Part II: Platforms, Energy and OS

1. Part II: Platforms, Energy and OS

2. Outline Platforms Energy consumptions TinyOs

3. Sensor Platforms (Processing) • Crossbow mote family • IRIS, MICAz, MICA2 , Imote2, TelosB, Cricket Module • Sun Spots • UCLA iBadge • MIT’s AMPs • Many more others • RSC WINS & Hidra Sensoria WINS • UCLA’s Medusa MK-II

4. Platform Examples Cricket IRIS MicaZ Sun Spots Mica2 TelosB Imote2

5. Mica2 Characteristics Mica2

6. MicaZ MicaZ

7. TelosB Characteristics TelosB

8. Imote2 Characteristics Imote2

9. IRIS Characteristics IRIS

10. Important Differences between Platform

11. Sensor Boards Ambient light, Temperature Accelerometer (2 Axis, 3Axis) Barometric pressure GPS Magnetic field Microphone Photo-sensitive light Photoresistor, thermistor sensor And many others…

12. Outline Platforms Energy consumptions TinyOs

13. Where Does the Energy Go? • Processing • excluding low-level processing for radio, sensors, actuators • Radio • Sensors • Actuators • Power supply

14. Processing • Common sensor node processors: • Atmel AVR, Intel 8051, StrongARM, XScale, ARM Thumb • Power consumption all over the map, e.g. • 16.5 mW for ATMega128L @ 4MHz • 75 mW for ARM Thumb @ 40 MHz • Low-power ≠ energy-efficiency! • 242 MIPS/W for ATMega128L @ 4MHz (4nJ/Instruction) • 480 MIPS/W for ARM Thumb @ 40 MHz (2.1 nJ/Instruction) • Power management to exploit energy efficiency • Idle and sleep modes, variable voltage and frequency II-14

15. Radio Energy per bit in radios is a strong function of desired communication performance and choice of modulation Range and BER for given channel condition (noise, multipath and Doppler fading) Watch out: different people count energy differently Mote’s RFM radio is only a transceiver, and a lot of low-level processing takes place in the main CPU While, typical 802.11b radios do everything up to MAC and link level encryption in the “radio” Transmit, receive, idle, and sleep modes Variable modulation, coding Currently around 150 nJ/bit for short ranges More later… II-15

16. Computation & Communication Radios benefit less from technology improvements than processors The relative impact of the communication subsystem on the system energy consumption will grow Energy breakdown for MPEG Energy breakdown for voice Decode Decode Transmit Encode Encode Receive Receive Transmit Processor: StrongARM SA-1100 at 150 MIPS Radio: Lucent WaveLAN at 2 Mbps II-16

17. Sensing Several energy consumption sources transducer front-end processing and signal conditioning analog, digital ADC conversion Diversity of sensors: no general conclusions can be drawn Low-power modalities Temperature, light, accelerometer Medium-power modalities Acoustic, magnetic High-power modalities Image, video, beam forming II-17

18. Actuation • Emerging sensor platforms • Mounted on mobile robots • Antennas or sensors that can be actuated • Some thoughts: • Actuation often done with fuel, which has much higher energy density than batteries • E.g. anecdotal evidence that in some UAVs the flight time is longer than the up time of the wireless camera mounted on it • Actuation done during boot-up or once in a while may have significant payoffs • E.g. mechanically repositioning the antenna once may be better than paying higher communication energy cost for all subsequent packets • E.g. moving a few nodes may result in a more uniform distribution of node, and thus longer system lifetime II-18

19. Radio Energy Management During operation, the required performance is often less than the peak performance the radio is designed for Leading to duty-cycle Tx Rx ? ? time II-19

20. Energy in Radio: the Deeper Story…. Wireless communication subsystem consists of three components with substantially different characteristics Their relative importance depends on the transmission range of the radio Tx: Sender Rx: Receiver Incoming information Outgoing information Channel Power amplifier Transmit electronics Receive electronics II-20

