林永隆 (Youn-Long Lin)Department of Computer Scienc

eNational Tsing Hua University

High-Level Synthesisof VLSIs

THEDA Tsing Hua Electronic Design Automation

2

VLSI Design Tools

• Design Capturing/Entry• Analysis and Characterization• Synthesis/Optimization

– Physical (Floor planning, Placement, Routing)

– Logic (FSM, Retiming, Sizing, DFT)– High Level(RTL, Behavioral)

• Management

3

Design Methodology Progress

Capture and Simulate

Describe and Synthesis

Specify and ???

4

Productivity

Re-Targetability

Correctness

Why Synthesis?

Unsynthesizability

Performance Loss

Inertial

Why not Synthesis?

5

Structural Behavioral

Physical

X’tor

Gate

RTL

Block

Boolean

FSM

Algorithm

GDSII

Placement

Floorplan

Y-ChartDan D Gajski

6

Structural Behavioral

Physical

X’tor

Gate

RTL

Block

Boolean

FSM

Algorithm

GDSII

Placement

Floorplan

LayoutSynthesis

7

Structural Behavioral

Physical

X’tor

Gate

RTL

Block

Boolean

FSM

Algorithm

GDSII

Placement

Floorplan

LogicSynthesis

8

Structural Behavioral

Physical

X’tor

Gate

RTL

Block

Boolean

FSM

Algorithm

GDSII

Placement

Floorplan

High-LevelSynthesis

9

High Level Synthesis

CDFG

Parsing

Transformation

Synthesis

StructuralRTL

BehavioralDescription

10

What Went Wrong?

• Too much emphasis on incremental work on algorithms and point tools

• Unrealistic assumption on component capability, architectures, timing, etc

• Lack of quality-measurement from the low level

• Too much promising on fully automation (silicon compiler??)

11

Essential Issues

• Behavioral Specification Languages

• Target Architectures

• Intermediate Representation

• Operation Scheduling

• Allocation/Binding

• Control Generation

12

Behavioral Specification Languages

• Add hardware-specific constructs to existing languages– HardwareC

• Popular HDL– Verilog, VHDL

• Synthesis-oriented HDL– UDL/I

13

Target Architectures

• Bus-based

• Multiplexer-based

• Register file

• Pipelined

• RISC, VLIW

• Interface Protocol

14

Design Space Exploration

Arch I

Arch II

Arch III

Dela

y

Area

15

FSM with Data Path (FSMD)

FSMDataPath

FSMDataPath

FSMDataPath

Interactive FSMDs

16

Intermediate Representation

* *+

Control Flow Graph

Data Flow Graph

17

Scheduling (Temporal Binding)

• Time & Resource Tradeoff• Time-Constrained

– Integer Linear Programming (ILP)– Force-Directed

• Resource-Constrained– List Scheduling

• Other Heuristics– Simulated Annealing, Tabu Search, ...

18

Allocation/Binding

Functional UnitsOperations

StorageVariablesSignals

Bus/Wire/MuxData Transfers

19

RF

FUFU

RF

Variables/Signals

Data Transfer

Operations

20

Controller Specification Generation

ScheduledCDFG

AllocatedDatapath

Micro-Operationsfor

Every Control Step

21

HLS Quality Measures

• Performance

• Area Cost

• Power Consumption

• Testability

• Reusability

22

Hardware Variations

• Functional Units– Pipelined, Multi-Cycle, Chained, Multi-

Function

• Storage– Register, RF, Multi-Ported, RAM, ROM,

FIFO, Distributed

• Interconnect– Bus, Segmented Bus, Mux, Protocol-Based

23

Functional Unit Variations

+**

**

-+

Step 1

Step 2

Step 3

Step 4

+

++

24

Storage/Interconnect Variations

RF

FUFU

RFSegmentedBuses

DistributedFIFO

Mux

Chaining

Multi-Port

25

Architectural Pipelining

FSMDataPath

26

THEDA’s Work on HLS

• ILP-based Scheduling• Bipartite Weighted Matching for Datapath

Allocation• Performance-Driven Interconnect Synthesis• Loop Folding & Retiming• Integrating Synthesis and Layout• DSP Core Generation• Book on HLS

27

Integer Linear Programming for Scheduling

• Given # Control Steps• ASAP + ALAP ==> Possible Steps for

each Operations• Tight Constraints on

– Dependency– One Scheduled Step per Op– Resource Usage per Step

• Many Extensions

28

Advanced Scheduling for Loop Folding

1

2

33

2

1

1 iteration per 3 cycles 1 iteration per 2 cycles

29

Loop Folding(cont.)

1

2

3

Prologue

Epilogue

Folded Body

30

Retiming and Loop Folding

1

2

3

BA C D E F BA C D E F

1

2

3

BACD

E

F B

AC

D

E

F

31

Integrating Layout and Synthesis

HDL Description

HDL Synthesis RC Extraction &Delay Calculation

Chip Layout

Post-LayoutTiming Analysis

Module Resynthesis

Timing Ok & no morearea improvement

P&R

Soft-MacroPlacement

Block Placement

Soft-MacroFormation

No

Module ResynthesisSoft-MacroPlacement

Soft-MacroFormation

32

HLS Techniques for DSP Code Generation

Memory Allocation

SchedulingAddress Generation

33

Applications of HLS Technology

• Code generation for embedded processors

• Retargetable compilers for application-specific instruction-set processors (ASIP)

• Reconfigurable computing

• Advanced features in logic synthesizer

34

System-on-a-Chip

Processor Memory

ExternalMemoryInterface

IPBus Master UART

WirelessB

ridg

e US

B

35

SOC with PLDs

Processor Memory

ExternalMemoryInterface

FPGABus Master FPGA

WirelessB

ridg

e US

B

36

WaferFoundry

SystemHouses/

IC Vendors(Fabless)

Integrators

Library/IP

Vendors(Chipless)

EDAVendors

Paradigm Shift

37

IP and Synthesis

• Authoring IP for Synthesis

• Synthesis utilizing IP

• Synthesizing IPs

Executable Data Sheets

38

Executable Data Sheets

IP

IP WrapperMore thanjust thePort Interface

39

Future Directions

• Realistic Methodology– Evolutional Transition from Current

Practice– Domain Specific

• IP-Centric– As both Authoring Aid and Integrator

• Software– Co-design and Code Generation

40

Valu

e

Time

EDA

IP

IC