LOW-LEAKAGE REPEATERS LOW-LEAKAGE REPEATERS FOR FOR
NETWORK-ON-CHIP INTERCONNECTSNETWORK-ON-CHIP INTERCONNECTS
Arkadiy Morgenshtein, Israel Cidon, Avinoam Kolodny, Ran Arkadiy Morgenshtein, Israel Cidon, Avinoam Kolodny, Ran GinosarGinosar
Technion – Israel Institute of Technology
QNoC
Research
Group
QNoC Research GroupElectrical Engineering Department
Technion – Israel Institute of TechnologyHaifa, Israel
22 Low-Leakage Repeaters for NoC CommunicationsLow-Leakage Repeaters for NoC Communications ISCAS 2005
HighlightsHighlights
• Selecting the Repeater Type
• Optimizing Repeater Insertion
• Utilization-Oriented Analysis
• Leakage in NoC links with repeaters
33 Low-Leakage Repeaters for NoC CommunicationsLow-Leakage Repeaters for NoC Communications ISCAS 2005
Networks-on-Chip (NoC)Networks-on-Chip (NoC)
Router
Module
Repeater
NoC characteristics
• Packet-based data routing
• Multiple Quality-of-Service levels
Physical layer of NoC
• Low link utilizationLow link utilization Most links idle most of the time!
Leakage power is importantLeakage power is important
44 Low-Leakage Repeaters for NoC CommunicationsLow-Leakage Repeaters for NoC Communications ISCAS 2005
Leakage Reduction in LogicLeakage Reduction in Logic
• Sleep Transistors
• Dual Threshold
• more…
Subthreshold leakage is dominant at high temperatures
Solutions:
55 Low-Leakage Repeaters for NoC CommunicationsLow-Leakage Repeaters for NoC Communications ISCAS 2005
Leakage Reduction in Leakage Reduction in RepeatersRepeaters
??Lw
Lw/n Lw/n Lw/n1 2 n-1
large sizes
no transistor stack
very high wire loads
specific solutions neededunique characteristics
Solutions:
66 Low-Leakage Repeaters for NoC CommunicationsLow-Leakage Repeaters for NoC Communications ISCAS 2005
Existing Repeater TypesExisting Repeater Types
LVT – Low-Vt RepeatersLVT – Low-Vt Repeaters
SVT - Staggered-VtSVT - Staggered-Vt
wire wireLH
LH L
HInidle 0=
wire wireHInidle 0= H H
wire wireL L L
[16] Sylvester et al.
HVT – High-Vt RepeatersHVT – High-Vt Repeaters
• fast• high leakage
• slow• low leakage
• fast (In 01)• slow (In 10)• low leakage (idle)
77 Low-Leakage Repeaters for NoC CommunicationsLow-Leakage Repeaters for NoC Communications ISCAS 2005
Research OutlineResearch Outline
Network-on-ChipNetwork-on-Chip
Selecting the Repeater Type
Utilization-Oriented Analysis
Optimizing Repeater Insertion
Utilization-Dependant Optimal Number of
Repeaters
SR – Sleep Repeaters
DTD – Dual-Vt Domino Repeaters
Low & Varying Utilization
&
88 Low-Leakage Repeaters for NoC CommunicationsLow-Leakage Repeaters for NoC Communications ISCAS 2005
Dual-Threshold Domino (DTD) Dual-Threshold Domino (DTD) RepeatersRepeaters
wire wire wire wire
wire wire
L
H
H
L
wire wire
L
H
H
L
wire wire
L
H
H
L
wire wire
L
H
H
L
Da
ta [
1:n
]
Clock
synchronized Clk link
High-Vt Evaluation Transistors
Low-Vt Pre-charge Transistors
99 Low-Leakage Repeaters for NoC CommunicationsLow-Leakage Repeaters for NoC Communications ISCAS 2005
DTD Repeaters OperationDTD Repeaters Operation
• Precharge transistors disconnected
• CLK line is synchronized with Data
• Evaluation by HVT transistors – slower but tolerant to Vt fluctuations
• Each Evaluation transistor drives only one transistor at next stage – faster and can be down-sized
Data
Clock
1 0
EvalStbyP
re-c
har
ge
Tsetup
Eval
Pre
-cha
rgeX
X
X
X
X
X
X
X
wire wire wire wire
wire wire
L
H
H
L
wire wire
L
H
H
L
Da
ta
Clock
argprech esetup PD linksT t t
1010 Low-Leakage Repeaters for NoC CommunicationsLow-Leakage Repeaters for NoC Communications ISCAS 2005
DTD Repeaters OperationDTD Repeaters Operation
X
X
X
X
X
X
X
X• Evaluation transistors disconnected
• Precharge to low-leakage mode
• Precharge by LVT transistors - fast
wire wire wire wire
wire wire
L
H
H
L
wire wire
L
H
H
L
Da
ta
Clock
Data
Clock
1 0
EvalStbyP
re-c
har
ge
Tsetup
Eval
Pre
-cha
rge
