©2008 R. Gupta, UCSD COSMOS Summer 2008 Embedded Systems Rajesh K. Gupta Computer Science and Engineering University of California, San Diego

©2008 R. Gupta, UCSD

COSMOS Summer 2008

Embedded Systems

Rajesh K. Gupta

Computer Science and Engineering

University of California, San Diego.


Roadmap

• Topic:– What are embedded systems?

– What has that got to do with computers and ‘chips’?

• This lecture– Concepts covered: computing, computers, computer

architecture

– Computer peripherals

• Next lecture– Computer interfaces and networks: I2C, SPI

• Reference– None

Keywords:Embedded ComputerComputing MachinesComputer ApplicationComputer ArchitectureComputer OrganizationCPU, Memory, BusISA


Conventions (if I can follow them• Important concept words are usually

highlighted – Or strongly highlighted.

• “Memory” means more than it says

• Challenges and Teasers– Teaser questions are not meant to be answered


http://images.google.com/imgres?imgurl=wetpc.com.au/html/Assets/jpg/general/WetPC1.jpg&imgrefurl=http://wetpc.com.au/html/newsroom/&h=2774&w=1813&prev=/images%3Fq%3Dwearable%2Bcomputer%26start%3D20%26svnum%3D10%26hl%3Den%26lr%3D%26ie%3DUTF-8%26oe%3DUTF-8%26sa%3DN

http://www.gsmworld.com/images/3g/nokia2_lrg.jpg

http://images.google.com/imgres?imgurl=www.albright.edu/images/reporter/wint02/cellphone.jpg&imgrefurl=http://www.albright.edu/reporter/wint02/lastword-wint02.html&h=213&w=140&prev=/images%3Fq%3Dcellphone%26start%3D40%26svnum%3D10%26hl%3Den%26lr%3D%26ie%3DUTF-8%26oe%3DUTF-8%26sa%3DN


Embedded Systems

• “Systems” that are part of another “Application”

• We are interested in “Embedded Computer Systems”– Why? Hold that thought for now. (Hint: wait until ‘chips’)

• Computers are machines that are designed either for general-purpose applications or for specific applications.

• Computing refers to problem solving using Computers– machine-centric problem solving.

• In the past, computing are confined to scientific applications, and machines were expensive and necessarily shared.


Examples of Computational Problem Solving• Can you think of examples where you need

computers to solve problems?– Day-to-day

– In-the-interest-science-and-humanity

• Actually by far the largest application of computing was in building computers (hw, sw)


Problem Solving

• Problem: – Find greatest common divisor of two numbers: 6, 15.

• Solutions:1. Mathematical:

gcd(a, b) = gcd(a-b, b) assume w.l.o.g. a >=b

gcd(a, 0) = a

2. Procedural (Sequential): Chinese Remainder Theorem. if (x != 0 and y!= 0) {

repeat {while (x>=y)

x = x - y;swap x, y;} until (y=0);

write gcd = x;


Traditional Problem Solving using Computers• Describe the method in a programming

language

• Compile this program into a machine language

• Execute machine program– supply input data


The Computing Experience• The Computer Center

– Mainframe computing

• The Personal Computer– Desktop, laptop, palm top computing

• The Ubiquitous Embedded Computer– Mobile, purpose-built.


Computing Machines: Touchpoints in History• Generation 0: Mechanical machines

– Difference engine by Babbage (1834)

• Generation 1: Vacuum Tubes (1945-1955)– ENIAC by Eckert and Mauchly (1943)

• Generation 2: Transistors (1955-1965)– PDP-1 by DEC (1960): first microcomputer

• Generation 3: Integrated Circuits (1965-1980)– IBM 1401, 7094 and System/360 (1964)

• Generation 4: PCs and VLSI (1980-continuing)


The Computer

• Computers manipulate information by means of programmed instructions

• A computer hardware that makes this possible is called a stored program computer.

• A computer system designer must – evaluate applications for which the computer is to be used

– build a system architecture from software to its hardware organization

– (by architecture we often mean how the system appears to the system programmer, though it is not strictly correct..)

• The lexicon: architecture, organization, usage.


Computer Architecture

• Architecture provides– A model to organize, implement system parts

– A model to use the system

• Architectures can be diverse…

Architectural Design Paradigms

SpecializedAmbitious (and never finished)

The sacrificial altar

Engineered

“Organically grown”

The Planned Community


Hardware Organization

• Computer Organization refers to the structure of a computer:

DataPathController

controlenablesselects

dataconditions

Memory

CPUAddress

R/W

Data


Software ‘Architecture’

Assembler

Hardware

Micro-operations

Application

Compiler


A Personal Computer (PC)

• Uses commodity components and standard interfaces to build the machine

• Performance/cost variations due to choice of components and (sometimes) their interconnection.


