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EE 260: Introduction toDigital Design

Overview

Yao ZhengDepartmentofElectrical Engineering

UniversityofHawaiʻiat Mānoa

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Class Objectives

Basicsequentialprocessor~50,000 Transistors 18

PhotoofBerkeleyRISCI,©UniversityofCalifornia (Berkeley)

• Fundamentals of logic design

• Understand the functionalities of TTL devices

• Basic usage of Hardware Design Language

• Design small-to-moderate digital systems

Class Logistic• Lectures (50 minutes)• Recommended Readings• Problem Sets• Labs• Midterm (2)• Final Exam(orProject)

Class Logistic

n Lecturer:n Yao Zheng

(yao.zheng@hawaii.edu)n TA:

n Joshua Chen (jschen2@hawaii.edu)

n Grader:n Nicholas Yama

(nyama8@hawaii.edu)

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Class Logisticn Lecture:

Mondays, Wednesdays, and Fridays 9:30am-10:20am, Marine Science Building 100.

n Laboratory:Tuesdays 9:00am-11:45am, Holmes Hall 451.

n Office hours:Mondays and Wednesdays 14:00pm-

16:00pm or email for appointment, Holmes Hall 437.

Class Logisticn Course website:

n http://www2.hawaii.edu/~yaozheng/course/ee260_spring_2018/

n Piazza:n https://piazza.com/hawaii/spring2018/ee260

n Github Classroomn https://ee260-2018-spring-

signup.herokuapp.com

Course Logisticn Textbook:

Required: Digital Design Principles and Practice with Verilog (5th Edition):

n Interactive Digital Access Program (through Laulima)

n Bookstore

n Optional: FPGA Prototyping By Verilog Examples: Xilinx Spartan-3 Version

n Amazon

Course Logisticn Grading:

Homework 25%n Discussion 10%n Midterms (2) 20%n Final Exam 20%n Lab Work 25%

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Course Logisticn Basic Topics:

n Boolean algebran Combinational logicn Sequential building blocksn Finite state machine

n Advanced Topics:n Arithmetic structuresn Pipelinen Cache and Memory

n Hardware Description Languagen Verilog

Know What you are Getting into

~700,000,000Transistors

The materials in this class

The state-of-the-art

Application

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What is Computer Design? What is Computer Design?

Physics

Application

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What is Computer Design?

Physics

Application

Gaptoolargetobridgeinone step

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What is Computer Design?

Initsbroadestdefinition,computerdesign isthedesignoftheabstraction/implementationlayers that allow us toexecuteinformationprocessingapplicationsefficientlyusingmanufacturing technologies

Physics

Application

Gaptoolargetobridgeinone step

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What is Computer Design?

Initsbroadestdefinition,computerdesign isthedesignoftheabstraction/implementationlayers that allow us toexecuteinformationprocessingapplicationsefficientlyusingmanufacturing technologies

Physics

Application

Gaptoolargetobridgeinone step

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Abstractions in ModernComputing Systems

ApplicationAlgorithm

Programming Language

OperatingSystem/Virtual Machines

InstructionSet ArchitectureMicroarchitecture

Register-Transfer LevelGates

Circuits

Devices

Physics

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Abstractions in ModernComputing Systems

ApplicationAlgorithm

Programming Language

OperatingSystem/Virtual Machines

InstructionSet ArchitectureMicroarchitecture

Register-Transfer LevelGates

Circuits

Devices

Physics

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What is an Application

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• The first digital systems were mechanical and used base-10 representation.

• Most popular applications: arithmetic and scientific computation

The Babbage Difference Engine (1834)25,000 parts cost: £17,470

Why Digital

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• 1854: George Boole shows that logic is math, not just philosophy!

• Boolean algebra: the mathematics of binary values

000

01

10

0

0

11 1

0 1

1 0

AND OR NOT

000

01

10

1

1

11 1

Digital Electronics

Key Link Between Logic and Circuits

• Despite existence of relays and introduction of vacuum tube in 1906 digital electronics did not emerge for thirty years!

