Characteristics and Quality Attributes of Embedded System

Prepared by Prof. Anand H. D., Dept. of ECE, Dr. AIT, Bengaluru-56
Characteristics and Quality
Attributes of Embedded System
Mr. Anand H. D.
1
Department of Electronics & Communication Engineering
Dr. Ambedkar Institute of Technology
Bengaluru-56
Characteristics and Quality Attributes of Embedded Systems

Prepared by Prof. Anand H. D., Dept. of ECE, Dr. AIT, Bengaluru-56 2
Characteristics of an Embedded system
Quality attributes of Embedded Systems.
Topics to be covered:

Let us discuss about
Quality attributes of Embedded Systems.

Unlike general purpose computing systems, embedded systems possess certain specific
characteristics and these characteristics are unique to each embedded system.
Some of the important characteristics of an embedded system are:
1. Application and domain specific
2. Reactive and Real Time
3. Operates in harsh environments
4. Distributed
5. Small size and weight
6. Power concerns

Application and Domain Specific
If you closely observe any embedded system, you will find that each embedded system is
having certain functions to perform and they are developed in such a manner to do the
intended functions only.
They cannot be used for any other purpose. It is the major criterion which distinguishes an
embedded system from a general purpose system. For example, you cannot replace the
embedded control unit of your microwave oven with your air conditioner's embedded
control unit, because the embedded control units of microwave oven and airconditioner are
specifically designed to perform certain specific tasks.
Also you cannot replace an embedded control unit developed for a particular domain say
telecom with another control unit designed to serve another domain like consumer
electronics.

Reactive and Real Time
As mentioned earlier, embedded systems are in constant interaction with the Real world
through sensors and user-defined input devices which are connected to the input port of the
system.
Any changes happening in the Real world (which is called an Event) are captured by
the sensors or input devices in Real Time and the control algorithm running inside the unit
reacts in a designed manner to bring the controlled output variables to the desired level.
The event may be a periodic one or an unpredicted one. If the event is an unpredicted one
then such systems should be designed in such a way that it should be scheduled to capture
the events without missing them.
Embedded systems produce changes in output in response to the changes in the input. So
they are generally referred as Reactive Systems.

Real Time System operation means the timing behaviour of the system should be
deterministic; meaning the system should respond to requests or tasks in a known amount
of time.
A Real Time system should not miss any deadlines for tasks or operations.
 It is not necessary that all embedded systems should be Real Time in operations.
Embedded applications or systems which are mission critical, like flight control systems,
Antilock Brake Systems (ABS), etc. are examples of Real Time systems.
The design of an embedded Real time system should take the worst case scenario into
consideration

Operates in Harsh Environment
It is not necessary that all embedded systems should be deployed in controlled environments.
The environment in which the embedded system deployed may be a dusty one or a high temperature
zone or an area subject to vibrations and shock.
Systems placed in such areas should be capable to withstand all these adverse operating
conditions. The design should take care of the operating conditions of the area where the system is
going to implement.
For example, if the system needs to be deployed in a high temperature zone, then all the
components used in the system should be of high temperature grade. Here we cannot go for a
compromise in cost.
Also proper shock absorption techniques should be provided to systems which are going to be
commissioned in places subject to high shock.
Power supply fluctuations, corrosion and component aging, etc. are the other factors that
need to be taken into consideration for embedded systems to work in harsh environments.

Distributed
The term distributed means that embedded systems may be a part of larger systems. Many
numbers of such distributed embedded systems form a single large embedded control unit.
An automatic vending machine is a typical example for this. The vending machine contains a
card reader (for pre-paid vending systems), a vending unit, etc. Each of them are independent
embedded units but they work together to perform the overall vending function.
Another example is the Automatic Teller Machine (ATM). An ATM contains a card reader
embedded unit, responsible for reading and validating the user's ATM card, transaction unit for
performing transactions, a currency counter for dispatching/vending currency to the authorized
person and a printer unit for printing the transaction details. We can visualize these as independent
embedded systems. But they work together to achieve a common goal.
Another typical example of a distributed embedded system is the Supervisory Control And Data
Acquisition (SCADA) system used in Control & Instrumentation applications, which contains
physically distributed individual embedded control units connected to a supervisory module

Small Size and Weight
Product aesthetics is an important factor in choosing a product. For example, when
you plan to buy a new mobile phone, you may make a comparative study on the pros
and corns of the products available in the market.
Definitely the product aesthetics (size, weight, shape, style, etc.) will be one of the
deciding factors to choose a product. People believe in the phrase "Small is beautiful".
Moreover it is convenient to handle a compact device than a bulky product. In
embedded domain also compactness is a significant deciding factor. Most of the
application demands small sized and low weight products.

