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Notes of Embedded System [CT 655]

Introduction to Embedded System


Embedded System Overview

Embedded system is an optimized computing system consisting of the mechanical or electrical system, often with real time computing constraints designed for performing some dedicated functions.

Characteristics of Embedded System:

The common characteristics of embedded system are as follows:-

1. Single Functioned
An embedded system is designed to perform specific tasks repeatedly. Newer program version update can be done in some rare cases.

2. Tightly Constrained
An Embedded system has tightly constrained design matrices such as low cost, portable size, high performance, and limited power consumption and so on.

3. Reactive and Real Time
An Embedded system should continuously react to changes in the system’s environment and should provided output in a real time within a specified time frame. Delayed amputation may result in system failure.

For e.g.: Digital Camera
-It is designed to capture image or videos repeatedly.
-It is cheap, single chip system, small in size and low power system.
-It is reactive to some extent i.e. auto flash mode, smile detection mode etc.

Classification of Embedded System

Classification based on generation

1. First generation embedded system
First generation embedded system is designed with 8 bit microprocessor or 4 bit microcontroller. They have very simple hardware circuits. The firmwares are designed in assembly language. For Example: digital telephone keypad, stepper motor control etc.

2. Second generation embedded system
Second generation embedded system are designed with 16 bit up or 8 bit uc . They have complex hardware configuration than first generation. They may contain embedded OS. For example DAS

3. Third generation embedded system
Third generation embedded system are designed with 32 bit up or 16 bit uc . They consist of application specific IC. The concept of DSP emerges. E.g. Robotics

4. Fourth generation embedded system
Fourth generation ES are designed with 64 bit up or 32 bit uc. They consist of system on chip and multi core processors with tight integration and miniaturization. E.g Smartphones

Hardware and Software in an Embedded System

Embedded System Design Metrics

Design metrics are the measures of implementational features of system.

Some of the common design metrics are as follows:
1. Unit cost ( Monetary cost of manufacturing each copy of system )
2. NRE cost ( one time monetary cost of designing system)
3. Size (Physical space in bytes or gates required)
4. Performance (Execution time of system)
5. Power (Amount of power consumed by the system)
6. Flexibility (ability to change functionality without incurring NRE cost)
7. Time to prototype (time needed to build working version)
8. Time to market (time required to develop a system up to release)
9. Maintainability (ability to modify system after initial release)
10. Correctness (correct functioning by the system)
11. Safety (Probability that system will not cause harm)
Design metrics are the measures of implementational features of system.

Embedded System vs. General Purpose Computing System

1. Embedded System consists of specific hardware, embedded operating system. GPCS consists of generic hardware, GPOS.
2. Embedded System is designed to perform specific set of functions while GPCS is designed to perform various functions.
3. OS in embedded system is mandatory but in GPCS it is compulsory.
4. Performance is key factor of GPCS.
5. Maximum power saving requirements for ES.
6. Embedded system is time critical.
7. Embedded system is deterministic.
8. Programs in GPCS are alterable by end users.

Q) How can we meet best optimization of Embedded System?

There are many design metrics that impacts the embedded system design. The key challenge is that improving one metric leads to worsening of another. So, to meet best optimization, the designer must be comfortable with various implementation technologies and must be able to migrate from one technology to another. This ensures best implementation for a given system.

Q) Simplified Revenue Model

1. It is used to investigate loss of revenue occurs due to delayed entry of product in the market.
2. It assumes peak of market occurs at halfway point (W) of a product life even for delayed entry.
3. The revenue for an on-time market entry is area of Δ on time.
4. The revenue for delayed entry is area of delayed

Therefore. Revenue loss = A(on time) - A(delayed)
Percentage Revenue Loss = { A(on time) - A(delayed)} / on time * 100%

Let market rise angle be θ,
So, A(on time) = 2(½ b*h ) = 2 (½ *W*Wtanθ ) = W^2 * tanθ
A(delayed) = ½ * (2W- ) * ( (W- Δ)tanθ)
Percentage revenue loss = [ W^2 * tanθ - W^2 * tanθ + 3/2 * W Δ tanθ - ½ Δ^2 * tanθ ] W^2 * tanθ * 100%
= [ 1/(2 * W^2) * ( 3W Δ - Δ^2 ) ] * 100%

Q) NRE and Unit Cost

Total Cost = NRE cost + Unit Cost * no of units
Pre Product Cost = Total Cost / No of Units

Q) The design of disk drive has NRE cost $100,000 and unit cost $20. How much will we have to add to cost of each product to cover NRE cost assuming sell of 100 units?


Added cost = Amortized NRE cost = NRE Cost / no of units
= 100,000 / 100 = $1000

Purpose and Application of Embedded System

Purpose of Embedded System

1. Data collection, storage and representation
2. Data communication
3. Data processing
4. Monitoring
5. Control
6. Application Specific UI

Applications of Embedded System

1. Consumer Electronics (Camera , Radio )
2. Home appliances (TV DVD Player , Washing machine)
3. Home Automation and Security (CCTV, Burlgar Alarm , Fire Alarm)
4. Industry Automation (Engine Control)
5. Telecommunication (Cell Phones)
6. Networking (Routers , Switch)
7. Computer Peripherals (printer, fax)
8. Health Science (ECG Machine, disease identification system)
9. Biometrics (Finger Print Recognition, face detection)
10. Banking (ATM ,Currency Counter)

Q) Moore’s Law

IC transistor capacity doubles every 18 months.

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