1111 Low-Leakage Repeaters for NoC CommunicationsLow-Leakage Repeaters for NoC Communications ISCAS 2005
wire wire wire wire
wire wire
L
H
H
L
wire wire
L
H
H
L
Da
ta
Clock
DTD Repeaters OperationDTD Repeaters Operation
X
X
X
X
0 1
1
1 0
0X
X
X
X
0 1
1
1 0
0
• HVT transistors are “off” – low leakage
Data
Clock
1 0
EvalStbyP
re-c
har
ge
Tsetup
Eval
Pre
-cha
rge
1212 Low-Leakage Repeaters for NoC CommunicationsLow-Leakage Repeaters for NoC Communications ISCAS 2005
DTD Repeaters OperationDTD Repeaters Operation
X
X
X
X
X
X
X
X
1
1 0
0 1
1 0
0X
X
X
X
X
X
X
X
• For Data=‘0’ - no transition occurs
wire wire wire wire
wire wire
L
H
H
L
wire wire
L
H
H
L
Da
ta
Clock
Data
Clock
1 0
EvalStbyP
re-c
har
ge
Tsetup
Eval
Pre
-cha
rge
1313 Low-Leakage Repeaters for NoC CommunicationsLow-Leakage Repeaters for NoC Communications ISCAS 2005
DTD Repeaters OperationDTD Repeaters Operation
X
X
X
X
X
X
X
X
wire wire wire wire
wire wire
L
H
H
L
wire wire
L
H
H
L
Da
ta
Clock
Data
Clock
1 0
EvalStbyP
re-c
har
ge
Tsetup
Eval
Pre
-cha
rge
1414 Low-Leakage Repeaters for NoC CommunicationsLow-Leakage Repeaters for NoC Communications ISCAS 2005
DTD HighlightsDTD Highlights
Application of domino and double-Vt techniques to low-leakage repeaters
Benefits
+ Effective leakage reduction during standby
+ Reduced load on each repeater allowing downscaling and area reduction
+ Tolerance to VT fluctuations by using HVT evaluation transistors
Drawbacks
- Increased dynamic power consumption due to signaling in domino protocol
- Overhead of clock line and pre-charge wiring
1515 Low-Leakage Repeaters for NoC CommunicationsLow-Leakage Repeaters for NoC Communications ISCAS 2005
Sleep Transistors in Sleep Transistors in RepeatersRepeaters
MTCMOSMTCMOS
SRSR
LogicLogic
RepeatersRepeaters
Evolution
1616 Low-Leakage Repeaters for NoC CommunicationsLow-Leakage Repeaters for NoC Communications ISCAS 2005
MTCMOS in RepeatersMTCMOS in Repeaters
• Common sleep transistors insertion + Both NMOS and PMOS are used
- All stages enter and exit “sleep” mode simultaneously
- LARGE sleep transistors
- High routing complexity and wiring overhead
1717 Low-Leakage Repeaters for NoC CommunicationsLow-Leakage Repeaters for NoC Communications ISCAS 2005
Repeaters with Repeaters with Per-Stage Sleep TransistorPer-Stage Sleep Transistor
• Distributed sleep transistors along the link • Each stage of repeaters has a separate pair of sleep transistors
+ One stage of repeaters is active - others are in low-leakage standby
- Sleep Transistor is heavily loaded and has to be scaled with link width
clk
1818 Low-Leakage Repeaters for NoC CommunicationsLow-Leakage Repeaters for NoC Communications ISCAS 2005
Repeaters with Repeaters with Per-Stage Sleep TransistorPer-Stage Sleep Transistor
• Distributed sleep transistors along the link • Each stage of repeaters has a separate pair of sleep transistors
+ One stage of repeaters is active - others are in low-leakage standby
- Sleep Transistor is heavily loaded and has to be scaled with link width
clk
active sleep sleep
1919 Low-Leakage Repeaters for NoC CommunicationsLow-Leakage Repeaters for NoC Communications ISCAS 2005
Repeaters with Repeaters with Per-Stage Sleep TransistorPer-Stage Sleep Transistor
• Distributed sleep transistors along the link • Each stage of repeaters has a separate pair of sleep transistors
+ One stage of repeaters is active - others are in low-leakage standby
- Sleep Transistor is heavily loaded and has to be scaled with link width
clk
activesleep sleep
2020 Low-Leakage Repeaters for NoC CommunicationsLow-Leakage Repeaters for NoC Communications ISCAS 2005
Repeaters with Repeaters with Per-Stage Sleep TransistorPer-Stage Sleep Transistor
• Distributed sleep transistors along the link • Each stage of repeaters has a separate pair of sleep transistors
+ One stage of repeaters is active - others are in low-leakage standby
