1. Software Engineering CSCI 3321 Computer Science Department
Agile Development &
Real Time Systems
Dr. Thomas Hicks
Computer Science Department
Trinity University 4 1

2. Agile Development & Real Time Systems
Chapter 4
Software Engineering : A Practitioner’s Approach
Agile Development & Real Time Systems
Dr. Thomas E. Hicks Computer Science Department Trinity University
Thanks To Ian Sommerville & Roger Pressman For Much Of The Slide Content

3. Agile
Development
Lite or Lean Methods

4. The Manifesto for Agile Software Development
“We are uncovering better ways of developing software by doing it and helping others do it. Through this work we have come to value:
Individuals and interactions over processes and tools
Working software over comprehensive documentation
Customer collaboration over contract negotiation
Responding to change over following a plan
That is, while there is value in the items on the right, we value the items on the left more.”
Kent Beck et al
The_Agile_Manifesto_SDMagazine.pdf

5. “Agility 1, Everything Else 0”
Tom Demarco

6. Politics Agile Software Development
“Considerable Debate about the benefits and applicability”
Pro Agile : “Traditional methodologies are a bunch of stick-in-the-muds who’d rather produce flawless documentation than a working system that meets business needs.”
Pro Traditional: “Lightweight, agile methodologists are a bunch of glorified hackers who are going to be in for a heck of a surprise when they try to scale up their toys into enterprise-wide software”
This methodology risks degenerating into a religious war.
Pressman

7. Ivar Jacobson - 1
“Agility has become today’s buzz word when considering a modern software process. An agile team is a nimble team able to appropriately respond to changes.
Changes in the software being built, changes in the team members, changes because of new technology, changes of all kinds that may have impact upon the product they build or the project that creates the product.

8. Ivar Jacobson – 2
Support for changes should be built-in every thing we do in software, something we embrace because it is the heart and soul of software.
An agile team recognizes that software is developed by individuals working in teams and that the skills of those people, their ability to collaborate, is at the core for the success of the project.”

9. 7 Human Factors Of Agile Software Development
Proponents of the Agile Process emphasize the human factors:
Competence – innate talent and overall knowledge of the process – teach needed info to all team members
Common Focus – the agile team will focus the different talents working on different portions of the project on the deliverable.
Collaboration – quality software requires the collaboration & communication of customer & software engineers
Decision Making Ability – teams must be able to make those decisions necessary to control their destiny
Pressman

10. 7 Human Factors Of Agile Software Development
Proponents of the Agile Process emphasize the human factors:
Fuzzy-Problem-Solving-Ability – managers realize teams deal with ambiguity and change – sometimes must accept the fact that problem solving today will be different than problem solving tomorrow – maybe use some of same code.
Mutual Trust & Respect – Agile teams must become what DeMarco & Lister call “Jelled Teams” – whole greater than sum of its parts.
Self Organization – self organized to complete work, meet deadlines, etc. Moral booster.
Pressman

11. “There is no substitute for rapid feedback, both on the developer process and on the product itself”
Martin Fowler

12. 12 Principles Adopted By The “Agility Conference” 1-4
Highest Priority is to satisfy the customer through early and continuous delivery of valued software.
Welcome change requirements even late in the development. Agile processes harness change for the customer’s competitive advantage.
Deliver working software frequently, from a couple of weeks to a couple of months, with a preference to the shorter time scale.
Business people, and developers, must work together daily throughout the project.

13. 12 Principles Adopted By The “Agility Conference” 5-8
Build projects around motivated individuals. Give them the environment and the support they need. Trust them to get the job done.
The most efficient and effective method of conveying information to and within a development team is face to face conversation.
Working software is the primary measure of progress.
Agile processes promote sustainable development. The sponsors, developers, users should be able to maintain constant pace indefinitely.

14. 12 Principles Adopted By The “Agility Conference” 9-12
Continual attention to technical excellence and good design enhances agility.
Simplicity, the art of minimizing the amount of work not done, is essential.
The best architectures, requirements, and designs emerge from self organizing teams.
At regular intervals, the team reflects on how to become more effective, then tunes and tunes and adjusts its behavior accordingly.

