Embedded Systems Design 1 By AJAL.A.J ASSISTANT PROFESSOR Electronics & Communication Engineering Dept
Nov 28, 2014
Embedded Systems Design
1
By AJAL.A.J ASSISTANT PROFESSOR Electronics & Communication Engineering Dept
Name of University - Class Title
What Is An Embedded System ?What Is An Embedded System ?
A type of computer system. Some of the Most Common Traditional Definitions :
– Embedded systems are more limited in hardware and/or software functionality then the PC.
– An embedded system is designed to perform a dedicated function
– … Why don’t these definitions entirely apply, today?
Name of University - Class Title
What is an Embedded System [Continued] ?What is an Embedded System [Continued] ?
Automotive– i.e. : Ignition Systems, Engine Control, Antilock Braking System, …
Consumer Electronics– i.e. : TVs, STBs, appliances, toys, automobiles, cell phones …
Industrial Control– i.e. : robotics, control systems…
Medical– i.e. : Infusion Pumps, Dialysis Machines, Prosthetic Devices,Cardiac
Monitors, … Networking
– i.e. : routers, hubs, gateways, … Office Automation
– i.e. : fax machines, photocopiers, printers, monitors, …
** Aside from being types of computer systems, there is no single definition or characterization of embedded systems reflecting them all. **
Systems engineering point of view:
• When approaching embedded systems architecture design from a systems engineering point of view, several models can be applied to describe the cycle of embedded system design.
• Most of these models are based upon one or
some combination of the following four development models:
System Engineering Life Cycle Models
four development models:
four development models:
1.The big-bang model2.The code-and-fix model3.The waterfall model
4.The spiral model
big-bang model
• The big-bang model, in which there is
essentially no planning or processes in place before and during the
development of a system.
Ad HOC MODEL
Name of University - Class Title
Big-Bang ModelBig-Bang Model Developer receives problem
statement.
Developer works in isolation for some extended time period.
Developer delivers result.
Developer hopes client is satisfied.
code-and-fix model
The code-and-fix model, in which
product requirements are defined But
no formal processes
are in place before the start of development.
waterfall model
The waterfall model, in which there is a process for developing
a system in steps,
where results of one step flow into the next step.
These slides prepared by Prof. Bob Keller of Harvery Mudd College and printed for ERAU/Prescott SE300 usage with his kind permission. Slides avaialble online at http://www.cs.hmc.edu/courses/2005/spring/cs121/slides/slides05.ppt
Waterfall Model with Back Flow(sometimes this is implied by “waterfall”)
Requirements
Design
Implementation
TestAdjustments made to immediately previous phase based on issues with successive phase.
These slides prepared by Prof. Bob Keller of Harvery Mudd College and printed for ERAU/Prescott SE300 usage with his kind permission. Slides avaialble online at http://www.cs.hmc.edu/courses/2005/spring/cs121/slides/slides05.ppt
Why Not Waterfall?
0
10
20
30
40
50
60
10 100 1000 10000 100000
Project Size in Function Points
Cre
epin
g R
eq's
as
% o
f O
rig
1. Complete Requirements Not Known at Project Start
Source: Applied Software Measurement, Capers Jones, 1997. Based on 6,700 systems.
These slides prepared by Prof. Bob Keller of Harvery Mudd College and printed for ERAU/Prescott SE300 usage with his kind permission. Slides avaialble online at http://www.cs.hmc.edu/courses/2005/spring/cs121/slides/slides05.ppt
Function Point?
A function point is a unit of complexity used in software cost estimation. Function points are based on number of user interactions, files to be read/written, etc.
SLOC means number of source lines of code, also a measure of program complexity.
These slides prepared by Prof. Bob Keller of Harvery Mudd College and printed for ERAU/Prescott SE300 usage with his kind permission. Slides avaialble online at http://www.cs.hmc.edu/courses/2005/spring/cs121/slides/slides05.ppt
Why Not Waterfall?
2. Requirements are not stable/unchanging.
Source: Craig Larman
The market changes—constantly.
The technology changes.
The goals of the stakeholders change.
These slides prepared by Prof. Bob Keller of Harvery Mudd College and printed for ERAU/Prescott SE300 usage with his kind permission. Slides avaialble online at http://www.cs.hmc.edu/courses/2005/spring/cs121/slides/slides05.ppt
Why Not Waterfall?
