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Dataflow Architectures

Topic 7

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Outline

What is data flow technique?

History of Data Flow Machines

Data Flow Models Types of Data Flow Systems

Macrodataflow

Conclusion

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Mechanism on Architectures

Control flow mechanism-von Neumann

Data driven or dataflow mechanism Demand flow mechanism

Pattern flow mechanism

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Data Flow Technique

Alternative computer design to storedprogram systems.

The Difference

Traditional MethodsAn instruction executed when the previous instruction in a

defined sequence has been executed

In this model,It is executed when the operands required become

available.

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History

developed in 1960s by Karp and Miller as

graphic means of representing

computations.

In the early 1970s Dennis and others

began to develop computer architectures

based upon the dataflow computational

model.

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Data Flow Models

It uses a directed graph called a data dependence graph ordataflowgraph

+ nodes

arcs

The general flow of the model is top to down

Each node of a data graph can be represented as an activity template

Add

[ ]

[ ]

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Terminology

Data, data dependency graph

Arcs :

flow of the data

Nodes :

represent operations

Token :

represent data and operations

Firing:

when data is available, operation is started,

then result is sent to destination.

Handshaking:

Result is consumed

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Data flow example

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Switch and Merge

to buildcondional and

loop operations

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Loop graph

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Static dataflow

Recursion is not implemented

Each node can fired only as once instance

Firing rules

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Firing rules on static

Nodes fire

when all input tokens available

output tokens have been consumed

input token are then removed

output tokens are generated

Acknowledgement

destination sends back signal to source

PE when token consumed

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Token format in static

OPCODE OPERAND DESTINATION

VALUE DESTINATION

PE receives operation packes of the form

PE sends packets of the form

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static dataflow diagram

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Dynamic data flow

Firing rule

A node fires all input tokens with the same tag

appear

More than one token is allowed on each arc

Previous output need not be consumed

before the node fire again

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Dynamic data flow architecture

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Disadvantages of dynamic dataflow

Overhead involved in matching tokens is heavy

Resourse allocation is a complicated process

The long instunction cycle

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Other types of dataflow mechanism

Pure dataflow

Macro dataflow

Hybrid dataflow

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Pure Dataflow machines

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MACRO DATA FLOW

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Conclusion

Dataflow has had a fairly long development

time, with a few groups studying the

technique without it becoming widespread in

commercial use. Compitability with existing system inhibit the

introduction of a radically different computer

system requiring a different style of

programming and different programminglanguages.