Power Concerns
Power management is another important factor that needs to be considered in designing
embedded systems.
Embedded systems should be designed in such a way as to minimise the heat dissipation
by the system. The production of high amount of heat demands cooling requirements like
cooling fans which in turn occupies additional space and make the system bulky.
Nowadays ultra low power components are available in the market. Select the design
according to the low power components like low dropout regulators, and controllers
/processors with power saving modes.
Also power management is a critical constraint in battery operated application. The
more the power consumption the less is the battery life.

Let us discuss about
Quality attributes of Embedded Systems

Quality attributes are the non-functional requirements that need to be documented properly in
any system design. If the quality attributes are more concrete and measurable it will give a positive
impact on the system development process and the end product.
The various quality attributes that needs to be addressed in any embedded system development are
broadly classified into two, namely ‘Operational Quality Attributes' and 'Non-Operational Quality
Attributes'.
Operational Quality Attributes:
The operational quality attributes represent the relevant quality attributes related to the
embedded system when it is in the operational mode or 'online' mode. The important quality
attributes coming under this category are listed below:
1. Response
2. Throughput
3. Reliability
4. Maintainability
5. Security
6. Safety

1. Response
Response is a measure of quickness of the system. It gives you an idea about how fast
your system is tracking the changes in input variables. Most of the embedded systems
demand fast response which should be almost Real Time.
For example, an embedded system deployed in flight control application should
respond in a Real Time manner. Any response delay in the system will create potential
damages to the safety of the flight as well as the passengers.
It is not necessary that all embedded systems should be Real Time in response. For
example, the response time requirement for an electronic toy is not at all time-critical.
There is no specific deadline that this system should respond within this particular timeline.

2. Throughput
Throughput deals with the efficiency of a system.
In the case of a Card Reader, throughput means how many transactions the Reader can
perform in a minute or in an hour or in a day.
Throughput is generally measured in terms of Benchmark .
A 'Benchmark' is a reference point by which something can be measured.
In general it can be defined as the rate of production or operation of a defined process over
a stated period of time. The rates can be expressed in terms of units of products, batches
produced, or any other meaningful measurements.
Benchmark can be a set of performance criteria that a product is expected to meet or a
standard product that can be used for comparing other products of the same product line.

3. Reliability
Reliability is a measure of how much you can rely upon the proper functioning of the
system or what is the % susceptibility of the system to failures.
Mean Time Between Failures (MTBF) and Mean Time To Repair (MTTR) are the terms
used in defining system reliability.
MTBF gives the frequency of failures in hours/weeks/months.
MTTR specifics how long the system is allowed to be out of order following a failure.
For an embedded system with critical application need, it should be of the order of
minutes.
Maintainability deals with support and maintenance to the end user or client in case
of technical issues and product failures or on the basis of a routine system checkup.
4. Maintainability
Reliability and maintainability are considered as two complementary disciplines. A
more reliable system means a system with less corrective maintainability requirements and
vice versa.

As the reliability of the system increases, the chances of failure and non-functioning also
reduces, thereby the need for maintainability is also reduced.
Maintainability is closely related to the system availability. Maintainability can be
broadly classified into two categories, namely,
'Scheduled or Periodic Maintenance (preventive maintenance) and
Maintenance to unexpected failures (corrective maintenance)'.
Some embedded products may use consumable components or may contain components
which are subject to wear and tear and they should be replaced on a periodic basis. The
period may be based on the total hours of the system usage or the total output the system
delivered.
A printer is a typical example for illustrating the two types of maintainability. An inkjet
printer uses ink cartridges, which are consumable components and as per the
printer manufacturer the end user should replace the cartridge after each 'n' number of
printouts to get quality prints. This is an example for Scheduled or Periodic
maintenance'.

