1 wright state university, college of engineering dr. t. doom, computer science & engineering...

1Wright State University, College of EngineeringDr. T. Doom, Computer Science & Engineering

EGR 191Intro. to Engineering

Dr. Travis Doom

Wright State University

Computer Science and Engineering

A beginning engineer’s guideA beginning engineer’s guideto the digital computerto the digital computer



What What isis a computer? a computer?

What is computation? There are many sorts of computing devices, they fall into two categories:

– Analog: machines that produce an answer that measures some continuous physical property such as distance, light intensity, or voltage. Examples?

– Digital: machines that perform computations by manipulating a fixed finite set of elements. Examples?

– The difficulty with analog devices is that it is very hard to increase their accuracy. Before modern digital computers, the most common digital machines were

adding machines.– Adding machines perform exactly one sort of operation.

Computers also perform one operation… but their operation is to accept a set of instructions that tell it how to do any sort of computation.



Universal computing devicesUniversal computing devices

Turing’s Thesis: Computer scientists believe that ANYTHING that can be computed, can be computed by a computer (provided that it has enough time and enough memory).

What does this imply?– All computers (from the least expensive to the most expensive) are capable of

computing EXACTLY the same things IF they are given enough time and enough memory.

– Some computers can do things faster, but none can do more than any other computer.

– All computers can do exactly the same same things!

Thus, any given problem is either computable or it is not computable– Problems may be computable, but still not feasible (NPC)



How How dodo we get the electrons to do the work? we get the electrons to do the work?

We describe our problems in English or some other natural language. Computer problems are solved by electrons flowing around inside the computer.

It is necessary to transform our problem from a natural language to the voltages that influence the flow of electrons.

This transformation is really a sequence of systematic transformations, developed and improved over the last 50 years, which combine to give the computer the ability to carry out what may appear to be very complicated tasks. In reality, these tasks must be simple and straight-forward.



The principle of design abstractionThe principle of design abstraction

General model for Engineering (Byrne, 1992)

Existing System Target System

Implementation

Design

Requirements Requirements

Con-ceptual

Con-ceptual

Design

Implementation

re-think

re-specify

re-design

re-build

Alteration

ReverseEngineeringAbstraction

ForwardEngineeringRefinement



Levels of abstraction in digital computationLevels of abstraction in digital computation

Design Process

Algorithm & Language

The Problem

ISA & Microarchitecture

Circuits & Devices

Software level

Hardware level

Logic level

Computer Science

Computer Engineering

Computer/Elect. Engineering



The statement of the problemThe statement of the problem

We describe problems that we wish to solve with a computer in a “natural language.”

Natural languages are fraught with a lot of things unacceptable for providing instructions to a computer.

The most important of these unacceptable attributes is ambiguity. To infer the meaning of a sentence, a listener is often helped by context that the computer does not have.

Example: “Time flies like an arrow.”– How fast time passes– Track meet– Gossip

A computer is an electronic idiot and can not deal with any ambiguity, thus…


The Problem


Circuits & Devices



The algorithmThe algorithm

The first step in the sequence of transformations is to transform the natural language description of the problem to an algorithm.

An algorithm is a step-by-step procedure:– That transforms an input (possibly NULL) into

some output (or output action)– That is guaranteed to terminate

Definiteness: Each step is precisely stated. Effective computability: Each step must be

something the computer can perform Finiteness: The procedure must terminate For any computable problem, there are an

infinite number of algorithms to solve it.– Which solution is best?


The Problem


Circuits & Devices



The programming languageThe programming language

The next step is to transform the algorithm into a computer program

Programming languages are unambiguous “mechanical” languages

There are two kinds of programming languages:– High-level languages are machine independent.

They are “far above” the (underlying) computer

– Low-level languages are machine dependent. They are tied to the computer on which the program will execute. There is generally only one such language per machine (referred to as its ASSEMBLY language).


The Problem


Circuits & Devices



The instruction set architecture (ISA)The instruction set architecture (ISA)

The next step is to translate the program into the instruction set of the particular computer that will be used to carry out the work of the program.

The Instruction Set Architecture (ISA) is the complete specification of the interface between programs that have been written and the underlying hardware that must carry out the work of those programs.

– Examples: IA-32 (Intel, AMD, and others), PowerPC (Motorola)

Programs are translated from high languages in to the ISA of the computer on which they will be run by a program called a compiler (specific to the ISA).

