Design Methodology
for
State based Embedded Systems
Case Study: Robot Controller
Phaneendra Vanka
Graduate Student (Masters’ Program)
Department of Computing and Information Sciences
Kansas State University
Contents
Introduction
 Demo
 Design Methodology for Time-Triggered State
Machine based systems
 Case Study: Robot Controller
 Questions

Department of Computing and Information Sciences
Kansas State University
Introduction
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Behavior Control
Behavior – tasks that process external/internal
sensory information and issues an action.
 Reactive robot control architecture.
 Complex behavior – series of alternations of
simple behaviors.
 Hierarchical Model.

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LEGO MINDSTORMS
Robotics Invention System Kit consists of
motors, touch sensors, light sensors, bricks,
gears etc.
 RCX Brick
- Hitachi H8/3292 series microcontroller.
- 16 MHz of clock speed.
- 16Kb ROM.
- 32 Kb external RAM.

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leJOS
Java Platform for the RCX Brick.
 leJOS API
- java.lang, java.util and java.io
- classes to control motors, sensors,
buttons, IR communication, navigation
etc.

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Behavior Control API
Behavior
boolean takeControl( )
void action( )
void suppress( )
Arbitrator
public Arbitrator (Behavior[ ] behaviors)
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Kansas State University
Robot Controller
A modification of the Navigator robot as given
in Brian Bagnall’s book “Core Lego Mindstorms
Programming”.
 Sensors and Inputs: Touch sensor, Timer and
two Rotation Sensors.
 Actuators: Three motors.

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Kansas State University
Behavior’s of Robot Controller

MOVE (true):


COMMAND (Input from IR transceiver):


Travels 20 units in backward direction.
GO HOME (Timer as input):


Travel to a predefined point. If there is an obstacle go around
that obstacle
BUMP (Input from touch sensor):


Travel to a random point
Travel to the starting point
ARM ROTATE (Timer as input):

.
Rotate the arm
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Robot Controller’s Behavior Model
Timer
GO HOME
Touch Sensor
BUMP
S
Command
COMMAND
S
Default
MOVE
Timer
ARM ROTATE
S
S
Motors
Point of Suppression
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DEMO
Department of Computing and Information Sciences
Kansas State University
Design Methodology for Time-Triggered
State Machine based systems
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Kansas State University
Rational Unified Process
Actors
Class Diagrams
Use-Cases
Use-Case
realizations
Use-Case Model
Analysis/Design
(what)
(how)
Implementation
Actual code
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Use-Case realizations
WAIT
WAKEUP
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Use-Case realizations with asynchronous
waits
Allocating a thread for each scenario with
synchronization code
 Finite State Machine based implementation

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Allocating a thread for each scenario
Actors
Class Diagrams
Use-Cases
Use-Case
realizations
Component code
Identify regions in which
synchronization is required
Global
invariants
(patterns)
Coarsegrained
solution
Complete
code
Fine-grained
code
A Structured Approach to Develop Concurrent Programs in UML,
Masaaki Mizuno, Gurdip Singh, Mitchell Nielsen
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Kansas State University
Finite State Machine based implementation
Actors
Class Diagrams
Use-cases
Use-case
realizations
Revised Class
Diagram
Scenarios for
threads
Original Class
Diagram + State
information +
Active Classes
Implementation
Time Triggered
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Event Triggered Systems
Boundary Class
Other Classes
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Time Triggered Systems
Boundary Class
Active Class
Other Classes
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Kansas State University
From the above discussion we have the
following combinations

Time Triggered

Event Triggered
State Machine based
implementation
Thread for each scenario
Department of Computing and Information Sciences
Kansas State University
Case Study : Robot Controller
Department of Computing and Information Sciences
Kansas State University
Use Cases for Robot Controller

MOVE (true):




COMMAND (Input from IR transceiver):



Travel 20 units in backward direction.
GO HOME (Timer as input):



Calculate the angle and distance to (MAXX, MAXY).
Rotate for the angle and travel the distance in straight line.
BUMP (Input from touch sensor):


Pick up a random point (x,y) to reach.
Calculate the angle and distance to (x,y).
Rotate for the angle and travel the distance in straight line.
Calculate the angle and distance for initial point (0,0).
Rotate for the angle and travel the distance in straight line.
ARM ROTATE (Timer as input):


