VAST 20002 Computers and Society

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VAST 200-02 Computers and Society

• Lecture 4 - Building Hardware and Software
• Spring 2004

Pentium 4 Chip Die Image couresy Intel Corporati
on
Prof. John NestorECE DepartmentLafayette
CollegeEaston, Pennsylvania 18042nestorj_at_lafayet
te.edu
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Roadmap for the Term Major Topics

• Course Introduction
• Computer Systems Overview
• Computer History
• Technology Trends
• The Art of Building Hardware and Software \
• Current Issues
• Looking to the Future

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Readings - HW and SW Design

• 1. M. Reilly, "Designing an Alpha
  Microprocessor", IEEE Computer, July 1999.
  
• 2. C. Hoare, "The Emperor's Old Clothes (Turing
  Award Lecture)", Communications of the
  ACM,    February 1981.
  
• 3. D. Parnas, "Software Aspects of Strategic
  Defense Systems", Communications of the ACM,
  December 1985.
  
• 4. M. Baer, The New X-Men, Wired, Issue 11.09,
  September 2003(available at http//www.wired.com/
  wired/archive/11.09/xmen.html)

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Comparing HW and SW Design

• Hardware
• Function relatively well-defined (e.g.
  instruction set)
  
• Complexity limited by specified function
• Tight performance constraints
• Tight resource constraints
• Manufacturing expense dominates cost in high
  volume
  
• Software
• Function often not well-defined (e.g. list of
  desired features)
  
• Complexity is arbitrary (features easily added!)
• Tight performance constraints (sometimes)
• Development expense dominates cost

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Hardware Design

• Product Definition
• Exploring Architectural Design Space
• Technology Development
• Feasibility Studies
• CAD Tool Development
• Register-Transfer-Level (RTL) Design
• Functional Verification
• Schematic Design
• Logic Verification
• Layout
• Circuit Verification
• Fabrication

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Hardware Design - Product Definition

• Goal determine performance goals and features
• What will it do? (i.e., execute IA-32
  instructions)
  
• What is its intended application?
• What is desired performance?
• How much power will it use?
• What technology will be used to realize it?

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Hardware Design - Exploring the Architectural
Design Space

• What are the major features of the design
• Major components
• Size speed
• Floor plan
• What is the predicted performance
• Predict using performance simulation
• Explore ideas and tradeoffs

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Hardware Design - Feasibility Studies

• What kind of low-level components will be used?
  (e.g., flip-flop storage elements)
  
• What new circuit designs are possible in new
  technology?
  
• What parts of design will be difficult to
  implement?

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Hardware Design - CAD Tool Development

• CAD tools are essential for chip design
• Lower-end design purchase commercial CAD tools
• Higher-end design combine commercial and custom
  CAD tools

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Hardware Design - RTL Modeling / Functional
Verification

• RTL (Register Transfer Level) Modeling
• Simulation model using Hardware Description
  Language (HDL)
  
• Detailed operation of hardware components
• Detailed interaction between hardware components
• Becomes the spec. for lower levels of design
• Functional verification
• Make sure that RTL design really implements
  spec.
  
• Identify and remove design errors (7,855 found
  in Pentium 4 Design)
  
• Typical approach
• Massive simulation using farms of workstations
  or PCs
  
• Compare simulation result to reference model

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Hardware Design - Schematic Design / Logic
Verification

• Schematic Design
• Create detailed circuit designs for each RTL
  block
  
• Alternative approaches
• Human designer - higher quality, but longer
  design time
  
• Synthesis CAD tool - lower quality, but shorter
  design time
  
• Logic Verification
• Verify that each logic block correctly implements
  RTL
  
• Typical approach compare RTL and logic
  simulations

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Hardware Design - Layout / Circuit Verification

• Layout Design
• Convert circuit schematics to geometric mask
  patterns
  
• Alternative approaches
• Human designer - higher quality, but longer
  design time
  