3. The design may need to change during implementation.
Source: Craig Larman
Requirements are incomplete and changing.
Too many variables, unknowns, and novelties.
A complete specification must be as detailed as code itself.
Software is very “hard”. Discover Magazine, 1999: Software characterized as the
most complex “machine” humankind builds.
spiral model
The spiral model, in which there is a process for developing a system in steps,
and
throughout the various steps, feedback is obtained and incorporated back into the
process.
These slides prepared by Prof. Bob Keller of Harvery Mudd College and printed for ERAU/Prescott SE300 usage with his kind permission. Slides avaialble online at http://www.cs.hmc.edu/courses/2005/spring/cs121/slides/slides05.ppt
“Life-Cycle” Models ….
Iterative Models Spiral Model & Variants
ROPES Model Controlled Iteration Model: Unified Process Time Box Model
Scrum Model Fountain Model
These slides prepared by Prof. Bob Keller of Harvery Mudd College and printed for ERAU/Prescott SE300 usage with his kind permission. Slides avaialble online at http://www.cs.hmc.edu/courses/2005/spring/cs121/slides/slides05.ppt
Boehm Spiral Model(of which some other models are variants)
An iterative model developed by Barry Boehm at TRW (1988), now Prof. at USC
Iterates cycles of these project phases:1 Requirements definition2 Risk analysis3 Prototyping 4 Simulate, benchmark5 Design, implement, test 6 Plan next cycle (if any)
Prof. Barry Boehm
These slides prepared by Prof. Bob Keller of Harvery Mudd College and printed for ERAU/Prescott SE300 usage with his kind permission. Slides avaialble online at http://www.cs.hmc.edu/courses/2005/spring/cs121/slides/slides05.ppt
Boehm Spiral Model
These slides prepared by Prof. Bob Keller of Harvery Mudd College and printed for ERAU/Prescott SE300 usage with his kind permission. Slides avaialble online at http://www.cs.hmc.edu/courses/2005/spring/cs121/slides/slides05.ppt
Risk? What risk?
One major area of risk is that the scope and difficulty of the task is not well understood at the outset.
This is the so-called “wicked problem” phenomenon.
These slides prepared by Prof. Bob Keller of Harvery Mudd College and printed for ERAU/Prescott SE300 usage with his kind permission. Slides avaialble online at http://www.cs.hmc.edu/courses/2005/spring/cs121/slides/slides05.ppt
“Wicked Problems”
Many software development projects have been characterized as “wicked problems”, meaning: “problems that are fully understood only after they are solved the first time” (however poorly)
Does not apply only to software
These slides prepared by Prof. Bob Keller of Harvery Mudd College and printed for ERAU/Prescott SE300 usage with his kind permission. Slides avaialble online at http://www.cs.hmc.edu/courses/2005/spring/cs121/slides/slides05.ppt
Source of some of this
Prentice-Hall, 1990
basically a criticism of thewaterfall model
“wicked” term first used in H. Rittel and M. Webber, Dilemmas in a general theory of planning, Policy Sciences, 4, pp. 155-169, Elsevier, 1973.
These slides prepared by Prof. Bob Keller of Harvery Mudd College and printed for ERAU/Prescott SE300 usage with his kind permission. Slides avaialble online at http://www.cs.hmc.edu/courses/2005/spring/cs121/slides/slides05.ppt
Some Roots of Wickedness
Risk: A customer not knowing exactly what he/she wants; changing expectations as project progresses.
Risk: Staff who are inexperienced in the problem domain, or with the appropriate implementation techniques.
These slides prepared by Prof. Bob Keller of Harvery Mudd College and printed for ERAU/Prescott SE300 usage with his kind permission. Slides avaialble online at http://www.cs.hmc.edu/courses/2005/spring/cs121/slides/slides05.ppt
The Waffle Principle
“Plan to throw the first one away; you will anyhow.”
Fred Brooks, “The Mythical Man-Month: Essays on Software Engineering”, Addison Wesley, 1975.Revised in 1995.
another indication that building a large software system is wicked
These slides prepared by Prof. Bob Keller of Harvery Mudd College and printed for ERAU/Prescott SE300 usage with his kind permission. Slides avaialble online at http://www.cs.hmc.edu/courses/2005/spring/cs121/slides/slides05.ppt
Wicked Problems
The presence of wickedness is what makes the iterative / incremental approaches most appealing.
