Slide 1

18 - 322 Lecture 26

VLSI DESIGN FLOW / TRENDS

Questions for :What kind of company are you?What product do you make?How do you design and fab product?

Three Design StrategiesFull-custom, Semi-custom, Structure ASICs, Programmable Logic

The Productivity Gap

Slide 2

Semiconductor Companies

• Semiconductor Companies (with Fab)

Intel, National, Motorola, Lucent

• Fabless Semiconductor Companies: Sun, Xilinx, Altera

• Merchant Fabs: TSMC, UMC, Charter Semi, Seiko…

• The Product:

• How many do you make/sell?

• How many other companies make it?

Slide 3

Product Life Cycle

[# waf./day]

Time

[%]

Time

Volume

Yield

Volume after testing

(b)

[#die/day]V(t)

Y0

N ( t )w

Y(t)

t1p t2

t1p t 2

[$]

Unit price P(t)

Time

(d)(a)

Revenue R(t)

t1p t2

Time

(e)[$/day]

(c)

Time

Slide 4

Product Life Cycle

[# waf./day]

Time

[%]

Time

Volume

Yield

Volume after testing

(b)

[#die/day]V(t)

Y0

N ( t )w

Y(t)

t1p t2

t1p t 2

(a)

[$]

Unit price P(t)

Time

(d)

Revenue R(t)

t1p t2

Time

(e)[$/day]

(c)

Time

RV(t) =N ( t )Y(t) N (w= wch )a ,b ,

Slide 5

Product Life Cycle

[# waf./day] Time

[%]

Time

Volume

Yield

Volume after testing[#die/day]

V(t)

Y0

N ( t )w

Y(t)

t1t1p t2

t1p t 2

(b)

[$]

Unit price P(t)

Time

(d)(a)

Revenue R(t)

t1p t2

Time

(e)[$/day]

(c)

TimeRV(t) =N ( t )Y(t) N (w= wch )a ,b ,

Slide 6

Product Life Cycle

[#/day]Volume

t1p t

(a)

(d)Design Cost Rate[$/day]Time2

[$]Wafer Cost

Time

[$/day]Manufacturing Costs

t 1p t2

Time

(b)

(c)

Time

Cost Rate [$/day

Time

] (e)

Slide 7

Product Life Cycle

[#/day]Volume

t1p t

(a)

(d)Design Cost Rate[$/day]Time2

[$]Wafer Cost

Time

[$/day]Manufacturing Costs

t 1p t2

Time

(b)

(c)

Time

Cost Rate [$/day

Time

] (e)

Slide 8

Objective of VLSI Design

[$/day]

Time

Revenue Rate

Cost RateC(t)

R(t)

t1t1p

t2

⌡Profit = [R(t) - C(t)] dt

t1

t 2⌡

[$/day]

MAX { Profit [ Price (Performance),Cost,Time]}

Slide 9

Economic Reality of VLSI Production

Rising cost of manufacturing facilities;

Shrinking profit margins;

Shrinking product opportunity windows;

Two main objectives of any IC development cycle:

1. Highest possible manufacturing efficiency.

2. Shortest possible time-to-market

[$]

t

Price"war"

COSTS

REVENUE

Slide 10

Volume Issues

[$]

t

COSTS

High Volume

[$]

t

COSTS

Low Volume

Minimize Design Time & Cost!Minimize Manufacturing Cost!

Slide 11

Design Methodologies

• Full Custom

• Semi-custom

• Standard Cells

• Mask Programmable Gate Arrays (MPGA)

• Via Patterned Gate Arrays / Structured ASICs

• Programmable Logic

• Field Programmable Gate Arrays (FPGA)

• Complex Programmable Logic Devices (CPLD)

Slide 12

Design Styles - Full Custom

PowerPC 750

Design Cost & Time: HIGH

Manufacturing Cost: LOW

Examples: microprocessors, RAMs

Slide 13

Design Styles - Semi-Custom

Standard Cell: Place and Routepre-characterized cells

MPGA: Transistors already placed,only change metal masks

Design Cost & Time: Medium

Manufacturing Cost: Medium

Examples: PC chipsets, modems, cell phones ...

Slide 14

Design Styles - Programmable Logic

FPGA: Pre-fabbed chip (high volume)configurable after fab

Design Cost & Time: LOW

Manufacturing Cost: HIGH

Examples: prototypes, network devices, telecom...

