.•Thedevicerecognizestheaddress,andrespondsthecommandsonthecontrolsignal

3、s.2AccessingI/Odevices(cont.)TwomethodstoaddresstheI/OdevicesbyprocessorßMemory-mappedI/O©I/Odevicesandmemorysharethesameaddressspace©AnymachineinstructionthatcanaccessmemorycanbeusedtotransferdatatoorfromanI/Odevice.ßSpecialI/Oinstruction©DedicatedI/Oinstructionsisusedtoin

4、theprocessor.©Options•AseparateaddressspaceforI/Odevicesorshare–Theformerone:I/Odevicesmaydealwithfeweraddresslines–Usuallyaspartofaddresslines,withacontrolsignaltoindicatewhetheritisamemoryaddressoranI/Oaddress.©Intelx86•INandOUT3I/OinterfaceAddresslinesBusDatalinesControl

5、linesAddressControlDataandI/OdecodercircuitsstatusregistersinterfaceInputdeviceI/OinterfacecircuitcoordinatesI/Otransfers.•I/OdeviceisconnectedtothebususinganI/Ointerfacecircuitwhichhas:-Addressdecoder,controlcircuit,anddataandstatusregisters.•Addressdecoderdecodestheaddres

6、splacedontheaddresslinesthusenablingthedevicetorecognizeitsaddress.•Dataregisterholdsthedatabeingtransferredtoorfromtheprocessor.•StatusregisterholdsinformationnecessaryfortheoperationoftheI/Odevice.•Dataandstatusregistersareconnectedtothedatalines,andhaveuniqueaddresses.4A

7、ccessingI/Odevices(cont.)ßI/OdevicescommunicatingwiththeprocessorDataratesofdiversityI/Odevices5AccessingI/Odevices(cont.)ßSynchronizingmethodsareneeded©Polling(Program-controlledI/O)•PeriodicallycheckingthestatusofanI/Odevicetodeterminetheneedtoservicethedevice•Simplestway

8、•Wastealotofprocessortime©Interrupt-drivenI/O•Employsinterruptstoindicatetotheproc