PC Components

• Case:– desktop, minitower, mid case, mid tower, full tower, large tower– include a power supply (typically 200 watts)

• CPU and CPU fan– sold as a chip

• Motherboard– single-board computer – contains place holders for CPU and Memories– Memory modules

• Interfaces– Video (card and monitor)– Others: (I/O card) “Floppy, CD-ROM, Keyboard, Hard drive,

Sound card, Speakers, Modem, Tape/zip drive, Mouse”


168-pin SDRAM

184-pin DDR-SDRAM

The Stuff at Fry’s


Personal Computing

• “Low cost and general purpose”

CPU MEM

BUS

CPU DATA

BUS

INST


Computer Organization

CPU MEM

BUS

DevicesDevicesDevices

DrivesInput devices

Output devicesNetworking Interface

1

2

3

4


Memory

CPU MEM

BUS

DevicesDevicesDevices

2-3 GHz 50 ns SIMMPC2-5300 667 MHz DIMM


Lexicon: Non-intuitive & Not-obvious• Random Access: RAMs

– static

– dynamic

– quasi-static

• Read Only: ROMs– PROM

– EPROM

– EEPROM

– Flash EPROM

– “CMOS”

• “Cache”?

CPU

Cache

Memory

What are L1, L2, L3?


Buses

• Functions:– transmit information

– coordinate activities

– interface standard

• Bandwidth, width/xfr * xfr/sec

• Memory addressing, addr/word, addr/block

• Latency tolerance: low, medium, high

• Length: microns, mm, inches, feet, km, 1000s km


Buses

• CPU -- L1 Cache– very high bandwidth, 50-500

MB/sec, addr/word

• L1 Cache -- L2 Cache

• Cache -- Main Memory– very high bandwidth, 1-200

MB/sec

• Main Memory -- Disk– high bandwidth, 2 MB/sec,

addr/block

• Network -- Main Memory– similar to disk-memory

• Memory/CPU -- Display– high bandwidth, 1-20 MB/sec

• Computer -- Computer– medium bandwidth, kbps to

Mbps, addr/message.


CPU – Memory Interaction

DataPathController


dataconditions

Memory

CPUAddress

R/W

Data

• CPU controlled by a clock pulse.• Memory is controlled by R/W control signals.

• CPU must synchronize its memory read, write operations with respect to its internal clock.

• Example: 5 MHz clock, 500 ns access time.

Clock

clock

addr VALID

select

R/W’

VALIDdata

WRITE CYCLE

200 ns

500 ns


CPU Operation

• A computing machine delivers its functionality using instructions.– instruction set architecture (ISA)

• A CPU executes each instruction in steps:– Fetch instruction

– Decode instruction

– Execute instruction

• Fetch instruction– location pointed by the Program Counter


CPU Simplified

ALU

A B

FileRegister

Accumulator


The Assembly Language

• Machine defined by an ISA

• A program is translated into an object program

• An assembly language consists of– statement corresponding to machine instructions

– represented mnemonically: easier to remember than numbers and bits

– typical mnemonics: ADD, SUB, MUL

– machine dependent


Level 0

Level 1

Level 2

Level 3

A B

mux

C

ALU

MEM

SR

SA

Lc

Controller


dataconditions

Data Path

Hardware View Software View

ALU

A B

FileRegister

Accumulator

Program

CPU prog.

data


Let us see how a programmer would build a CPU...

Step 1: PC points to an instruction in the memory.

Mem

PC




Mem

PC

Step 2: Memory responds with “data” that represent an instruction to be stored in IR.

Mem

PC

IR




Mem

PC

Step 2: Memory responds with “data” that represent an instruction to be storedin IR.

Mem

PC

IR

Mem

PC

IR

Step 3: an instruction is decoded into“control” lines by the control block.

control




Mem

PC

Step 2: Memory responds with “data” that represent an instruction to be storedin IR.

Mem

PC

IR

Mem

PC

IR

Step 3: an instruction is decoded into“control” lines by the control block.

control

Step 4: Memory also provides “data” that is used by the ALU to compute variable values.

Mem

PC

IR

control

ALU

Acc


CPU Building (contd.)

Step 5: ALU output is stored back into memory; the ALU may also compute address, in which case ACC output it input to PC. ALU also computes data which is stored in memory.

Mem

PC

IR

control

ALU

Accsave data into memory.

load new address into PC, jump operation. addr

data in

data out


The Changing Computer

Instrumented wide-area spaces

Personal area spaces

Internet end-points

In-body, in-cell, in-vitro spaces


Driven By “Chips” Underneath

Graphics ControllerGraphics ControllerCellphone BasebandCellphone Baseband


Embedded Systems: Sensor Node



Recap

• A computer is a ‘Computing Machine’

• We saw what a computer looks like– Beyond what you see at Fry’s

– Architectural components & interfaces

• CPU, ALU, Memory, Bus

• Application = What can we do with computers– Traditional numeric problem solving replaced by ‘special-

purpose’ functions

• Sensing, control, media,…

• Next: what are peripherals and how we connect to these?

Documents

©2008 R. Gupta, UCSD COSMOS Summer 2008 Embedded Systems Rajesh K. Gupta Computer Science and Engineering University of California, San Diego