Slide 15

Standard Cell Design Process

Design Entry and Simulation» Schematics» Verilog / VHDL

Logic Synthesis» Input: Verilog/VHDL and Cell Library» Estimated Timing» Simulation

Timing Analysis» Determine worst-case clock speed

Formal Verification» Check equivalence of Gates and Specification

Design Hand-off

Slide 16

Standard Cell Design ProcessFloorplanning

» Localize major functions of the chip» Consider global timing» Partition design

Placement» Find locations for all circuits» Consider detail timing» Assure proximity of critical nets

Global Routing» Resolve congestion» Localize nets» Give critical nets best paths

Detail Routing» Locate shortest paths» Create net geometry» Route critical nets first

Tape-out to manufacturing

Slide 17

D Flip Flop: Standard Cell

Slide 18

Slide 19

Slide 20

Slide 21

Slide 22

Slide 23

Slide 24

Design Styles - MPGAs

a.k.a.: Sea-of-gates, or just Gate Array

Chip cost ~ # of masks

VDD

PMOS

NMOS

GND

Four input NORPolysilicon

Slide 25

Design Styles - MPGAs

IO

IO

IO

IO

IO IO IO IO IO IO

IO

IO

IO

IO

IO IO IO IO

Slide 26

MPGAs: Gate Isolation

VDD

PMOS

NMOS

GND

Slide 27

MPGAs: Isolation

VDD

PMOS

NMOS

GND

Slide 28

MPGAs: Destiny

1980s: ASICs are 1 or 2 metal

Transistor masks dominate costs

MPGAs are significantly cheaper

1990s: ASICs move to 3, 4, 5, and 6 metal layers

Metal masks dominate costs

MPGAs are not nearly as cheap

Emergence of the FPGA

Rebirth in the “Structured ASIC”

Slide 29

Manufacturing Costs

00.20.40.60.8

11.21.41.61.8

2

250 nm 180 nm 130 nm 90 nm 65 nm

Technology Generation

Mas

k C

osts

(in

mill

ion

$)

Slide 30

Geometrical Regularity• Difficult to anticipate potential nanoscale failures • Increasing problems with printability

– Optical wavelengths approach critical distances– Resolution enhancement becomes challenging as we scale to 65nm and

below

130 nm lithography with OPC (courtesy of IBM)

130 nm lithography without OPC

Slide 31

Structured ASIC Idea

• Make more of the design “regular”– Replicated across the die– Used by multiple customers

• Provide some mechanism for “customization”– A restricted set of metal masks– Restricted rules on the routing of metal– Vias and only vias (VPGA)

Slide 32

VPGA• Via Patterned Gate Array

– Regular logic blocks that are via configurable– Mask (through M2) and design amortization over multiple applications– Regular power distribution and clock like an FPGA– Carefully crafted regular geometrical patterns and redundant vias– Simplified physical design and verification – Predictable and testable– Ability to contain more of the

proprietary fab information

Slide 33

Design Styles - Programmable Logic

FPGA: Pre-fabbed chip (high volume)configurable after fab

Design Cost & Time: LOW

Manufacturing Cost: HIGH

Examples: prototypes, network devices, telecom...

Slide 34

Programmable Logic: FPGAs

LogicBlock

LogicBlock

Slide 35

Programmable Logic: Logic Blocks

Slide 36

Programmable Logic: LUTs

LUTs are little RAMs

INPUTS XOR000 0001 1010 1011 0100 1101 0110 0111 1

ConfigurationShift Register

InputsMUX

Output(XOR)

Slide 37

Programmable Logic: Interconnect

Slide 38

Another FPGA Architecture: FLEX 8k

LAB

IOE

LAB LAB

IOE

LAB LAB LAB

IOE IOE IOE

Slide 39

FLEX 8k LAB

• Logic Array Block– Complete Interconnect To Row

Interconnect

4 LUT4 LUT4 LUT4 LUT4 LUT4 LUT4 LUT4 LUT

Loca

l Int

erco

nnec

t

8

4FromGlobal

24

To Column Interconnect

Slide 40

FLEX 8k Place and Route

• Every LUT drives one row channel• Every LUT drives up to 2 column channels• Can’t connect ANY two LUTs

– Not every row channel visible– Small netlist changes -> Huge physical changes– Place so routable

• Predictable timing– Three Rules– Global Interconnect = Long Delay

Slide 41

FPGA Design Flow

• Synthesis• Technology Mapping• Placement• Routing• Timing Analysis• Bitstream Generation and Download

What’s missing?(simulation)