15. Agile  Lite  Less Time Planning  Faster Coding

16. Agility Software Development Research Tells Us That :
Effective response to change; rapid and adaptive
Effective communication among all stakeholders
Drawing the customer onto the team
Organizing a team so that it is in control of the work performed
Yields …
Rapid, incremental delivery of software

17. About The Agile Process
Agile Process is driven by customer descriptions of what is required; these descriptions are called scenarios
Agile Process recognizes that plans are short-lived
Agile Process develops software iteratively with a heavy emphasis on construction activities
Agile Process delivers multiple ‘software increments’
Agile Process adapts as changes occur

18. XP
Extreme Programming

19. Extreme Programming (XP) 4 Step XP Planning Process
The most widely used agile process, originally proposed by Kent Beck
XP Planning
XP Planning begins with the creation of “user stories”
An XP Agile team assesses each story and assigns a cost
These XP Stories are grouped to for a deliverable increment
A commitment is made on delivery date

20. About Extreme Programming (XP) Design
XP Design follows the KIS principle
XP Design encourage the use of CRC cards (see Chapter 8)
Class Responsibility Collaborator
For difficult design problems, XP suggests the immediate creation of “spike solutions”; spikes solutions are an operational design prototype of the problem area.
XP design encourages “refactoring”; refactoring an iterative refinement of the internal program design – it is cleaning up the code after it has been written.

21. About Extreme Programming (XP) Coding
XP coding recommends the construction of a unit test for a story before coding commences
XP coding encourages “pair programming” – two people work together at one computer to complete code for one story.

22. About Extreme Programming (XP) Testing
XP testing recommends that all unit tests be executed daily to encourage regression analysis (i.e. to make sure code still works after it has been modified)
“XP testing requires “acceptance tests”, also called “customer tests” that are defined by the customer and executed to assess customer visible functionality

23. “Extreme Programming is a discipline of software development based on values of simplicity, communication, feedback, and courage.”
Ron
Jeffries

24. Adaptive Software Development
ASD
Adaptive Software Development

25. Adaptive Software Development (ASD)
ASD was originally proposed by Jim Highsmith
6 Distinguishing Features Of ASD 1-3
ASD uses mission-driven planning; accomplish the task
ASD partitions the project into components; it is a component-based focus
Uses “time-boxing” – each task associated with a box; if the project cannot be delivered on time, the work moves forward to the next task when ~90% of the task is complete. Although this is not always acceptable, it is often the case that the last 10% can be completed later.

26. Adaptive Software Development (ASD)
ASD was originally proposed by Jim Highsmith
6 Distinguishing Features Of ASD – 4-6
ASD explicitly considers all of risks
ASD emphasizes collaboration for requirements gathering
ASD emphasizes “learning” throughout the process

27. 3 Major Steps of Adaptive Software Development (ASD)
Speculation
Use the customer mission statement, project constraints, and basic requirements to define sets of cycles (software releases) for the project.
Collaboration
The collaboration method is central to all of the agile processes. Using highly motivated people, working collaboratively together to multiply their talents beyond individual expectations. Trust is central.
Create Requirements and Mini-Specs.
Learning
Implement and test components
Technical Reviews
Focus Group Feedback

28. Adaptive Software Developmentc y l n g u s m o r j b q - x R h J A D / f k w

29. “I like to listen. I have learned a great deal from listening carefully. Most people never listen.”
Ernest Hemingway

30. Dynamic Software Development Method
DSDM
Dynamic Software Development Method

31. Dynamic Systems Development Method - DSDM
DSDM—distinguishing features
Similar in most respects to XP and/or ASD
8 Guiding Principles Of DSDM – 1-4
Active user involvement is imperative.
DSDM teams must be empowered to make decisions.
The focus is on frequent delivery of products.
Fitness for business purpose is the essential criterion for acceptance of deliverables.
Promoted by the DSDM Consortium (

32. Dynamic Systems Development Method - DSDM
8 Guiding Principles Of DSDM 5 - 8
Iterative and incremental development is necessary to converge on an accurate business solution.
All changes during development are reversible.
Requirements are baselined at a high level
Testing is integrated throughout the life-cycle.

