Modular Specification of Hybrid Systems in CHARON

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Modular Specification of Hybrid Systems in
CHARON
R. Alur, R. Grosu, Y. Hur, V. Kumar, I.
Lee University of Pennsylvania SDRL and GRASP

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Software Framework for the Deployment of
Multiple Robots

• 1. High-level modeling language
• - platform independent
• hierarchical and modular
• specify modes and constraints
• hierarchical and sequential composition of modes
• parallel composition of agents

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Software Framework for the Deployment of
Multiple Robots

• 2. Tools for design, programming, and analysis
• simulation and execution
• analysis and optimization
• automated generation of code
• 3. Demonstrate on multiple coordinating robots

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Challenges in Coordinating Multiple Robots

• Large number of modes
• Individual modes are
• well understood, but not
• their interaction.
• Software design
• modes are designed
• bottom up.
• coordination protocols
• are traditionally designed
• top down.

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Charon Framework Architecture
CHARON Code (High level language)
Charon to Java Translator
Java Libraries
Drivers
Java Code
Simulator Code Generator
Control Code Generator
Analysis
Human Interface
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Charon Language

• Individual components described as agents
• Composition, Instantiation, and Hiding
• Individual behaviors described as modes
• Encapsulation, Instantiation, and Scoping
• Support for concurrency
• Shared variables as well as message passing
• Support for discrete and continuous behavior
• Well-defined formal semantics

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Robot Team Approaching a Target
T
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Architectural Hierarchy
Variables Specifiers Range discrete/analog Compu
tation diff/alg Access read/write/local
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Architectural Hierarchy
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Behavioral Hierarchy
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Related Work

• Hybrid automata ACH95
• Analysis, model checkers HyTech AHH96, HHW95
• No compositional models, no hierarchy
• I/O automata LSVW96 and Hybrid Modules AH97
• Compositional models
• No behavioral hierarchy
• SHIFT DGS97 and HyCharts GSB98
• Allow hierarchic specification of hybrid
  behavior
• No concern for modular simulation
• UML BJR97and (hybrid) Statecharts Har87
• Hierarchical but not modular
• Stateflow
• Hierchic specification but only for dynamic
  behavior

Charon is a modeling language for hybrid systems
reflecting the current state of the art both in
formal and object oriented methods (UML)
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Modular Simulation

• Goal
• Simulation is efficient and accurate
• Integration of modes at different time scales
• Integration of agents at different time scales
• Modes are simulated using local information
• Submodes are regarded as black-boxes
• Submodes are simulated independently of other
  ones
• Agents are simulated using local information
• Agents are regarded as black-boxes
• Agents are simulated independently of other ones

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The Simulator
4. The agent executes an update round to
synchronize the discrete variables with the
analog ones.
5. The state of the agent get visible to other
agents
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Time Round of a Mode (Agent)
2. While (time t 0 t lt d) do
- Increment t te.
3. Return s and d
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Update Round of a Mode (Agent)

• Innermost transitions
• have higher priority
• Default transitions are
• taken if all other
• transitions are disabled
• Group transitions start
• at the default exit points
• Transitions to history
• are transitions to the
• default entry point

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Hysteresis Example
inc dX1
dec
inc
dec dX1
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Global vs Modular Simulation
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Modular Simulation Error
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Current Implementation Status
CHARON Specification

• Work to date
• CHARON semantics
• Parser for CHARON
• Internal representation
• Current work
• Type checker
• Modular simulation scheme
• Internal representation generator

CHARON Parser
Type Checker
Syntax Tree
Internal Representation Generator
Internal Representation
Simulator Generator
Control Code Generator
Model Checker
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Ongoing Research

• Distributed simulation
• Accurate event detection
• And modes and And/Or hierarchies
• Exploiting the hierarchy in model checking

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Wrap-Up

• Charon is a language for embedded systems
• reflecting the current state of the art both
• in formal and object oriented methods (UML)
• Its explicit support for a mixed visual/textual
  notation should improve communication among the
  various communities involved in an embedded
  system project.