Methodologies and organizational techniques can help control the degree of wickedness.
These slides prepared by Prof. Bob Keller of Harvery Mudd College and printed for ERAU/Prescott SE300 usage with his kind permission. Slides avaialble online at http://www.cs.hmc.edu/courses/2005/spring/cs121/slides/slides05.ppt
US Air Force Risk Classification
Performance risk: The project might not meet requirements or otherwise be fit for use.
Cost risk: The budget might get overrun.
Support risk: The software might not be adaptable, maintainable, extendable
Schedule risk: The project might be delivered too late.
These slides prepared by Prof. Bob Keller of Harvery Mudd College and printed for ERAU/Prescott SE300 usage with his kind permission. Slides avaialble online at http://www.cs.hmc.edu/courses/2005/spring/cs121/slides/slides05.ppt
Ways to Manage Risk
Risk cannot be eliminated; it must be managed. Do thorough requirements analysis before
the design. Use tools to track requirements,
responsibilities, implementations, etc. Build small prototypes to test and
demonstrate concepts and assess the approach, prior to building full product.
Prototype integration as well as components.
These slides prepared by Prof. Bob Keller of Harvery Mudd College and printed for ERAU/Prescott SE300 usage with his kind permission. Slides avaialble online at http://www.cs.hmc.edu/courses/2005/spring/cs121/slides/slides05.ppt
Front-Loading Tackle the unknown and harder parts earlier
rather than later.
Better to find out about infeasible, intractable, or very hard problems early.
The easy parts will be worthless if the hard parts are impossible.
Find out about design flaws early rather than upon completion of a major phase.
These slides prepared by Prof. Bob Keller of Harvery Mudd College and printed for ERAU/Prescott SE300 usage with his kind permission. Slides avaialble online at http://www.cs.hmc.edu/courses/2005/spring/cs121/slides/slides05.ppt
ROPES Model - Similar to SpiralRapid Object-Oriented Process for Embedded Systems
Bruce Douglass
http://www.sdmagazine.com/breakrm/features/s999f1.shtml
Iterates the following sequence of phases repeatedly: Requirements analysis System analysis Object analysis Architectural design Design Mechanistic design
Detailed design Coding Unit testing Integration testing Validation testing Iterative prototypes
These slides prepared by Prof. Bob Keller of Harvery Mudd College and printed for ERAU/Prescott SE300 usage with his kind permission. Slides avaialble online at http://www.cs.hmc.edu/courses/2005/spring/cs121/slides/slides05.ppt
ROPES ModelRapid Object-Oriented Process for Embedded Systems
Bruce Douglass
These slides prepared by Prof. Bob Keller of Harvery Mudd College and printed for ERAU/Prescott SE300 usage with his kind permission. Slides avaialble online at http://www.cs.hmc.edu/courses/2005/spring/cs121/slides/slides05.ppt
Controlled-Iteration Model
Four phases per major cycle Inception: Negotiate and define product for
this iteration Elaboration: Design Construction: Create fully functional
product Transition: Deliver product of phase as
specified The next phase is started before the end of
the previous phase (say at 80% point).
These slides prepared by Prof. Bob Keller of Harvery Mudd College and printed for ERAU/Prescott SE300 usage with his kind permission. Slides avaialble online at http://www.cs.hmc.edu/courses/2005/spring/cs121/slides/slides05.ppt
Rational Unified Process(a form of controlled iteration)
ManagementEnvironment
Business Modeling
Implementation
Test
Analysis & Design
Preliminary Iteration(s)
Iter.#1
PhasesProcess Workflows
Iterations within phases
Supporting Workflows
Iter.#2
Iter.#n
Iter.#n+1
Iter.#n+2
Iter.#m
Iter.#m+1
Deployment
Configuration Mgmt
Requirements
Elaboration TransitionInception Construction
These slides prepared by Prof. Bob Keller of Harvery Mudd College and printed for ERAU/Prescott SE300 usage with his kind permission. Slides avaialble online at http://www.cs.hmc.edu/courses/2005/spring/cs121/slides/slides05.ppt
Time-Box Requirement(can be used in iterative or incremental)
Requirements analysis Initial design while( not done )
{Develop a version within a bounded timeDeliver to customerGet feedbackPlan next version}
These slides prepared by Prof. Bob Keller of Harvery Mudd College and printed for ERAU/Prescott SE300 usage with his kind permission. Slides avaialble online at http://www.cs.hmc.edu/courses/2005/spring/cs121/slides/slides05.ppt
Scrum, A cure for the Wicked?
