Chapter 3 MobileEmbedded Devices and Tools

1
Chapter 3Mobile/Embedded Devices and Tools

• Limitations of Mobile/Embedded Devices
• Principles of Object Identifiers and RFID
• Highlights of J2ME for Mobile Applications
• Sensors and Programming in TinyOS

2

• Limitations of Mobile/Embedded Devices
• and
• Design of Pervasive Computing Systems

3
Pervasive Devices and Tools

• Pervasive Devices (more than mobile devices)
• User devices (i.e., mobile devices and
  electronics) to access to different types of
  (real-time) information
• Sensor (embedded) devices for capturing real-time
  environmental data
• New tools and operation environment for pervasive
  devices
• Integration with other computing systems and
  devices
• Limitations of the devices gt the current tools
  for system development and operation may not be
  suitable (requiring a powerful CPU and large
  memory) gt reduced versions
• To meet the proactive and smart requirements
• I.e., New techniques are needed in job
  processing, i.e., pushing model, real-time
  scheduling and localized processing
• The techniques need to fit into the limitations
  imposed by the devices and operating environment

4
From Old to New

• How to migrate from Old computing systems to
  New (pervasive) computing systems?
• Modify the current one OR build a new one
• Devices are easier to have new, BUT, systems
  (i.e., network and operating systems) are NOT
• OR Both gt until the technologies become mature
• I.e., Using the mobile network as an example to
  see the problem
• Support data transmission services over the 2G
  mobile network. How?
• The mobile network is initially designed for
  voice communication
• WAP and GPRS for data transmission in 2G network
• In addition of 2G, we also have 3G network at the
  same time
• What will be the future? 4G WiFi??

5
Limitations of Mobile/Embedded Devices

• Need to know the limitations of the
  mobile/embedded devices in building pervasive
  computing systems. Why?
• They affect the operations and design of the
  systems. How?
• Consider two simple applications (1) Queries to
  (continuously) monitor the highest temperature of
  the class room and (2) a real-time news
  reporting system for car drivers
• What are the similarity and differences between
  the two applications?
• (1) is a surveillance application (rule events
  -gt action) (2) is a reporting system pushing
  news for reading
• Updates/news reports are generated continuously
  from sensors/agents
• Update generation period? Processing cost, memory
  cost, energy cost and network transmission cost
• (1) Local processing to filter out updates. (2)
  unconditional mostly

6
How do they affect the operations and design of
the systems?

• Mobile computers are resource poor
• Reduce program size interpret script languages
  (mobile Java?)
• Specific codes (i.e., machine codes) for specific
  hardware
• Any data aggregation (from low-level to
  higher-level)?
• Where to put the database? Front-end or backend.
  Any caching/pre-caching? When/what to
  pre-caching? Caching unused data wastes resource.
  Real-time data will become totally useless if
  they are too old. What are real-time data? How
  to maintain (refresh) the cached data? Cache size
  is usually limited
• When to load data (i.e., maps) and programs into
  a mobile device for execution? Pre-load or
  on-demand?
• Adaptation to network and display
• Any trans-coding of the contents before
  transmission/displaying them in the client
  devices
• The front-end may perform some pre-processing,
  i.e., input validation, to reduce communication
  overheads

7
How do they affect the operations and design of
the systems?

• Energy saving, how? What is the biggest factor
  affecting the rate of energy consumption?
• Transmit/receive, disk spinning, display, CPUs,
  connection
• Need energy efficient hardware (CPUs and memory)
  and system software to manage the resources
• Planned disconnection doze mode of operations
• Communication range Vs power consumption
• Where to perform the computation? Distributed Vs.
  centralized
• Computation and communication load cannot be
  distributed equally
• Processing at front-end minimize the data
  transmission workload
• Processing at backend relieves the limitations
  of the front-end hardware
• Multi-levels in processing gt multi-levels of
  divisions
• How to divide the tasks into sub-tasks for
  execution at the mobile devices and powerful
  servers?

