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Lecture 1: Hardware Platforms

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Title: Lecture 1: Hardware Platforms


1
Lecture 1 Hardware Platforms
  • Anish Arora
  • CIS788.11J
  • Introduction to Wireless Sensor Networks
  • Thanks to
  • Hui Cao, Emre Ertin, Brian Dupaix

2
Outline
  • Brief overview of hardware platform architecture
  • Case study 1 XSM platform
  • Case study 2 XSS (Stargate) platform
  • Readings
  • The platforms enabling wireless sensor networks
  • XSM SPOTS paper
  • System architecture directions for networked
    sensors
  • Next Century Challenges Mobile Networking for
    "Smart Dust"

3
Requirements
  • Cost
  • Lifetime (when almost always on, when almost
    always off)
  • Performance
  • Speed (in ops/sec, in ops/joule)
  • Comms range (in m, in joules/bit/m)
  • Memory (size, latency)
  • Capable of concurrent operation
  • Flexibility (?)
  • Reliability, security, size, packaging

4
Types of sensor-actuator hardware platforms
  • RFID equipped sensors
  • Smart-dust tags
  • typically act as data-collectors or trip-wires
  • limited processing and communications
  • Mote/Stargate-scale nodes
  • more flexible processing and communications
  • More powerful gateway nodes, potentially using
    wall power

5
A Closer Look
6
A Generic Sensor Network Architecture
PROCESSING SUB-SYSTEM
COMMUNICATION SUB-SYSTEM
SENSING SUB-SYSTEM
POWER MGMT. SUB-SYSTEM
ACTUATION SUB-SYSTEM
SECURITY SUB-SYSTEM
7
Processing Subsystem
  • Microcontroller
  • von Neumann architecture (same address and data
    bus)
  • typical 4 bit, 8 bit, 16 bit or 32 bit
    architectures
  • speed 4 MHz-400MHz with 10-300 or more MIPS
  • operate at various power levels
  • fully active 1 to 50 mW
  • sleep (memory standby, interrupts active, clocks
    active, cpu off)
  • sleep (memory retained, interrupts active, clocks
    active, cpu off)
  • sleep (memory retained, interrupts active, clocks
    off, cpu off) 5uW
  • latency of wakeup is an issue
  • fixed point or floating point operations
  • multiple processors may be used (potentially on
    same core)
  • could be DSP, FPGA

8
Processing Subsystem Memory
  • Considerations Speed, capacity, price, power
    consumption, memory protection
  • SRAM typical, 0.5KB-64MB
  • Typical power consumption
  • retained 100ua read/write 10ma if separate
    chip
  • retained 2ua-100ua, read/write5ma if in core
  • DRAM high power consumption in retained mode
  • EEPROM4KB-512KB, often used as program store
  • Flash 256KB-1GB or beyond
  • Typical power consumption
  • retained negligible read/write 7/20ma
  • erase operation is expensive
  • Large flashes are outside of core

9
Processing Subsystem (contd.)
  • Peripheral interfaces
  • (for sensors, actuators, I/O, power)
  • (whether analog and digital)
  • (multiple busses with bridges between them)
  • SPI Serial Peripheral Interface
  • I2C
  • UART Serial communication
  • USB
  • PCI
  • Clocks
  • Hardware Timers
  • Dividers

10
Processing Subsystem Peripherals
  • Interrupts
  • Asynchronous breaks in program execution
  • Press of a button expiration of a timer
    completion of sensing data collection, of DMA
    transfer, of transmission event,
  • When interrupt occurs, processor transitions to
    the corresponding interrupt handler to service
    interrupt and then resumes execution
  • Can have multiple priority levels
  • Interrupts are enabled and disabled through
    registers for each peripheral
  • I/O Ports
  • General Purpose Input Output pins (GPIO)

11
Hardware Timers
Holds the value that initializes the timer at
startup
Holds value to compare against
Controls the mode (interval or one-shot) Starts
and stops the timer Enables/disables the
interrupts for this timer
12
Clock Dividers
13
Sensor Subsystem
  • Multiple types of sensors may be used
  • Environmental pressure, gas composition,
    humidity, light
  • Motion or force accelerometers, rotation,
    microphone, piezoresistive strain, position
  • Electromagnetic magnetometers, antenna, cameras
  • Chemical/biochemical
  • Digital or analog output
  • MEMS enabling size, cost and power
    miniaturization nano coming
  • Components
  • Transducer
  • Analog signal conditioning circuits
  • Analog to digital conversion
  • Digital signal processing

14
Sensor Subsystem Considerations
  • Energy consumption in active/passive mode is
    relevant
  • Sampling rate (1Hz or lower to 5Khz or higher)
  • Signal resolution
  • ADC bits 8, 10, 12, 16, 20 bit (affects cost)
  • On-chip or not
  • Sensitivity, drift, offset
  • Sensor calibration or reset frequency
  • Interference, cross-talk

