outline - brandon luciaa bug in an intermittent program main {while (true) {m, n =...

Outline

Energy-harvesting devices

Debugging intermittent programs

Energy-interference-free Debugger (EDB)

Evaluation: debugging with EDB

Related work and conclusion●

2

Anatomy of an Energy-Harvesting Computer

4

Energy Harvester Processor

Energy Harvesting DeviceEnergy Source

Capacitor

A Bug in an Intermittent Program

main { while (TRUE) {

m, n = get_last_two_elements(fib_list) append_element(fib_list, m + n) }}

Source Code: fibonacci.c

7

1 1

Expected program state Time Observed program state

Non-volatilememory

fib_list

1 1 2

1 1 2 3

1 1 2 3 5

tail

A Bug in an Intermittent Program

main { while (TRUE) {

m, n = get_last_two_elements(fib_list) append_element(fib_list, m + n) }}

Source Code: fibonacci.c

8

1 1 1 1

Expected program state Time Observed program state

Non-volatilememory

fib_list

1 1 2 1 1 2

1 1 21 1 2 3

1 1 2 3 5 1 1 2 3 8

3

tail

A Bug in an Intermittent Program

main { while (TRUE) {

m, n = get_last_two_elements(fib_list) append_element(fib_list, m + n) }}

Source Code: fibonacci.c

9

1 1 1 1

Expected program state Time Observed program state

Non-volatilememory

fib_list

1 1 2 1 1 2

1 1 21 1 2 3

1 1 2 3 5 1 1 2 3 8

3

implementation is not correct if interruptedtail

reboot

Debugging an Intermittent Program

Option Clog events on device

Option AJTAG debugger

Option BOscilloscope

10

Debugging an Intermittent Program

JTAG

gdb>WISP

Option Clog events on device

Option AJTAG debugger

Option BOscilloscope

Hides bugs

11

Debugging an Intermittent Program

JTAG

gdb>WISP WISP

Option Clog events on device

Option AJTAG debugger

Option BOscilloscope

Hides bugs No program state

12

Debugging an Intermittent Program

JTAG

gdb> WISPWISP WISP

Option Clog events on device

Option AJTAG debugger

Option BOscilloscope

13

Costs energy and spaceHides bugs No program state

Debugging an Intermittent Program

JTAG

gdb> WISPWISP WISP

Option Clog events on device

Option AJTAG debugger

Option BOscilloscope

14

EDB

Passiv

e

Inte

r-fe

renc

e -fr

e e

Interactive

Costs energy and spaceHides bugs No program state

Our main contribution is the design and implementation of EDB, an energy-interference-free debugger for intermittent energy-harvesting platforms.

EDB: Energy-interference-free Debugger

Energy-harvestingdevice

EDB

En

erg

y

Implementation possibilities:

● off board● on board● in silicon

15

Energy-harvesting Device

EDBMCU

Digital Level Shifters

USB host

Charge / Discharge Analog

Buffers

Vre

g

Vca

p

RFI

D I/O

Inte

rru

pt

Code M

ark

ers

UA

RT

EDB Capabilities

Passive

Trace energy level

Trace program events

Decode I/O messages

16

Active

Save energy level

Set energy level

Supply power

Mechanisms

EDB is energy-interference-free

Properties

2.0 2.5 3.0 3.5 4.0 4.5 5.01.7

1.8

1.9

2.0

2.1

2.2

2.3

2.4

Time (s)

Capa

Cap

aci

tor

Volt

ag

e (

V)

EDB Joins Energy and Program Events

EDB enables new debugging primitives

> break at line 42> break at voltage 1.85V> runBREAKPOINT at line 42, V=2.05V

> continueBREAKPOINT at line 64, V=1.85V

EDB console

Energy-awareWatchpoints

EnergyGuards

I/OMonitors

Keep-aliveAssertions

Energy State Program State

17

Outline

Energy-harvesting devices

Debugging intermittent programs

Energy-interference-free Debugger (EDB)

Evaluation: debugging with EDB

Related work and conclusion●

18

Evaluation Roadmap

Case studies: applying EDB to debugging tasks

● (I) Zero-cost instrumentation● (II) Keep-alive assertions● (III) I/O monitoring

Quantifying energy-interference

● Leakage current● Save-restore resolution

19

Evaluation Case-Study (I):Zero-cost Instrumentation

Program: generate a list of Fibonacci values

main:

while True: append(list, value)

broken_fibonacci.c

20

Evaluation Case-Study (I):Zero-cost Instrumentation

Program: generate a list of Fibonacci values

Problem: invalid values observed on harvested energy●

main:

while True: append(list, value)

broken_fibonacci.c

1 1 2 3 8

21

Evaluation Case-Study (I):Zero-cost Instrumentation

Program: generate a list of Fibonacci values

Problem: invalid values observed on harvested energy●

Approach: add an invariant check

main:

while True: append(list, value)

broken_fibonacci.c

ni = n

i-2 + n

i-1

1 1 2 3 8

22

Evaluation Case-Study (I):Zero-cost Instrumentation

Program: generate a list of Fibonacci values

Problem: invalid values observed on harvested energy●

Approach: add an invariant check

main:

while True: append(list, value)

broken_fibonacci.c

for value in list: assert(value is valid)

ni = n

i-2 + n

i-1

1 1 2 3 8

} invariant check on reboot

23

2.0

2.5

Loop

40 50 60 70 80 90 100

Volt

age (

V) 3.0

+ 40 + 50 + 60 + 70 + 80 + 90 + 100

Time (ms)

...

