Networked Sensors

1
Networked Sensors
TinyOS
Operating System for Networked Sensors
Jason Hill, Robert Szewczyk, Alec Woo Spring
2000
System Structure
The Study

• Implement and investigate an event-based
  Operating Environment for a wireless network of
  deeply embedded sensors.
• The Problem
• Limited computational ability energy supply
• High levels of concurrency required
• Limited physical parallelism
• Diversity in design and usage
• Robust operation is required

• What is a Networked Sensor?
• Small (I.e. 2x2 and smaller)
• Onboard processor and communication device (e.g
  IR, Radio)
• Self-contained power source (e.g. Battery, Solar)
• Mote (mOt) noun a small particle
• A sub-device with attached sensor(s). Autonomous
  Sensor Node.

• System image consists of scheduler and a graph of
  components
• Higher-level components issue commands to and
  respond to events from Lower-level components
• Components contain Set of command handlers, Set
  of event handlers, A fixed size storage frame,
  Collection of simple threads which can be
  scheduled

• Designed to be
• Embedded throughout the environment
• Low Cost
• Non-obtrusive
• Un-attended or Un-managed
• Dynamically reprogrammed

• Commands and Events are non-blocking requests or
  signals
• Threads perform primary work, run to completion,
  and are atomic with respect to each other
• Two level scheduling system allows events to
  preempt threads

• We leverage aspects of an event based programming
  model and component based object model to
• Support composition of diverse applications
• Provide a natural paradigm for supporting
  interaction with the physical world
• Minimize dynamic memory resources required

Example Component
/ 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)()

• Our Example Networked Sensor
• ATMEL 8535 Microcontroller (4Mhz, 512B SRAM, 8KB
  Flash)
• Communication RF (916.5 MHz), 10Kbps raw
• Sensors Light, Temperature
• Features Wireless reprogramming, 3 LEDs
• Has the ability to be re-programmed wirelessly

• We demonstrate
• A compact system with highly efficient resource
  utilization
• An efficient mechanism for achieving modularity
• The support of concurrency intensive operations
• A rich set of applications enabled by our
  architecture

Composing Components
Analysis

• Software Footprint
• 3.4KBytes for complete sensing communication
  application
• Power consumption (sleep idle states)
• Transmission cost 1uj per bit
• Inactive state 5 ? A
• Peak Load 19.5mA
• Efficient Concurrency support
• Even during periods of active communication with
  bit-level processing, CPU is sleeping 50 of the
  time.
• Efficient Modularity
• Event can propagate through our entire
  communication stack in under 40 ?s.

• Use CAD tools to compose
• Each component is created with a CAD symbol
  specifying the names of commands and events used
  and handled by the component
• Schematic drawings are used to link together
  components
• Structural VHDL is exported and used at compile
  time
• Internally, components only refer to the
  interfaces described in their declaration (IE
  refer to their own pins)
• Example
• If the application depicted on the left wanted to
  use a different messaging component, the author
  would use the schematic editor to replace the
  messaging component with the desired one, export
  VHDL and recompile.
• This would automatically re-target events and
  command of neighboring components to the new
  component as well as target its commands and
  events.

Sample Application Future Work

• Route discovery application
• Nearest neighbor with a single, static root (the
  base station mote)
• Each mote broadcasts a beacon every 1 second
• Neighbor mote responds if it knows how to get to
  base station
• Beacons propagate to base-station/host

• Future Work
• Provide additional communication interfaces
  (more complex MAC layers or messaging
  protocols)
• Dynamic uploading of handler functions.
• Comparison with other models
• Extension to multiple hardware platforms

Screen Shot of Routing Application