Design Methodology

© Digital Integrated Circuits2nd and F. Brewer 2003 Design Methodologies

Design Design MethodologyMethodology


The Design Productivity ChallengeThe Design Productivity Challenge

Source: ITRS’97

A growing gap between design complexity and design productivity

58%/Yr. compoundComplexity growth rate

21%/Yr. compoundProductivity growth rate

1981

Logi

c Tr

ansis

tors

per

Chi

p (K

)

Prod

uctiv

ity (T

rans

./Sta

ff-M

onth

)

100

1,000

10,000

100,000

1,000,000

10,000,000

1001,000 10,000

100,000

1,000,000

10,000,000

100,000,000

10

1985

1989

1993

1997

2001

2005

2009


The Custom Approach The Custom Approach

Intel 4004

Courtesy Intel


Transition to Automation and Regular StructuresTransition to Automation and Regular Structures

Intel 4004 (‘71)Intel 4004 (‘71)Intel 8080Intel 8080 Intel 8085Intel 8085

Intel 80286Intel 80286 Intel 80486Intel 80486Courtesy Intel


Automating DesignAutomating Design Exploitation By Algorithms

Regular Structures Logic Synthesis Regularization of Connection

Floorplanning (Localization of function) System Level Performance/Power/Cost Allocation of Physical Resources

Communication/Interconnect Hierarchy based on Sensitivity to Latency Wires to Link Protocols


A System-on-a-Chip: ExampleA System-on-a-Chip: Example

Courtesy: Philips


Design MethodologyDesign Methodology

• Design process traverses iteratively between three abstractions: behavior, structure, and geometry• More and more automation for each of these steps


FloorplanningFloorplanning

A Protocol Processor for Wireless


Implementation ChoicesImplementation Choices

Custom

Standard CellsCompiled Cells Macro Cells

Cell-based

Pre-diffused(Gate Arrays)

Pre-wired(FPGA's)

Array-based

Semicustom

Digital Circuit Implementation Approaches


Impact of Implementation ChoicesImpact of Implementation ChoicesE

nerg

y E

ffici

ency

(in

MO

PS

/mW

)

Flexibility(or application scope)

0.1-1

1-10

10-100

100-1000

None Fullyflexible

Somewhatflexible

Har

dwire

d cu

stom

Con

figur

able

/Par

amet

eriz

able

Dom

ain-

spec

ific

proc

esso

r(e

.g. D

SP

)

Em

bedd

ed m

icro

proc

esso

r


Implementation StrategiesImplementation Strategies PLA

Technology confined in cell macros (tiling) Cell based logic

Technology confined to cells (area) Both 1-d and 2-d solutions

Transistor Arrays (Gate arrays) Technology confined to layers (Below M1

fixed)


PLA: Programmable Logic ArrayPLA: Programmable Logic Array

x0 x1 x2

ANDplane

x0x1

x2

Product terms

ORplane

f0 f1


Two-Level LogicTwo-Level Logic

Inverting format (NOR-NOR) more effective

Every logic function can beexpressed in sum-of-productsformat (AND-OR)

minterm


PLA Layout – Exploiting RegularityPLA Layout – Exploiting Regularity

f0 f1x0 x0 x1 x1 x2 x2Pull-up devices Pull-up devices

VDD GNDAnd-Plane Or-Plane


Breathing Some New Life in PLAsBreathing Some New Life in PLAsRiver PLAs A cascade of multiple-output PLAs. Adjacent PLAs are connected via river routing.

PRE-CHARGE

PRE-

CH

AR

GE

PRE-CHARGE

PRE-

CH

AR

GE

BUFFER

BUFFER

BU

FFER

BU

FFER

PRE-CHARGE

PRE-

CH

AR

GE

BUFFER

BU

FFER

PRE-CHARGE

PRE-

CH

AR

GE

BUFFERB

UFF

ER

• No placement and routing needed. • Output buffers and the input buffers

of the next stage are shared.

