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Design Methodology for

State based Embedded SystemsCase Study: Maze Navigator

Vivek SubramaniamGraduate Student (Masters’

Program)

Department of Computing and Information SciencesKansas State University

Contents

Introduction Design methodology for state based

time triggered systems Case Study: Maze Navigator Demo Questions

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Introduction

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Behavior Control

Behavior – tasks that process external/internal sensory information and issues an action.

Complex behavior – series of alternations of simple behaviors.

Hierarchical Model. Reactive robot control architecture.

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Behavior Control API

Behaviorboolean takeControl( )void action( )void suppress( )

Arbitratorpublic Arbitrator (Behavior[ ]

behaviors)

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Time triggered Architecture

Initiated at predetermined instances of real-time.

Event inputs or interrupts are queued and polled periodically.

Relatively easy to validate, test and certify.

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Maze Navigator

A modification of the Navigator robot as given in Brian Bagnall’s book “Core Lego Mindstorms Programming”.

Sensors and Inputs: Touch sensor, Light Sensor, Timer and two Rotation Sensors.

Actuators: Two motors. Due to limitations of system, a

simulation was developed

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Maze Navigator’s Behavior Model

HOMEHOME

BUMPBUMP

MOVEMOVE

Light SensorLight

Sensor

Touch SensorTouch Sensor

MotorsMotors

SS

SS

SS Point of Suppression

TrueTrue

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Design MethodologyFor

State based Time Triggered systems

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Definition

“Rational Unified Process (RUP) is a framework that can be used to describe specific development process”

- Grady Booch

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Rational Unified Process

ActorsUse-Cases

ActorsUse-Cases

Class DiagramsUse-Case Realizations

Class DiagramsUse-Case Realizations ImplementationImplementation

Use-Case Model(what)

Analysis/Design Models(how)

Actual Code

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Use-Case Realization

WAITWAKEUP

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Use-case realizations with asynchronous waits

Allocating a thread per scenario with Synchronization

Finite State Machine based Implementation

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RUP for Concurrent Programs using Synchronization

ActorsUse-cases

ActorsUse-cases

Class DiagramScenarios

Class DiagramScenarios

Component Code

Component Code

Complete code

Complete code

Global invariants(patterns)

Global invariants(patterns)

Coarse-grained solution

Coarse-grained solution

Fine-grained

code

Fine-grained

code

RUP

Synchronization aspect code development

Specify global invariant

Scenarios identify synchronization regions in which synchronization is required

(A structured approach to develop concurrent programs in UML)

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RUP for time triggered systems using FSM

ActorsUse-Cases

ActorsUse-Cases

Class DiagramsUse-Case realizations

Class DiagramsUse-Case realizations

Revised Class Diagrams

+Scenarios for

threads

Revised Class Diagrams

+Scenarios for

threads

ImplementationImplementation

Use-Case Model

(what)

Analysis/Design Models

(how)

Actual Code

Original Class Diagram +

State information + Active Classes

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Event Triggered Systems

Boundary ClassesBoundary Classes Other ClassesOther Classes

The flow of control is from the Boundary Classes to other classes

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Time Triggered System

Boundary ClassesBoundary Classes Active ClassesActive Classes Other ClassesOther Classes

The flow of control is from Active class to boundary and other classes.

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From this discussion we can see that we have these four options.

Event TriggeredEvent Triggered

Time TriggeredTime Triggered Allocating threadPer scenario

Allocating threadPer scenario

Finite StateMachine

Finite StateMachine

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Methodology

Identify the Use Cases Describe the Use Case realizations

and class diagrams Identify states and thread scenarios Revise Class Diagram and use-case

realization Form the Finite State Machine

Translate to code

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Case Study: Maze Navigator

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Use Cases for Maze Navigator MOVE (true):

Scan for an unvisited/ least visited cell. Determine random No. of steps in the direction of

picked cell. Travel the required No. of steps in that direction.

BUMP (Input from touch sensor): Travels back to the last cell location.

GO HOME (Timer as input): Calculate the angle and distance for initial point (0,0). Rotate for the angle and travel the distance in straight

line. STEER (Inputs from Rotation Sensors):

Uses rotation sensor to find angle rotated and distance traveled.

Keeps the travel in straight line.

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Use Case Model for Maze Navigator

true

Rotation Sensor(right)

Touch Sensor

Light Sensor

Maze Navigator

Motor (right)

Move

Bump

Home

1

1

1

1

1

1

1

1

1

1

1

1

1

1

1

1

1

1

Rotation Sensor (left)Motor (left)

1

1

1

1

11

1

1

1

1

1

1

Steer

1

1

1

1 1

1

1

1

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Class Diagram

Rotation Sensor

+get direction()+get steps()+travel()+forward()+backward()+stop()+get current state()+set current state()+get command()+set command()

Rotation Navigator

Motor

Touch Sensor

Light Sensor

Move Bump Home

Navigator

11

1

1

+take control()+suppress()+action()

«interface»Behavior

2

1

1 2

1

1

1

11

1

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Use Case Realization Example

Scan for a unvisited or least visited cellCalculate random No. of steps to take in

that directionCalculate angle and distanceStart the motorsWait Until required angle is rotated.Stop motorsUpdate geometryStart the motorsWait Until required distance is traveledStop motorsUpdate geometry

Maze Navigator : MOVE Behavior

Asynchronous waits

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Revised Use Case Realization ExampleWait until input trigger

Move Behavior :Scan for unvisited/ least visited cellCalculate random steps in that cells

directionCalculate angle and distanceStart the motors Wait Until required angle is rotated.

Stop motorsUpdate geometryStart the motorsWait Until required distance is traveledStop motorsUpdate geometry

States

Arbitrator thread

Rotation Sensor thread

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takeControlC

takeControlB

takeControlA

actionA

actionC

actionB

Arbitrator thread

Rotation sensor thread

DONE

Finite State Machine Method – Action Call

Legend:

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Revised Class Diagram

+get next state()+set next state()+get action()+set action()

-next state

State Table

+get current state()+set current state()+next state()

Rotation sensor thread

Rotation Sensor+get direction()+get steps()+travel()+forward()+backward()+stop()+get current state()+set current state()+get command()+set command()

Rotation Navigator

Motor

Touch Sensor

Light Sensor

Arbitrator

Current State

Move Bump Home

Navigator

1

1

1

1

+take control()+suppress()+action()

«interface»Behavior

1

1

1

1

2

1

1

1

11

1 2

1

1

1

1

1

111

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Demo

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Acknowledgement

Dr. Masaaki Mizuno Dr. Rodney R. Howell Dr. Mitchell L. Nielsen

Department of Computing and Information SciencesKansas State University

Questions ???