Question and Answers

Q1. What are the Hierarchical components in a embedded system design.

Ans:




Q.2. What is LVDS?


Ans:

Known as Low Voltage Differential Signaling. The advantages of such a standard is low noise and low interference such that one can increase the data transmission rate. Instead of 0 and 5 V or ±5V a voltage level of 1.5 or 3.3 V is used for High and 0 or 1 V is used for Low. The Low to High voltage swing reduces interference. A differential mode rejects common mode noises.

Q.3. Is there any actuator in your mobile phone?


Ans:

There is a vibrator in a mobile phone which can be activated to indicate an incoming call or message. Generally there is a coreless motor which is operated by the microcontroller for generating the vibration.

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Structure of an Embedded System

On the other hand a desktop computer may contain all these units on a single Power Circuit Board (PCB) called as the Mother Board. Since these computers handle much larger dimension of data as compared to the embedded systems there has to be elaborate arrangements for storage and faster data transfer between the CPU and memory, CPU and input/output devices and memory and input/output devices. The storage is accomplished by cheaper secondary memories like Hard Disks and CDROM drives. The data transfer process is improved by incorporating multi-level cache and direct memory access methods. Generally no such arrangements are necessary for embedded systems. Because of the number of heterogeneous components in a desktop computer the power supply is required at multiple voltage-levels (typically ±12, ± 5, ± 3, 25 volts). On the other hand an Embedded Systems chip may just need one level DC power supply (typically +5V).
In a desktop computer various units operate at different speeds. Even the units inside a typical CPU such as Pentium-IV may operate at different speeds. The timing and control units are complex and provide multi-phase clock signal to the CPU and other peripherals at different voltage levels. The timing and control unit for an Embedded system may be much simpler.

The typical structure of an embedded system is shown in Fig. 3.2. This can be compared with that of a Desktop Computer as shown in Fig. 3.3. Normally in an embedded system the primary memory, central processing unit and many peripheral components including analog-to-digital converters are housed on a single chip. These single chips are called as Microcontrollers. This is shown by dotted lines in Fig. 3.2.

The typical structure of an Embedded System
(Fig. 3.2)



The structural layout of a desktop Computer
(Fig. 3.3)



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Components of Embedded Systems

Introduction

The various components of an Embedded System can be hierarchically grouped as System Level Components to Transistor Level Components. A system (subsystem) component is different than what is considered a "standard" electronic component. Standard components are the familiar active devices such as integrated circuits, microprocessors, memory, diodes, transistors, etc. along with passives such as resistors, capacitors, and inductors. These are the basic elements needed to mount on a circuit board for a customized, application-specific design.

A system component on the other hand, has active and passive components mounted on circuit boards that are configured for a specific task. (Fig. 3.1) System components can be either single- or multi-function modules that serve as highly integrated building blocks of a system. A system component can be as simple as a digital I/O board or as complex as a computer with video, memory, networking, and I/O all on a single board. System components support industry standards and are available from multiple sources worldwide.



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Questions and Answers of Real Time Embedded Systems

Q1. Give one example of a typical embedded system other than listed in this lecture. Draw the block diagram and discuss the function of the various blocks. What type of embedded processor they use?

Ans:
Example 1: A handheld Global Positioning System Receiver





A GPS receiver receives signals from a constellation of at least four out of a total of 24 satellites. Based on the timing and other information signals sent by these satellites the digital signal processor calculates the position using triangulation.

The major block diagram is divided into (1) Active Antenna System (2)RF/IF front end (3) The Digital Signal Processor(DSP)

The Active Antenna System houses the antenna a band pass filter and a low noise amplifier (LNA)

The RF/IF front end houses another band pass filter, the RF amplifier and the demodulator and A/D converter.

The DSP accepts the digital data and decodes the signal to retrieve the information sent by the GPS satellites.

Q2. Discuss about the Hard Disk Drive housed in your PC. Is it an RTES?

Ans:



Hard drives have two kinds of components: internal and external. External components are located on a printed circuit board called logic board while internal components are located in a sealed chamber called HDA or Hard Drive Assembly.

The big circuit is the controller. It is in charge of everything: exchanging data between the hard drive and the computer, controlling the motors on the hard drive, commanding the heads to read or write data, etc.

All these tasks are carried out as demanded by the processor sitting on the motherboard. It can be verified to be single-functioned, tightly constrained,
Therefore one can say that a Hard Disk Drive is an RTES.


Q3. Elaborate on the time-to-market design metric.


Ans:

The time required to develop a system to the point that it can be released and sold to customers. The main contributors are design time, manufacturing time, and testing time. This metric has become especially demanding in recent years. Introducing an embedded system to the marketplace early can make a big difference in the system’s profitability.


Q4. What is Moore’s Law? How was it conceived?

Moore's law is the empirical observation that the complexity of integrated circuits, with respect to minimum component cost, doubles every 24 months. It is attributed to Gordon E. Moor, a co-founder of Intel.



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Design Methodology

The design task can be further segregated into the following steps:

System level Design

Find out the possible subsystems of the system and the interconnections between them.

Sub-system or Node Level design

Each of these subsystems can be termed as the nodes. Elaborate on each of these subsystems and further make the block diagram and component level interconnections.

Processor Level Design

Each subsystem may consist of processor, memory, I/O devices. Specification and design at this level is required now.

Task Level Design

Complete interconnection of these subsystems depending on the tasks they would perform



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The Performance Design Metric

Performance of a system is a measure of how long the system takes to execute our desired tasks.

The two main measures of performance are:

Latency or response time:

This is the time between the start of the task’s execution and the end. For example, processing an image may take 0.25 second.


Throughput:

This is the number of tasks that can be processed per unit time. For example, a camera may be able to process 4 images per second
These are the some of the cost measures for developing an RTES. Optimization of the overall cost of design includes each of these factors taken with some multiplying factors depending on their importance. And the importance of each of these factors depends on the type of application. For instance in defense related applications while designing an anti-ballistic system the execution time is the deciding factor. On the other hand, for de-noising a photograph in an embedded camera in your mobile handset the execution time may be little relaxed if it can bring down the cost and complexity of the embedded Digital Signal Processor.

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Design Issues

The constraints in the embedded systems design are imposed by external as well as internal specifications. Design metrics are introduced to measure the cost function taking into account the technical as well as economic considerations.

Design Metrics

A Design Metric is a measurable feature of the system’s performance, cost, time for implementation and safety etc. Most of these are conflicting requirements i.e. optimizing one shall not optimize the other: e.g. a cheaper processor may have a lousy performance as far as speed and throughput is concerned.

Following metrics are generally taken into account while designing embedded systems:

NRE cost (nonrecurring engineering cost)


It is one-time cost of designing the system. Once the system is designed, any number of units can be manufactured without incurring any additional design cost; hence the term nonrecurring.

Suppose three technologies are available for use in a particular product. Assume that implementing the product using technology ‘A’ would result in an NRE cost of $2,000 and unit cost of $100, that technology B would have an NRE cost of $30,000 and unit cost of $30, and that technology C would have an NRE cost of $100,000 and unit cost of $2. Ignoring all other design metrics, like time-to-market, the best technology choice will depend on the number of units we plan to produce.


Unit cost

The monetary cost of manufacturing each copy of the system, excluding NRE cost.


Size

The physical space required by the system, often measured in bytes for software, and gates or transistors for hardware.


Performance

The execution time of the system.

Power Consumption

It is the amount of power consumed by the system, which may determine the lifetime of a battery, or the cooling requirements of the IC, since more power means more heat.


Flexibility

The ability to change the functionality of the system without incurring heavy NRE cost. Software is typically considered very flexible.


Time-to-prototype

The time needed to build a working version of the system, which may be bigger or more expensive than the final system implementation, but it can be used to verify the system’s usefulness and correctness and to refine the system’s functionality.

Time-to-market

The time required to develop a system to the point that it can be released and sold to customers. The main contributors are design time, manufacturing time, and testing time. This metric has become especially demanding in recent years. Introducing an embedded system to the marketplace early can make a big difference in the system’s profitability.

Maintainability

It is the ability to modify the system after its initial release, especially by designers who did not originally design the system.

Correctness

This is the measure of the confidence that we have implemented the system’s functionality correctly. We can check the functionality throughout the process of designing the system, and we can insert test circuitry to check that manufacturing was correct.

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