Scrum first mentioned in “The New New Product Development Game” (Harvard Business Review 86116:137-146, 1986)
These slides prepared by Prof. Bob Keller of Harvery Mudd College and printed for ERAU/Prescott SE300 usage with his kind permission. Slides avaialble online at http://www.cs.hmc.edu/courses/2005/spring/cs121/slides/slides05.ppt
Scrum Model(incremental model,
includes some aspects of team structure, as well as process)
A small group is responsible for picking up the ball and moving it toward the goal.
See http://www.cetus-links.org/oo_ooa_ood_methods.html
Start
Goal
These slides prepared by Prof. Bob Keller of Harvery Mudd College and printed for ERAU/Prescott SE300 usage with his kind permission. Slides avaialble online at http://www.cs.hmc.edu/courses/2005/spring/cs121/slides/slides05.ppt
Argument for the Scrum Model over other iterative models
A software development project might not be compartmentalizable into nice clean phases as the Spiral models suggest.
Scrum may be “just the thing” for wicked problems, because the team can quickly react to new information.
These slides prepared by Prof. Bob Keller of Harvery Mudd College and printed for ERAU/Prescott SE300 usage with his kind permission. Slides avaialble online at http://www.cs.hmc.edu/courses/2005/spring/cs121/slides/slides05.ppt
Some Principles of Scrum Model
Always have a product that you can theoretically ship: “done” can be declared at any time.
Build early, build often.
Continuously test the product as you build it.
Assume requirements may change; Have ablility to adapt to marketplace changes during development.
Small teams work in parallel to maximize communication and minimize overhead.
These slides prepared by Prof. Bob Keller of Harvery Mudd College and printed for ERAU/Prescott SE300 usage with his kind permission. Slides avaialble online at http://www.cs.hmc.edu/courses/2005/spring/cs121/slides/slides05.ppt
Concepts Used in Scrum(from http://www.controlchaos.com/ap.htm)
Backlog - an identification of all requirements that should be fulfilled in the completed product. Backlog items are prioritized.
Objects/Components - self-contained reusable modules
Packets - a group of objects within which a backlog item will be implemented. Coupling between the objects within a packet is high. Coupling between packets is low.
Team - a group of 6 or fewer members that works on a packet.
Problem - what must be solved by a team member to implement a backlog item within an object(s) (includes removing errors)
Issues - Concerns that must be resolved prior to a backlog item being assigned to a packet or a problem being solved by a change to a packet
Solution - the resolution of an issue or problem
Changes - the activities that are performed to resolve a problem
Risks - the risk associated with a problem, issue, or backlog item
These slides prepared by Prof. Bob Keller of Harvery Mudd College and printed for ERAU/Prescott SE300 usage with his kind permission. Slides avaialble online at http://www.cs.hmc.edu/courses/2005/spring/cs121/slides/slides05.ppt
Use of Iteration in Scrum http://www.controlchaos.com/scrumwp.htm
Each iteration consists of all of the standard Waterfall phases,
but each iteration only addresses one set of functionality.
Overall project deliverable has been partitioned into prioritized subsystems, each with clean interfaces.
Test the feasibility of subsystems and technology in the initial iterations.
Further iterations can add resources to the project while ramping up the speed of delivery.
Underlying development processes are still defined and linear.
These slides prepared by Prof. Bob Keller of Harvery Mudd College and printed for ERAU/Prescott SE300 usage with his kind permission. Slides avaialble online at http://www.cs.hmc.edu/courses/2005/spring/cs121/slides/slides05.ppt
Fountain Model(Ian Graham, et al., The OPEN Process Specification
OPEN = Object-oriented Process Environment and Notation )
These slides prepared by Prof. Bob Keller of Harvery Mudd College and printed for ERAU/Prescott SE300 usage with his kind permission. Slides avaialble online at http://www.cs.hmc.edu/courses/2005/spring/cs121/slides/slides05.ppt
Additional Models/Acronyms
RAD (Rapid Application Development):time-boxed, iterative prototyping
JAD (Joint Application Development): Focus on developing models shared between users and developers.
