SDRL and GRASP University of Pennsylvania 6/27/00 MoBIES 1 Design, Implementation, and Validation of Embedded Software (DIVES) Contract No. F C-1707 Rajeev Alur, Vijay Kumar, Insup Lee (PI), and George Pappas Department of Computer and Information Science Department of Electrical Engineering Department of Mechanical Engineering and Applied Mechanics University of Pennsylvania

SDRL and GRASP University of Pennsylvania 6/27/00 MoBIES 2 Our Group Prof. Rajeev Alur (CIS) Prof. Vijay Kumar (MEAM, CIS) Prof. Insup Lee (CIS) Prof. George Pappas (EE, CIS) Dr. Rafael Fierro (Postdoc) Dr. Oleg Sokolsky (Research associate) Joel Esposito (Ph.D. student) Yerang Hur (Ph.D. student) Franjo Ivancic (Ph.D. student)

SDRL and GRASP University of Pennsylvania 6/27/00 MoBIES 3 Outline Goal and approach Modeling language for hybrid systems Analysis approaches Toolset Summary

SDRL and GRASP University of Pennsylvania 6/27/00 MoBIES 4 The DIVES Project Goal –Develop languages, algorithms and tools for hybrid systems to facilitate the development of reliable embedded systems Approach –Design and modeling language (called CHARON) with formal semantics –Analysis, verification, and validation techniques –Programming environment and software tools –Methodology for hybrid embedded systems development

SDRL and GRASP University of Pennsylvania 6/27/00 MoBIES 5 CHARON: Modeling Language Compositional and Modular specification of multi- agent hybrid systems Individual components described as agents –Composition, instantiation, and hiding Individual behaviors described as modes –Encapsulation, instantiation, and scoping Support for both discrete and continuous behavior –Differential as well as algebraic constraints –Discrete transitions can call library routines Resource requirements and constraints Well-defined formal semantics

SDRL and GRASP University of Pennsylvania 6/27/00 MoBIES 6 Architectural Hierarchy in CHARON Each agent can be represented as a parallel composition of sub-agents Agent Robot1 Robot2 sensor actuator processor Input Port Output Port sensor actuator processor

SDRL and GRASP University of Pennsylvania 6/27/00 MoBIES 7 Behavioral Hierarchy in CHARON main awayTargetatTarget controlsensing Entry Port Exit Port Modes Each agent consists of modes or behaviors Modes can in turn consist of submodes

SDRL and GRASP University of Pennsylvania 6/27/00 MoBIES 8 Modes main awayTargetatTarget controlsensing Each agent consists of modes or behaviors A mode describes flow of control inside an agent. Modes contain –Control points (entry points, exit points) –Variables (private, input, output) –Continuous dynamics –Invariants –Transitions –Nested submodes

SDRL and GRASP University of Pennsylvania 6/27/00 MoBIES 9 Specification of Continuous Behavior in CHARON Differential Equations –diff position robot_Pos; –diffEqn diffStop { d (robot_ Pos.x) = 0.0; d (robot_ Pos.y) = 0.0; } Continuous Equations –cont robotEST; –contEqn contEST { robotEST = foo(x) +bar(x); } Invariant Constraints in Modes –inv invTUCost { lub <= x<=gub; }

SDRL and GRASP University of Pennsylvania 6/27/00 MoBIES 10 Sample code in CHARON macro target { x=50.0; y=50.0;} agent Robot ( diff analog position initPos, real speed) { input channel of estimate inLink[5]; output channel of estimate outLink[5]; extern estimate updateEstimate(position, estimate); mode main() { diff analog position myPos; … trans init from main to awayTarget when true do { myPos = initPos; … } mode awayTarget() { inv invAway {myPos != target;} mode moving() { … } mode updating() { … } trans … from … to … when … { … } } trans arrived from awayTarget to atTarget when (myPos == target ); mode atTarget() { diff diffStop { d(myPos.x) = 0.0; d(myPos.y) = 0.0; } robot1 = Robot (iPos, spd) [inLink[1..5],outLink[1..5] = r12inLink,r12outLink,r13inLink, r13outLink,r14inLink,r14outLink, r15outLink,r15outLink; … robot5 = Robot (iPos, spd) [inLink[1..5],outLink[1..5] = r51inLink,r51outLink,r52inLink, r52outLink,r53inLink,r53outLink, r54outLink,r54outLink; Sys = robot1 || robot2 || robot3 || robot 4 || robot5

