SOS - Dynamic operating system for sensor networksEmbedded Sensor NetworksRe-tasking sensor networksRe-programming ChallengesSensor Network OS State of the ArtTowards general purpose sensor OSSOS Operating SystemSOS ApplicationContributionsOutlineArchitecture OverviewSOS OverviewDesigning Safety FeaturesInstalling Dynamic ModulesInter-module CommunicationDynamic Linking OverviewDynamic Linking DesignDynamic Linking Safety FeaturesMessage Passing SystemMessaging Safety FeaturesModule-Kernel CommunicationDynamic Memory AllocationGarbage CollectionSlide 24EvaluationApplication Performance ComparisonPerformance OverheadUpdate CostsLessons LearntSummaryFuture WorkQuestions ?Extra SlidesProgrammingMemory FootprintMicro BenchmarksRe-programming CostSOS ApplicationsMobisys 2005 1SOS - Dynamic operating system for sensor networksSimon Han, Ram Kumar, Roy Shea, Eddie Kohler and Mani Srivastavahttp://nesl.ee.ucla.edu/projects/sosMobisys 20052Embedded Sensor NetworksEmergency ResponseHabitat MonitoringStructural MonitoringResource Constrained NodesLarge scale ad-hoc networksDesign Goal - Long lifetimeMobisys 20053Re-tasking sensor networksData GatheringBird LocalizationFire EmergencyRe-tasking a deployed networkRequires in-situ re-programmingMobisys 20054Re-programming ChallengesSevere resource constraints on nodes4 KB RAM, 128 KB FLASH Instruction Memory, 2 AA batteriesAvoiding crashesUnattended operation - Crashed node is uselessNo architecture support for protection e.g. MMUBalancing flexible and concise updatesUpdate applications, services and driversEnergy efficient distribution and storageMobisys 20055Sensor Network OS State of the ArtTinyOS - Application specific OSApplication, OS and drivers are NesC componentsSelect app components, statically analyze and optimizeExtensive set of well-tuned componentsSupports full binary upgradesMaté - Application specific Virtual MachineDomain specific bytecode interpreter on TinyOSPrograms are small scripts containing VM instructionsBetter suited for application specific tuningInterpreter updates require fallback to TinyOSMobisys 20056Towards general purpose sensor OSTinyOS and MatéApplication and OS are tightly linkedDesign Goal: An application independent sensor OSIndependently written & deployed apps run on one networkTowards traditional kernel space/user space programming modelRe-programming via binary modulesRisk: Lose safety provided by static analysis or dynamic interpreterDesign ChallengeProvide general purpose OS semantics on resource constrained embedded sensor nodesMobisys 20057SOS Operating SystemDynamic operating system for sensor networksKernel and dynamically-loadable modulesPorted to Mica2, MicaZ, XYZ and TelosConvenient, yet compact, kernel interfaceDynamic function links - 10 bytes overhead/functionSafety features through run-time checksType safe linkage, Memory overflow checksPerformanceNo worse than TinyOS for real world applicationsMobisys 20058SOS ApplicationNavigationNavigationObstacle DetectionObstacle DetectionLocalizationLocalizationMotor ControllerMotor ControllerRagobot - Mobile Sensor Node SoftwareAll modules are dynamically loadableInstall new robot behaviors by updating navigation moduleFuture ragobot versions will support hot-swap of peripheralsSOS provides automatic driver updatesMobisys 20059ContributionsFramework for binary modular re-programmingDynamic linkingMessage PassingDynamic MemoryInexpensive safety mechanisms for an embedded OSType safe linkingMonitored memory allocationGarbage collecting scheduler and error stubWatchdog mechanismGeneral purpose OS semantics on sensor nodesMobisys 200510OutlineIntroductionSOS ArchitectureEvaluationConclusionMobisys 200511Architecture OverviewDynamicMemoryDynamicMemoryMessageSchedulerMessageSchedulerDynamicLinkerDynamicLinkerKernelComponentsSensorManagerSensorManagerMessagingI/OMessagingI/OSystemTimerSystemTimerSOSServicesRadio*Radio*I2CI2CADC*ADC*DeviceDriversTree RoutingModuleTree RoutingModuleData CollectorApplicationData CollectorApplicationPhoto-sensorModulePhoto-sensorModuleDynamicallyLoaded modulesStatic SOS Kernel* - Drivers adapted from TinyOS for Mica2Mobisys 200512SOS OverviewProgrammed entirely in CCo-operatively scheduled systemEvent-driven programming modelSystem provides no memory protectionMobisys 200513Designing Safety FeaturesDynamically evolving systemUnspecified behavior resulting from transient statesGoalsEnsure system integrityGraceful recovery from failuresDesignMinimal set of run-time checksDesigned for low resource utilizationDoes not cover all failure modesMobisys 200514<Empty Space>Installing Dynamic ModulesModules implement specific function or taskPosition independent binaryLoader stores module at arbitrary program memory locationMinimal state maintenance8 bytes per moduleStores module identity and versionSOS KernelBootloaderModule 1FLASH Layout<Empty Space>Mobisys 200515Inter-module CommunicationModule FunctionPointer TableDynamicLinkingMessagePassingMessageBufferModule AModule AModule BModule BModule AModule AModule BModule BDynamic LinkingSynchronous communicationBlocking function calls that return promptlyMessage PassingAsynchronous communicationLong running operationsMobisys 200516Dynamic Linking OverviewGoalsLow latency inter-module communication comparable to direct function callsFunctional interface is convenient to programChallengesSafety features to address missing and updated modulesConstraintsMinimize RAM usageMobisys 200517Dynamic Linking DesignPublish functions for the other parts of system to useSubscribe to functions supplied by other modulesIndirection provides support for safety featuresDynamic function call overhead21 cycles compared to 4 cycles for direct function callModule AModule AModule BModule B<foo, B, FOO_ID, Type> <foo, B, FOO_ID, Type> Function Control Block Table (FCB)SubscribePublishMobisys 200518Dynamic Linking Safety FeaturesModule AModule A<foo, B, FOO_ID, Type> <foo, B, FOO_ID, Type> Function Control Block TableModule BModule BError StubError StubRun-time Type CheckingModule updates can introduce new function prototypeType mismatches are detected, error flag is raisedMobisys 200519Tree RoutingModuleTree RoutingModuleData
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