Richard Voyles

Professor and Director, Purdue Robotics Accelerator

Purdue University

Real-Time and Embedded Systems

Software Engineering

Real-Time and Embedded Systems Software Engineering - 2

Where Have We Been?

Scheduling - Periodic Tasks

Scheduling - Sporadic Tasks

Communication and Synchronization

What Now?

Software Engineering Software Life Cycle

Specification Methods Natural Language

Flowcharts

State Transition Diagrams

Structure Charts

Data Flow Diagrams

Petri Nets

Real-Time and Embedded Systems Software Engineering - 3

Software Life Cycle (Software Engineering)

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Software Engineering Life Cycle Phases

Concept Phase needs and goals

management directive, customer input, technology, etc.

features and feasibility (design and testing)

Requirements Phase Software Specification

timing, accuracy, user interface, etc.

software/hardware interfaces

testing plan

budget and schedule

Functional and Non-functional requirements

Complete, correct, consistent, testable

Real-Time and Embedded Systems Software Engineering - 5

Software Engineering Life Cycle Phases (cont.)

Design Phase

Convert Requirements to Detailed Design Spec.

Module partitioning

Programming Phase

Convert to code, incremental test, documentation

Test Phase

Formal test cases

Does it meet the specs?

Maintenance Phase

Customer support, bug fixes

Real-Time and Embedded Systems Software Engineering - 6

The Real Software Life Cycle

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Software Specification and Design

Natural Language Written description of the functionality

Required, but should be redundant

Mathematical Specification Precise, maps to code, provable (?)

Flowcharts Well understood, but promotes use of GOTO

Parallel flow interaction not easily represented

Timing issues difficult to represent

Example: Roomba – Home Vacuum with Real-Time Controller

• IR Cliff Sensors

• Back-up

• Turn (90o, 60o, 45o)

• Go straight

Roomba Cliff Response

It is assumed the Roomba is placed in the center of the room and then the “Clean” button is pressed. The robot starts the suction motor and then loads the spiral trajectory and starts moving in a growing spiral to cover the room. If a bump sensor is activated, the robot rotates in place, away from the sensor direction (right, left) up to 90 degrees to align with the wall sensor peak value. The robot then moves forward in a straight line. At any time, if the cliff sensor is activated, the robot will backup 1 cm, then rotate 90o, 45o, or 60o based on the cliff sensor activated (forward, edge, or both, respectively) and move in a straight line.

Roomba – Natural Language Spec

Flowcharts

Start / Stop

Execution

If / Then

No

Yes

Flow of Program Execution

Roomba FlowchartStart

Suction Motor

“Clean” Pressed?

Load Spiral Trajectory

Bump Sensor?

Cliff Sensor?

Execute Trajectory

NoYes

Backup 1 cm

Forward AND

Edge?

No

Load Straight Trajectory

Rotate 60o

Edge?

Rotate 45o Rotate 90o

Yes

Yes Yes

No No

No

Left?

Rotate Right

Rotate Left

Peak Sensor?

Peak Sensor?

Load Straight Trajectory

No

No

NoYes

YesYesYes

Real-Time and Embedded Systems Software Engineering - 13

State Transition Diagrams

State (circle) Represents “equilibrium

points” of the system

Transitions (arrow) Changes of state

Occurs when “condition” is met

“Actions” are taken during transition

System must have Discrete States

Determine What Events Cause Changes in State

Mealy = output during transition

Moore = output within state

Real-Time and Embedded Systems Software Engineering - 14

Roomba State Transition Diagram

Waiting

Execute Trajectory

Backup 1 cm

Rotate Right

Rotate LeftRotate

Delta Angle

Start

Real-Time and Embedded Systems Software Engineering - 15

Structure Charts

“Calling Trees”

Left-to-Right implies: Execution order

o - denotes conditional execution

* - denotes repetitive execution

Top-to-Bottom implies: Increasing detail

Represents program flow, not data flow

Example in [PL] text is poor

Jackson Extensions

Real-Time and Embedded Systems Software Engineering - 16

Roomba Structure Chart

Roomba Robotic Vacuum Cleaning

Accept Button

Suction On

Spiral Trajectory

React to Sensors

*

*

React to Bumps

React to Cliffs

oo

Right/Left Bumper

Rotate Left/Right

Stop at Peak

Stop at 90o

o oStraight

Trajectory