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基于VXI总线的中断接口设计.docx

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基于VXI总线的中断接口设计 Introduction VXI(VMEeXtensionsforInstrumentation)isabusstandardcreatedfortestandmeasurementequipment.VXIderivesfromtheVMEbus,apopularbusstandardforindustrialcomputersintroducedinthe1980s.VXIimprovesonVMEbusbyaddingfeaturesspecificallyforthetestandmeasurementindustry,suchastriggerlines,clocklines,andinterrupthandling.Inthispaper,wewilldiscussthedesignofaninterruptinterfacebasedonVXIbus. Interrupts Beforediscussingthedesignoftheinterruptinterface,letusbrieflyreviewtheconceptofinterrupts.Aninterruptisasignalthatinterruptsthenormalflowofexecutionofaprogram.Whenaninterruptoccurs,theprocessorstopsexecutingthecurrentprogramandjumpstoaspecialroutinecalledaninterrupthandler.Theinterrupthandlerperformssomespecifictaskrelatedtotheinterrupt,suchasservicinganexternaldevice,andthenreturnscontroltotheinterruptedprogram.Interruptscancomefromhardwaredevices(e.g.,akeyboard)orsoftware(e.g.,asystemcall). InterruptInterfaceDesign InaVXI-basedsystem,interruptsarehandledusingadedicatedinterruptermodule.Theinterruptermoduleisresponsibleforreceivinginterruptrequestsfromvarioussourcesandforwardingthemtotheappropriateinterrupthandlers.TherearetwotypesofinterruptermodulesinVXI:anon-queuedinterrupterandaqueuedinterrupter. Non-queuedInterrupter Anon-queuedinterrupterisasimpleinterrupterthathandlesonlyoneinterruptrequestatatime.Whenaninterruptrequestisreceived,theinterrupterassertsanIRQsignaltotheprocessorandsuppliesaninterruptvectortotheprocessor.Theprocessorthenjumpstotheinterrupthandlerpointedtobytheinterruptvector.Oncetheinterrupthandlerhasfinishedprocessingtheinterrupt,controlreturnstotheinterruptedprogram. Thenon-queuedinterrupterissuitableforsystemswheretheinterruptrateislowandtheinterruptprocessingtimeisshort.However,insystemswheremultipleinterruptsourcesarepresent,aqueuedinterruptermaybenecessary. QueuedInterrupter Aqueuedinterrupterisaninterrupterthatcanhandlemultipleinterruptrequestsatthesametime.Whenaninterruptrequestisreceived,theinterrupterstoresitinaqueue.Thequeuecan