• Place/Route CAD tool - lower quality, but shorter
  design time
  
• Circuit Verification
• Verify that layouts correctly realize circuit
  designs
  
• Account for non-ideal circuit behavior, e.g.
• leaky transistors
• Noise
• Parasitic components capacitance and resistance
• Process variation

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Hardware Design - Fabrication / Debug

• Tape out Mask patterns sent to fab
• Manufacture masks
• Manufacture first chips
• Turnaround time 4-6 weeks
• Non-recurring engineering cost (NRE)
  costtooling cost for masks first chips (now
  1 million)
  
• Debug
• Initial testing
• Measure performance parameters (e.g. clock speed)

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Hardware Design - Perspective

• Design process takes years for microprocessors
• Example Pentium 4
• RTL Design Began - 1996
• RTL Design Complete - 1998
• A-step tapeout - December 1999
• First packaged parts - January 2000
• Production - October 2000
• Verification is crucial, but absence of bugs
  cannot be guaranteed.
  
• When bugs are found, workarounds are used until a
  corrected chip goes into production.

Source B. Bentley, Validating the Intel
Pentium 4 Microprocessor, Proceedings Design
Automation Conference, June 2001
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Case study The Pentium FDIV Bug,1994

• July 1994 Intel discovers bug in floating point
  divide (FDIV) which resulted in slightly
  inaccurate results. Fix planned for later
  version of chip, but bug not publicized.
• Sept. 1994 Math professor T. Nicely discovers
  bug and attempts to report it to Intel. When
  they dont respond, Nicely posts bug on the
  Internet.
• Nov. 7 1994 Electronic Engineering Times breaks
  story in media
  
• Nov. 22,1994 Intel responds by attempting to
  minimize the error by calling it a glitch that
  introduces errors in the ninth digit of
  calculations
• Dec. 12, 1994 IBM Research disputes Intels
  assertion, claims that common spreadsheets would
  have errors approx. once very 24 days. IBM stops
  all shipments of Pentium PCs.
• Dec. 21, 1994 Intel apologizes, offers to replace
  every faulty Pentium chip at estimated cost of
  300 million
  

Source D. Patterson and J. Hennessy, Computer
Organization and Design, Morgan-Kaufmann 1997.
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Coming Up

• Software Design
• Is Software harder than hardware?
• Estimating Software Complexity
• Software design methods
• Software Engineering as an emerging field
• Faults Failures

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Measuring SW Complexity

• Source Lines of Code (SLOC)
• Measures how many lines (statements) in a
  program
  
• Useful as a measure of software complexity
• SOME SLOC Estimates

Sources D. Wheeler, More Than A Gigabuck
Estimating GNU/Linuxs Size, http//www.dewheeler
.com/sloc/ Wikipedia ( wikipedia.org).
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SW Development - Waterfall Model
Integration
Product Verif.
Product design
System feasibility
Verification
System Test
Detailed Design
Operations Maint.
Verification
Revalidation
Source A Spiral Model of Software Development
and Enhancement, IEEE Computer, May 1988.
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SW Development - Spiral Model
Source A Spiral Model of Software Development
and Enhancement, IEEE Computer, May 1988.
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Outline - Course Overview

• Administrative Details \
• Course Overview and Introduction
• Computer Systems Overview
• General Concepts
• History and Trends
• The Creative Process
• Hardware Design
• Software Design
• Current Issues Computers and Society
• Faults and Failures
• Privacy and Encryption

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The Illusion of Privacy

• 1993 - On the Internet, nobody knows youre a
  dog -- New Yorker cartoon, 1993
  
• 1998 On the Internet, nobody knows youre a
  police officer posing as a 14-year old
  
• 2002 On the Internet, nobody knows youre a
  Carnivore
  
• 2003 On the Internet, nobody knows youre the
  RIAA

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The Internet - A Network of Networks

• Common addressing scheme
• Routers connect networks,
• TCP/IP
• IP Addresses - what identifies computers on the
  internet
  
• Static addresses - permanently assigned
• Dynamic addresses