1212 An Abstract Modeling Approach Towards System-Level Design-Space Exploration F.N. van Wijk 1,...

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An Abstract Modeling Approach Towards System-

LevelDesign-Space Exploration

F.N. van Wijk1, J.P.M. Voeten1, and A.J.W.M. ten Berg2

1Information and Communication Systems GroupFaculty of Electrical Engineering, Eindhoven University of

Technology

2Philips Research Laboratories Eindhoven

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An Abstract Modeling Approach Towards System-Level Design-Space Exploration

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12Contents

• Motivation• Modeling concepts• Simulation• Performance analysis• Design-space exploration exercise• Case study• Summary

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12MotivationTraditional hardware/software co-design methods

suffer from too many iterations that consume too much costly development time.

eed for specification and design methods that support fast exploration of design alternatives at an early stage of the design trajectory at a system-level of abstraction

Embedded systems have heterogenous architecture.Use Y-chart

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12The Y-chart

Application(s) Architecture

Mapping

PerformanceAnalysis

Source: A.C.J. Kienhuis. Design Space Exploration of Stream-based Dataflow Architectures: Methods and Tools, Ph.D. thesis, Delft University of Technology, 1999.

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12MotivationTraditional hardware/software co-design methods

suffer from too many iterations that consume too much costly development time.

eed for specification and design methods that support fast exploration of design alternatives at an early stage of the design trajectory at a system-level of abstraction

Embedded systems have heterogenous architecture.Use Y-chartUse abstract executable modelsTaking well-founded design decisions requires a well-

defined modeling languageUse POOSL

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12Contents


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12Model structure

Mapping

System Model

Functional Model

Resource Model

Performance Analysis

R1 R2 R3 R4

T3T1

T2

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12Resource ModelThree basic, parameterizable resource types:• Processing Resource (P)• Communication Resource (C)• Storage Resource (S)

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12Resource ModelThree basic, parameterizable resource types:• Processing Resource (P)

Operate()()

| instruction: String; instructionDelay: Real |

task?resourceRequest(instruction);

instructionDelay := instructionTable getDelay(instruction);

delay(instructionDelay);

task!acknowledge;

Operate()().

• Communication Resource (C)• Storage Resource (S)

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12Resource ModelThree basic, parameterizable resource types:• Processing Resource (P)• Communication Resource (C)

Operate()()

| packetSize, duration: Real |

fifo?requestBW(packetSize);

delay(transferDelay * packetSize);

fifo!ready;

Operate()().

• Storage Resource (S)

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12Resource Model• Storage Resource (S)

Operate()()

| packetSize: Real |

sel

[room > 0]fifo?malloc(packetSize);

if room > packetSize then room := room - packetSize

else packetSize := room; room := 0 fi;

fifo!grant(packetSize, room)

or

fifo?free(packetSize);

room := room + packetSize;

fifo!ready(room)

les;

Operate()().

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12An example communication channel

Resource Model

C1 S2 P2P1 S1

M a p p i n g

Functional Model

T1 FIFO1

conceptually unbounded FIFO

T2FIFO2

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12Contents


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12Structure diagram

StorageResource

ComputationResource

StorageResource

Communi-cations

Resource

Producer FifoA FifoB Consumer

ComputationResource

Functional Model

Resource Model

M a p p i n g

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12Message flow diagram

StorageResource

ComputationResource

StorageResource

Communi-cations

Resource


ComputationResource

packet(Packet)

ok()

packet(Packet)

ok()

packet(Packet)

ok()

reso

urce

Req

uest

(Str

ing,

Obj

ect)

ackn

owle

dge(

)

gran

t(In

tege

r, I

nteg

er)

free

(Int

eger

)

mal

loc(

Inte

ger)

read

y(In

tege

r)

gran

t(In

tege

r, I

nteg

er)

free

(Int

eger

)

mal

loc(

Inte

ger)

read

y(In

tege

r)

requ

estB

W(I

nteg

er)

read

y()

reso

urce

Req

uest

(Str

ing,

Obj

ect)

ackn

owle

dge(

)