If the paper feeding part of the printer fails the printer fails to print and it requires
immediate repairs to rectify this problem. This is an example of Maintenance to
unexpected failure'.
In both of the maintenances (scheduled and repair), the printer needs to be brought offline
and during this time it will not be available for the user.
Hence it is obvious that maintainability is simply an indication of the availability of the
product for use. In any embedded system design, the ideal value for availability is
expressed as
A - MTBF/(MTBF + MTTR)
where A = Availability in the ideal condition,
MTBF = Mean Time Between Failures, and
MTTR Mean Time To Repair

5. Security
Confidentiality, 'Integrity', and 'Availability (The term 'Availability' mentioned here is not
related to the term 'Availability' mentioned under the Maintainability' section) are the three major
measures of information security..
Confidentiality deals with the protection of data and application from unauthorised disclosure.
Integrity deals with the protection of data and application from unauthorised modification.
Availability deals with protection of data and application from unauthorized users.
A very good example of the Security' aspect in an embedded product is a Personal Digital Assistant
(PDA). The PDA can be either a shared resource (e.g. PDAs used in LAB setups) or an individual one.
If it is a shared one there should be some mechanism in the form of a user name and password to
access into a particular person's profile-This is an example of 'Availability'.
Also all data and applications present in the PDA need not be accessible to all users. Some of them
are specifically accessible to administrators only. For achieving this, Administrator and user levels
of security should be implemented -An example of Confidentiality.
Some data present in the PDA may be visible to all users but there may not be necessary
permissions to alter the data by the users. That is Read Only access is allocated to all users-An
example of Integrity.

6. Safety
'Safety and Security are two confusing terms. Sometimes you may feel both of
them as a single attribute. But they represent two unique aspects in quality attributes.
Safety deals with the possible damages that can happen to the operators, public and the
environment due to the breakdown of an embedded system or due to the emission of
radioactive or hazardous materials from the embedded products.
The breakdown of an embedded system may occur due to a hardware failure or a firmware
failure.
Safety analysis is a must in product engineering to evaluate the anticipated damages and
determine the best course of action to bring down the consequences of the damages to an
acceptable level.
 As stated before, some of the safety threats are sudden (like product breakdown) and some
of them are gradual (like hazardous emissions from the product).

Non-Operational Quality Attributes:
The quality attributes that needs to be addressed for the product "not' on the basis of operational
aspects are grouped under this category. The important quality attributes coming under this
category are listed below.
1. Testability & Debug-ability
2. Evolvability
3. Portability
4. Time to prototype and market
5. Per unit and total cost.
1. Testability & Debug-ability
Testability deals with how easily one can test his/her design, application and by which means
he/she can test it.
For an embedded product, testability is applicable to both the embedded hardware and firmware.
Embedded hardware testing ensures that the peripherals and the total hardware functions in the
desired manner, whereas firmware testing ensures that the fimmware is functioning in the
expected way.

Debug-ability is a means of debugging the product as such for figuring out the probable
sources that create unexpected behavior in the total system.
2. Evolvability
Evolvability is a term which is closely related to Biology. Evolvability is referred as the
non-heritable variation.
For an embedded system, the quality attribute 'Evolvability refers to the ease with which the
embedded product (including firmware and hardware) can be modified to take advantage of
new firmware or hardware technologies.
Debug-ability has two aspects in the embedded system development context, namely,
hardware level debugging and firmware level debugging.
Hardware debugging is used for figuring out the issues created by hardware problems
whereas firmware debugging is employed to figure out the probable errors that appear as a
result of flaws in the firmware.

The ease with which an embedded product can be ported on to a new platform is a direct measure
of the re-work required.
3. Portability
Portability is a measure of system independence. An embedded product is said to be portable if
the product is capable of functioning as such in various environments, target processors /controllers
and embedded operating systems..
A standard embedded product should always be flexible and portable. In embedded products, the
term 'porting' represents the migration of the embedded firmware written for one target
processor (e.g. Intel x86) to a different target processor (say Hitachi SH3 processor).
If the firmware is written in a high level language like 'C' with little target processor-specific
functions (operating system extensions or compiler specific utilities), it is very easy to port the
firmware for the new processor by replacing those 'target processor-specific functions with the ones
for the new target processor and re-compiling the program for the new target processor specific
settings.
Re-compiling the program for the new target processor generates the new target processor-specific
machine codes.