8

• Pervasive Computing Devices
• Mobile Devices and
• Sensor/Embedded Devices
• Their properties and limitations

9
Mobile User Devices

• Mainly for reading and storing information/data
• Various intelligent electronic devices, i.e.,
  camera, MP3, games
• PDA (Personal Digital Assistant) and smart phones
• Pocket PCs, tablet PCs and notebooks
• How do you feel about the operations/functions of
  these devices? Easy of operation, quality of
  outputCan be improved
• Limitations of mobile user devices
• High variation in processing capability and
  interface, i.e., display screen sizes and
  resolutions
• Hard disk or diskless and limitations in memory
  sizes
• Wireless/fixed connection to networks, i.e. using
  infra red or radio signals (limited bandwidth and
  unstable performance)
• Why do they have these properties? Development is
  step by step and driven by customer marketThe
  future will be better???
• Separated and closed systems. Needs to work with
  back-end (middleware) servers to provide better
  services. But network is

10
Sensor and Embedded Devices

• Sensors for capturing/monitoring the status of
  environment
• I.e., light intensity, pressure, velocity and
  position
• Note radio receivers and video camera are
  sensors???
• What is a sensor? Capturing a physical property
  of the environment
• Why do we use sensors? Robust can operate in
  harsh environment for a long period of time
  non-stop, and also, small in size, cheap in
  price, large in number
• Limitations processing power, energy, memory,
  connection, bandwidth (mostly connected by
  wireless LAN or ad hoc network)
• They may be embedded into other devices and
  electronics to make them to be smart, i.e., smart
  home and intelligent navigator
• Simple and limited interface (control panel)
  mainly for displaying texts to show the current
  operation status and for command input by users
• CPU memory gt programmable and functionalities
  can be adjusted and enhanced
• Networking capability gt cooperative to provide
  smart services
• Energy saving operations (doze mode) and event
  driven processing

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MOTES (Sensors)

• Two Board Sandwich
• CPU/Radio board
• Sensor Board temperature, light
• Size
• Mote 1?1 inch
• Pocket PC 5.2?3.1 inch
• CPU
• Mote 4 MHz, 8 bit
• Pocket PC 133 MHz, 32 bit
• Memory
• Mote 512 B RAM 8K ROM
• Pocket PC 32 MB RAM 16 MB ROM
• Radio
• 900 Hz, 19.2 kbps
• Bluetooth 433.8 kbps (symmetric)

• Lifetime (Power)
• Mote 3-65 days
• Pocket PC 8 hrs
• Cost
• Mote 100 (expected to drop dramatically in the
  future, down to 1)
• Pocket PC 400

• http//www.xbow.com/Products/Product_pdf_files/Wir
  eless_pdf/MICA.pdf

12
Object Identifiers

• A unique identifier to label an attached object
  or a category of objects, i.e., HKID, ISBN and
  telephone number
• Bar code (a series of strips) simple, cheap and
  small
• Two-dimension bar code
• Data are encoded in both the horizontal and
  vertical dimensions
• As more data is encoded (i.e., using matrix or
  stacked algorithms), the size of data included
  can be increased in both the horizontal and
  vertical directions
• More durable and robust and reliable (comparing
  with bar code)
• Smart cards
• More expensive and embedded processing units with
  memory
• I.e., SIM cards for labeling a mobile phone and
  electronic ID for security control
• Radio frequency identifier (RFID) a unique
  identifier using encoded radio signals. A reader
  reads radio frequencies generated from a tag to
  identify the presence of the object
• What is the difference between smart card and
  RFID? Octopus is a smart card or an RFID?

