?

/PERATING?3YSTEM?%XTENSIONS?FOR?$YNAMIC

2EAL 4IME?!PPLICATIONSffi

3TEVEN?3OMMER?AND?*OHN?0OTTER

-ICROSOFT?2ESEARCH?)NSTITUTE?ffl
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)NTRODUCTION

4RADITIONAL?REAL TIME?SYSTEMS?;?=?USE?OFF LINE?TECHNIQUES?TO?GUARANTEE?A?PRIORI?THAT?TASKS?WILL MEET? THEIR? DEADLINESffi? 4HESE? TECHNIQUES? ARE? INSUFFICIENT? FOR? HANDLING? REAL TIME? TASKS? WITHIN CONVENTIONAL?OPERATING?SYSTEMS ? WHICH?DO?NOT?HAVE?A?PRIORI?KNOWLEDGE?OF? THE? TASK?SET?AND MUST? SUPPORT? COMPETING? TASKS ? RESOURCE? SHARING ? PROTECTION? BETWEEN? APPLICATIONS DISTRIBUTIONfi?AND?HETEROGENEOUS?ENVIRONMENTSffi

4HIS? PAPER? DESCRIBES? EXTENSIONS? TO? CONVENTIONAL? OPERATING? SYSTEMS? THAT? ALLOW? THEM? TO GUARANTEE? THAT? REAL TIME? TASKS? WILL? MEET? THEIR? DEADLINESffi? 7E? DISCUSS? OUR? SUCCESSFUL IMPLEMENTATION?WITHIN?7INDOWS?.4??AND?DETAIL? THE? MOST? IMPORTANT? COMPONENTSae? A? NEW TYPE? OF? REAL TIME? TASKoe? A? REAL TIME? SCHEDULERoe? AN? ADMISSION? MECHANISMoe? AND? A? METHOD? FOR DYNAMICALLY?ENFORCING?REALflTIME?GUARANTEESffi

4HESE? EXTENSIONS? HAVE? BEEN? DESIGNED? AS? PART? OF? THE? $REAMS? ?$ISTRIBUTED? 2EAL 4IME %XTENSIONS? WITH? !PPLICATION? TO? -ULTIMEDIA? 3YSTEMS?? PROJECT ? WHICH? AIMS? TO? PROVIDE? A COMPLETE?SET?OF?EXTENSIONS? TO? A? CONVENTIONAL? OPERATING? SYSTEM? FOR? RELIABLY? SCHEDULING? AND DISTRIBUTING? DYNAMIC? REAL TIME? APPLICATIONSffi? 4O? MAXIMISE? EASE? OF? ADOPTION? OF? THESE EXTENSIONS ? THEY? AIM? FOR? MINIMAL? IMPACT? ON? THE? CONVENTIONAL? BEHAVIOR? OF? THE? OPERATING SYSTEM?AND?THE?APPLICATION?PROGRAMMING?MODELffi

%XAMPLES?OF?CONVENTIONAL?APPLICATIONS?WHICH?HAVE?REAL TIME?DEMANDS?INCLUDE?VIRTUAL?REALITY VIDEO ?!4- ?MULTIMEDIA ?GENERATED?ANIMATION ?AND?THE?MORE?TRADITIONAL?REAL TIME?TASKS?SUCH AS?ENVIRONMENTAL?PROCESS?MONITORINGfi?SAMPLINGfi?AND?CONTROLffi

/THER?SYSTEMS?HAVE?COMPONENTS?SIMILAR?TO?THOSE?IN?OUR?MODELffi?4HERE?ARE?DYNAMIC?REAL TIME SYSTEMS? THAT? SIMPLY? SCHEDULE? USING? THE? EARLIEST? DEADLINE? FIRST? ALGORITHM? ;?= ? EGffi ? 24 -ACH ;?<==ffi?4HESE?OFFER?NO?ADMISSION?OR?ENFORCEMENT?MECHANISMSffi

4HE?3PRING?+ERNEL?;??=?IS?A?SPECIALISED?REAL TIME?SYSTEM?WHICH?PERFORMS?ON LINE?SCHEDULINGffi )TS? ADMISSION? POLICY? INVOLVES? FINDING? A? POSSIBLE? SCHEDULE? BY? USING? A? FAST? OFF LINE? TYPE HEURISTIC? ANALYSIS? ON? A? CUSTOMISED? PROCESSING? CHIP? RUNNING? IN? PARALLEL? TO? THE? MAIN PROCESSORSffi?!S?A?REAL TIME?SYSTEM ?ALL?TASKS?ARE?PART?OF?A?COHERENT?APPLICATION?AND?PROCESSES ARE? A? PRIORI? GUARANTEED? NEVER? TO? EXCEED? THEIR? RESOURCES ? SO? DYNAMIC? ENFORCEMENT? IS? NOT REQUIREDffi

4HE?!LPHA?+ERNEL?;?=?DEALS?WITH?SYSTEM?OVER COMMITMENT?AS?IT?ARISES?RATHER?THAN?THROUGH?AN ADMISSION?POLICYffi? )T? RESOLVES?CONFLICT?USING? THE? TASKS?? SPECIFIED? VALUE? FUNCTIONS? WHICH?ALLOW THE?SYSTEM?TO?COMPARE?THE?IMPORTANCE?OF?ONE?TASK?AGAINST?ANOTHERffi

4O?SUPPORT?CONTINUOUS?MEDIA?THE?$!3(?SYSTEM?;?=?RESERVES?COMPONENTS ? INCLUDING?SUFFICIENT #05? TIME? TO? PROCESS? A? MESSAGEffi? ROCESSES? ARE? SCHEDULED? BASED? ON? THE? DEADLINE? OF? THE
MESSAGEffi? .ORTHCUTT? ;ss=? ADDRESSES? A? SIMILAR? PROBLEM? OF? TIME CRITICAL? INFORMATION? STREAMS