• Claude Shannon notices similarities between Boolean and electronic telephone switches

• Shannon’s 1937 MIT Master’s Thesis introduces the world to binary digital electronics

01 0

10 1

+

Lee de Forest, 1906

The Vacuum

Tube

Claude ShannonCourtesy of Jonah Sacks. Used with permission.

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Evolution of Digital Electronics

UNIVAC, 1951

1900 adds/sec

Vacuum Tubes

ENIAC, 1946

IBM System/360, 1964

500,000 adds/sec

Transistors

First Transistor Bell Labs, 1948

VLSI Circuits

Intel Itanium, 2003

2,000,000,000adds/sec

4004, 1971

[from Kurzweil]

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Major Technolog

y Generation

sBipolar

CMOS

nMOS

pMOS

Relays

VacuumTubes

Electromechanical

Sequential ProcessorPerformance

23FromHennessyandPattersonEd.5ImageCopyright©2011,ElsevierInc.Allrights Reserved.

RISC

24FromHennessyandPattersonEd.5ImageCopyright©2011,ElsevierInc.Allrights Reserved.

Sequential ProcessorPerformance

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Sequential ProcessorPerformance

RISC

Move to multi-processor

25FromHennessyandPattersonEd.5ImageCopyright©2011,ElsevierInc.Allrights Reserved.

Hardware Implementation

Boolean Logic and State

Building Digital Systems• Goal: Building binary digital solutions to computational

problems

Behavioral Description

conversion to binary, Booelan algebra

device selectionand wiring

algorithm selection, flowcharts, etc.

Problem Statement• Labs & Design project• Product specs

• Algorithms, RTL, etc.• Flowcharts• State transition diagram

• Logic equations• Circuit schematics

• TTL Gates (AND,OR,XOR…)• Modules (counter, shifter)• Programmable Logic

Hardware Implementation

HDL Description

Building Digital Systems

Behavioral Descriptionsoftware-like programming

automated synthesis

algorithm selection, flowcharts, etc.

Problem Statement• Labs & Design project

Product specs

• Algorithms, RTL, etc.• Flowcharts• State transition diagram

• Verilog code• VHDL code

• Programmable logic• Custom ASICs

• Logic synthesis using a Hardware Description Language (HDL)automates the most tedious and error-prone aspects of design

A/D

Sync.

digitize

Digital System Model

• Digital processing systems consist of a datapath, memory, and control Early machines for arithmetic had insufficient memory, and often depended on users for control

• Today’s digital systems are increasingly embedded into everyday places and things

• Richer interaction with the user and environment

Data Processing

Controlsynchronize

MemoryAnalog Inputs

(sensors, audio, video, tablet)

Digital Inputs(peripherals,

buses, switches)

D/A

Digital Outputs

(peripherals, buses, lights)

Analog Outputs

(actuators, motors, multimedia)

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Digital System Model

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Memory: stores programs, i/o dataDatapath: perform arithmetic and other data-processing operationsControl Unit: supervises the flow of informationI/O: places program into memoryCPU: executes program from memory instruction by instruction. Control unit manipulates datapath to execute instructions.

Processor: contains CPU, FPU and MMUFPU (Floating Point Unit) : perform f-p operationsMMU (Memory Management Unit): layers of memory that helps instruction fetching and data I/O. Internal/external cache (very fast), RAM (between disk and cache)

Example Digital Systemsn Digital Computer

n Usually design to maximize performance. "Optimized for speed"

- Usually designed to minimize cost. “Optimized for low cost”

- Of course, low cost comes at the expense of speed.

• Handheld Calculator

Example Digital Systemsn Digital Watch

n Low power operation comes at the expense of:n lower speedn higher cost Designed to minimize power.

Single battery must last for years.