13
Making Use of Object Identifiers

• Locating and positioning (Context-aware services)
• Tracking the current location of mobile objects
• Providing location-dependent services (different
  services are provided for objects at different
  locations, i.e., at home, in the office or
  school)
• Load and resource management (workload depends on
  object density), i.e., channels management in
  cellular networks
• Proactive services (Context-aware and proactive
  services)
• Tracking the locations as a function of time, we
  can summary the movement behavior of the objects
• Based on the movement behavior, the system can
  make some prediction for proactive services .
• Counting
• Inventory control and cashier check-out
• Authentication
• Unique ID for security control and authentication

14
RFID Technologies

• Types
• Active and passive RFIDs
• Locator active tags (adding multiple base
  stations for positioning)
• Battery-assisted passive tags
• Energy source Passion Vs. active RFIDs
• Passive RFID
• It consists an antenna, a semi-conductor chip and
  the encapsulation
• The antenna captures energy from the tag reader
  to transfers the tags ID to the tag reader
• Active RFID
• It has a power source and more powerful
• It can operate up to 100m from the tag reader
  (range depends on power supply)
• It includes a processor and a memory to store
  data
• The life-span depends on the power supply
• Read-only and read/write tags

15
RFID Technologies

• Passive RFID using Near-field
• A tag reader passes a large alternating current
  through a coil resulting in an alternating
  magnetic field in its locality
• A tag that incorporates a small coil in this
  field generates an alternating voltage due to
  induction
• The voltage is rectified and coupled to a
  capacitor
• A reservoir of charge accumulates to power the
  tag chip
• The tag sends data (including its pre-assigned
  ID) back to the reader using load modulation
• Any current drawn from the tag coil will give
  rise to its own small magnetic field which will
  oppose the readers field
• The reader coil detects the change in magnetic
  field as a small change in current which is
  proportional to the load applied to the tags
  coil
• The energy for induction decreases as a function
  of distance from the reader coil, 1/r3
• The power from the reader has to be strong while
  the power from the tag is usually weak. This
  limits the scope of detecting the tag (5m)

16
RFID Technologies

• Locator active tags
• A special category of active tag (Real Time
  Locating System)
• For positioning instead of just detecting the
  presence of an object
• The RTLS tags are provisioned to emit a strong
  Beacon signal periodically
• The signal is used by the RTLS infrastructure
  consisting of locator base stations to locate the
  physical location of the tag (similar to
  positioning using in GPS), i.e., by
  triangulation. How to draw a triangle?
• Battery-assisted tags
• A tradeoff between passive and active tags
• Active tags are expensive but passive tags are
  too limited
• A passive tag with a battery but it is not for
  powering the tag for signal transmission
• The battery is mainly to support recording input
  sent to the tag for processing

17
RFID Technologies

• Read only Vs. read/write tags
• Many passive tags are read-only due to the
  limited power supply and processing power
• The tags unique ID was created and burned into
  the tags IC by the manufacturer. It usually
  cannot be changed
• The primary function of a tag is then to respond
  the signals from the reader by generating signals
  (load modulation) to represent its unique ID to
  the tag reader
• Read/write tags
• In addition to the ID, it contains memory (i.e.
  128k) for storing other data in processing. Thus,
  better processing capability but require higher
  power supply for processing
• I.e., Tracking the processing history of a tag
  and recording the operator ID into the tag

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RFID Processing Models Problems

• When and where to collect the detected RFID?
• Passive tags
• A tag is identified when it comes close (less 1m)
  to the reader
• The reader collects the tag information (ID) and
  sends to the event servers immediately with its
  ID as a transaction (a lot of update transactions
  to the event server)
• Batching the collected data and send transactions
  periodically???

Tag reader
updates
Passive tags
Applications
Detection range
19
RFID Processing Models Problems

• Active tags
• A tag is identified when it is within the
  detection range of the tag reader. The range may
  be quite large. How to ensure that it is within
  the target region and moving in the right
  direction? Using an excitor
• An excitor emits highly range-restricted and
  severely directional-controlled signal (limiting
  the range)
• A tag may be identified multiple times. How to
  eliminate double reading? Updating the tag to
  storage the reading information