Slide 42

Design Styles -Standard Cell vs. FPGA

Warning: Your mileage WILL vary!10,000 Gate ChipStandard Cell FPGA

Design Cost $20,000 $8,000Days 50 20Cost/Day $400 $400

CAD Software $40,000 $1,000

Design for Test $2,000 $0Days 5 0Cost/Day $400

NREMasks $50,000 $0Test Progra $10,000 $0

Total Fixed Costs $122,000 $9,000

Part Cost $8 $39

Slide 43

An “X” Graph

FPGA

ASICCost/part

Volume

Slide 44

Implications of SIA Road Map: Design

Transistors/chip [k]1,000,000 10,000,000

1800 Staff Yrs.

800 Staff Yrs.100,000 1,000,000

10,000 100,000

1,000 10,000

1000

** *

Transistors/Staff-No.100

1092 94 96 98 2000 02 04 06 08 Year

SEMATECH

Slide 45

Implications of SIA Road Map: Design

Designer Productivity GapDesigner Productivity Gap•• Size of ICs growing faster than our ability to design themSize of ICs growing faster than our ability to design them•• Shortened product life cycles put greater timeShortened product life cycles put greater time--toto--market pressuremarket pressure

Companies that can address the Companies that can address the productivity gap will thrive.productivity gap will thrive.

Others will die.Others will die.

Slide 46

Productivity Gap: Product Standardization

Inherent Conflict:• Build fewer products: reduce design cost, tune process for one product

• Differentiate products more

The Universal Compute Engine (?!?)• All product differentiation is “software”

• Candidates:

• Microproccesor ?

• FPGAs ?

• Hybrid ?

Slide 47

Software Differentiation

Observation: Software last longer than hardware

Case-in-point: Y2K!

Requirements for a Universal Compute Engine

a.) Execute old code, but do it faster than before

b.) Execute lots of different code: X86, IA64, JVM

Microprocessors have done (a.) really well.

Do this requirements eliminate the FPGA?

Slide 48

Virtual Hardware

• Like Virtual Memory:– If you don’t have enough real memory– Time-multiplex the memory that you do have

• Observation:– Hardware design in FPGAs is specification of BITS– Move it into executing hardware when it it needed– Move it to memory when it is not needed

Slide 49

Virtual Hardware: Scenario

Virtual JPEG Design(DCT, Quantization, Entropy)

Still Camera Video CameraLow cost,Low performance

High cost,High performance

Slide 50

Pipelined Applications

• Example: FIR Filter

1

2

3

4

5

6

7

8

x y

W2x + y

x y

W1x + y

Slide 51

Time-Multiplexing on FPGAs

1

2

3

4

5

6

7

8Sta

tic Im

plem

enta

tion:

Reconfigure

Tim

e

1

2

3

4

5

6

7

8

Reconfigure

Dyn

amic

Impl

emen

tatio

n:

FPGARAM

RAM

Slide 52

Pipeline Reconfiguration

1

2

3

4

5

6

7

8

1

2

3

4

5

6

7

8

1

2

3

4

5

6

7

8

2

3

4

1

5

6

7

8

...

Clock1

2

3

4

5

6

7

8

FPGA

Slide 53

Pipeline Reconfiguration

More hardware = More Throughput

1

2

3

4

5

6

7

8

1

2

3

4

5

6

7

8

1

2

3

4

5

6

7

8

Slide 54

PipeRench Architecture

• Objective: Configure 1 stage per cycle1

2

3

4

5

6

7

8

1

2

3

4

5

6

7

8

FPGA Fabric

Configuration Cache

On-chip ConfigurationWide Configuration Bus

Slide 55

Productivity Gap: “Evolva-ware”

Human solution to complexity: divide and conquer• Standard cells, logical design, core-based design

Nature’s solution to complexity: natural selection• Mutate, select using criteria (survival)

• Can this be used to design chips?

001010010100101010100101001001001110010101101010100101101010100101010010100101111010101010101010110101

001010010100101010100101001001001110010101101010100101101010100101010010100101111010101010101010110101

001010010100101010100101001001001110010101101010100101101010100101010010100101111010101010101010110101

001010010100101010100101001001001110010101101010100101101010100101010010100101111010101010101010110101

001010010100101010100101001001001110010101101010100101101010100101010010100101111010101010101010110101

001010010100101010100101001001001110010101101010100101101010100101010010100101111010101010101010110101

FPGA

Mutate, crossover, selectConfigurations New Configurations

Slide 56

A Curious Evolvable HW Experiment

• Goal: Get FPGA to detect 100 Hz input (light up LED)

• Progressively harder goals:– Light up the LED– Have the LED occasionally toggle– Have the LED on when fast frequency on input, off when

low frequency– Those designs that fail to meet the goal die and do not

reproduce

• After 400 generations, it worked!

Slide 57

Mysterious Results

• Only one particular FPGA worked– Only at a particular temperature

• It was not clear how this worked… – Analog behavior, coupling between wires, etc– Not the traditional breakdown approach