See http://faculty.babson.edu/osborn/cims/rad.htm for additional points.
These slides prepared by Prof. Bob Keller of Harvery Mudd College and printed for ERAU/Prescott SE300 usage with his kind permission. Slides avaialble online at http://www.cs.hmc.edu/courses/2005/spring/cs121/slides/slides05.ppt
Extreme Programming (XP)
(cf. http://www.extremeprogramming.org/rules.html)
User stories (something like use cases) are written by the customer.
Complex stories are broken down into simpler ones (like a WBS).
Stories are used to estimate the required amount of work.
Stories are used to create acceptance tests. A release plan is devised that determines
which stories will be available in which release. Don’t hesitate to change what doesn’t work.
These slides prepared by Prof. Bob Keller of Harvery Mudd College and printed for ERAU/Prescott SE300 usage with his kind permission. Slides avaialble online at http://www.cs.hmc.edu/courses/2005/spring/cs121/slides/slides05.ppt
Extreme Programming (XP)
Each release is preceded by a release planning meeting.
Each day begins with a stand-up meeting to share problems and concerns.
CRC cards are used for design. [XP and CRC were created by the same person, Kent Beck.]
Spike solutions are done to assess risks. The customer is always available.
These slides prepared by Prof. Bob Keller of Harvery Mudd College and printed for ERAU/Prescott SE300 usage with his kind permission. Slides avaialble online at http://www.cs.hmc.edu/courses/2005/spring/cs121/slides/slides05.ppt
Extreme Programming (XP)
All code must pass unit tests, which are coded before the code being tested (test-driven design).
Refactoring is done constantly. Integration is done by one pair. Integration is done frequently. Optimization is done last. Acceptance tests are run often.
These slides prepared by Prof. Bob Keller of Harvery Mudd College and printed for ERAU/Prescott SE300 usage with his kind permission. Slides avaialble online at http://www.cs.hmc.edu/courses/2005/spring/cs121/slides/slides05.ppt
These slides prepared by Prof. Bob Keller of Harvery Mudd College and printed for ERAU/Prescott SE300 usage with his kind permission. Slides avaialble online at http://www.cs.hmc.edu/courses/2005/spring/cs121/slides/slides05.ppt
System Metaphor?“Choose a system metaphor to keep the team on the same page by naming classes and methods consistently. What you name your objects is very important for understanding the overall design of the system and code reuse as well. Being able to guess at what something might be named if it already existed and being right is a real time saver. Choose a system of names for your objects that everyone can relate to without specific, hard to earn knowledge about the system.
For example the Chrysler payroll system was built as a production line. At another auto manufacturer car sales were structured as a bill of materials. There is also a metaphor known as the naive metaphor which is based on your domain itself. But don't choose the naive metaphor unless it is simple enough.”