Tag reader
Detection range
20
RFID Advantages, Limitations Applications

• Advantages
• Small and low cost (more expensive comparing with
  bar codes)
• Can operate without any direct energy supply
  (passive tags)
• Fast, easy for identification and reliable in
  accuracy
• Limitations
• Although cheap but still cannot be totally
  ignored gt cannot be used as a disposable
  electronic ticket for large population
• It is still difficult to determine the exact
  location with a high precision gt mainly for
  determining the presence of object within an area
• Needs to combine with other technologies for
  positioning
• In general, applications of RFID can be used for
  identification, localization and monitoring of
  physical objects, i.e., tracking of materials,
  i.e., in the airport, inventory control and
  library. Any more??? Many

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Comparison of Bar Code RFID
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Applications of RFID in Frankfort Airport

• Mobile applications for asset maintenance, i.e.,
  checking of fire shutters
• To protect against fire, the airports
  air-conditioning and ventilation system has
  22,000 fire shutters and numerous fire doors and
  smoke detectors. They are required to be examined
  at least once a year
• Manual paper-based process generation of paper
  exam list gt examine the fire shutters by
  technicians gt generation of exam report (error
  prone, time-consuming, inefficient, heavy
  maintenance costs of the reports, i.e., storage
  problems, retrieval/access difficulties)
• Replacing the paper-based process with mobile and
  RFID technologies
• All fire shutters are installed with RFID tags
  that stored maintenance information and an unique
  ID
• All technicians carry an RFID tag for
  authentication and a tag reader
• Using the tag reader, a technician can identify
  the tag and the fire shutter for maintenance.
  Defect can be registered using comprehensive
  damage codes

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• Operating Systems and Tools
• Reduced Versions for
• Transition from OLD to NEW

24
Operating and Development Environment for Mobile
User Devices

• PocketPC? Mobile phones? Smart phones? What are
  the differences?
• General purposes Vs. specific purposes
• Windows Embedded CE (WinCE)
• A specific operating system and development
  environment for limited processing power devices,
  mostly mobile devices
• It has a similar interface as other Microsoft
  operating systems but its development is totally
  different (not a reduced version)
• It is specially designed for limited devices gt
  reliable performance???
• Not a real-time operating system (real-time OS
  requires predictable performance)
• http//www.microsoft.com/windows/embedded/eval/win
  ce/default.mspx
• Symbian OS a platform for wireless devices
  developed by Symbian consortium for 2G, 2.5G and
  3G data enabled mobile phones/PDA
  (www.symbian.com)

25
What is J2ME?

• NEITHER a specific piece of software /
  specification
• A collection of Java classes, interfaces
  dedicated to small, mobile devices

http//java.sun.com/j2me/docs/index.html
26
J2ME System Model

• J2ME framework is divided into Configurations and
  Profiles

http//java.sun.com/j2me/docs/index.html
27
Scope of J2ME

• J2ME defines
• A series of Java virtual machines each for use on
  different types of small devices
• A group of libraries and APIs that can be run
  under each of the virtual machines
• Various tools for deployment and device
  configuration
• Configuration
• Mobile devices have different capabilities
  (limitations). J2ME defines configurations for a
  horizontal grouping of devices based on
  availability of memory and processing power of
  the devices
• Profiles
• Defines a set of APIs that reside on top of a
  configuration that offers the program access to
  device-specific capabilities

28
Scope of J2ME
http//java.sun.com/j2me/docs/index.html

• MIDP (mobile information device profile) is
  designed to be used with the configuration
  (CLDC), and provides a set of APIs for use by
  limited resources devices, i.e., mobile phones

29
J2ME System Model Configurations

• Designed for a specific kind of device based on
  memory constraints and processor power (i.e.
  defines a minimum Java platform for a family of
  devices)
• Usually specifies a JVM that can be easily ported
  to devices supporting the configuration (called
  KVM)
• Specifies the characteristics and features of
  virtual machine present, minimum Java libraries
  that are supported and minimum set of features
  for a category of devices
• Major Configurations in current specification
  include
• Connected Device Configuration (CDC)
• Connected, Limited Device Configuration (CLDC)

