# Generating Supply Voltage Islands In Corebased SystemonChip Designs - PowerPoint PPT Presentation

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## Generating Supply Voltage Islands In Corebased SystemonChip Designs

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### Voltage islands are regions where nearby IP blocks use a supply voltage ... Analyzing the most effective way of detecting possible voltage islands ... – PowerPoint PPT presentation

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Title: Generating Supply Voltage Islands In Corebased SystemonChip Designs

1
Generating Supply Voltage Islands In Core-based
System-on-Chip Designs
• Final Presentation
• Steven Beigelmacher
• Gall Gotfried
• www.ece.cmu.edu/ggall
• 04/26/2005

2
Overview
• Review
• What are we doing?
• How are we doing it?
• How We Did It
• Methodology
• Experimental setup
• Results
• Future directions

3
Review
• Voltage islands are regions where nearby IP
blocks use a supply voltage different from the
full-chip supply
• We propose reducing energy consumed in a
core-based SoC design by generating these voltage
islands
• A coarse-grained placement problem

4
Review
• Different classes of placement algorithms exist
• Integer Linear Programming, Recursive, Iterative
• We went with an iterative solver
• Want to avoid greedy algorithms
• Simulated annealing locally bad choices can be
globally good
• Parquet S. Adya, H. Chan, I. Markov
• Pronunciation pär-'kA
• to make of parquetry
• Parquetry -- work in the form of usually
geometrically patterned wood laid or inlaid
especially for floors

5
Review
• Simulated annealing loops are made up of two
phases
• What are the set of perturbations I can make to
the current solution? (move function)
• What is the relative goodness of that change?
(cost function)
• Move Function
• Move block to spot (x,y), swap two blocks, block
rotation, block scaling, etc

6
Review
• Cost Function
• Calculate a number quantifying the goodness of
the solution
• How good a solution is will depend on the area,
aspect ration, wire length, etc
• What are we doing?
• Analyzing the most effective way of detecting
possible voltage islands
• Modifying the cost function to take into account
these voltage islands
• Quantifying energy savings

7
Sequence Pairs
• Used to speed up and simplify move functions
• Simple graphical approximation
• Rectangular coordinate system
• Approximates relative location of blocks in graph
• Blocks represented by sequential numbering in X
and Y directions

8
Simulated Annealing (Parquet)
• The initial locations of blocks in S.P.
• Arbitrary
• Only used to simplify the simulated annealing
move function
• Upon completion of a random move
• Sequence pairs
• Get matched up with (x,y) coordinates
• Checked and adjusted to not overlap and meet
aspect ratio requirements

9
Sequence Pair Example
• X lt 3 2 5 4 1 gt
• Y lt 1 2 3 4 5 gt

10
Selecting a Move
Randomly picking which move to make
Making the move
11
Checking the Cost
• Parquet uses different linear cost functions
depending on emphasis of aspect ratio, wire
length, or area

AR and minWL
AR
minWL
None
Calculation of these delta components changes as
t ? 0
12
Cost Function Measures
• How do we assess the goodness of current
solution with respect voltage islands?
• Number of islands
• Number of nodes in islands
• Size of the largest island
• Reduction in power
• The above are all important to our modified cost
function

13
• Need solutions that increase the quantity of any
of the previous parameters to have reduced cost
• but without breaking up the entire placer
• Voltage islands with blocks laid on top of each
other dont do us much good
• Make voltage island friendly solutions good,
without making them too good

14
Calculating the Modified Cost
• Calculate the cost (delta) as before
• If a perturbation improves one of the voltage
island parameters, scale delta
• Scaling is cumulative
• Scaling is weighted towards certain measures
• Stop doing this as t?0
• Why do we do this?

15
Accepting a Move
Accept good moves
Else, accept bad moves with some probability that
decreases as t ? 0
Once t equals 0, run a few more greedy iterations
16
What Did Our Changes Do?
• A delta lt 0 is always accepted
• A voltage island friendly solution that was
already good will still be accepted
• A delta gt 0 is accepted with some probability
(declines over time)
• Scaling increases the probability of being
accepted, without forcing it
• Only effective on solutions that werent that bad
to begin with

17
Methodology
• Benchmarks are tested with set vdds and checked
for power saved after placement
• We define power saved as
• (Num-nodes in an island)(voltage of the island)
• Quantified by the amount of power saved by
reduction in voltage converting FIFOs
• Less islands means more voltage conversion hence
more power consumed

18
Methodology Purpose
• Our experiments were designed to show
• Function of 4 cost functions
• Voltage islands
• Nodes in islands
• Power saved!!! (emphasis here)

19
Experimental Setup
• Before applying any cost functions we calculate
the total initial power saved by the pre-placed
islands
• These are islands created by luck in the
initialization phase
• The total initial power saved is used
• Compare and determine worth of solution
• Initial power saved Current power saved -gt more
negative numbers mean better solution
• Determine the percent saved in final solution

20
Benchmarks used
21
Results AMI
• AMI33 has room to increase nodes in islands to
save power
• AMI49 has even vdd node distribution
• Cost function becomes more sensitive
• increasing distinct voltage islands to save power

22
Results HP
• HP6 has majority of blocks with high vdd
• Less room for optimization
• HP11 shows an increase in nodes in islands used
to save power
• Attributed to the fact more nodes have higher vdd

23
Future Work
• We have created an open source vdd/vt island
creation tool
• Move function must be modified to account for
multiple voltages in selecting moves
• Cost functions can be easily extended
• To create various placements based on multiple
VDD islands
• To create placements based on multiple Vt islands

24
You Got Questions