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Outcomes

Explain the Characteristics of Embedded System

Describe the quality attributes of Embedded Systems

Illustrate Application- specific Embedded Systems with examples

Illustrate Domain - specific Embedded Systems with examples

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Characteristics of an Embedded System

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:

Application and domain specific
Reactive and Real Time
Operates in harsh environments
Distributed
Small size and weight
Power concerns

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1. Application and domain specific

An Embedded System is designed for a specific purpose only. It will not do any other task.
Certain embedded systems are specific to a application:

Eg. Air conditioner's embedded control unit, it cannot replace microwave oven…
Eg. A washing machine can only wash, it cannot cook..
The control units of microwave oven and air conditioner are specifically designed to perform certain specific tasks.

Certain embedded systems are specific to a domain:

Eg. A hearing aid is an application that belongs to the domain of signal processing and telecom with another control unit designed to serve another domain like consumer electronics.

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2. Reactive and Real Time

Certain embedded systems are designed to react to the events that occur in the nearby environment. These events also occur real-time.
Eg. Flight control systems, Antilock Brake Systems (ABS), etc. are examples of Real Time systems
Eg. An air conditioner adjusts its mechanical parts as soon as it gets a signal from its sensors to increase or decrease the temperature when the user operates it using a remote control.
An embedded system uses Sensors to take inputs and has actuators to bring out the required functionality

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3. Operation in Harsh Environment

Certain embedded systems are designed to operate in harsh environments like a dusty one or a high temperature zone or an area subject to vibrations and shock or very high temperature of the deserts or very low temperature of the mountains or extreme rains.
These embedded systems have to be capable of sustaining the environmental conditions it is designed to operate in.

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4. Distributed

The term distributed means that Embedded Systems may be a part of a larger system.
These components are independent of each other but have to work together for the larger system to function properly.
Ex. Automatic Teller Machine (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.

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5. Small Size and Weight

An embedded system that is compact in size and has light weight will be desirable or more popular than one that is bulky and heavy.
Ex. Currently available cell phones. The cell phones that have the maximum features are popular but also their size and weight is an important characteristic.

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6. Power Concerns

It is desirable that the power utilization and heat dissipation of any Embedded System be low.
If more heat is dissipated then additional units like heat sinks or cooling fans need to be added to the circuit.
Ex. 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.

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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
Non-Operational Quality Attributes

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1. 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:

Response
Throughput
Reliability
Maintainability
Security
Safety

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a. Response

Response is a measure of quickness of the system.
It gives you an idea about how fast your system is tracking the input variables.
Most of the embedded system demand fast response which should be real-time.
Eg. - 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.
Eg. - The response time requirement for an electronic toy is not at all time-critical.

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b. Throughput

Throughput deals with the efficiency of system.
It can be defined as rate of production or process 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.
In case of card reader like the ones used in buses, throughput means how much transactions the Reader can perform in a minute or hour or day.
Throughput is generally measured in terms of ‘Benchmark’. A Benchmark is a reference point by which something can be measured.
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.

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c. Reliability

Reliability is a measure of how much percentage you rely upon the proper functioning of the system or what is the % susceptibility of the system to failure.
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 specifies 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.

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d. Maintainability

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.
Reliability and maintainability are considered as two complementary disciplines. A more reliable system means a system with less corrective maintainability requirements and vice versa.
Maintainability can be classified into two types:

Scheduled or Periodic Maintenance (Preventive Maintenance) - An inkjet printer uses ink cartridges, which are consumable components and as per the printer manufacturer the end use should replace the cartridge after each n - number of printouts to get quality prints.
Maintenance to Unexpected Failures (Corrective Maintenance) - If the paper feeding part of the printer fails the printer fails to print and it requires immediate repairs to rectify this problem. 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 Where A_i=Availability in the ideal condition, MTBF =Mean Time Between Failures, and MTTR = Mean Time To Repair.