30
Connected Device Configuration (CDC)

• Device requirements A connected device (CD) has
  a minimum 512KB of ROM, 256KB of RAM, 32-bit
  processors, and some network connection with
  limited bandwidth
• CDC is designed for "more powerful" wireless
  devices like TV set-top boxes, car navigation
  systems, and high-end PDAs.
• CDC specifies that a full-featured Java Virtual
  Machine (JVM) (defined in J2EE) is supported

31
Connected, Limited Device Configuration (CLDC)

• Covers mobile devices like mobile phones, PDAs,
  pagers, and other "tiny" wireless devices
• For smaller devices than CDC, with limited
  capacity and network connection (e.g., lt 9.6Kbps
  for mobile phones)
• For devices with 160KB to 512 KB of memory
  available for Java platform
• For devices with limited power supply
• Built on "scale-down" version of JVM called KVM
  (Sun 'K Virtual Machine, with size in tens of
  kilobytes, rather than JVM with tens of megabytes)

32
MIDP Requirements

• MIDP (mobile information device profile) is
  designed to be used with the configuration
  (CLDC), and provides a set of APIs for use by
  limited resources devices, i.e., mobile phones
• A Mobile Information Device (MID) has the
  following characteristics
• 128KB of non-volatile memory for MIDP
  implementation
• 32KB of volatile memory for runtime heap
• 8KB of non-volatile memory for persistent data
• A screen of a least 96 x 54 pixels
• Some capacity for input, either by keypad,
  keyboard, or touch screen
• Two-way network connection, possible intermittent
• Detail information about MIDP (Mobile Information
  Device Profile) can be found in
  http//java.sun.com/products/midp/

33
MIDlets

• MIDP enables application development with mobile,
  wireless-connected devices like cellular phones
  and two-way pagers
• MIDlets
• Small applications that run under the MIDP are
  called MIDlets
• A MIDlet is a Java application that uses the MIDP
  and the CLDC
• In a mobile phone, application management
  software (AMS) controls start, stop and execute
  MIDlet (controls the entire lifecycle)

34

• Sensor and TinyOS for Event Control and
  Monitoring
• Event Driven and Concurrent Components
• Real-time Applications

35
Sensor Nodes and TinyOS Programming

• A sensor node consists of two main components
• Sensing unit Light, sound, velocity,
  temperature, etc
• Processing unit
• Usually has with limited processing power, energy
  supply, communication and memory capability
• Operating system (TinyOS) application programs
  (i.e., in nesC)
• Example sensor nodes Mica Motes developed in UC
  Berkeley and manufactured by www.xbow.com
• Characteristics and requirements
• Very small in size and cheap, and can be deployed
  in large number
• Energy saving and can operation for a long period
  of time non-stop
• Continuous monitoring of the surrounding
  environment and generation of sensor data (stream
  data)
• Automatically form a wireless sensor network
  (WSN) with other nodes (communication range from
  a few m to km with an antenna). An example of
  mobile ad hoc network (MANET)
• Robust and reliable (can work in harsh
  environment)

36
Mote Evaluation
Services
Networking
TinyOS
www.xbow.com
37
Mote Applications

• Example application areas
• Object tracking and intrusion detection
• Environment and habitat monitoring, many others
  
• Basic components
• A number of sensor nodes
• Base stations
• Gateway/Server
• Networks
• Fixed/wireless network connecting the base
  stations/servers to the gateway
• Wireless sensor network connecting the sensor
  nodes to the gateways
• http//www.xbow.com/Products/Product_pdf_files/Wir
  eless_pdf/MSP410_Datasheet.pdf

38
Wired Network
Server
MANET
Base Station
WLAN WWAN
Wireless Sensor Networks
Ad hoc network
Queries
Gateway
Local processing to minimize the responses to
events and transmission workload through the
networks
Results
Applications
39
Basic Operations of Mote

• Periodic
• Sleep majority of the time
• Wakeup quickly start processing
• Active minimize work return to sleep
• Triggered Events
• Detection/Notification
• Infrequently occurs
• But must be reported quickly and reliably
• Long Lifetime
• Months to years without changing batteries
• Power management is the key to WSN success
• Sleep isolating and shutting down individual
  circuits
• Using low power hardware

processing data acquisition communication
active
Power
wakeup
sleep
Time
www.xbow.com
40
TinyOS Programming in Mica Motes