Programs are translated from assembly to the ISA by an assembler

Analogy: A car– The car’s ISA describes what the driver sees/uses.


The Problem


Circuits & Devices



The microarchitectureThe microarchitecture

The next step is to transform the ISA into an implementation. The detailed organization of an implementation is called its microarchitecture.

– The IA-32 has been implemented by several different processors over the past twenty years 8086 (Intel, 1979), 8286, 8386, 8486, Pentium, PentiumII, Athlon, PentiumIII.

– Each implementation is an opportunity for computer designers to make different trade-offs between cost and performance. [Computer design is always an exercise in trade-offs.]

Analogy: A car– The implementation of a car’s ISA is what goes on

under the hood. Here all automobiles makes and models are different. Some with fuel injection, some have eight cylinders, some are turbocharged… in each case the “microarchitecture” of a specific automobile is the result of the automobile designers’ decisions regarding cost and performance.


The Problem


Circuits & Devices



The logic circuitThe logic circuit

The next step is to implement each element of the microprocessor out of simple logic circuits.

Here there are also choices, as the logic designer decides how to best make the trade-offs between cost and performance.

Even in the case of addition, there are several choices of logic circuits to perform this operation and differing speeds and corresponding costs.


The Problem


Circuits & Devices



The devicesThe devices

Finally, each basic logic circuit is implemented in accordance with the requirements of the particular device technology used.

So, CMOS circuits are different from NMOS circuits, which are different, in turn, from gallium arsenide circuits.


The Problem


Circuits & Devices

Vin

Vout

GND

Vcc

Rc

Rb



Electronic aspects of digital designElectronic aspects of digital design

Vin low Ib = 0

– transistor cut off: Vout = Vcc

Vin high Ib > 0

– transistor “on”: Vout = GND

Vin

Vout

GND

Vcc

Rc

Rb

VccVIHminVOLmax

Vin

VOLmax

VOHmin

GND

Vcc

VCESat

Vout

Abnormal except for switching

VOLmax: max output voltage in low state

VOHmin: min output voltage in high state

VILmax: max input voltage recognized as low

VIHmin: min input voltage recognized as high



Digital devicesDigital devices

Analog characteristics– Continuous signal levels

– Very small, smooth level changes

Digital characteristics– Discrete signal levels (voltage usually)

– Two levels: on/off, high/low 1/0 (binary)

– Disjoint or quantized level changes

Digital Concepts and Devices– Digital Design also called Logic Design

– Logic Gates - the most basic digital devices

– Digital devices have analog electronic aspect

t

v

v

t



Basic logic circuitsBasic logic circuits

AND gate– Output Z = 1 only when inputs A and B are both 1

OR gate– Output Z = 1 only when inputs A or B or both are 1

NOT gate or inverter– Output Z = 1 only when input A is 0

Simple alone, but combine a few

million gates and…

A

BZ

A

BZ

ZA

/A

/ B

F



Complex logic circuitsComplex logic circuits

Logic circuits divide into two major types:

Combinational Logic– Current output depends on current input only

– Examples: gates, decoders, multiplexors (MUXs), ALUs

Sequential Logic– Current output depends on past inputs as well as current input

– Thus has a memory (usually called the state)

– Examples: latches, flip-flops, state machines, counters, shift registers

+

*p

mn

p * (m + n)

Design:avg (w,x,y,z)a^2+2ab+b^2



STATE- A collection of state variables whose values at any one time contain all the information about the past values necessary to account for future behavior.

Example: A TV tuner could have a current channel stored internally, so the next channel can be predicted as a function of the inputs, i.e. the UP button increases the channel by one, the DOWN button decreases the channel by one. What is the state of this TV tuner?

Digital sequential logic– State variables are binary values– Circuit with n binary state variables has 2n possible states– Also known as a finite state machine (FSM).– Changes usually synchronized with a system clock

Sequential logic definitions



Bistable ElementBistable Element

The simplest possible feedback sequential logic circuit is shown below:

It is bistable because it has two stable states:– State 1: If Q (Q=Vout1=Vin2) is high, the bottom inverter output

(/Q =Vout2=Vin1) is low, which keeps the top inverter output Q high.

– State 2: If Q is low, the bottom inverter output /Q is high, which keeps the top inverter output Q low.

