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FlockLab : A Testbed for Distributed, Synchronized Tracing and Profiling of Wireless Embedded Systems. IPSN 2013 NSLab study group 2013/04/08 Presented by: Yu-Ting. Outline. Introduction Architecture Benchmark Application. Introduction.

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flocklab a testbed for distributed synchronized tracing and pro ling of wireless embedded systems

FlockLab: A Testbed for Distributed, SynchronizedTracing and Profiling of Wireless Embedded Systems

IPSN 2013

NSLab study group 2013/04/08

Presented by: Yu-Ting

outline
Outline
  • Introduction
  • Architecture
  • Benchmark
  • Application
introduction
Introduction
  • A testbed with 30 observers (4 at outdoors) and a set of servers
  • Support 4 different targets (nodes)
  • Other than serial port service,these nodes can synchronously:
    • Trace GPIO
    • Actuate GPIO
    • Power profiling
    • Adjust supply voltage
  • Much better than multiple logic analyzers, mixed-signal oscilloscopes, and power analyzers
outline1
Outline
  • Introduction
  • Architecture
  • Benchmark
  • Application
hardware

9 LEDs

By GPIO or UART

Hardware

5V for embedded Com

3.3V for others

1000 USD

Step: 0.1V

Can also control

USB fan foroutdoor nodes

Shunt resistor

Amplify the volt across shuntby a gain of 100

To profile power

CPU: 624MHz

RAM: 128MB

Flash: 32MB

8GB

This selection is doneby two 8-bitsignal translator

Map slot withtarget boardsby serial ID chiip

For outdoor nodes without Ethernet

more about measuring power
More about measuring power
  • Resolution in power: 10nA
  • Limit: 160mA (enough)
  • ADC sample at 56kHz in high-speed mode and 28kHz in high-resolution (SNR = 109dB) mode with 14.3MHz clock source=> resolution in time: 35.7us or 17.85us
software
Software
  • OS: OpenEmbedded Linux
  • NTP client: Chrony, synchronize every 1-2min with NTP server of FlockLab

Efficient data handling

(caching)

backend infrastructure
Backend Infrastructure
  • Time Synchronization server (NTP server)=> sync by another server on campus and PPS by GPS receiver
  • Web server
  • Test management server (also stores data)
  • Database server
  • Monitoring server
deployment
Deployment
  • Indoor * 26 (in same LAN segment)
  • Outdoor * 4
  • Yellow level: RSSI value when idle
outline2
Outline
  • Introduction
  • Architecture
  • Benchmark
  • Application
time accuracy gpio
Time Accuracy - GPIO
  • Use GPIO to trace PPS of same GPS clock
  • Use mixed-signal oscilloscope to actuate GPIO
  • Pairwise timing error
  • GPIO tracing VS PPS: normal distribution
time accuracy power profiling
Time Accuracy – Power Profiling
  • SFD rise -> toggle GPIO & turn on LEDSFD fall ->turn off LED
  • SFD events happen at the same time (< 1us)
  • Most error of same observer comes from random delay of GPIO event and the following power sample
  • Error of different observer is comparable topairwise timing error of GPIO events
power accuracy
Power Accuracy
  • Test by high-precision power analyzer
  • Target resistance: 259mΩAA batteries: 947mΩ
  • Calibration: Use linear regression to estimate more accurate constant of offset and gain of current-sense amplifier, and shunt resistor

Relative error: observer VS power analyzer

limits in capturing gpio events
Limits in Capturing GPIO Events
  • No new events can be captured until the respective flag is cleared
  • Minimum required interval between consecutive GPIO events to be captured=> depends on the interrupt delay and ISR execution time
  • SFD events may still loss for small packet(<9bytes)
outline3
Outline
  • Introduction
  • Architecture
  • Benchmark
  • Application
analysis of tasks without flocklab
Analysis of Tasks Without FlockLab
  • Generally speaking, they are:
    • More intrusive and less accurate
    • Need to recompile due to code changes
    • Need to change existing codes for different platform
  • Power profiling
    • Energest in Contiki, but also intrusive
    • Customize yourselves in TinyOS…
  • End-to-end delay
    • Timestamps in serial logging, but it’s inaccurate
    • Run time synchronization protocol=> Multiple protocols may cause performance losses or even failures
  • Actuate events (controlling) for multiple nodes
    • Also need time synchronization
  • Using network simulators like Cooja
comparative multi platform analysis
Comparative Multi-Platform Analysis
  • Run CTP on top of LPL: how each platform affects the trade-offs between metrics
  • Observation
    • 200ms is best for such topology & traffic load
    • Tmote Sky is most sensitive, while IRIS is best
    • The trades are the same
finding and fixing bugs
Finding and Fixing Bugs
  • Bug: the initial results with LPL wake-up intervals of 500 ms and 1s from Tinynodeand Opal nodes were significantly worse
  • Reason: children were transmitting at most one packet during an LPL wake-up interval, although they had multiple packets ready to be sent
controlling and pro ling applications
Controlling and Profiling Applications
  • Purpose
    • One node to generate a packet every 2s for 260s, from t = 30s to t = 290s
    • In the mean time, measure the energy consumption
  • Task 1 is easily done by GPIO actuation
  • Comparison of task 2 between different methods
    • FlockLab is non-intrusive and highly accurate
measuring clock drift
Measuring Clock Drift
  • Enable FTSP every 3s and get the clock drifts of each node compared with the root
  • Toggle a GPIO pin every 0.5s
  • Compare the difference between GPIO timestamp interval and 0.5s with clock drifts
    • Average over 5min to limit GPIO timing errors