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ExecutionTime
Executiontimeshouldbeexpressedininstructioncycleswhereastheperiodexpressedinmicroseconds.
Worst-caseexecutiontimemustbeaccompaniedwithaprecisedescriptionoftherun-timeassumptions
requiredtoreproducethisupperbound.Forexample,placementofcodeanddataininternalorexternal
memory,placementofspecifiedbuffersindual-accessorsingleaccesson-chipmemory,etc.Inparticular,
theworst-caseexecutiontimemustbeaccompaniedbyatableofmemoryrequirements(described
above)necessarytoachievethequotedexecutiontime.Notethattheentriesinthistablearenotrequired
tobeconstants;theymaybefunctionsofthealgorithm'sinstancecreationparameters.
OperationPeriodWorst-CaseCycles/Period
process()22500µs198000
Insomecases,analgorithm'sworst-caseexecutiontimeisaperiodicfunctionoftheframenumber.
Suppose,forexample,thatanaudioencoderconsumes10millisecondsframesofdataatatimebutonly
outputsencodeddataonevery20milliseconds.Inthiscase,theencoder'sworst-caseexecutiontimeon
evenframeswilldiffer(perhapssignificantly)fromtheworst-caseexecutiontimeforoddnumbered
frames;theoutputofdataonlyoccursonoddframes.Inthesesituations,itisimportanttocharacterize
theworst-caseexecutiontimeforeachframe;otherwise,systemintegratorsmay(falsely)concludethatan
algorithmwillnotbeabletobecombinedwithothers.
Allsuchalgorithmsmustcharacterizetheirperiodicexecutiontimerequirementsbyfillinginthetable
below;thenumberofCycles/PeriodcolumnscanbeanyfinitenumberM.Theworst-casenumberinthe
Cycles/PeriodNcolumnmustbetheworst-casenumberofcyclesthatcanoccuronframenumberk*M+
N,wherekisanypositiveinteger.
OperationPeriodCycles/Period
0
Cycles/Period
1
process()22500µs59000198000
SPRU352G–June2005–RevisedFebruary2007AlgorithmPerformanceCharacterization43
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