If you look into various programming languages for application development for desktop
applications, you will see that certain applications developed on certain languages run only
on specific operating systems and some of them run independent of the desktop
operating systems.
If the firmware is written in Assembly Language for a particular family of processor (say
x86 family), it will be very difficult to translate the assembly language instructions to the new
target processor specific language and so the portability is poor.
For example, applications developed using Microsoft technologies (e.g. Microsoft Visual C++
using Visual Studio) is capable of running only on Microsoft platforms and will not
function on other operating systems; whereas applications developed using Java' from Sun
Microsystems works on any operating system that supports Java standards.

The commercial embedded product market is highly competitive and time to market the product is
a critical factor in the success of a commercial embedded product..
4. Time-to-Prototype and Market
Time-to-market is the time elapsed between the conceptualization of a product and the time at
which the product is ready for selling (for commercial product) or use (for non-commercial products).
There may be multiple players in the embedded industry who develop products of the same
category (like mobile phone, portable media players, etc.). If you come up with a new design and if it
takes long time to develop and market it, the competitor product may take advantage of it with their
product.
Also, embedded technology is one where rapid technology change is happening. If you start your
design by making use of a new technology and if it takes long time to develop and market the
product, by the time you market the product, the technology might have superseded with a new
technology.
Product prototyping helps a lot in reducing time-to-market. Whenever you have a product idea,
you may not be certain about the feasibility of the idea. Prototyping is an informal kind of rapid
product development in which the important features of the product under consideration are
developed technology.

is a factor which is closely monitored by both end user (those who buy the product) and product
manufacturer (those who build the product).
5. Per Unit Cost and Revenue Cost
The time to prototype is also another critical factor. If the prototype is developed faster, the actual
estimated development time can be brought down significantly. In order to shorten the time to
prototype, make use of all possible options like the use of off-the-shelf components, re-usable assets,
etc.
Cost is a highly sensitive factor for commercial products. Any failure to position the cost of a
commercial product at a nominal rate, may lead to the failure of the product in the market.
Proper market study and cost benefit analysis should be carried out before taking a decision on the
per-unit cost of the embedded product.
From a designer/product development company perspective the ultimate aim of a product is to
generate marginal profit.
So the budget and total system cost should be properly balanced to provide a marginal profit.

The product idea generation, prototyping, Roadmap definition, actual product design and
development are the activities carried out during this phase.
 Every embedded product has a product life cycle which starts with the design and development
phase.
During the design and development phase there is only investment and no returns. Once the
product is ready to sell, it is introduced to the market. This stage is known as the Product
Introduction stage.
During the initial period the sales and revenue will be low. There won't be much competition and
the product sales and revenue increases with time. In the growth phase, the product grabs high
market share.
During the maturity phase, the growth and sales will be steady and the revenue reaches at its
peak.
The Product Retirement/Decline phase starts with the drop in sales volume, market share and
revenue.
The decline happens due to various reasons like competition from similar product with enhanced
features or technology changes, etc.
At some point of the decline stage, the manufacturer announces discontinuing of the product.

 The different stages of the embedded products life cycle-revenue, unit cost and profit in each stage-
are represented in the following Product Life-cycle graph
From the graph, it is clear that
the total revenue increases from
the product introduction stage to
the product maturity stage.
The revenue peaks at the
maturity stage and starts falling
in the decline/retirement stage.
The unit cost is very high during the introductory stage (a typical example is cell phone; if you
buy a new model of cell phone during its launch time, the price will be high and you will get the same
model with a very reduced price after three or four months of its launching).
 The profit increases with increase in sales and attains a steady value and then falls with a dip in sales.
You can see a negative value for profit during the initial period. It is because during the product
development phase there is only investment and no returns.
Profit occurs only when the total returns exceed the investment and operating cost

Reference
Shibu K V, “Introduction to Embedded
Systems”, First Edition, Tata McGraw Hill
Education Private Limited, 2009
For Further Studies:

30
Prof. Anand H. D.
M. Tech. (PhD.)
Assistant Professor,
Department of Electronics & Communication Engineering
Dr. Ambedkar Institute of Technology, Bengaluru-56
Email: anandhd.ec@drait.edu.in
Phone: 9844518832

Characteristics and Quality Attributes of Embedded System

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