21. Examples Nokia C021 Wireless LAN Medusa Sensor Node (UCLA) GSM nJ/bit nJ/bit nJ/bit ~ 50 m ~ 10 m ~ 1 km • The RF energy increases with transmission range • The electronics energy for transmit and receive are typically comparable II-21

22. Energy Consumption of the Sender Parameter of interest: energy consumption per bit Tx: Sender Incoming information RFDominates Electronics Dominates Energy Energy Energy Transmission time Transmission time Transmission time II-22

23. Outline Platforms Energy consumptions TinyOs

24. TinyOS Overview Application = scheduler + graph of components Compiled into one executable Event-driven architecture Single shared stack No kernel/user space differentiation Main (includes Scheduler) Application (User Components) Actuating Sensing Communication Communication Hardware Abstractions

25. TinyOS Component Model Component has: Frame (storage) Tasks: computation Interface: Command Event Frame: static storage model - compile time memory allocation (efficiency) Command and events are function calls (efficiency) Messaging Component Internal State Internal Tasks Commands Events

26. TinyOS Two-level Scheduling Tasks do computations Unpreemptable FIFO scheduling Bounded number of pending tasks Events handle concurrent dataflows Interrupts trigger lowest level events Events prempt tasks, tasks do not Events can signal events, call commands, or post tasks Tasks Preempt POST FIFO events commands commands Interrupts Time Hardware

27. How to Handle Multiple Data Flows? Data are handled by A sequence of non-blocking event/command (function calls) through the component graph Post tasks for computations that are not “emergent” Preempting tasks to handle new data http://tinyos.millennium.berkeley.edu

28. A Complete Application sensing application application Routing Layer routing Messaging Layer messaging Radio Packet packet Radio byte (MAC) Temp byte photo SW HW RFM ADC i2c bit clocks

29. Receiving a Message Timing diagram of event propagation How to make sure all the events/tasks are processed in time?

30. Handling Network Messages Socket/TCP/IP? Too much memory for buffering and threads Data are buffered in network stack until application threads read it Application threads blocked until data is available Transmit too many bits (sequence #, ack, re-transmission) Tied with multi-threaded architecture TinyOS solution: active messages http://tinyos.millennium.berkeley.edu

31. Active Message Every message contains the name of an event handler Sender Declaring buffer storage in a frame Naming a handler Requesting Transmission Done completion signal Receiver The event handler is fired automatically in a target node No blocked or waiting threads on the receiver Behaves like any other events Single buffering http://tinyos.millennium.berkeley.edu

32. Power Breakdown… Lithium Battery runs for 35 hours at peak load and years at minimum load! That’s three orders of magnitude difference! A one byte transmission uses the same energy as approx 11000 cycles of computation. Panasonic CR2354 560 mAh http://tinyos.millennium.berkeley.edu

33. Time Breakdown… 50 cycle thread overhead (6 byte copies) 10 cycle event overhead (1.25 byte copes) Components Packet reception work breakdown CPU Utilization Energy (nj/Bit) AM 0.05% 0.20% 0.33 Packet 1.12% 0.51% 7.58 Ratio handler 26.87% 12.16% 182.38 Radio decode thread 5.48% 2.48% 37.2 RFM 66.48% 30.08% 451.17 Radio Reception - - 1350 Idle - 54.75% - Total 100.00% 100.00% 2028.66 http://tinyos.millennium.berkeley.edu

34. Grading TinyOS Small memory footprint  Non-preemptable FIFO task scheduling Power efficient  Put microcontroller and radio to sleep Efficient modularity  Function call (event, command) interface between components Concurrency-intensive operations  Event-driven architecture Efficient interrupts/events handling (function calls, no user/kernel boundary) Real-time  Non-preemptable FIFO task scheduling NO real-time guarantees or overload protection http://tinyos.millennium.berkeley.edu