Reconfigurable computing

Eduardo Sanchez

EPFL

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Reconfigurable computing

• Methods for execution of algorithms:

• hardwired technology: high performance

• software-programmed microprocessors: high flexibility

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• Why hardwired solutions are faster than software solutions?

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• Reconfigurable computing is intended to fill the gap betweenhard and soft, achieving potentially much higher performancethan software, while maintaining a higher level of flexibility thanhardware (Compton and Hauck, “Reconfigurable computing”,ACM Computing Surveys, June 2002)

• Reconfigurable computing:

• systems incorporating some form of hardware programmability

• when we talk about reconfigurable computing we are usually talkingabout FPGA-based systems design

• Main motivations:

• accelerators for computing intensive applications

• tools for system validation: prototyping, emulation

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Moore's law

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410 millionItanium 2

125 millionPentium 4

37 millionMoore's law

(2x - 24 months)

3.3 billionMoore's law

(2x - 18 months)

27.4 trillionMoore's law

(2x - 12 months)

Transistors

(actual in 2004)

Transistors

(predicted for 2004)

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• Intel introduces a new chip-fabrication process every twoyears:

• 2001: 0.13 micron

• 2003: 90 nm

• 2005: 65 nm

• 2007: 45 nm

• 2009: 32 nm

• ....

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Problem: Wirth's law

• Software is slowing faster than hardware is accelerating

• Expressed in Biblical cadences:rov ive and Ga ake awa

Andy GroveIntel Chairman

Bill GatesMicrosoft President

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• Computing requirement increases even faster than Moore'slaw

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Problem: time to market

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Problem: power consumption

400MHz

200MHz

100MHz

50MHz

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Embedded systems

• Embedded systems, which are hidden from the user andcannot usually be manipulated or reprogrammed, are found invirtually all electronic equipment used today, from wirelesstelephones and DVD players to cars and airplanes

• A fifth of the value of each car produced in the EU is due toembedded electronics, a value that is expected to rise to about40 percent by 2015

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Pervasive computing

• "The most profound technologies are those that disappear.They weave themselves into the fabric of everyday life untilthey are indistinguishable from it"Mark Weiser, "The Computer for the 21st Century", ScientificAmerican, Septiembre, 1991

• In a near future, the computer will disappear for beingeverywhere: it will be ubiquitous, pervasive

• Pervasive systems will be so integrated with theirs users thatthey will be invisible, they will disappear

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• Evolution of computer systems:

• mainframes: one computer, many users

• PCs: one computer, one user

• pervasive systems: many computers, one user

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remote communication fault tolerancehigh availability

remote information accessdistributed security

mobile networkingadaptive applications

energy-aware systemsmobile information access

location sensitivity

smart spacesinvisibility

localized scalabilityuneven conditioning

distributed systems

mobile computing

pervasive systems

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Smart Dust project

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• A 20 MIPS CPU embedded in a shoe

• Four times more powerful than early Silicon Graphics workstations (Motorola68000)

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• A lot of new devices to design

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Integrated circuits

Full-custom(ASIC)

Hand-made

Libraries

Semi-custom

Maskprogrammable

Fieldprogrammable

Gate array ROMPROMPALPLA

CPLD FPGA

Standard circuits

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Field Programmable Gate Arrays

• Array of logic cells

• Each cell is able to implement a logic function, chosen amongseveral possible functions: the choice is done by programming

• Interconnections between cells are also programmable

• Two types, depending on the cell’s complexity:

• fine grain

• coarse grain

• Two types, depending on the programming mode:

• RAM: every logic cell contains a LUT (look-up table), accompanied by aflip-flop, and all interconnected with programmable routing pathways

• anti-fuses

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programmableinterconnections

programmablefonctions

configuration

I/O celllogic cell

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Programmable

interconnect

Programmable

logic blocks

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|

&a

b

cy

y = (a & b) | !c

Required function Truth table

1011101

000

001

010

011

100

101

110

1111

y

a b c y

00001111

00110011

01010101

10111011

SRAM cells

Programmed LUT

8:1

Multi

ple

xer

a b c

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• An example of logic cell:

LUTCarry &Control

SP

D

EC

RC

Q

G4

G3

G2

G1

BY

YQ

YYB

Cout

Cin

• Functional frequencies are design-dependant

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16-bit SR

flip-flop

clock

mux

y

qe

a

b

c

d

16x1 RAM

4-input

LUT

clock enable

set/reset

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16-bit SR

16x1 RAM

4-input

LUT

LUT MUX REG

Logic Cell (LC)

16-bit SR

16x1 RAM

4-input

LUT

LUT MUX REG

Logic Cell (LC)

Slice

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CLB CLB

CLB CLB

Logic cell

Slice

Logic cell

Logic cell

Slice

Logic cell

Logic cell

Slice

Logic cell

Logic cell

Slice

Logic cell

Configurable logic block (CLB)

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Columns of embedded

RAM blocks

Arrays of

programmable

logic blocks

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RAM blocks

Multipliers

Logic blocks

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x

+

x

+

A[n:0]

B[n:0] Y[(2n - 1):0]

Multiplier

Adder

Accumulator

MAC

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uP

RAM

I/O

etc.

Main FPGA fabric

Microprocessorcore, special RAM,

peripherals andI/O, etc.

The “Stripe”

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uP

(a) One embedded core (b) Four embedded cores

uP uP

uP uP

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Configuration data in

Configuration data out

= I/O pin/pad

= SRAM cell

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Serial load with FPGA as master

Mode Pins Mode

Serial load with FPGA as slave

Parallel load with FPGA as master

Parallel load with FPGA as slave

0 0

0 1

1 0

1 1

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Configuration data in

Mem

ory

Dev

ice

Control

Configuration

data out

FPGA

Cdata In

Cdata Out

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Configuration data [7:0]

Mem

ory

Dev

ice

Control FPGA

Cdata In[7:0]

Address

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Configuration data [7:0]Mem

ory

Dev

ice Control FPGA

Cdata In[7:0]

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Mem

ory

Devic

e

Control

Mic

rop

roce

ss

or

Address

Data

Peri

ph

era

lP

ort

, etc

.

FPGA

Cdata In[7:0]

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• Total area = active logic + configuration memory + interconnect

interconnect

active logic

configuration memory

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• Advantages over PLDs:

• enhanced flexibility

• reduced board space, power and cost

• increased performance

• Advantages over ASICs:

• reprogrammability

• off-the-shelf availability

• zero NRE (non-recurring engineering) costs

• reduced time-to-market

• ease-of-use

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CumulativeNRE + Unit Cost

CumulativeVolume K Units

ASIC .15

ASIC .25

FPGA .25 FPGA .15

ASIC costs starthigher, but slopeis flatter

For each technologyadvance, FPGAs becomemore cost effective

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• As performance requirements increase, the implementation ofcontrol elements in embedded applications is moving from 8-bits to 32-bits

• At the same time, the implementation vehicle of choice forembedded applications is moving from ASICs to FPGAs due tocost and time-to-market pressures

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Synthesis methodology

configuration bit-string

schematic

graphic editor VHDL

placement

routing

partition

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Registertransfer level

RTL

Logic

Simulator

RTL functionalverification

LogicSynthesis

Gate-levelnetlist

Logic

Simulator

Place-and-Route

Gate-level functionalverification

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Graphical State Diagram

Graphical Flowchart

When clock rises If (s == 0) then y = (a & b) | c; else y = c & !(d ^ e);

Textual HDL

Top-level

block-level

schematic

Block-level schematic

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Intellectual property (IP)

• A semiconductor IP block is a predesigned function to beimplemented in a semiconductor device. In some cases, thefunctions are parametrisable, allowing a degree ofcustomization. These functions include physical libraryfunctions (analog or digital), basic blocks (such as countersand muxes) and system-level macros (also known as cores orvirtual components) - including memory blocks

• Market:

• 1999: 442 millions dollars (semiconductors total : 196’136 M$)

• 2000: 620 millions dollars (total semiconductors total : 231’601 M$)

• 2004: 2’940 millions dollars (semiconductors total : 339’545 M$)

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System-on-a-chip (SOC)

SOC

ASIC FPGA

· expensive circuit· lower performance· higher consumption· lower development cost· faster adaptation to change

