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Berkeley COMPSCI 252 - Power evaluation of SmartDust remote sensors

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Power evaluation of SmartDust remote sensorsApplication: remote sensorPlatform: SmartDustMappingInitial evaluationExperimental setupMeasurementsExplorationMethodology: Power aware simulatorResults and conclusionsAcknowledgmentsSpring 2000, 4/27/00 Power evaluation of SmartDust remote sensorsCS 252 Project PresentationRobert SzewczykAndras FerenczSpring 2000, 4/27/00 Application: remote sensor•Periodic measurements–light, temperature, humidity•Data processed in the infrastructure–thin client model–communication is necessary•Participation in routing protocols•Unattended mode of operationSpring 2000, 4/27/00 Platform: SmartDust•Low-power wireless communication–RFM TR1000 transceiver, bit-level interface•Range of digital and analog sensors–Light sensor - photo resistor–Temperature sensor - I2C interface•Low-power microcontroller –ATMEL AVR 90LS8535, Harvard architecture, 8KB program, 512 byte dataSpring 2000, 4/27/00 Mapping•TinyOS framework–software modules consisting of•event handlers•threads to perform arbitrary computation asynchronously–hardware abstraction or replacement•RFM bit-level interface•byte-level radio interface, similar to UART–active message-like communication scheme and execution model•Crucial resource: energySpring 2000, 4/27/00 Initial evaluation•Methodology: –logic analyzer timing diagrams–processor power consumption from datasheets–RFM power measurements•Wireless communication costs–2.0 μJ/bit radio cost–software costs, going from bits to bytes: 690 nJ/bit–longest path through the time-critical code: 40 μs–communicating processor at 4MHz idle 50% of the time –radio draws constant power regardless of data ratesSpring 2000, 4/27/00 Experimental setup•Tools–HP 16550A logic analyzer–HP 16532A digital oscilloscope–2.84V DC power supply •Current measurements–10 Ohm 5% tolerance in series with mote–data point extraction from oscilloscope images–typical settings: 1 ms total interval analyzed, dynamic range: 160 mV–differential analysis to extract contributions of individual components–typical variation of successive experiments: 5%Spring 2000, 4/27/00 MeasurementsInstruction typeEnergy per cycle (nJ)Energy per instr (nJ)idle 1.70 1.70noop 3.39 3.39arithmetic/ logic3.41 3.41memory read*3.66 7.32memory write*3.75 7.50Device Energy per CPU cycleEnergy per quantumLED 1.89 1.89 nJ/cyclePhoto 0.08 - 0.28 0.08 - 0.28 nJ/cycleADC 0.36 - 0.30 4.62 - 3.95 nJ/conversionRMF send 100 μs pulse2.56 2050 nJ/bitRFM receive 2.44 1950 nJ/bitAVR 90LS8535, 2.84 [email protected] *memory instructions take 2 cyclesSpring 2000, 4/27/00 Exploration•Implications–current configuration: data rates up to 25Kbps or can reduce clock speed by a factor of 2–dedicate a more sophisticated interface to the radio–speed up the transmission rate: transmit and turn off•Research question:–should we dedicate a separate microcontroller to each IO device?–Evaluate 2 processor system: •a processor dedicated to the radio •a processor dedicated to other sensors•UART communication between subsystems•scale frequency and voltage to minimize power usageSpring 2000, 4/27/00 Methodology: Power aware simulator•ATMEL AVR instruction-set simulator–power-aware•incorporate the measurements from the real system–IO device simulation•timers, pins, and UART•use per cycle energy data from the real measurements–thread safe (need to simulate a multiprocessor system)•Communication system–Initially a UART evaluation–Shared memory models•TinyOS application–TinyOS naturally supports a multiprocessing environment–split the application at the byte-level radioSpring 2000, 4/27/00 Results and conclusions•Simulator status–tested single processor configuration, agreement with empirical measurements–dual processor configuration in progress•Estimates–RFM processor - run at 2MHz, 5% idle, require 3mA current–Master processor - can run as slow as 200kHz, in order to handle peripherals –Inter-processor communication costs related to interconnect are small (cf. UART data)–Inter-processor communication costs related to software overhead are significant (interrupt handling, busy waiting or inability to power-down)Spring 2000, 4/27/00 Acknowledgments•SmartDust members–Kris Pister, Seth Hollar •TinyOS (ASPLOS 2000 submission)–David Culler, Jason Hill, Rob Szewczyk, Alec


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