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12Message flow diagram

StorageResource

ComputationResource

StorageResource

Communi-cations

Resource


ComputationResource

packet(Packet)

ok()

packet(Packet)

ok()

packet(Packet)

ok()

reso

urce

Req

uest

(Str

ing,

Obj

ect)

ackn

owle

dge(

)

gran

t(In

tege

r, I

nteg

er)

free

(Int

eger

)

mal

loc(

Inte

ger)

read

y(In

tege

r)

gran

t(In

tege

r, I

nteg

er)

free

(Int

eger

)

mal

loc(

Inte

ger)

read

y(In

tege

r)

requ

estB

W(I

nteg

er)

read

y()

reso

urce

Req

uest

(Str

ing,

Obj

ect)

ackn

owle

dge(

)

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12Contents


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12Performance Analysis• Simulation-based reflexive performance

analysis:– Specify performance metrics as (temporal) rewards– Determine the long-run average metric values– Analyze their accuracy based on confidence intervals

• Use POOSL library classes:– Long-Run Sample Average (e.g. latency)– Long-Run Time Average (e.g. utilization)– Long-Run Rate Average (e.g. throughput)

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12Long-Run Time Average: utilization

Init()()utilization := new(LRTimeAverage) withConfidence(CL);Operate()().

Operate()()| instruction: String; instructionDelay, t: Real |task?resourceRequest(instruction);instructionDelay := instructionTable getDelay(instruction);timestamp t;utilization sampleRC(1,t,false);delay(instructionDelay);timestamp t;utilization sampleRC(0,t,true);task!acknowledge;Operate()().

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12Long-Run Rate Average: throughput

Init()()

LRMPEGDecoderOutputFrameRate := new(LRRateAverage) withConfidence(CL) setBatchSize(BS);

TOutput()().

TOutput()()

| t: Real |

OutputFrame()();

timestamp t;

LRMPEGDecoderOutputFrameRate sample(1,t);

TOutput()().

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12Contents


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12Example: Producer-Filter-Consumer (PFC)

P1 P2 P3S2 C1 S5 S4 S7

Producer Filter Consumer

Fifo Fifof fl l

alternative 1

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12Example: Producer-Filter-Consumer (PFC)

alternative 2

P1 P2 P3S2 C1 S5 S4 S7

Producer Filter Consumer

Fifo Fifof fl l

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12PFC-example (cont’d)

Fu

nct

ion

al

Mo

de

lM

ap

pin

gS

che

du

lers

/

Arb

iters

Re

sou

rce

Mo

de

l

alternative 1

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12PFC-example (cont’d)

Fu

nct

ion

al

Mo

de

lM

ap

pin

gS

che

du

lers

/

Arb

iters

Re

sou

rce

Mo

de

l

alternative 2

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12PFC-example: Performance Analysis

[22.38,22.78]22.58Throughput Consumer (fps)

[0.2227,0.2271]0.2249Utilization P3

[0.2224,0.2268]0.2246Utilization P2

[0.2232,0.2275]0.2253Utilization P1

Confidence IntervalPoint EstimationMetric

Alternative 1 (90% confidence, 1% relative error bound)

[21.13,21.54]21.33Throughput Consumer (fps)

[0.2127,0.2169]0.2148Utilization P2

[0.4264,0.4349]0.4307Utilization P1

Confidence IntervalPoint EstimationMetric

Alternative 2 (90% confidence, 1% relative error bound)

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12Contents


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12Picture-in-Picture TV case study• Functional model of PiPTV application mapped on

resource model of media processor, co-processors and central data bus => 64 (functional) + 17 (resource) + 6 (environment) = 87 parallel processes (total).

• Analyze long-run average bus and (c0-)processor utilizations and MPEG picture decoding time and frame rate.

• Compare results with outcome of similar experiments with Cadence VCC tool and prototype measurement results => judgement of applicability of developed method.

• Compare models at different levels of abstraction => explore accuracy vs. modeling time and simulation speed trade-off.

• Currently finishing off validation phase. Results of experiments expected early 2003.

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12Contents


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12Summary• An abstract modeling approach to system-level design-

space exploration for complex heterogeneous systems has been presented.

• The approach supports fast exploration of alternative realizations using abstract executable formal models.

• Functional models are mapped onto Resource models (strict coupling, mutually disconnected resources) and together form a System Model.

• Strict coupling enables the modeling of non-determinism.• Both control and data oriented behavior can be

expressed.• Modeling of resource sharing is straightforward.• Simulation-based performance analysis yields

performance figures. Based on the formal semantics of POOSL, their accuracy can be estimated using confidence intervals.

1212 An Abstract Modeling Approach Towards System-Level Design-Space Exploration F.N. van Wijk 1,...

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