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ASIC SOC

24012020SRAM Mb/cm2

400022001000MIPS/watt

200x10630x1065x106Gates/cm2

0.050.090.18Technology

201120042000

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MicroBlaze soft processor• Thirty-two 32-bit general purpose registers

• 32-bit instruction word with three operands and two addressingmodes

• Separate 32-bit instruction and data buses that conform to IBM’sOPB (On-chip Peripheral Bus) specification

• Separate 32-bit instruction and data buses with direct connectionto on-chip block RAM through a LMB (Local Memory Bus)

• 32-bit address bus

• Single issue, 3-stage pipeline (instruction fetch, operand fetch,execution)

• Hardware multiplier

• Big-endian

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Virtex-II Pro family• Virtex-II Pro FPGAs provide up to four embedded 32-bit IBM PowerPC 405

RISC processors, each delivering over 420 Dhrystone MIPS at 300 MHz

• 16KB data / 16KB instruction caches

• memory management unit

• variable page size (1KB-16MB)

• five-stage datapath pipeline

• integer multiply/divide unit

• 32x32 bit general purpose registers

• dedicated on-chip memory interface

• it takes up as little as 2% of the total die area of XC2VP50

• it does not have a hardware floating point unit

• Up to twenty-four on-chip 3.125 Gbps Rocket I/O transceivers

• Based on a 0.13μ, 9-layer copper/low-K dielectric technology

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Virtex-4 family from Xilinx

• Columnar architecture

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• A Configurable Logic Block (CLB) contains 4 interconnectedslices

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• A simplified view of the slice is:

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• BRAM • Multipliers (DSP) blocks

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• Integrated PowerPC 405• Fully integrated Ethernet

Media Access Controller(EMAC)

• Bitstreams encrypted with256-bit AES algorithm

• 90-nm, 11-layer technology

• 500MHz for memory andmultipliers

• Lowest power

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• Three platforms:

Logic

Memory

DCMs

DSP

Logic

Memory

DCMs

DSP

Logic

Memory

DCMs

DSP

RocketIO

PowerPC

SX PlatformOptimized for

high-performancesignal processing

FX PlatformOptimized for

embedded processing andhigh-speed serial

connectivity

LX PlatformOptimized for

high-performance logic

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2442192896209,936142,128XC4VFX14

0

2042160768126,76894,896XC4VFX10

0

1642128576124,17656,880XC4VFX60

12424844882,59241,904XC4VFX40

8213232041,22419,224XC4VFX20

-2132320464812,312XC4VFX12

---51264085,76055,296XC4VSX55

---19244883,45634,560XC4VSX35

---12832042,30423,040XC4VSX25

---96960126,048200,448XC4VLX20

0

---96960125,184152,064XC4VLX16

0

---96960124,320110,592XC4VLX10

0

---80768123,60080,640XC4VLX80

---6464082,88059,904XC4VLX60

---6464081,72841,472XC4VLX40

---4844881,29624,192XC4VLX25

---32320486413,824XC4VLX15

RocketIO

transceiv

er

10/100/

1000

EMAC

PowerP

C

XtremeDS

P Slice

SelectI

O

DC

M

Block

RAM

[Kb]

Logic

CellsDevice

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Virtex-5 family from Xilinx

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• 32-Kb block RAM running at 550 MHz

• Compared to Virtex-4, Virtex-5 devices offer 30% higheraverage speed and 65% higher capacity in the largest device.Dynamic power consumption is reduced by 35% and chip areais 45% smaller

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Stratix II family from Altera

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• Each Logic Array Block (LAB) contains 4 Adaptive Logic Modules(ALM)

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Stratix III family from Altera

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• Adaptive Logic Module (ALM)

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Cyclone II family from Altera

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Nios soft processor

• RISC-like processor

• Full 32-bit instruction set, data path and address space

• 32 general-purpose registers

• 32 external interrupt sources

• Single-instruction 32x32 multiply and divide producing a 32-bitresult

• Single-instruction barrel shifter

• 6-level pipeline

• Branch prediction

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Fusion family from Actel

• This FPGA family integrates thestandard programmable logicwith configurable analog andFlash memory

• Configurable analog to digitalconverter (ADC), supportingresolutions up to 12 bits, andsample rates up to 600 ksamples per second

• A 32-bit ARM7 soft-core isavailable

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• VersaTile configurations:

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