SDRL and GRASP University of Pennsylvania 6/27/00 MoBIES 11 Analysis Algorithms and Techniques Robust and scalable simulation –Modular –Distributed Model checking Synthesis of embedded hybrid systems Runtime monitoring and checking Theme: Scalability by exploiting modular/hierarchical structure

SDRL and GRASP University of Pennsylvania 6/27/00 MoBIES 12 Modular Simulation x. y. z. 1.Hierarchical modes can be integrated at different time scales 2.Submodes viewed as black-boxes 3.Initial experimental results encouraging , x, inv1 ,x,y,inv2 Goal: To speed up simulation by exploiting the modular structure of specification Challenges: Robustness Scalability Accuracy

SDRL and GRASP University of Pennsylvania 6/27/00 MoBIES 13 Distributed Simulation Process allocation can be done at –Agent level –Mode level Synchronization approach –Conservative: LP (Logical Process) executes only after all values are available Cons: LPs do not utilize concurrency fully –Optimistic: LP executes even though all the values are not ready and roll back later if necessary Cons: rollbacks cause communication overhead Develop an integrated approach Challenges –Speedup –Integrated simulation with real components

SDRL and GRASP University of Pennsylvania 6/27/00 MoBIES 14 Conservative vs. Optimistic time LPs A1 A2  t time LPs A1 A2 A3 t

SDRL and GRASP University of Pennsylvania 6/27/00 MoBIES 15 Model Checking Goal: Atomically determine if a Charon program satisfies a temporal requirement Current technology: symbolic reachability analysis using polyhedra (Hytech, Kronos) Challenges –Scalability –How to handle complex dynamics? Research directions –Discrete approximation using abstractions –Assume-guarantee –Exploiting hierarchical structure

SDRL and GRASP University of Pennsylvania 6/27/00 MoBIES 16 Hierarchical Synthesis for Hybrid Systems Hierarchical synthesis methods require property preserving abstractions of –Continuous systems –Hybrid systems Concurrency theory + control theory Hybrid/timed abstractions of hybrid systems Optimal control of real time systems Mode switching controllers

SDRL and GRASP University of Pennsylvania 6/27/00 MoBIES 17 Runtime Monitoring and Checking Run-time monitoring and checking to validate an implementation Execution is monitored for compliance with formal requirements The approach can be used to –detect incorrect execution of an application –predict error and steer computation –measure statistics of actual execution which can not be measured in either testing or formal verification –certify plug-in components –increase the assurance of a running system

SDRL and GRASP University of Pennsylvania 6/27/00 MoBIES 18 Monitoring and Checking Framework Model Spec Model Spec Property Formal verification Design System Implementation System Implementation Monitoring Script Monitoring Script Implementation Checker/ Corrector Checker/ Corrector System Filter Communication Run-time Check Event Handler Event Handler Corrector Checker

SDRL and GRASP University of Pennsylvania 6/27/00 MoBIES 19 The Overall Architecture Checking based on hybrid system model Distributed monitoring and checking

SDRL and GRASP University of Pennsylvania 6/27/00 MoBIES 20 DIVES Programming Environment CHARON Code (High level language) Java Code Charon to Java Translator Control Code Generator Java Libraries Human Interface Analysis Simulator Code Generator Drivers Model Checker Runtime Monitor Formal Requirements

SDRL and GRASP University of Pennsylvania 6/27/00 MoBIES 21 Toolset components CHARON to intermediate internal representation (IR) Simulator generation from IR Model checking from IR Graphical user interface Error trace generator Runtime monitor and checker generator

SDRL and GRASP University of Pennsylvania 6/27/00 MoBIES 22 Methodology Compositional modeling Stepwise refinement Hierarchical abstractions of physical constraints

SDRL and GRASP University of Pennsylvania 6/27/00 MoBIES 23 Summary DIVES:includes high-level modeling language (Charon) and a design environment reflecting the current state of the art both in formal and object oriented methods (UML) Tools for Formal Analysis –Simulation –Model checking –Controller synthesis –Runtime monitoring Emphasis on hierarchy and compositionality