Vin1

Vin2

Vout1

Vout2

Q

/Q



S-R LatchS-R Latch

S R Q /Q

0

0

1

1

0

1

0

1

Last Q

0

1

0

Last /Q

1

0

0

S

RQ

/Q

S

R

Q

Q

Schematic

Symbol

Hold

Reset

Set

ILLEGAL

Function Table

Set

Reset

Characteristic Equation: Q(t+1) = S + R’Q(t)



Clocked Synchronous State-machine StructureClocked Synchronous State-machine Structure

Next-stateLogic

F

StateMemory

clock

OutputLogic

G

excitationinputs

clock

current state outputs

(Mealy machine)

R



Random Access Memory (RAM)Random Access Memory (RAM)

A circuit with n + b inputs and b outputs:

2n x bRAM

Address n b Dataoutputs

Memory values determined by user Volatile contents lost without power Uniform (Random) Access delay is uniform for all addresses

b/Data inputs

Write Enable



Instruction Format: Opcode [15:12], Op A [11:8], Op B [7:4], Op C [3:0]Example Instruction: x2021Opcode 2 Format: M[A] M[B]Instruction: M[0] M[2]

-processor

Instruction

Start

Reset

Clock >

RAM

Ready

AddressData In

Write

Data OutAddress Out

Data Out

Write Enable

Data In

4

4

4

16

Ram Contents (Before) ADDR DATA x0 x4 x1 xF x2 x9 … ...

Ram Contents (After) ADDR DATA x0 x9 x1 xF x2 x9 … ...

A simple microprocessorA simple microprocessor



-processor

Instruction

Start

Reset

ClockReady

16 Address Out

Data Out

Write Enable

Data In

4

4

4

Control Unit Data Unit

VNCZ4

14

4Constant

ControlWord

>

>

Example Instruction: x2021Opcode 2 Format: M[A] M[B]Instruction: M[0] M[2]

• R0 Constant B• Address Out R0, R1 Data In• R0 Constant A• Address Out R0, Data Out R1, Write Enable• Return to IDLE state (Sequencing Instruction)

A simple microarchitectureA simple microarchitecture



Instruction

Start

Reset

Clock

Ready

16

Write Enable

VNCZ4

14

4Constant

ControlWord

OperandSelect

>CLR

CAR

DATA LD/CNT’

Generate Data Signal Logic

Generate Load Signal Logic

CONTROLSTORE(ROM)

Generate Ready

Mode

Condition Code

Next Address

Operand Select

Address Datamicroinstruction

? ?

12:0

16:13

A simple microarchitectureA simple microarchitecture

• R0 Constant B• Address Out R0, R1 Data In• R0 Constant A• Address Out R0, Data Out R1, Write Enable• CAR x00 (IDLE STATE)



A simple microprocessorA simple microprocessor

Central Processing Unit– Control Unit, Integer Datapath (Load/Store, Integer ALU)

Floating Point Unit– Floating Point Datapath

Internal Cache– SRAM for Instruction Cache (i-cache) and Data Cache (d-cache)

Memory Management Unit– Controls communication with Main Memory and other I/O

FPU

CPU

Internal Cache

MMU

Bus



A simple computer architectureA simple computer architecture

Generic Computer System.– Current architectures are performance driven, and vary widely.

Processor– Uniprocessor systems

ASIC (Application Specific Integrated Circuit)– Performs a specific task, not a general purpose processor (e.g. Voodoo)

I/O Device– Accesses data devices (e.g. Graphics Adapter, Disk Controller, et al.)

Processor

Memory

ASIC

I/O Device

ASIC

I/O Device

Bus



A contemporary architectureA contemporary architecture

Front Side Bus100 MHz?

MicroprocessorsMemory Chipset

Bridge Back Side BusPCI - 33MHz

Main Memory

Graphics Adapter(non-AGP)

AGP

External Cache

Disk Interface(EIDE,uSCSI-2)

Network Interface Card (NIC)

Serial/Parallel I/O(keyboard, mouse, printer)

ISA devices Compatibility Bridge(South-side, ISA)

Registers 2nsL1 On-chip 4nsL2 On-chip 5nsL3 Off-chip 30nsMemory 220nsPaged VM > 1 ms!



