Crossbow: Smarter Sensors in Silicon

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Crossbow Smarter Sensors in Silicon

• Johann Ammerlahn

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Crossbow Platform Review

• Overview and Goals
• History
• Design Approach
• Current System
• Hardware
• Software
• Future Directions

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Overview and Goals

• Big Idea Ubiquitous sensing
• How?
• Necessarily cheap
• This is the military. Cheap is relative.
• Necessarily small
• (more survivable, low profile, etc.)
• Necessarily many
• (economies of scale, higher measurement
  granularity, lower power comms, etc.)
• Necessarily robust
• Common case no maintenance

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Crossbow Mote History

Network Embedded Systems Technology Program
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Hardware Development Cycle
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Current Design Analysis Mica Series

• Integrate sensors, computation and communication
  in single unit
• Basic board has radio, processor, memory
• Sandwich sensor boards in layers
• Just like the rockgreat cleavage
• Open-source hardware/software concept
• Software is TinyOS (TOS) and TinyDB (TDB)
• Hardware design and Intel networking technology
  is licensed to Crossbow
• Modular design allows fast development

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Available Mote Designs MICA

• Crossbow 2nd generation wireless sensor, 4th from
  Berkeley Labs
• Atmel ATMEGA103/128L
• 4 Mhz 8-bit CPU
• 128KB Instruction Memory
• 4KB SRAM and EEPROM
• 4 Mbit flash (AT45DB041B)
• SPI interface
• 1-4 uj/bit r/w
• RFM TR1000 Radio (916/433 MHz)
• 50 kb/s ASK
• Focused hardware acceleration
• 1 to 300 ft. range, RSSI
• 51-pin connector
• Analog ADC comparators, I2C, SPI, interrupts,
  PWM, ext. SRAM, UART
• 100-400 depending upon configuration

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Available Mote Designs MICA

• Three low-power modes
• Idle Processor is turned off
• Power Down Everything but the
• watch-dog is turned off
• Power Save Only asynchronous
• timer powered on
• 100 mW power consumption
• Processors, radio, typical sensor load
• 30 uW power consumption
• All components asleep

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Available Mote Designs MICA2

• Crossbow 3rd generation wireless sensor
• Design changes to MICA
• Processor now offers standalone boot-loader
• New radio (Chipcon 1000)
• 500 to 1000 ft. range, 38.4 Kbaud
• Better noise immunity, linear RSSI
• FM modulated (vs Mica AM)
• Digitally programmable output power
• Built-in Manchester encoding
• Software programmable freq.
• hopping within bands
• Tiny OS v. 1.0 - improved network stack,
  debugging
• Wireless remote programming
• 512 Kb serial flash

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Available Mote Designs MICA2DOT

• Crossbow 3rd generation wireless sensor
• Similar feature set to MICA2
• Degraded I/O capabilities 18 pins vs. 51
• 6 analog inputs, digital bus,
• serial or UART
• Integrated temperature and battery
• voltage sensors, status LED
• Battery is 3V coin cell instead of AA x 2
• 25 mm diameter, 6 mm height
• Compatible with MICA2

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Next Generation Mote Spec

• Single-chip mote
• 2 mm x 2.5 mm
• RISC core
• 3k Memory
• 8-bit on-chip ADC
• FSK 19.2 kbps RF transmitter
• Paged memory
• SPI, RS232 compatible UART
• 4-bit input/4-bit output port
• Hardware support for comms encryption
• Hardware OEM costs Under 1 in quantity (w/o
  antenna and sensors)

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Next Generation Mote Spec (Cont.)
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Sensor External Modules

• Each sensor has individual power control
• MTS300
• Light, temperature, acoustic, sounder
• MTS310
• 2-axis accelerometer, 2-axis magnometer, MTS300
  feature set
• MTS101
• Thermistor, light sensor/photocell, 24-point
  general prototyping area
• MDA500
• Connects MICA2DOT I/O signals to thru holes
• WSC100
• Four-channel analog (12-bit digital, 100hz)
  Bluetooth radios
• Single module dedicated to either input or output
• 100 ft range

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Operating System TinyOS

• Tiny Microthreading Operating System
• Tiny - 4k OS program memory limit
• Microthreading - processor directly handles
  almost all data (radio, sensors, etc.)
• OS - allows platform for future development
• - convenient abstractions for hardware
• Designed to do the job fast and then turn off
  everything allowed
• Open source

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Design Considerations

• Make best use of most constrained asset battery
  power
• Network self-configuration
• Manage complexity, respond to unplanned events
• Sensor self-configuration (?)
• Glue and go
• Real-time
• Limited buffering available
• Network robustness and maintenance
• Multiple points of failure, self-healing ability
• Heterogeneous end environments
• Application specific rather than general purpose
  (?)
• Fast creation of efficient, specific applications
  w/o too much HW-specific nastiness

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Example Software Layer Structure
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Example Memory Allocation
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Example Utilization Radio Receive
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TinyOS Programming

• Structural VHDL puts the pieces together
• Schematics are (usually) easier to put
• together and understand than code
• Industry standard design model
• Scripts take VHDL description and
• compile the resultant code base
• Components are aggregated and
• easily reused
• Low-level component software written
• In C and/or assembly
• But, this is largely hidden from view for
• standard modules

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TinyOS Example Code
/ Messaging Component Declaration
/ //ACCEPTS char TOS_COMMAND(AM_SEND_MSG)(char
addr,char type, char data) void
TOS_COMMAND(AM_POWER)(char mode) char
TOS_COMMAND(AM_INIT)() //SIGNALS char
AM_MSG_REC(char type, char data) char
AM_MSG_SEND_DONE(char success) //HANDLES char
AM_TX_PACKET_DONE(char success) char
AM_RX_PACKET_DONE(char packet) //USES char
TOS_COMMAND(AM_SUB_TX_PACKET)(char data) void
TOS_COMMAND(AM_SUB_POWER)(char mode) char
TOS_COMMAND(AM_SUB_INIT)()
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TinyDB Overview

• Imposes SQL-like querying ability on nodes
• Treats distributed network like a database (!)
• Allows specification of which data should be
  sent, update rate, etc.
• Filters and aggregates before displaying on PC
  screen (Java interface)
• Saves bandwidth and power by allowing nodes to
  only transmit requested data
• Graphical query-builder
• Download self-configuring runtime to motes, no C
  coding

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Crossbow Motes Conclusion

• Crossbow motes are very cool
• Probably cheap enough for us to buy a couple for
  playing with?
• Otherwise, maybe just TinyOS emulation?
• Sensor Hardware
• Cheap, publicly-available, modular, integrated,
  power-efficient, extensible, tiny
• Sensor Software
• Free, open-source, modular, abstract,
  power-efficient, extensible, small