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Crosstalk-Aware Energy Efficient Encoding for Instruction Bus through Code Compression. Balaji Vaidyanathan, Yuan Xie Department of CSE Pennsylvania State University, University Park PA-16801. Index Terms. Energy reduction Code-compression hardware crosstalk. Presentation Summary.

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crosstalk aware energy efficient encoding for instruction bus through code compression

Crosstalk-Aware Energy Efficient Encoding for Instruction Bus through Code Compression

Balaji Vaidyanathan, Yuan Xie

Department of CSE

Pennsylvania State University, University Park

PA-16801

index terms
Index Terms
  • Energy reduction
  • Code-compression hardware
  • crosstalk
presentation summary
Presentation Summary
  • Introduction and Motivation
  • Background
  • Energy-aware code assignment
  • Experimental Setup
  • Experimental Results
  • Conclusion
presentation summary1
Presentation Summary
  • Introduction and Motivation
  • Background
  • Energy-aware code assignment
  • Experimental Setup
  • Experimental Results
  • Conclusion
introduction and motivation
Introduction and Motivation
  • Power aware embedded system design is necessary.
  • Interconnect power is a major power consumer.
    • Comparable to cache, memory controller, core power [1].
  • Interconnect dynamic power due to
    • toggling (↓) with technology scaling
    • crosstalk (↑) with technology scaling

[2]

[1] Lahiri et al., CODES-ISSS’04

[2] Sotirsadis et al., ICCAD’04

Magen et al., Intel Corporation,

SLIP’04

introduction and motivation1
Introduction and Motivation

A

B

Inter-wire or

crosstalk capacitance

GND

L

Self

Capacitance

W

CA_to_B

L.T

T

H

α

CB_to_GND

L.W

S

introduction and motivation2
Introduction and Motivation

A

B

L

GND

W

2T

CA_to_B

2.(L.T)

H

α

CB_to_GND

L.W

S

introduction and motivation3
Introduction and Motivation

CA_to_B

λ. (L.T)

α

CB_to_GND

L.W

1.742 in 250nm

9.82 in 70nm

Inter-wire coupling capacitance will dominate total interconnect capacitance in future technologies.

introduction and motivation4
Introduction and Motivation
  • Code compression reduces code size and power.
    • But increases entropy.
  • Is there a compression scheme that can be utilized to reduce interconnect power ?
    • Variable-to-Fixed (V2F) compression scheme (explained later)
  • Tunstall introduced V2F coding
    • Xie et al. used it to reduce code size and interconnect toggle power (not crosstalk induced power).
presentation summary2
Presentation Summary
  • Introduction and Motivation
  • Background
  • Energy-aware code assignment
  • Experimental Setup
  • Experimental Results
  • Conclusion
background
W i d t h

0

[C2,W2]

[C3,W3]

[C1,W1]

1

3

0

2

0.2

1

3

0

2

0.2

0.8

0.8

6

4

[C4,W4]

[C5,W5]

[C6,W6]

D e p t h

5

7

4

6

0.3

D e p t h

5

7

4

6

0.3

0.6

0.4

0.7

2 bit

0.7

10

8

0.9

9

11

8

10

9

11

8

10

0.9

0.1

0.1

14

12

13

15

12

14

13

15

12

14

2

2

1

3

0

0

3

1

2

2

1

3

0

0

3

1

Background

Markov V2F code compression

Xie et al., ISSS-CODES ‘02.

[C0,W0]

background1
[C2,W2]

[C3,W3]

[C1,W1]

0 1 0 1 1 1 0 1 0 0 0 0

[C4,W4]

[C5,W5]

[C6,W6]

N bit

1 0 0 0 0 0 0 1 1 1 1 0

Background

Markov V2F code compression

Xie et al., ISSS-CODES ‘02.