33. Dynamic Systems Development Method

34. “Our profession goes through Methodologies like a 14 year-old goes through clothing”
Stephen Hawrysh &
Jim Ruprecht

35. Scrum

36. Scrum – (rugby match term)
Developed by Jeff Sutherland in early 1990’s
Expanded upon by Schwaber and Beedle in 2001
Scrum—distinguishing features – very “agile like”
Scrum has small teams to maximize communication and minimize costs
The Scrum process must be adaptable to business and technological changes
The Scrum process yields software that can be inspected, adjusted, tested, documented, and built on.
The Scrum process partitions the project into low-coupling partitions, or “packets”. w

37. Scrum (cont)
The Scrum process constantly tests and documents as the project is built.
The Scrum process provides the ability to declare the product “done”
Scrum work occurs in “sprints” and is derived from a “backlog” of existing requirements
Scrum meetings are very short and sometimes conducted without chairs
Scrum “demos” are delivered to the customer with the time-box allocated

38. Scrum

39. “Scrum allows us to build Software..”
Mike Beetle et al.

40. Crystal

41. Proposed by Cockburn and Highsmith Crystal—distinguishing features
Actually a family of process models that allow “maneuverability” based on problem characteristics
Face-to-face communication is emphasized
Suggests the use of “reflection workshops” to review the work habits of the team

42. FDD Feature Driven Development

43. Feature Driven Development (FDD)
Originally proposed by Peter Coad et al as a process model for OOP
FDD—distinguishing features
Emphasis is on defining “features”
a feature “is a client-valued function that can be implemented in two weeks or less.”
Uses a feature template
<action> the <result> <by | for | of | to> a(n) <object>
A features list is created and “plan by feature” is conducted
Design and construction merge in FDD

44. Feature Driven Development

45. Agile Modeling

46. Originally proposed by Scott Ambler
Agile Modeling
Originally proposed by Scott Ambler
Suggests a set of agile modeling principles
Model with a purpose
Use multiple models
Travel light
Content is more important than representation
Know the models and the tools you use to create them
Adapt locally

47. Computer World
Computer World Link

48. Real Time Software Design

49. Real-time Software Design
Real-time Software Design is designing embedded software systems whose behaviour is subject to timing constraints

50. Real Time Systems

51. Real-time systems are used to monitor and control their environment
Real-time systems inevitably are associated with hardware devices
Sensors: Collect data from the system environment
Actuators: Change (in some way) the system's environment
Time is critical. Real-time systems MUST respond within specified times

52. Real-time Definitions
A real-time system is a software system where the correct functioning of the system depends on the results produced by the system and the time at which these results are produced
A ‘soft’ real-time system is a system whose operation is degraded if results are not produced according to the specified timing requirements
A ‘hard’ real-time system is a system whose operation is incorrect if results are not produced according to the timing specification

53. Stimulus & Responses

54. Stimulus/Response Systems
Given a stimulus, the system must produce a response within a specified time
Periodic Stimuli: Stimuli which occur at predictable time intervals
For example, a temperature sensor may be polled 10 times per second
Aperiodic stimuli: Stimuli which occur at unpredictable times
For example, a system power failure may trigger an interrupt which must be processed by the system

55. Architectural Considerations
Because of the need to respond to timing demands made by different stimuli/responses, the system architecture must allow for fast switching between stimulus handlers
Timing demands of different stimuli are different so a simple sequential loop is not usually adequate
Real-time systems are usually designed as cooperating processes with a real-time executive controlling these processes

56. A Real-time System Model

57. Real Time System Elements

58. Real-time System Elements
Sensors control processes
Collect information from sensors. May buffer information collected in response to a sensor stimulus
Data processor
Carries out processing of collected information and computes the system response
Actuator control
Generates control signals for the actuator

59. Sensor/Actuator Processes

60. Real Time Design
Hardware & Software

61. Real-time System Design – 2 Stages
Real-time system engineers must design both the hardware and the software associated with system.
Real-time system engineers then partition functions to either hardware or software
Design decisions should be made on the basis on non-functional system requirements
Hardware delivers better performance but potentially longer development and less scope for change

62. Hardware & Software Design

63. R-T Systems Design Process – 6 Steps
The first step in the R-T design process is to identify the stimuli to be processed and the required responses to these stimuli
The second step in the R-T design process is to identify the timing constraints for each stimulus and response
The third step in the R-T design process is to aggregate the stimulus and response processing into concurrent processes. A process may be associated with each class of stimulus and response.

