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GlossaryofTerms
Endian—Referstowhichbytesaremostsignificantinmulti-bytedatatypes.Inbig-endianarchitectures,
theleftmostbytes(thosewithaloweraddress)aremostsignificant.Inlittle-endianarchitectures,
therightmostbytesaremostsignificant.
HP,IBM,Motorola68000,andSPARCsystemsstoremulti-bytevaluesinbig-endianorder,while
Intel80x86,DECVAX,andDECAlphasystemsstoretheminlittle-endianorder.Internetstandard
byteorderingisalsobig-endian.TheTMS320C6000isbi-endianbecauseitsupportsbothsystems.
Frame—Algorithmsoftenprocessmultiplesamplesofdataatatime.Thissetofsamplesissometimes
referredtoasaframe.Inadditiontoimprovingperformance,somealgorithmsrequirespecific
minimumframesizestoproperlyoperate.
Framework—Aframeworkisthatpartofanapplicationthathasbeendesignedtoremaininvariantwhile
selectedsoftwarecomponentsareadded,removed,ormodified.Verygeneralframeworksare
sometimesdescribedasapplicationspecificoperatingsystems.
Instance—Thespecificdataallocatedinanapplicationthatdefinesaparticularobject.
Interface—Asetofrelatedfunctions,types,constants,andvariables.Aninterfaceisoftenspecifiedvia
aCheaderfile.
InterruptLatency—Themaximumtimebetweenwhenaninterruptoccursanditscorresponding
InterruptServiceRoutine(ISR)startsexecuting.
InterruptServiceRoutine(ISR)—AnISRisafunctioncalledinresponsetoaninterruptdetectedbya
CPU.
Method—Thetermmethodisasynonymforafunctionthatcanbeappliedtoanobjectdefinedbyan
interface.
Module—Amoduleisanimplementationofone(ormore)interfaces.Inaddition,allmodulesfollow
certaindesignelementsthatarecommontoallstandard-compliantsoftwarecomponents.Roughly
speaking,amoduleisaClanguageimplementationofaC++class.Sinceamoduleisan
implementationofaninterface,itmayconsistofmanydistinctobjectfiles.
Multithreading—Multithreadingisthemanagementofmultipleconcurrentusesofthesameprogram.
Mostoperatingsystemsandmoderncomputerlanguagesalsosupportmultithreading.
Preemptive—Apropertyofaschedulerthatallowsonetasktoasynchronouslyinterrupttheexecutionof
thecurrentlyexecutingtaskandswitchtoanothertask;theinterruptedtaskisnotrequiredtocall
anyschedulerfunctionstoenabletheswitch.
ProtectionBoundary—Aprotectionboundaryprotectsonesoftwaresubsystemonacomputerfrom
another,insuchawaythatonlydatathatisexplicitlysharedacrosssuchaboundaryisaccessible
totheentitiesonbothsides.Ingeneral,allcodewithinaprotectionboundarywillhaveaccesstoall
datawithinthatboundary.
Thecanonicalexampleofaprotectionboundaryonmostmodernsystemsisthatbetween
processesandthekernel.Thekernelisprotectedfromprocesses,sothattheycanonlyexamineor
changeitsinternalstateincertainstrictlydefinedways.
Protectionboundariesalsoexistbetweenindividualprocessesonmostmodernsystems.This
preventsonebuggyormaliciousprocessfromwreakinghavoconothers.
Whyareprotectionboundariesinteresting?Becausetransferringcontrolacrossthemisoften
expensive;ittakesalotoftimeandwork.MostDSPshavenosupportforprotectionboundaries.
Reentrant—Pertainingtoaprogramorapartofaprograminitsexecutableversion,thatmaybe
enteredrepeatedly,ormaybeenteredbeforepreviousexecutionshavebeencompleted,andeach
executionofsuchaprogramisindependentofallotherexecutions.
RuntoCompletion—Athreadexecutionmodelinwhichallthreadsruntocompletionwithoutever
synchronouslysuspendingexecution.Notethatthisattributeiscompletelyindependentofwhether
threadsarepreemptivelyscheduled.Runtocompletionthreadsmaybepreemptonanother(e.g.,
ISRs)andnon-preemptivesystemsmayallowthreadstosynchronouslysuspendexecution.Note
thatonlyonerun-timestackisrequiredforallruntocompletionthreadsinasystem.
86GlossarySPRU352G–June2005–RevisedFebruary2007
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