Variable length bit stream

to

Fixed length Codes

background2
Background

Markov V2F code compression

  • We can assign random codes
    • why not do a power aware assignment ?
  • Each code book is re-coded with power aware codes
    • Based on application profiling (algorithm explained later)
  • Note
    • no change in compression algorithm or its efficiency.
    • Only code-bit mapping changes
    • No h/w change required (for both compression and de-compression)
background3
Background

Crosstalk and Power Models

Pdyn = 0.5 * Ctotal * Vdd2 * f

Ctotal = Cs * Nt

Wire-to-substrate/

Self capacitance

Nt = Ns + λ* Nc

1.742 in 250nm

9.82 in 70nm

Coupling Transition

Self transition /

Hamming distance

Sotiriadis et al., IEEE CICC, 2000.

background4
Background

Crosstalk and Power Models

Pdyn = Constant * Ctotal

Ctotal= Self Capacitance * (Toggles +

λ* Crosstalk_Transitions)

= Self Capacitance * (Ns + λ* Nc)

background5
Background

Nt = Ns + λ* Nc

Total Transition Table

Head = (0000)

λ = 3

= 4

= 11

presentation summary3
Presentation Summary
  • Introduction and Motivation
  • Background
  • Energy-aware code assignment
  • Experimental Setup
  • Experimental Results
  • Conclusion
energy aware code assignment
Source Code

Compilation

Profiling

Energy-aware

Compression

Object Code

Decompression

Hardware

Energy-aware code assignment

Implementation flow

energy aware code assignment1
[C2,W2]

[C3,W3]

[C1,W1]

[C4,W4]

[C5,W5]

[C6,W6]

N bit

S1

S2

1 0 1 0

1 0 0 0

A

C

0 0 0 1

0 1 0 0

D

B

[C3,W3]

[C1,W1]

A

[C2,W2]

A2

A1

E7

E6

E1

A

B

[C5,W5]

[C2,W2]

Energy-aware code assignment
  • The instructions in the application are assigned dummy codeword.
  • Vertical and horizontal adjacency of codeword is collected from the application profile.
  • The codeword to be assigned are picked in pairs that are most vertically connected.
  • The Codeword pairs are assigned cross-talk aware binary bits.
  • Horizontal adjacency is used to take care of boundary conditions
presentation summary4
Presentation Summary
  • Introduction and Motivation
  • Background
  • Energy-aware code assignment
  • Experimental Setup
  • Experimental Results
  • Conclusion
experimental setup
Experimental Setup
  • Cycle accurate TMS320C6x (Texas Instruments DSP VLIW processor) simulator.
  • Media benchmarks are compiled using Code Composer Studio IDE.
  • BPTM model for bus is used.
  • 4-bit length codewords are used.
presentation summary5
Presentation Summary
  • Introduction and Motivation
  • Background
  • Energy-aware code assignment
  • Experimental Setup
  • Experimental Results
  • Conclusion
experimental results
Experimental Results

% contribution of inter-wire in uncompressed approach

75-95% of Interconnect dynamic power is

inter-wire coupling transition

~250nm

70nm

experimental results1
Experimental Results

% power reduction compared to

uncompressed approach

42-68% inter-wire coupling power reduction

55-71% total dynamic power reduction

using 32x32 Markov model

Toggle Power

~250nm

~70nm

experimental results2
Experimental Results

225% power increase due to random codeword

assignment compared to optimized case

% power of random-case compared to

optimized approach

~250nm

~70nm

experimental results3
Experimental Results

570-670% power increase due to worst-case

codeword assignment compared to optimized case

% power of worst-case compared to

optimized approach

~250nm

~70nm

presentation summary6
Presentation Summary
  • Introduction and Motivation
  • Background
  • Energy-aware code assignment
  • Experimental Setup
  • Experimental Results
  • Conclusion
conclusion
Conclusion
  • Code compression hardware considering inter-wire coupling transition is proposed.
  • No extra delay, power or area overhead incurred.
  • 55-71% reduction in interconnect dynamic power is obtained.
  • 2X power reduction compared to random-case.
slide29
Thank You

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