64. R-T Systems Design Process – 6 Steps
The fourth step in the R-T design process is to design algorithms for each concurrent process. These must meet the given timing requirements
The fifth step in the R-T design process is to design a scheduling system which will ensure that processes are started in time to meet their deadlines
The sixth step in the R-T design process is to integrate the real-time executive with an operating system (if necessary)

65. Real Time Timing Constraints

66. Timing Constraints
Meeting timing constraints may require extensive simulation and experiment to ensure that these are met by the system
Meeting timing constraints may mean that certain design strategies such as object-oriented design cannot be used because of the additional overhead involved
Meeting timing constraints may mean that low-level programming language features have to be used for performance reasons

67. Real Time State Machines

68. State Machine Modelling
The effect of a stimulus in a real-time system may trigger a transition from one state to another.
Finite state machines can be used for modelling real-time systems.
However, FSM models lack structure. Even simple systems can have a complex model.
The UML includes notations for defining state machine models

69. Microwave Oven State Machine

70. Real Time Programming

71. Real-time Programming & Languages
Hard-real time systems may have to programmed in assembly language to ensure that deadlines are met
Languages such as C allow efficient programs to be written but do not have constructs to support concurrency or shared resource management
Ada as a language designed to support real-time systems design so includes a general purpose concurrency mechanism

72. Java As a Real-time Language
Java supports lightweight concurrency (threads and synchronized methods) and can be used for some soft real-time systems
Java 2.0 is not suitable for hard RT programming or programming where precise control of timing is required
Not possible to specify thread execution time
Uncontrollable garbage collection
Not possible to discover queue sizes for shared resources
Variable virtual machine implementation
Not possible to do space or timing analysis

73. Real Time Executives

74. Real-time executives do not include facilities such as file management
Real-time executives are specialized operating systems which manage the processes in the RTS
Real-time executives are responsible for process management and resource (processor and memory) allocation
Real-time executives may be based on a standard RTE kernel which is used unchanged or modified for a particular application
Real-time executives do not include facilities such as file management 14

75. R-T Executive Components
Real-time clock
Provides information for process scheduling.
Interrupt handler
Manages aperiodic requests for service.
Scheduler
Chooses the next process to be run.
Resource manager
Allocates memory and processor resources.
Dispatcher
Starts process execution.

76. R-T Non-stop System Components
Configuration manager
Responsible for the dynamic reconfiguration of the system software and hardware. Hardware modules may be replaced and software upgraded without stopping the systems
Fault manager
Responsible for detecting software and hardware faults and taking appropriate actions (e.g. switching to backup disks) to ensure that the system continues in operation

77. Real-time Executive Components

78. Real Time Process Priority & Servicing

79. The processing of some types of stimuli must sometimes take priority
R-T Process Priority
The processing of some types of stimuli must sometimes take priority
Interrupt level priority. Highest priority which is allocated to processes requiring a very fast response
Clock level priority. Allocated to periodic processes
Within these, further levels of priority may be assigned

80. R-T Interrupt Servicing
Control is transferred automatically to a pre-determined memory location
This location contains an instruction to jump to an interrupt service routine
Further interrupts are disabled, the interrupt serviced and control returned to the interrupted process
Interrupt service routines MUST be short, simple and fast

81. R-T Periodic Process Servicing
In most real-time systems, there will be several classes of periodic process, each with different periods (the time between executions), execution times and deadlines (the time by which processing must be completed)
The real-time clock ticks periodically and each tick causes an interrupt which schedules the process manager for periodic processes
The process manager selects a process which is ready for execution

82. Real Time Process Management

83. R-T Process Management
Concerned with managing the set of concurrent processes
Periodic processes are executed at pre-specified time intervals
The executive uses the real-time clock to determine when to execute a process
Process period - time between executions
Process deadline - the time by which processing must be complete

84. R-T Process Management

85. Process Switching
The scheduler chooses the next process to be executed by the processor. This depends on a scheduling strategy which may take the process priority into account
The resource manager allocates memory and a processor for the process to be executed
The dispatcher takes the process from ready list, loads it onto a processor and starts execution