Basic Design Tradeoffs

n You can improve on one at the expense of worsening one or both of the others.

n These tradeoffs exist at every level in the system design - every sub-piece and component.

n Design Specification -n Functional Description. n Performance, cost, power constraints.

n As a designer you must make the tradeoffs necessary to achieve the function within the constraints.

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Cost vs Speed vs Energy

• X86Instruction Set• QuadCore• 125W• Decode3 Instructions/Cycle/Core• 64KBL1ICache,64KBL1D Cache• 512KBL2 Cache• Out-of-order• 2.6GHz

AMD PhenomX4 Intel Atom• X86Instruction Set• Single Core• 2W• Decode2 Instructions/Cycle/Core• 32KBL1ICache,24KBL1D Cache• 512KBL2 Cache• In-order• 1.6GHz

ImageCredit: Intel

ImageCredit: AMD35

Cost vs Speed vs Energy

• X86Instruction Set• QuadCore• 125W• Decode3 Instructions/Cycle/Core• 64KBL1ICache,64KBL1D Cache• 512KBL2 Cache• Out-of-order• 2.6GHz

AMD PhenomX4 IBM POWER7• PowerInstruction Set• Eight Core• 200W• Decode6 Instructions/Cycle/Core• 32KBL1ICache,32KBL1D Cache• 256KBL2 Cache• Out-of-order• 4.25GHz

ImageCredit: AMD

ImageCredit: IBMCourtesyofInternationalBusinessMachinesCorporation,©InternationalBusinessMachines Corporation.

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Design Representation Hierarchy in Designsn Helps control complexity -

n by hiding details and reducing the total number of things to handle at any time.

n Modulalizes the design -n divide and conquer n simplifies implementation and debugging

n Top-Down Design n Starts at the top (root) and works down by

successive refinement. n Bottom-up Design

n Starts at the leaves & puts pieces together to build up the design.

n Which is better?n In practice both are needed & used.

n Need top-down divide and conquer to handle the complexity.

n Need bottom-up because in a well designed system, the structure is influence by what primitves are available.

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Software Aspects of Design

n In computer-aided design (CAD) various tools are available today to improve productivity, correctness and the quality of designs.

n Ways of digital design in CAD:n Schematic entry: schematic diagrams to

be drawn on screen.n HDLs : Hardware description languagesn Simulators: debug and check

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Hardware structures can be modeled effectively in either VHDL and Verilog. Verilog is similar to c and a bit easier to learn.

Verilog and VHDL

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• Created by GatewayDesign Automation in 1985;now an IEEE standard

• Initially an interpreted language for gate-level simulation

• Less explicit typing (e.g., compiler will pad arguments of different widths)

• No special extensions for large designs

• Commissioned in 1981 by Department of Defense; now an IEEE standard

• Initially created for ASICsynthesis

• Strongly typed;potentiallyverbose code

• Strong support for package management and large designs

VHDL Verilog

Verilog• Behavioral or Algorithmic Level

D Highest level in the Verilog HDLD Design specified in terms of algorithm (functionality) without hardware

details. Similar to “c” type specificationD Most common level of description

• Dataflow LevelD The flow of data through components is specified based on the idea of how

data is processed• Gate Level

D Specified as wiring between logic gatesD Not practical for large examples

• Switch LevelD Description in terms of switching (modeling a transistor)D No useful in general logic design – we won’t use it

A design mix and match all levels in one design is possible.In general Register Transfer Level (RTL) is used for a combination of Behavioral and Dataflow descriptions

Verilog• Misconceptions

D The coding style or clarity does not matter as long as it worksD Two different Verilog encodings that simulate the same way will

synthesize to the same set of gatesD Synthesis just can’t be as good as a design done by humans

• Shades of assembly language versus a higher level language

• What can be SynthesizedD Combinational Functions

• Multiplexors, Encoders, Decoders, Comparators, Parity Generator Adders, Subtractors, ALUs, Multipliers

• Random logicD Control Logic

• FSMs

• What can’t be SynthesizedD Precise timing blocks (e.g., delay a signal by 2ns)D Large memory blocks (can be done, but very inefficient)

Understand what constructs are used in simulation vs. hardware mapping

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Electronic Aspects

n Digital circuits deal with voltages and currents and are built with analog components. We perform digital abstraction only.

