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, MatthiasLippunerAndres Gomez, Luca Benini, Lothar Thiele
Designing Reliable Transient Applica�ons
Dept. Electrical Engineering and Information Technology, ETH Zürich
Institut für Integrierte SystemeIntegrated Systems Laboratory
Energy harvesting is a clean, long-term supply of relatively low and volatile power.
Burst-based application design can operate efficiently over a wide input power range.
Burst-based design must satisfy certain constraints to provide application reliability:
Transient camera applicationsEnergy bursts
Experimental evaluation
Intermittent power and reliable execution can co-exist
t
Vcap
Vload,min
Vmax
cold-start energy build-up
taskexecution
tsleep ton
Power ranges
Energy Conservation:
Eactive = ηsystem * EinPin ∝
Pactive
ton
tsleep1) 2)
Quantized energy transfer [1]
Maximizes task-level energy efficiency.
Power-point tracking for both source and load.
Guarantees atomic task execution.
Optimizes capacitor size for reduced wake-up times.
Transducers(area = 1 cm2)
MCU's(Factive=1MHz)
Sensors(active)
Radios(PTX,avg: 0/10 dBm)
100nW
1µW
1mW
100mW
10µW
100µW
10mW
1W
Energy scalability
Motion estimation using MSP432
[1] A. Gomez et al. "Dynamic Energy Burst Scaling for Transiently Powered Systems," Proc. DATE Conf. 2016.
[2] A. Gomez et al. "Efficient Long-Term Logging of Rich Data Sensors using Transient Sensors Nodes," ACM Trans. Embed. Comput. Syst. 2017.
[3] A. Gomez et al. "Wearable, Energy-Opportunistic Vision Sensing for Walking Speed Estimation," Proc. SAS. 2017.
Minimum energy availability - necessary to guarantee application progress.
Temporal independence - necessary for functional correctness.
Non-volatility - necessary to guarantee data dependencies between bursts.
2)Walking speed estimation [3]
Track pixel displacement to estimateuser's walking speed.
1) Long-term logging [2]
Non-Volatile Memory Hierarchy (NVMH)reduces costs of logging images to SD Card.
Burst-based application using NVMH:
0 2 4 6 8 10 120
1
2
3
4
5
add DEBS
add NVMH
← better Energy per Image Stored [mJ]
←be
tter
Cap
acitor
Size[m
F]
Single BurstDEBS onlyNVMH onlyDEBS+NVMH
MCU
ADC
FlashDMA SPI
Application Circuit
digital controlanalog data
Energy Flow
Control Signals
StonymanCameraSolar
CellEMU
FRAM
Data Flow
GPIO
Transient Camera
Camera Schematic:
Wearable Prototype:
500 1000 1500 2000 2500 3000Frame Number
-101234567
Posit
ion in
x-Di
recti
on (m
)
block size = 96block size = 48block size = 32block size = 16Reference Points
Controlled displacement to measure accuracy:
Camera mounted on trolley without power constraints.
Accumulated error: 57 cm over 42 m.
0 20 40 60 80 100 120 140 160 180Estimation Number
0
0.5
1
1.5
2
Estim
ated
Vel
ocity
(m/s
)
raw datalow-pass filtered data
standing walking slowly standing walkingfast
st.
Real-world experiment to estimate walking speed.
Burst-based design guarantees functionalityindependently of harvester's properties.
Harvester selection relates only to application's performance (execution rate).
Efficient EMU design can minimize therequired harvester area for a desired performance.
0 500 1000 1500 2000 2500
101
102
103
Input Power [µW]
Start-UpTim
e[s]
Single Burst (2 000µF)DEBS Only (1 470µF)NVMH only (4 300µF)DEBS+NVMH (3300µF)
0 500 1'000 1'500 2'0000
5
10
15
20
25
Illuminance [lx]
Imag
esSt
ored
/Tim
e[m
in−
1] Apanel = 8 cm
2
Apanel = 28.5 cm2
Apanel = 42 cm2
Cost vs performance trade-offs
Dynamic Energy Burst Scaling (DEBS) canreduce the capacitance and the cost per image.
NVMH can reduce the cost per image further,but requires a larger capacitance.
Long-term logging using MSP430FR
Evaluate cost/performance of different EMUconfigurations for a long-term logging app.For each, there is an associated:
- Minimum energy guarantee (capacitance).
- Cost for storing an image.
- NVMH was configured with Nimg=10.
...FRAMAcquisition
Burst 1
SD init SD flush
Burst Nimg
FRAMAcquisition
Burst Nimg+1
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