Evaluation Case-Study (II):Keep-Alive Assertions

main:

while True: append(...)

broken_fibonacci.c

26

unexpectedbehavior

main loopruns

Without EDB

later

Without EDB

2.0

2.5

Loop

40 50 60 70 80 90 100

Volt

age (

V) 3.0

+ 40 + 50 + 60 + 70 + 80 + 90 + 100

Time (ms)

...

Evaluation Case-Study (II):Keep-Alive Assertions

main:

while True: append(...)

broken_fibonacci.c

27

unexpectedbehavior

main loopruns

Without EDB

later

Without EDB

2.0

2.5

Loop

40 50 60 70 80 90 100

Volt

age (

V) 3.0

+ 40 + 50 + 60 + 70 + 80 + 90 + 100

Time (ms)

...

Evaluation Case-Study (II):Keep-Alive Assertions

main:

while True: append(...) assert(...)

broken_fibonacci.c

28

unexpectedbehavior

main loopruns

Without EDB

later

Without EDB

Diagnosis strategy

2.0

2.5

Loop

LoopLoop

40 50 60 70 80 90 100

2.0

2.5

3.0

Volt

ag

e (

V)

Volt

ag

e (

V)

Time (ms)

3.0

+ 40 + 50 + 60 + 70 + 80 + 90 + 100

1

Tethered power

...

...

Evaluation Case-Study (II):Keep-Alive Assertions

main:

while True: append(...) assert(...)

broken_fibonacci.c

29

EDB keep-alive assert brings the familiar primitive to energy-harvesting platforms.

Assertfailed

Interactivesession

Diagnosis strategy

With EDB

later

Without EDB

later

Without EDB

With EDB

unexpectedbehavior

main loopruns

1.6

1.8

2.0

2.2

2.4

3.5 4.0 4.5 5.0 5.5 6.0 6.5 7.0

RSP_GENERIC

CMD_QUERY

CMD_QUERYREP

5.10 5.15 5.20 5.25

Time (s)

RSP_GENERIC

CMD_QUERY

Volt

ag

e (

V)

Mess

ag

e ID

Evaluation Case-Study (III):Monitoring of RFID I/O

REQUESTS

REPLIES

EDB I/O monitorenables protocoldebugging.

corr

elat

ed

energy level

I/O

30

Messages that reached the device

Energy state

Evaluation Roadmap

Case studies: applying EDB to debugging tasks

● (I) Zero-cost instrumentation● (II) Keep-alive assertions● (III) I/O monitoring

Quantifying energy-interference

● Leakage current● Save-restore resolution

31

Evaluation: Energy-interference:Worst-case Leakage Current

Energy Level Sense & Set

Program Event Monitoring

EDB-TargetInterop

I/OMonitoring

Ileak

≤ 850 nA⋍ 0.4% of min. MCU current

32

MCU MCU\Code Markers

Power System

Charge Monitor

Drain

n

InterruptCmd Interface

I/O Device #1

I/O Device #d

Monitor Rx/Tx

Monitor Rx/Tx

RF In

DC+

-

I/O Monitoring Program Event Monitoring

EDBEnergy-harvesting

device

Debugger-Target Interop

Energy Monitoring & Manipulation

Sources of leakage current

Time (s)

Cap

aci

tor

Volt

ag

e (

V)

Save to 1.8V, tether at 2.3V, restore to 1.8V

Evaluation: Energy-interference:Save-Restore Accuracy

∆V error

EDB saves andrestores energylevel with a finiteprecision, limitedby hardware.

∆V = 54 mV ≋ 4% of energy capacity on WISP device (47µF)

33

Save energy level

Restore energy level

Tetherpower

Related Work

Intermittent computing

Emulation and simulation of energy sources

Debugging battery-powered wireless sensor nodes

Ekho [J. Hester, T. Scott, J. Sorber. SenSys ’14]

CRFID Crash Test Sim [J. Gummeson, S. Clark, K. Fu, D. Ganesan. MobiSys ’10]

Clairvoyant [J. Yang, M. L. Soffa, L. Selavo, K. Whitehouse. SenSys ’07]

Mementos [B. Ransford, J. Sorber, K. Fu. ASPLOS '11]

DINO [B. Lucia, B. Ransford. PLDI '15]

34

Conclusion

35

Energy-interference-free Debugger (EDB) is the first system to bring advanced debugging capabilities

to intermittent energy-harvesting platforms.

http://intermittent.systems/