The instruction setThe instruction set

High-Level Language - C A = B + C;

– Memory-Transfer Equivalent Mem[A] Mem[B] + Mem[C] Mem[EA00] Mem[EA08] + Mem[EA10]

Machine-Level Equivalent – Assembly (human readable) ex: Machine (for a simple architecture)

Load R2, B E2EA08 Load R3, C E3EA10 R2 R2 + R3 0223 Store A, R2 F2EA00

The bits of a machine instruction are divided into fields– eg: E2EA08– E: Operation “Load”; 2: Destination Address R2; EA08: Address Field– The operation field (opcode) defines the format for the instruction



The instruction setThe instruction set

There are three basic types of computer instructions– Register Instructions: operate on values stored in registers

Arithmetic, Shift, and Logic instructions

– Move Instructions: move data between memory and registers Load/Store instructions Move/Copy portions of memory

– Branch Instructions: select one of two possible next instructions to execute Branch on condition, Unconditional branch (Jump) Only one address is explicit, the other operand is implict

– e.g.: Beq R2, R3, A

– If the contents of R2 = R3 then execute the instruction at location A next (explict)

– otherwise, execute the next instruction in the normal order (using the PC) (implict)



The Von Neumann architectureThe Von Neumann architecture

The Von Neumann model of computer processing– Program and data are both stored as sequences of bits in the computer’s

memory.

– The program in executed on instruction at a time under the direction of the control unit.

The instruction-execution cycle– Instruction Fetch (IF) stage

Get next instruction from the memory address referenced by the PC Place the new instruction in the Instruction Register Increment the PC to the next instruction address

– Execute operation (EX) stage Execute the operation specified in the opcode

– Branch instructions may update the PC

– Repeat



How do we specify the program?How do we specify the program?

Contemporary languages– C, C++, Perl, Java, and hundreds more.

Languages of Yore– Fortran, COBOL, and scores more.

Specialty languages– VHDL, simulation languages, and thousands more.

There are over 1,000 “standardized” programming languages today.

The only goal of these languages is to help humans implement their algorithms in the instructions available for a particular ISA



How do we execute the program?How do we execute the program?

HARDWARE

CPU

Memory

I/O Devices

APPLICATION PROGRAMS

Compilers

Databases

Games

Productivity Tools

USERS

How do we use the

resources?

OS

Limited Resources Many Demands

SOFTWARE



What is an Operating System?What is an Operating System?

Do we want all programs to have access to all instructions? The OS is a program that acts as an intermediary between the application

programs and the hardware resources– All communication requires hardware resources, thus the OS is also an

intermediary between users and applications The purpose of any OS is to provide an environment in which:

– users can (conveniently) execute programs and access data

– application programs can (efficiently and fairly) access system resources (processor time, memory, file space, I/O devices, etc.)

The OS need not perform any other useful function: it is a control environment (kernel) controls access to all resources– All other software is an application program

– How does the existence of an OS simplify coding an app?

– Do you trust others to protect your rights and data?



The algorithmThe algorithm

Developing an algorithm to solve a problem is non-trivial As with many issues in engineering, there are trade-offs to be made

between performance (the correctness of the solution) and cost (the time it takes for the algorithm to complete.

Consider the Traveling salesman problem:– You must visit, by car, n different cities. From each city, you can get to

any other city – but the distances between them vary.

– Your “Problem” is to find the shortest route that visits every city exactly once.



Exponential growthExponential growth

10^1 10^2 10^3 Number of students in the college of engineering 10^4 Number of students enrolled at Wright State University 10^6 Number of people in Dayton 10^8 Number of people in Ohio 10^10 Number of stars in the galaxy 10^20 Total number of all stars in the universe 10^80 Total number of particles in the universe 10^100 << Number of possible solutions to traveling salesman (100)

Travelling saleman (100) is computable but it is NOT feasible.



Optimization algorithmsOptimization algorithms

The knapsack problem– You stumble across some valuable

artifacts while out in the wild. Unfortunately, you can only add ten lbs to your pack and still make it back to civilization.

– What do you take?

Item Value Weight $/lb

A $150 10 lbs. 15

B $140 7 lbs. 14

C $100 5 lbs. 10

D $60 3 lbs. 20

E $45 3 lbs. 15



Bug brain demoBug brain demo

Your laboratory assignment this week is to gain some familiarity with the concept of solving relatively complex problems with very simple primitives.

1 wright state university, college of engineering dr. t. doom, computer science & engineering...

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