86. Real Time Scheduling Strategies

87. R-T Scheduling Strategies
Non pre-emptive scheduling
Once a process has been scheduled for execution, it runs to completion or until it is blocked for some reason (e.g. waiting for I/O)
Pre-emptive scheduling
The execution of an executing processes may be stopped if a higher priority process requires service
Scheduling algorithms
Round-robin
Rate monotonic
Shortest deadline first

88. Real Time Monitoring & Control Systems

89. Monitoring & Control Systems
Monitoring & control systems are an important class of real-time systems
Monitoring & control systems continuously check sensors and take actions depending on sensor values
Monitoring systems examine sensors and report their results
Control systems take sensor values and control hardware actuators

90. Real Time Monitoring Systems
Burglar Alarm

91. Designing A Burglar Alarm System Example Of A Monitoring System
A system is required to monitor sensors on doors and windows to detect the presence of intruders in a building
When a sensor indicates a break-in, the system switches on lights around the area and calls police automatically
The system should include provision for operation without a mains power supply

92. Sensors & Actions Of A Burglar Alarm System Example Of A Monitoring System
Movement detectors, window sensors, door sensors.
50 window sensors, 30 door sensors and 200 movement detectors
Voltage drop sensor
Actions
When an intruder is detected, police are called automatically.
Lights are switched on in rooms with active sensors.
An audible alarm is switched on.
The system switches automatically to backup power when a voltage drop is detected.

93. Real Time System Design

94. The 5 Step R-T System Design Process
Identify stimuli and associated responses
Define the timing constraints associated with each stimulus and response
Allocate system functions to concurrent processes
Design algorithms for stimulus processing and response generation
Design a scheduling system which ensures that processes will always be scheduled to meet their deadlines

95. Stimuli To Be Processed - A Burglar Alarm System
Power failure
Generated aperiodically by a circuit monitor. When received, the system must switch to backup power within 50 ms
Intruder alarm
Stimulus generated by system sensors. Response is to call the police, switch on building lights and the audible alarm

96. A Burglar Alarm System’s Timing Requirements

97. A Burglar Alarm System’s Architecture Diagram

98. Building_monitor process 1
A Burglar Alarm System’s Sample Code
Building_monitor process 1

99. Building_monitor process 2
A Burglar Alarm System’s Sample Code
Building_monitor process 2

100. Real Time Control Systems
Temperature Control

101. Control Systems
A burglar alarm system is primarily a monitoring system. It collects data from sensors but no real-time actuator control
Control systems are similar but, in response to sensor values, the system sends control signals to actuators
An example of a monitoring and control system is a system which monitors temperature and switches heaters on and off

102. A Temperature Control System

103. Data Acquisition Systems
Data Acquisition Systems collect data from sensors for subsequent processing and analysis.
Data collection processes and processing processes may have different periods and deadlines.
Data collection may be faster than processing e.g. collecting information about an explosion.
Circular or ring buffers are a mechanism for smoothing speed differences.

104. Nuclear Reactor Data Collection Another Control System Example
A system collects data from a set of sensors monitoring the neutron flux from a nuclear reactor.
Flux data is placed in a ring buffer for later processing.
The ring buffer is itself implemented as a concurrent process so that the collection and processing processes may be synchronized.

105. Nuclear Reactor Flux Monitoring Another Control System Example

106. A Ring Buffer

107. Mutual Exclusion
Producer processes collect data and add it to the buffer. Consumer processes take data from the buffer and make elements available
Producer and consumer processes must be mutually excluded from accessing the same element.
The buffer must stop producer processes adding information to a full buffer and consumer processes trying to take information from an empty buffer.

108. Java implementation of a ring buffer 1
A Circular Buffer Sample Code
Java implementation of a ring buffer 1

109. Java implementation of a ring buffer 2
A Circular Buffer Sample Code
Java implementation of a ring buffer 2

110. Software Engineering CSCI 3342
Dr. Thomas E. Hicks
Computer Science Department Trinity University
Textbook: Software Engineering By Roger Pressman
Textbook: Software Engineering By Ian Sommerville
Special Thanks To WCB/McGraw-Hill & Addison Wesley For Providing Graphics Of Some Of Text Book Figures For Use In This Presentation.