15
Sensor Subsystem
  • Wakeup circuits help reduce power consumption of
    processing
  • But startup time/power cycling latencies become
    an issue (1ms-1000ms or higher)
  • DMA of acquired sensor information is possible
  • Connector requirements positive contact,
    flexibility, robustness

16
Actuation Subsystem
  • Types
  • Leds, buzzers, motors, sliders, pumps, gears,
    solenoids
  • Energy consumption (idle O(uW) active 1-40 mW)
  • Startup time (1ms-1000ms or higher)
  • Higher voltage planes and noise
  • Coupling
  • Opto-coupler for control
  • communications, with
  • encoders for feedback
  • PWM drivers

17
Power Management Subsystem
  • Voltage regulator
  • typical ranges 1.8V, 3.3V, 5V
  • multiple voltages for various subsystem/power
    levels
  • Gauges for voltage or current
  • battery monitor (allows software to adapt
    computation)
  • Control of subsystems wakeup/sleep
  • latency is key in driving down the duty cycle
  • Control of platform clock rate, processor voltage
  • Run auxiliary hardware components from low speed
    oscillators (typically 32kHz)
  • perform ADC conversions, DMA transfers, and bus
    operations while microcontroller core is stopped

18
Power Management Subsystem
  • Energy source
  • volume energy density, mass energy density
  • peak and average current (discharge rate)
  • NiCd, NiMH, LiIon, LiPolymer, fuel cells
  • DC-DC conversion
  • Charger/energy harvesting/scavenging
  • solar, wind, vibration, heat
  • account for variations in supply
  • number of charge/discharge cycles have limits
  • Power supply may be external

19
Communication Subsystem
  • Considerations
  • speed, range, power consumption, startup time
  • energy efficiency joules/bit/m
  • signal propagation and interference
    characteristics
  • difference between receive power versus transmit
    power
  • not all devices need a receiver
  • choice of power level
  • antenna design
  • matching impedance

20
Communication Subsystem
Idle current
Startup time
Energy per bit
21
Communication Subsystem (contd.)
2.5 ms
1 10 ms typical
22
Security Subsystem
Some COTS radios offer security features
23
II. XSM node platform
  • Derived from Mica2 mote
  • Better sensor actuator range
  • 4 Passive Infrared 25m for SUV
  • Sounder 10m
  • Microphone 50m for ATV
  • Magnetometer 7m for SUV
  • Better radio range 30m
  • Other features
  • Grenade timer
  • Wakeup circuits (Mic, PIR)
  • Adjustable frequency sounder
  • Integrated Mag Set/Reset

24
XSM Processing Sub-System
  • Inherited from Mica2
  • Atmel AVR ATMEGA128L
  • RISC Architecture
  • 8 bit ALU/data-path
  • 128 KB FLASH Code
  • 4 KB SRAM Data
  • 512 Kb FLASH Storage
  • Peripherals
  • Clocks 7.37 MHz, 32KHz
  • UART 2400 bps to 115 kbps
  • SPI up to 1 Mbps
  • I2C up to 400 kbps, EEPROM, IO extenders, ADC
    converters, sensors, etc
  • Timer
  • Two 8-bit timers
  • Two 16-bit timers
  • Interrupts
  • LED 3 (green, yellow, red)

25
XSM Sensing Sub-System on Board
  • Passive infrared
  • Long range (15m)
  • Low power (10s of uW), 1s startup latency
  • Wide FOV (360 degrees with 4 sensors)
  • Gain 80dB
  • Hardware wakeup detector on-board
  • Microphone
  • LPF fc 100Hz 10kHz
  • HPF fc 20Hz 4.7kHz
  • Gain 40dB 80dB (100-8300)
  • Hardware wakeup detector on-board
  • Magnetometer
  • High power, .41ms startup latency
  • Gain 86dB (20,000)
  • Photo and Temperature
  • Accuracy 0.01oC

10 bit ADC
26
XSM Acoustics Sensing
27
XSM Communication Sub-System
  • Inherited from Mica2
  • ChipCon CC1000
  • No buffering (!)
  • Range 100s of feet
  • Frequency selectable from 300-1000 MHz, but board
    set to operate in 433 MHz band
  • FSK modulation w/ data rates 38.4 kbps, up to
    76.8 kbps
  • Hardware based Manchester encoding
  • Integrated bit synchronizer

28
XSM Radio Performance
29
XSM Power Management
  • Low-power operation 15 mW _at_ 4 MHz
  • Multiple sleep modes
  • Idle Mode 6 mW
  • CPU OFF, all peripherals ON
  • CPU woken up by interrupts
  • Power Down Mode 75 uW
  • CPU and most peripherals OFF
  • External Interrupts, 2 Wire Interface, Watchdog
    ON
  • Power Save Mode 120 uW
  • Similar to Power Down
  • Timer0 continues to run asynchronously

30
XSM Reliability through the Grenade Timer
  • Once started
  • You cant turn it off
  • You can only speed it up
  • Implementation