Courtesy B. Brayton


Experimental ResultsExperimental Results

Layout of C2670

Network of PLAs, 4 layers OTC

River PLA,2 layers no additional routing

Standard cell, 2 layers channel routing

Standard cell,3 layers OTC

0.2

0.6

1

1.4

0 2 4 6 area

dela

y

SC N PLA RPLA

Area: RPLAs (2 layers) 1.23 SCs (3 layers) - 1.00, NPLAs (4 layers) 1.31 DelayRPLAs 1.04SCs 1.00 NPLAs 1.09 Synthesis time: for RPLA , synthesis time equals design time; SCs and NPLAs still need P&R.Also: RPLAs are regular and predictable


2-d Cell Based: “Hard” Modules2-d Cell Based: “Hard” Modules

25632 (or 8192 bit) SRAMGenerated by hard-macro module generator


1-d Cell-based Design (standard cells)1-d Cell-based Design (standard cells)

Routing channel requirements arereduced by presenceof more interconnectlayers

Functionalmodule

(RAM,multiplier,

)

Routingchannel

Logic cellFeedthrough cell

Rows ofcells


Standard Cell — ExampleStandard Cell — Example

[Brodersen92]


Standard Cell – The New GenerationStandard Cell – The New Generation

Cell-structurehidden underinterconnect layers


Standard Cell - ExampleStandard Cell - Example

3-input NAND cell(from ST Microelectronics):C = Load capacitanceT = input rise/fall time


““Soft” MacroModulesSoft” MacroModules

Synopsys DesignCompiler


The “Design Closure” ProblemThe “Design Closure” Problem

Courtesy Synopsys

Iterative Removal of Timing Violations (white lines)


Gate Array — Sea-of-gatesGate Array — Sea-of-gates

rows of

cells

routing channel

uncommitted

VDD

GND

polysilicon

metal

possiblecontact

In1 In2 In3 In4

Out

UncommitedCell

CommittedCell(4-input NOR)


Sea-of-gate Primitive CellsSea-of-gate Primitive Cells

NMOS

PMOS

Oxide-isolation

PMOS

NMOS

NMOS

Using oxide-isolation Using gate-isolation


Sea-of-gatesSea-of-gates

Random Logic

MemorySubsystem

LSI Logic LEA300K(0.6 m CMOS)

Courtesy LSI Logic


The return of gate arrays?The return of gate arrays?

metal-5 metal-6

Via-programmable cross-point

programmable via

Via programmable gate array(VPGA)

[Pileggi02]

Exploits regularity of interconnect


Pre-wired Arrays:Pre-wired Arrays:Classification of prewired arrays (or field-programmable devices): Based on Programming Technique

Fuse-based (program-once) Non-volatile EPROM based RAM based

Programmable Logic Style Array-Based Look-up Table

Programmable Interconnect Style Channel-routing Mesh networks


Fuse-Based FPGAFuse-Based FPGA

antifuse polysilicon ONO dielectric

n+ antifuse diffusion

2

From Smith’97

Open by default, closed by applying current pulse


Array-Based Programmable LogicArray-Based Programmable Logic

PLA (flexible – sizing) PROM (dense) PAL (uniform load)

I 5 I 4

O0

I 3 I2 I1 I0

O1O2O3

Programmable AND array

ProgrammableOR array I5 I4

O0

I3 I2 I1 I0

O1O2O3

Programmable AND array

Fixed OR array

Indicates programmable connection

Indicates fixed connection

O0

I3 I2 I1 I0

O1O2O3

Fixed AND array

ProgrammableOR array


Programming a PROMProgramming a PROM

f0

1 X 2 X 1 X 0

f1NANA: programmed node


2-input mux 2-input mux as programmable logic blockas programmable logic block

FA 0

B

S

1

ConfigurationA B S F=0 0 0 00 X 1 X0 Y 1 Y0 Y X XYX 0 YY 0 XY 1 X X +Y 1 0 X1 0 Y1 1 1 1