These slides prepared by Prof. Bob Keller of Harvery Mudd College and printed for ERAU/Prescott SE300 usage with his kind permission. Slides avaialble online at http://www.cs.hmc.edu/courses/2005/spring/cs121/slides/slides05.ppt
Keller’s Roll-Your-OwnSoftware Life-Cycle Construction
Kit
Requirements Analysis
System Design
Program Design
Implement
Unit Test
Integration Test
Acceptance Test
Prototype
Design Review
Detailed Design
Requirements Elicitation
Requirements Specification
Risk Analysis
Fix Errors
Code Walkthrough
Validate
Verify
Integrate
Cost Analysis
Maintain
Configure
PortDocument
Simulate
Train
Evaluate
Party
Embedded Systems Design and Development Lifecycle Model
Lifecycle Model
Life Cycle Model
Embedded System Life Cycle Models
(1) 3V Model
(2) Multiple V Model
“V” ModelEach phase has corresponding test or validation
counterpart
Requirements Analysis
System Design
Program Design
Implementation
Unit Test
Integration Test
Acceptance Test
1. 3V model
3V model
Sawtooth Model (Brugge)
Requirements Analysis
System Design
Program Design
Implementation
Unit Test
Integration Test
Acceptance TestDemo Prototype 1 Demo Prototype 2
2. Multiple v model
Advanced Life Cycle Models
(1) MDA
(2) Y-Model
(3) Platform-Based Design
1. MDA MODEL
MODEL DRIVEN ARCHITECTURE
2. Y - MODEL
3. PLATFORM BASED DESIGN MODEL
Approach used in Platform based Model
Embedded design life cycle diagram
Different Stages(stage 1) having a strong technical Foundation(stage 2) understanding the Architectural Business
Cycle (stage 3) defining the architectural patterns and
models(stage 4) defining the architectural structures (stage 5) documenting the architecture (stage 6) analyzing and reviewing the architecture(stage 7) Maintenance
7 stages can be merged to 3 steps
1. Product specification2. Hardware/software partitioning3. Hardware/software integration
Tools used in the design process
Product specification
• R&D engineers want to incorporate everything:– Wastes time and resource
• Marketing and sales will usually execute the product specification
• Engineers, however, should be involved in some customer tours– CPIF - Cost Plus Incentive-Fee (Contract)
– Listening to the customer is good
Common success factors
• Design team shares a common vision of the product
• Failed projects probably did not share a common vision of project goals– Low cost medium performance versus time to
market versus high performance and medium cost• Often overlooked part of the product
specification phase - the requirement of the development tools
Common success factors
• Embedded systems projects are late to market because engineers do not have access to the best tools– Tools should be part of the product specification– Prevents unrealistic expectations
• is/is-not list, or musts and wants
Hardware/software partitioning• Embedded design usually involves hardware and
software• Hardware utilizes Micro-processors, Micro-
controllers and Digital Signal Processors but are neither used nor perceived as computers. Generally, software is used for features and flexibility, while hardware is used for performance.
• What is the partitioning decision?• Different than application developers
– Not a good idea to h/w enhance h/w to address part of a problem
– The old days of co-processors (FPUs) are over - emulated
Algorithm • Steps required to implement a design• Combination of hardware components and
software components• Hardware/software partitioning also involves
the hows of partitioning the algorithm (software only, hardware only, combination)
• Think about the simple algorithm of Fibonacci series
Embedded design requirements
• Price sensitive• Leading edge performers• Non-standard• Market competitive• Proprietary
• These are conflicting in many ways!
Embedded design requirements cont…
• Algorithm partitioning depends on the choice of processor used in the design– Several hundreds to choose from!
• Choice of CPU impacts the partitioning decision which impacts the tools decisions, etc…
Embedded design requirements cont…
• Variety of possible choices• Experience required to arrive at optimal
design• Solution surface is smooth
– Adequate solution not far off from the best solution
• Constraints dictate the decision path
Iteration and implementation
• Hardware and software paths begin to diverge• Early design work before the walls go up
(between H/W and S/W)• Design still very fluid• Major blocks partitioned
– Boundary can still be moved• Iteration is common
Iteration and implementation
• Hardware team– Simulation tools to model performance
• Software team– Running code benchmarks on self contained systems
(evaluation boards)– Convenient development environment until the hardware
arrives!• Tools are helping (keep h/w, s/w engaged longer)• More tools on their way…
Hardware/software integration
• Special tools and methods to manage the complexity
• Process of integrating h/w and s/w requires debugging and discovery
–Did the software team really understand the
hardware spec?
Hardware/software integration
• Real-time nature of embedded systems leads to highly complex, non-deterministic behavior– Can only be analyzed as it occurs
• Accurately modeling and simulating behavior may be very time consuming– But tools are getting better!
Product testing and release
• Testing is important when performance is key• Testing and reliability more stringent
Is system performing at close to its optimal capabilities?
Compliance testing
• Embedded systems radiate a lot of radio frequency energy– “all electronic devices must be turned off…”
• If embedded designer does not consider these things, compliance engineering (CE) will fail– Software must be running to pass this test– This is often overlooked
Maintaining and upgrading
• Not many tools to support applications already in the field
• 60% of embedded engineers maintain systems– Original engineer long gone– Must rely on experience, any existing documentation,
etc…– Tools might be handy…
Maintaining and upgrading
“time to market” must become
“time to reverse engineer” and
“time to insight”
Systems Product Life Cycle