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No Assembly line

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Assembly line - start up1. 2. 3. 4. 5.

ChassisAxels Motor Seats Body

Start up waste

t

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Assembly line - stop1. 2. 3. 4. 5.

ChassisAxels Motor Seats Body

Nothing to do

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Assembly line

At start: final stations idle

At stop: start stations idle

5 “stages” for each car

Each car still takes 5 stages but...

... we produce one car each step

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Assembly line

Time-set car

Cyclesinstruction

= 55 cycles 1 instr.

= 15 cycles 5 instr.

Without pipelining:

With pipelining

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Pipelining

T = Nq * CPI * Tc

We can bring this But what

down to 1 determines this?

The slowest pipeline stage

“Rate determining step”

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Pipeline is most efficient...

...when the work is equally shared

“critical path” delay same for each stage

or

as close as possible

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How do we break up a long critical path?

Insert flip - flops!

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But - “no free lunch”

Delay: 30 ns 10 ns Latency: 1 cycle 3 cycles

Also: The flip-flops have a cost!

30 ns

10 ns 10 ns10 ns

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Pipeline problem:

Start-up waste

Unexpected problem in a stage (stall)

No more orders (flush)

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Branch

logic

Sgn/Ze

extend

Zero ext.

ALU

A

B

31

0

4+

+

= =

= =