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• Electronic circuit design ensures that logic gates produce and recognize logic signals that are within the appropriate range.

Electronic Devices are not Ideal

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VOH = f (VOL) VOL = f (VOH) VM = f (VM)

IN OUT IN OUT

0 1

1 0

Truth Table

V(x)

Digital circuits perform operations on logical (or Boolean) variables

A logical variable is a mathematical abstraction. In a physical implementation, such a variable is represented by an electrical quantity

V(y)

VOH

VOL

VM

VOL

fV(y)=V(x)

(Switching Threshold)

VOHNominal Voltage Levels

Example Noise Sources in Digital Circuits

Capacitive coupling

v(t)

Power and ground noise

VDD

• Noise sources: coupling, cross talk, supply noise, etc• Digital circuits must be robust against such noise

sources

The Inverter: Noise Margin

IN OUT IN OUT

0 1

1 0

V(x)

V(y)

VOH

VOL

VIL IH

Slope = -1

Slope = -1

VOL V VOH

"1"

"0"

VOHVIH

VILVOL

Undefined Region

• Large noise margins protect against various noise sources

NML= VIL -VOL NMH= VOH-VIH

Truth Table

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Regenerative PropertyA chain of inverters

v0 v1 v2 v3 v4 v5 v6

V(V

olt) v0

v1v2

1

3

5

2 1 0 2 4 6 8 10

Simulated response

v2

v1

f (v)

finv(v)

outv3

v0 int (nsec)

| Voltage gain | should be > 1 between logic states

Verification and Testing• Design can be fun. Verification/testing is hard work.• Verification by simulation (and formally through test

benches) is a critical part of the design process.• The physical hardware must be tested to debug

tested mapping process and manufacturingdefects.

• Physical realizations often do not allow access to internalsignals. Need special tool to observe and control internalstate.

Verification and Design for Test (DFT) are important components of digital design

B3 B2 B1 B0 Val0 0 0 0 00 0 0 1 10 0 1 0 20 0 1 1 30 1 0 0 40 1 0 1 50 1 1 0 60 1 1 1 71 0 0 0 81 0 0 1 9

L1

L6

L2

L3

L7

L4

L5

Case Study of a Simple Logic Design:Seven Segment Display

n Chip to drive digital display

B3 B2 B1 B0 Val L1 L2 L3 L4 L5 L6 L7

0 0 0 0 0 1 0 1 1 1 1 1

0 0 0 1 1 0 0 0 0 0 1 1

0 0 1 0 2 1 1 1 0 1 1 0

0 0 1 1 3 1 1 1 0 0 1 1

0 1 0 0 4 0 1 0 1 0 1 1

0 1 0 1 5 1 1 1 1 0 0 1

0 1 1 0 6 1 1 1 1 1 0 1

0 1 1 1 7 1 0 0 0 0 1 1

1 0 0 0 8 1 1 1 1 1 1 1

1 0 0 1 9 1 1 1 1 0 1 1

L1

L6

L2

L3

L7

L4

L5

Case Study (cont.)

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Case Study (cont.)

n Implement L4:B3 B2 B1 B0 L4

0 0 0 0 1

0 0 0 1 0

0 0 1 0 0

0 0 1 1 0

0 1 0 0 1

0 1 0 1 1

0 1 1 0 1

0 1 1 1 0

1 0 0 0 1

1 0 0 1 1 Some gate level implementationof the Boolean function for L4

Case Study (cont.)

n Verilog Code: