Dalya Gaber. Definition:- Embedded system is any device that includes a computer but is not itself a general purpose computer. It has hardware & software.

EMBEDDED SYSTEMS

Dalya Gaber

Definition:-Embedded system is any device that includes a computer but is not itself a general purpose computer.

It has hardware & software.

It is usually a part of some larger systems and is expected to function without human intervention.

It is expected to respond, monitor, control external environment using sensors and actuators.

Examples:-Personal Digital Assistant (PDA)PrintersCell PhonesAutomobile: engine, brakes, dash, etc.TelevisionHouse Hold appliancesSurveillance systems (security)

Characteristics of E.S.Sophisticated Functionality.

Real Time operation (not always).

Low manufacturing cost.

In many cases, there are appliances use application dependent processor not general purpose processor which we find in computers.

Restricted memory.

Low power (excessive power consumption increases system cost even in wall-powered devices , due to dealing with heat dissipation).

Manufacturing Cost:-We have two aspects:

•Non-recurring engineering cost (design & development).•Production & marketing cost for each unit.

Best technology choice will depend on the number of units we plan to produce and the product importance and market.

Real Time operation:-They are operations must be finished by deadlines. There are two types:-

1. Hard real time: missing deadline causes large failure or even catastrophe.

2. Soft real time: missing deadline results in degraded performance.

Most of systems are multi-rate systems which must handle operations at widely varying rates.

Application dependent requirements:-Fault Tolerance & Reliability: continue operation despite hardware or software faults.

Safety: systems to avoid physical or economic damage to person or property.

Dedicated Systems:-Predefined functionality, accordingly hardware and software designed.

Programmability rarely used during life time of the system which means: once programmed, they are expected to work for long times without any user’s intervention and they are designed for just a specific task.

Real time, fault-tolerant, safe

Types of embedded systems:-Similar to general computing (no sensors or actuators)EX: PDA, video games, automatic teller machine.

Control systems (basic sensing and actuating)EX: feedback control of real time systems, vehicle engines, flight control, nuclear reactors.

Signal processingEX: Radar, Sonar, DVD players, MP3 players

Communication & networkingEX: Cellular phones, internet appliances

Nature of system functions:-Control laws (Actuating)

Sequencing logic (For a specific purpose or target)

Signal processing (For sensor inputting)

Application specific interfacing (Kinds of sensors and actuators)

Fault response (Graceful degradation)

Implementing E.S.:-1- Hardware:- -Processing element (microcontrollers, microprocessors) -Peripherals (Input & output devices, Interfacing sensors & actuators, Interfacing protocols) -Memory Design -Bus Design

2- Software:- -System Software (specialized operating system, cross compilers & cross assemblers, simulators & emulators, debugging tools) -Application Software

Hardware Evolution:-1 – General purpose microprocessors & microcontrollers. (low cost, faster clock rate, higher degree of integration)

2 – DSP

3 – Application Specific Processors. (you design your needed processor, higher cost)

4 – SOC: System On Chip. (less space, less power consumption, more functions)

Software Characteristics:--Programs must be logically and temporally correct.-Must deal with inherent physical concurrency (Reactive systems)-Reliability and fault-tolerance are critical issues.-Application Specific and single purpose.

Multitasking & Concurrency:-Embedded systems need to deal with several inputs and outputs and multiple events occurring independently.

Separating tasks simplifies programming but requires somehow switching back and forth among different tasks (multitasking)

Concurrency is the appearance of simultaneous execution of multiple tasks.

Challenges in E.S. design:-How much hardware do we need?(what is word size of the CPU? Size of memory?)

How do we meet our deadlines?(Faster hardware or cleverer software?)

How do we minimize power?(Turn off un-necessary logic? Reduce memory accesses?)

E.S. Design:-

Multi-objectiveDependabilityAffordabilitySafetySecurityScalabilityTimeliness

Multi-DisciplineElectronic HardwareSoftwareMechanical HardwareControl AlgorithmsHumansSociety/Institutions

Life CycleRequirementsDesignManufacturingDeploymentLogisticsRetirement

Design Goals:-Performance (overall speed, deadline)

Functionality & user interface

Manufacturing cost

Power Consumption

Other requirements (physical size, etc.)

Functional VS. Non-Functional requirements:-

Functional requirements: output as function of input.

Non-functional requirements: time required to compute output – size, weight, etc. – power consumption – reliability

Design & Development Process:-Requirements Specifications architecture Component design system integration.