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e. Security

‘Confidentially’, ‘Integrity’, and ‘Availability’ are three major measures of information security.
‘Confidentially’ deals with the protection of data an application from unauthorized disclosure.
‘Integrity’ deals with the protection of data and application from unauthorized modification.
‘Availability’ deals with protection of data and application from unauthorized users.
Certain embedded systems have to make sure they conform to the security measures.
Ex. An electronic safety Deposit Locker can be used only with a pin number like a password.

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f. Safety

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.

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2. Non Operational Attributes

The quality attributes that needs to be addressed for the product ‘not’ on the basic of operational aspects are grouped under this category. The important quality attributes coming under this category are listed below:

Testability & Debug-ability
Evolvability
Portability
Time to prototype and market
Per unit and total cost

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a. 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.
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.
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.

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b. 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.

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c. Portability

Portability is a measure of ‘system independence’.
An embedded product can be called portable if it is capable of functioning in various environments, target processors/controllers and embedded operating systems.
A standard embedded product should always be flexible and portable.

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d. 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).
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.
Product prototyping helps a lot in reducing time-to-market.

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e. Per Unit Cost and Revenue

Cost is a factor which is closely monitored by both end user (those who buy the product) and product manufacturer (those who build the product).
Cost is a highly sensitive factor for commercial products. Proper market study and cost benefit analysis should be carried out before taking decision on the per unit cost of the embedded product.
When the product is introduced in the market, for the initial period the sales and revenue will be low. There won’t be much competition when the product sales and revenue increase.
During the maturing phase, the growth will be steady and revenue reaches highest point and at retirement time there will be a drop in sales volume.

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Product life cycle (PLC) curve

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Specific Embedded System

Washing Machine-Application-Specific Embedded System
Automotive-Domain-Specific Examples of Embedded System

Embedded systems are application and domain specific, meaning; they are specifically built for certain applications in certain domains like consumer electronics, telecom, automotive, industrial control, etc.

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Washing Machine-Application-Specific Embedded System

The actuator part of washing machine consists of a motorized agitator, tumble tub, water drawing pump and inlet valve to control the flow of water into the unit.
The sensor part consists of the water temperature sensor, level sensor, etc.
The sensor data is feedback to the control unit and the control unit generates the necessary actuator outputs.
The control part contains a microprocessor/controller based board with interfaces to the sensors and actuators.
The control unit also provides connectivity to user interfaces like keypad for setting the washing time, selecting the type of material to be washed like light, medium, heavy duty, etc.
User feedback is reflected through the display unit and LEDs connected to the control board.

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Functional block diagram of a washing machine

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Washing Machine

The integrated control panel consists of a microprocessor/controller based board with I/O interfaces and a control algorithm running in it.
Input interface includes the keyboard which consists of wash type selector namely Wash, Spin and Rinse, cloth type selector namely Light, Medium, Heavy duty and washing time setting, etc.
The output interface consists of LED/LCD displays, status indication LEDs, etc. connected to the I/O bus of the controller. It is to be noted that this interface may vary from manufacturer to manufacturer and model to model.
The other types of I/O interfaces which are invisible to the end user are different kinds of sensor interfaces, namely, water temperature sensor, water level sensor, etc. and actuator interface including motor control for agitator and tub movement control, inlet water flow control, etc.

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Automotive-Domain-Specific Embedded System

Automotive embedded systems are the one where electronics take control over the mechanical systems.
The presence of automotive embedded system in a vehicle varies from simple mirror and wiper controls to complex air bag controller and antilock brake systems (ABS).
Automotive embedded systems are normally built around microcontrollers or DSPs or a hybrid of the two and are generally known as Electronic Control Units (ECUs).

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Automotive

The various types of electronic control units (ECUs) used in the automotive embedded industry can be broadly classified into two-High speed embedded control units and Low speed embedded control units.
High speed Electronic Control Units (HECUs) : High speed electronic control units (HECUs) are deployed in critical control units requiring fast response, like fuel injection systems, antilock brake systems, etc.
Low speed Electronic Control Units (LECUs) : Low speed electronic control units are deployed in applications where response time is not so critical. They are generally built around low cost microprocessors/microcontrollers and digital signal processors. Audio controllers, passenger and driver door locks, door glass controls, etc., are examples for LECUs.

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