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 1

Outline Introduction Architecture Benchmark Application 2

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 3

Outline Introduction Architecture Benchmark Application 4

Hardware 5 CPU: 624MHz RAM: 128MB Flash: 32MB 8GB For outdoor nodes without Ethernet To profile power Can also control USB fan for outdoor nodes 5V for embedded Com 3.3V for others Step: 0.1V 9 LEDs By GPIO or UART This selection is done by two 8-bit signal translator 1000 USD Shunt resistor Amplify the volt across shunt by a gain of 100 Map slot with target boards by serial ID chiip

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 6

Software OS: OpenEmbedded Linux NTP client: Chrony, synchronize every 1-2min with NTP server of FlockLab 7 Efficient data handling (caching)

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 8

Deployment Indoor * 26 (in same LAN segment) Outdoor * 4 Yellow level: RSSI value when idle 9

Outline Introduction Architecture Benchmark Application 10

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 11

Time Accuracy – Power Profiling SFD rise -> toggle GPIO & turn on LED SFD 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 to pairwise timing error of GPIO events 12

Power Accuracy Test by high-precision power analyzer Target resistance: 259mΩ AA batteries: 947mΩ Calibration: Use linear regression to estimate more accurate constant of offset and gain of current-sense amplifier, and shunt resistor 13 Relative error: observer VS power analyzer

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) 14

Outline Introduction Architecture Benchmark Application 15

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 16

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 17

Finding and Fixing Bugs Bug: the initial results with LPL wake-up intervals of 500 ms and 1s from Tinynode and 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 18

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 19

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 20

Multi-Modal Monitoring at Network Scale 21

Q&A 22