Rotate the arm in forward direction for 2 seconds
Rotate the arm in backward direction for 2 seconds
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 Robot Controller
1..1
Tippy Senior
default
1..1
Move Behavior
1..1
1..1
1..1
1..1
1..1
1..1
Command
1..1
1..1
1..1
1..1
Command Behavior
1..1
1..1
1..1
bump
Left Motor
1..1
Bump Behavior
1..1
1..1
1..1
1..1
1..1
1..1
GoHome timer
GoHome Behavior
1..1
1..1
1..1
1..1
1..1
1..1
1..1
1..1
1..1
1..1
1..1
Steer
1..1
1..1
1..1
1..1
1..1
1..1
1..1
Right Motor
1..1
1..1
1..1
1..1
Left Rotational Sensor
Arm Rotate
1..1
1..1
1..1
Right Rotational Sensor
1..1
Arm Motor
Arm timer
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Motor
Class Diagram
3
RotationNavigator
RotationSensor
2
1
+getX() : int
+getY() : int
+getAngle() : double
+rotate()
+gotoPoint()
+travel()
+forward()
+backward()
+updateCoordinate()
+updateAngle()
+halt()
+stop()
+setCommand()
+checkRotate()
+checkForward()
+checkBackward()
IRTransceiver
Touch Sensor
1
1
Timer
1
1
Navigator
1
1
1
1
1
1
1
1
1
1
1
Move
Command
Bump
GoHome
ArmRotate
1
«interface»
Behavior
+takecontrol() : bool
+action()
+suppress()
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Kansas State University
Use Case Realization Example
Robot Controller : MOVE Behavior
Wait Until MOVE is triggered
Pick a new point (x, y)
Calculate angle and distance
Start the motors
Wait Until required angle is rotated
Stop motors
Update geometry
Start the motors
Wait Until required distance is traveled
Stop motors
Update geometry
Department of Computing and Information Sciences
Kansas State University
Use Case Realization Example
Robot Controller : MOVE Behavior
Wait Until MOVE is triggered
Pick a new point (x, y)
Calculate angle and distance
Start the motors
Wait Until required angle is rotated
Stop motors
Update geometry
Start the motors
Wait Until required distance is traveled
Stop motors
Update geometry
Asynchronous waits
Department of Computing and Information Sciences
Kansas State University
Finite State Machine Method
actions
Behavior Action




Each behavior is a set of actions.
After completing one action it goes to the next action
of the behavior.
Describe the entire system using finite state machine.
Allocate threads to traverse through the state machine.

Needs only mutual exclusion of shared variables.
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Kansas State University
Use Case Realization Example
States
Tippy Senior : MOVE Behavior
Wait Until MOVE is triggered
Pick a new point (x, y)
Calculate angle and distance
Start the motors
Wait Until required angle is rotated
Stop motors
Update geometry
Start the motors
Wait Until required distance is traveled
Stop motors
Update geometry
Department of Computing and Information Sciences
Kansas State University
Revised Class Diagram
Motor
3
StateTable
RotationNavigator
1
+getNextState() : byte
+getActionToBeTaken() : Action
+setNextState()
+setActionToBeTaken()
RotationSensor
2
1
CurrentState
1
Rotation Sensor Thread
1
1
1
1
1
ArmState
+getCurrentState() : byte
+setCurrentState()
+nextState()
1
1
+getX() : int
+getY() : int
+getAngle() : double
+rotate()
+gotoPoint()
+travel()
+forward()
+backward()
+updateCoordinate()
+updateAngle()
+halt()
+stop()
+setCommand()
+checkRotate()
+checkForward()
+checkBackward()
Touch Sensor
1
1
Timer
1
IRTransceiver
1
1
1
Navigator
1
1
1
1
1
1
1
1
1
1
1
1
Move
Command
Bump
GoHome
ArmRotate
1
«interface»
Behavior
+takecontrol() : bool
+action()
+suppress()
1
*
Arbitrator
1
1
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Use Case Realization Example
Arbitrator
Tippy Senior : MOVE Behavior
Wait Until MOVE is triggered
Pick a new point (x, y)
Calculate angle and distance
Start the motors
Wait until required angle is rotated
Stop motors
Update geometry
Start the motors
Wait Until required distance is traveled
Stop motors
Update geometry
Rotation Sensor
Thread
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Arbitrator thread
Action (GO HOME)
takeControl
GO HOME
Action (BUMP)
takeControl
BUMP
takeControl
COMMAND
DONE
takeControl
MOVE
Action (COMMAND)
Action (MOVE)
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Rotation Sensor Thread
Action (GO HOME)
takeControl
GO HOME
Action (BUMP)
takeControl
BUMP
takeControl
COMMAND
DONE
takeControl
MOVE
Action (COMMAND)
Action (MOVE)
Department of Computing and Information Sciences
Kansas State University
Acknowledgement
Dr. Masaaki Mizuno
 Dr. Gurdip Singh
 Dr. Mitchell Nielsen

Department of Computing and Information Sciences
Kansas State University
Questions ???
Department of Computing and Information Sciences
Kansas State University