Testing & Debugging are important tasks at the end of that.

Top Down VS. Bottom Up:-1- Top Down Design:-Start from most abstract description.Work to most detailed.

2- Bottom Up design:-Work from small components to big system.

Real Design uses both techniques.

Stepwise Refinement (H.W. & S.W.):-At each level of abstraction, We must:-

Analyze the design to determine characteristics of the current state of the design.Refine the design to add detail.

Embedded System Hardware:-

It is used for processing input to produce output in task specific fashion.

Input interface Output interface

Information processing

system(processors)

Processors are microprocessors and microcontrollers. But in comparison to general purpose computing platforms, the considerations are:--Energy efficiency (led to enhanced battery life and less power consumption).-High code density in my instruction sets (would led to less requirement of program memory).

Microprocessors can be used for general purpose processes but microcontrollers are only used for special purpose processes.

Microprocessors:-CPU for computers.There are no RAM, ROM, I/O on CPU chip itself.Example: Intel’s X86, Motorola’s 680x0.

CPUGeneral purpose micro processor

RAM ROM I/O Port

Timer Serial port

Data bus

Address bus

General Purpose Microprocessor System

Microcontroller:-Basically, a microcontroller is a device which integrates a number of the components of a microprocessor system onto a single microchip.

A microcontroller combines onto the same microchip:-The CPU coreMemory (both RAM & ROM)Some parallel digital I/O and more.

CPU Memory I/O

Bus

Components of a microcontroller:-A timer module to allow the microcontroller to perform tasks for certain time periods and after that it can generate an interrupt to the process. So, it can be switching from one task to another task.

A serial I/O port to allow data to flow between the microcontroller and other devices such as a PC or another microcontroller.

An ADC to allow the microcontroller to accept analogue input data for processing. And in many cases, it also has DAC for the output.

ProgramMemory(expected toBe ROM)

Core

Parallel Port Parallel Port

Parallel Port

Data Memory(expected to be RAM)

SerialPort

SerialPort

Counter / Timer

More Detailed Block Diagram For Microcontroller

Why Microcontroller?Low cost, Small packaging.Low power consumption.Programmable, re-programmable.Lots of I/O capabilities.Easy integration with circuits.For applications in which cost, power, and space are critical.Single purpose.

VonNeuman Architecture:-Only one bus between CPU & memory for both address and data. I provide address from the CPU to the memory to fetch instruction as well as to fetch data and we use the bus to read the data as well as write the data onto that memory. in fact there is no difference between the data and instructions.RAM and program memory share the same bus and the same memory, and so must have the same bit width.Bottleneck: Getting instructions interferes with accessing RAM.

CPU

ProgramAndDatamemory

BUS

Harvard architecture:-Separate program bus and data bus, can be different widths.

Instruction pipelining easy

CPUProgrammemory

Datamemory8 bits12-14-

16 bits

CISC: Complex Instruction Set Computer

A large number of instructions each carrying out a different permutation of the same operation.

Instructions provide for complex operations.

Different instructions of different format.

Different instructions of different length.

Different addressing modes.

Requires multiple cycles for execution.

RISC: Reduced Instruction Set Computers

Instructions for simple operations that can be executed in a single cycle.

Each instruction of fixed length (facilitates instruction pipelining)

Large general purpose register set (can contain data or address, Symmetry)

Load-store architecture (no memory access for data processing instructions)

PIC microcontroller family

One of the leading architectures for low end applications

(applications need 4-8-16 bit processors)

PIC architecture:-PICs are “RISC”

Few instructions (usually<50)

Only a few addressing modes

Executes one instruction in one internal clock cycle (Tcyc)

Why PIC was designed as a RISC processor????The moment I have got simple set of instructions and can execute single set of instruction in one cycle, I can actually execute a large number of operations and I can have easy implementation of pipelining without having a complex hardware. Less complex hardware means less consumption of silicon area as well as less consumption of power

The PIC family: PackagesPICs come in a huge variety of packages.Examples:-8 pin : 12C50x (12bit) and 12C67x (14bit)18 pin : 16C5x (12bit), 16Cxxx (14bit)28 pin : 16C5x (12bit), 16Cxxx (14bit)40 pin : 16Cxxx (14bit), 17C4x (16bit)44 – 68 pin : 16Cxxx (14bit), 17C4x / 17Cxxx (16bit)