- Sleep Transistor is heavily loaded and has to be scaled with link width
clk
activesleep sleep
2121 Low-Leakage Repeaters for NoC CommunicationsLow-Leakage Repeaters for NoC Communications ISCAS 2005
SR – Sleep RepeatersSR – Sleep Repeaters
Parallel link using individual zigzag sleep transistors:
• One sleep transistor per repeater + Smaller sleep transistors
+ Simpler routing
• Zigzag connection:• Only to transistors that are off during sleep
+ Number of sleep transistors is reduced by 50%
clk
X1/32 X1/32
X1/32
X1/32 X1/32
X1/32
01
0
01
0
2222 Low-Leakage Repeaters for NoC CommunicationsLow-Leakage Repeaters for NoC Communications ISCAS 2005
Sleep Repeater HighlightsSleep Repeater Highlights
Novel: Efficient sleep transistors for repeaters
Benefits
+ Effective leakage reduction during standby
+ Optimized structure according to specifics of repeater insertion
Drawbacks
- Area overhead
- Increased dynamic power consumption due to additional transistors
2323 Low-Leakage Repeaters for NoC CommunicationsLow-Leakage Repeaters for NoC Communications ISCAS 2005
Simulation SetupSimulation Setup
• 65nm BPTM models for transistors and interconnect
• 32-bit link operating at 105°C temperature
• LVT design was used as baseline for repeater insertion:
Scaling factor was adjusted for SVT, DTD and SR to meet the delay target equal to LVT
• Area, delay and energy were obtained for each of the compared techniques
20.4,
0.7inv
inv inv inv
int tint intrep rep
t t t int
C RC R Lk h a
R C C R
3π 3π 3πDriver
2424 Low-Leakage Repeaters for NoC CommunicationsLow-Leakage Repeaters for NoC Communications ISCAS 2005
Total Repeater AreaTotal Repeater Area
+ DTD smallest area
- SR largest area
2525 Low-Leakage Repeaters for NoC CommunicationsLow-Leakage Repeaters for NoC Communications ISCAS 2005
Energy vs. UtilizationEnergy vs. Utilization
• SVT: Least energy at high utilization
+ SR: Least energy at low utilization
8mm link
2626 Low-Leakage Repeaters for NoC CommunicationsLow-Leakage Repeaters for NoC Communications ISCAS 2005
Set Target Delay (D<Dopt)
Optimal K for minimal Leakage Power - Kleak
Find for which utilization rates k_leak or k_dyn is optimal
Optimal K for minimal Dynamic Power - Kdyn
Repeaters Sizing for (1<K<n)
!=
Calculate Ratio of Total Power for Kdyn and Kleak vs. Utilization
Utilization-Dependant Utilization-Dependant Optimal Number of RepeatersOptimal Number of Repeaters
2727 Low-Leakage Repeaters for NoC CommunicationsLow-Leakage Repeaters for NoC Communications ISCAS 2005
Optimal Number of RepeatersOptimal Number of Repeaters
• For each k a suitable sizing factor h is found to meet the target delay
• Optimal k for minimal leakage is kleak=4
• Optimal k for minimal dynamic power is kdyn=6
Power vs. k for target D=309ps (instead of Dmin=280ps), L=10mm
19
20
21
22
23
24
25
26
3 4 5 6 7 8 9 10
K (number of repeaters)
Pd
yn
[m
W]
2
3
4
5
6
7
8
9
10
Ple
ak
[m
W]
Pdyn
Pleak
kleak kdyn
example
2828 Low-Leakage Repeaters for NoC CommunicationsLow-Leakage Repeaters for NoC Communications ISCAS 2005
Number of Repeaters vs. Number of Repeaters vs. UtilizationUtilization
• Total power as function of utilization for Kdyn and Kleak
• Power ratio is calculated for Kdyn and Kleak
+ Break-even point is at 40% utilization
+ The results of Kleak are up-to 17% better at low utilization rates
Power ratio of Kdyn vs. Kleak
Prefer Kdyn
Prefer Kleak
example
2929 Low-Leakage Repeaters for NoC CommunicationsLow-Leakage Repeaters for NoC Communications ISCAS 2005
SummarySummary
DTD (Dynamic Dual-Threshold) Repeaters
SR (Sleep Repeaters)
• Zig-zag structure
SR least power at low utilization
• Thanks to low leakage
Optimal number of repeaters depends on link utilization
3030 Low-Leakage Repeaters for NoC CommunicationsLow-Leakage Repeaters for NoC Communications ISCAS 2005
Questions?Questions?