XYX Y

XY


Logic Cell of Actel Fuse-Based FPGALogic Cell of Actel Fuse-Based FPGA

A

B

SA Y

C

D

SB

1

S1S0

1

1


LUT-Based Logic CellLUT-Based Logic Cell

Courtesy Xilinx

D4

C1....C4

clock

D3

D2

D1

F4

F3

F2

F1

Logicfunction

F

Logicfunction

H

Logicfunction

G

DinF’G’H’

H1

4

DinF’G’H’

G’H’

H2 H0 EC

H’F’

S/Rcontrol

S/Rcontrol

Multiplexer Controlledby Configuration Program

D

Y1

1

EC

QSD YQ

Bypass

X

XQBypass

RD

D

EC

QSD

RD

Xilinx 4000 Series


Array-Based Programmable WiringArray-Based Programmable Wiring

Input/output pinProgrammed interconnection

InterconnectPoint

Horizontaltracks

Vertical tracks

Cell

M


Mesh-based Interconnect NetworkMesh-based Interconnect NetworkSwitch Box

Connect Box

InterconnectPoint

Courtesy Dehon and Wawrzyniek


Transistor Implementation of MeshTransistor Implementation of Mesh



Hierarchical Mesh NetworkHierarchical Mesh Network

Use overlayed meshto support longer connections

Reduced fanout and reduced resistance



Altera MAXAltera MAX

From Smith97


Altera MAX Interconnect ArchitectureAltera MAX Interconnect Architecture

LAB2

PIA

LAB1

LAB6

tPIA

tPIA

row channelcolumn channel

LAB

Courtesy Altera

Array-based(MAX 3000-7000)

Mesh-based(MAX 9000)


Field-Programmable Gate ArraysField-Programmable Gate ArraysFuse-basedFuse-based

I/O Buffers

Program/Test/Diag nostics

I/O Buffers

I/O B

uffe

rs

I/O B

uffe

rs

Vertical ro utes

Rows o f logic m odule sRouting channels

Standard-cell likefloorplan


Xilinx 4000 Interconnect ArchitectureXilinx 4000 Interconnect Architecture

2

12

8

4

3

2

3

CLB

8 4 8 4

Quad

Single

Double

Long

DirectConnect

DirectConnect

Quad Long GlobalClock

Long Double Single GlobalClock

CarryChain

Long12 4 4

Courtesy Xilinx


RAM-based FPGA RAM-based FPGA

Xilinx XC4000ex

Courtesy Xilinx


Design at a crossroadDesign at a crossroadSystem-on-a-ChipSystem-on-a-Chip

RAM

500 k Gates FPGA+ 1 Gbit DRAMPreprocessing

Multi-

SpectralImager

Csystem+2 GbitDRAMRecog-nition

Ana

log

64 SIMD ProcessorArray + SRAM

Image Conditioning100 GOPS

Embedded applications: cost, performance, and energy are the issues!

DSP and control intensive Mixed-mode Software design is crucial


Addressing the Design Complexity IssueAddressing the Design Complexity IssueArchitecture ReuseArchitecture Reuse

Reuse comes in generationsGeneration Reuse element Status

1st Standard cells Well established

2nd IP blocks Established- marginal 3rd Architecture Need for Standards 4th IC Marketing Hype 5th Software Current Practice


Heterogeneous Programmable PlatformsHeterogeneous Programmable Platforms

Xilinx Vertex-II Pro

Courtesy: Xilinx High-speed I/O

Embedded PowerPcEmbedded memories

Hardwired multipliers

FPGA Fabric


SummarySummary

Design Choice forced by System Tradeoffs Deep Sub-micron Challenges

Regularity (Design flexibility at smallest scales) Power consumption! Interconnection Parasitics Nanoscopic Devices/ModulesNew circuit solutions are bound to emerge

Who can afford design in the years to come?

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