31
III. XSS (Stargate) Node Platform
32
Stargate
33
Stargate Architecture
34
XSS Processing Sub-system
  • PXA255 processor based on XScale
    microarchitecture
  • Successor to StrongARM family
  • Variable clock (100 - 400 MHz), less than 500 mW
    power
  • 64MB RAM, 32M Flash

35
XSS Communication Subsystem
36
XSS Communication Subsystem
  • Bluetooth
  • 2.4 GHz band, FHSS, Master-Slave arch., 0 to 20
    dBM
  • Connection oriented 3 seconds to form
    connection
  • Remote wakeup feature available
  • Event driven power management
  • 802.11
  • PCMCIA or Compact Flash slot available
  • Enables interaction with the Internet
  • Several wireless manipulation tools available
  • Wireless extensions API
  • HostAP driver
  • Enables a Stargate to act as an access point

37
XSS Mote interface
  • 51 pin mote connector
  • Talks to mote over the UART
  • Other GPIO lines connected to mote
  • Enables Stargate to act as a sensor network
    gateway

38
XSS Power Management Subsystem
Power gating provided for Bluetooth and 802.11
radios Overcomes inefficiencies in shutdown
modes of the radios Decreases shutdown mode
power of 802.11 card from 250mW to 1mW
Increases wakeup latency since radio needs to be
powered up first Gas gauge permits measurement
of battery voltage and current Enables battery
state aware energy management
39
XSS Power Management Subsystem (cont.)
40
Recent 802.15.4 Platforms
  • Focused on low power
  • Sleep - Majority of the time
  • Telos 2.4mA
  • MicaZ 30mA
  • Wakeup
  • Telos 290ns typical, 6ms max
  • MicaZ 60ms max internal oscillator, 4ms external
  • Process
  • Telos 4MHz 16-bit
  • MicaZ 8MHz 8-bit
  • TI MSP430
  • Ultra low power
  • 1.6mA sleep
  • 460mA active
  • Standards Based
  • IEEE 802.15.4, USB
  • IEEE 802.15.4
  • CC2420 radio
  • 250kbps
  • 2.4GHz ISM band
  • Ease of development and Test
  • Program over USB
  • Std connector header

UCB Telos
Xbow MicaZ
41
Telos rev B, aka TelosB
  • Standards Based
  • USB
  • IEEE 802.15.4
  • CC2420, 250kbps at 2.4GHz
  • Features
  • TI MSP430
  • 10kB RAM, 4Mhz 16-bit RISC, 48K Flash
  • 12-bit ADC and DAC (200ksamples/sec)
  • DMA transfers while CPU off
  • Integrated antenna
  • Standard IDC connectors

42
Front of mote
43
Back of mote
44
Processing subsystem block diagram
45
Block diagram
46
TelosB Power Consumption
47
Popular Nodes Overview
48
Manufacturers of Sensor Nodes
  • Intel Research
  • Stargate2, iMote, psiMote
  • Crossbow (www.xbow.com)
  • Mica2 mote, Micaz, Dot mote and Stargate Platform
  • Sentilla (www.sentilla.com) prev. Moteiv
    (www.moteiv.com)
  • Ember (www.ember.com)
  • Integrated IEEE 802.15.4 stack and radio on a
    single chip
  • Millenial Net (www.millenial.com)
  • iBean sensor nodes
  • Dust Inc
  • Smart Dust
  • Cogent Computer (www.cogcomp.com)
  • XYZ Node (CSB502) in collaboration with
    ENALAB_at_Yale
  • Sensoria Corporation (www.sensoria.com)
  • WINS NG Nodes

49
Units to keep in mind
  • Energy
  • (work done when force of 1 newton moves the point
    of its application a distance of 1 meter in
    direction of force) Joules
  • (electricity) milli Watt hours 1mWhr 3.6J
  • (thermal) Calories 1cal4.1868J
  • Power
  • (rate of energy conversion) milli Watts
  • 1W when one ampere flows through a potential
    difference of one volt
  • Charge
  • milli Ampere hours

50
References
  • TMote DataSheet (www.moteiv.com)
  • Atmel ATMEGA128L DataSheet (www.atmel.com)
  • ChipCon CC1000 DataSheet (www.chipcon.com)
  • RFM TR1000 DataSheet (www.rfm.com)
  • XBow Corp. (www.xbow.com)
  • J. Hill et.al., A wireless embedded sensor
    architecture for system-level optimization, ISCA
  • J.Polastre et.al.,Wireless Sensor Networks for
    Habitat Monitoring, WSNA02
  • J.Polastre et.al., The Mote Revolution Low
    Power WSN Devices
  • TinyOS Web (http//www.tinyos.net)
  • Andreas Savvides (http//www.eng.yale.edu/enalab/c
    ourses/eeng460a)
  • Vijay Raghunathan (http//nesl.ee.ucla.edu/courses
    /ee202a/2003f/lectures/GP03_Vijay.ppt)
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