• TinyOS is the operating system designed
  specifically for sensor devices, i.e., mica motes
  
• It is a tiny (less than 400bytes), open-source
  operating system developed by UC Berkeley
• It includes functions for radio messaging,
  scheduling, message hopping from mote to mote,
  low power (energy saving) mode of operation and
  sensor measurements and signal processing
• It is NOT a true OS. It builds from a set of
  reusable components together with application
  into an application-specific executable
• http//webs.cs.berkeley.edu/tos/download.html1.1.
  0
• Design goals
• Limited resources 1-MIP processor and tens
  kilobytes storage
• Flexibility for variations in hardware
  (different capabilities)
• Low power energy saving operations. How? Doze
  mode of operations
• Efficient modularity minimize the size of
  executable codes

41
Design goals

• Concurrency-intensive operations
• Multiple, high-rate data flows (radio, sensor,
  actuator)
• Component-based concurrency models for handling
  multiple events
• Concurrent events processing, receive input and
  communication
• Real-time responses
• Real-time query and feedback control of physical
  world (monitoring and surveillance purposes)
• TinyOS must process bit every 100 µs
• Little memory for buffering data must be
  processed on the fly
• TinyOS No buffering, missed deadline ? lost data
• But, TinyOS provides NO real-time guarantees
  (completion before a deadline). Why? How to
  provide real-time responses? Fast Real-time
  scheduling

42
TinyOS Overview

• A set of reusable system components together with
  a scheduler
• Application main components
• Compiled into one executable (unused components
  are not included, size may be just 1KB)
• Event-driven architecture (event-based
  concurrency model)
• No kernel/user space differentiation

Assembled into a single executable as binary
codes for execution by the hardware
Main (configuration modules)
scheduler
Applications (configuration modules)
download
actuating
sensing
communication
sensor
hardware
43
Programming in Mica Mote

• Applications are developed in nesC for TinyOS
• nesC is a C-like procedure language and can
  support event-based concurrency models and
  component based applications
• Why concurrency model? To respond to concurrent
  events
• Why components? reusable
• Concurrency model tasks and hardware event
  handlers
• An event-based concurrency model consists of
  run-to-completion tasks and interrupt handlers
• Task
• Once scheduled, runs to completion
• Hardware event handlers
• Hardware event handlers are executed in response
  to a hardware interrupts
• Run to completion, may preempt execution of
  functions/tasks or other event handlers
• Split phase operation a command starts the
  operation immediately, and a callback event
  indicates when the operation completes

44
Hardware interrupt
FIFO scheduling
Tasks Once started cannot be preempted by another
task but can be preempted by interrupts
scheduler
Concurrent events handling
The scheduler uses a non-preemptive, FIFO
scheduling
45
Command sense()
AppM (User)
TempM (Provider)
Event senseDone (value)
Split-phase operation
Provider must implement the sense command, which
represents a request to read a sensor User must
implement the senseDone which the provider
signals when the sensor read completes
46
Components and Concurrency Model

• A nesC application consists of one or more
  components linked to form an executable
• A component is an computational entity consisting
  of three abstractions commands, events and tasks
• A component provides and uses interfaces from
  other components
• An interface declares a set of functions called
  commands implemented by the interface provider
  and a set of events implemented by the interface
  user
• A command is a request to a component to perform
  some service, i.e., a sensor reading, while an
  event signals the completion of the service,
  split phase operation
• Commands and event handlers may post a task to be
  executed by the scheduler at a later time

47
Components and Concurrency Model

• Two types of components modules and
  configurations
• A module provides application code, implementing
  one or more interfaces
• Configurations are used to assemble other
  components together, connecting interfaces used
  by components to interfaces provided by others
  (wiring)
• Every nesC application is described by a
  top-level configuration that wires together the
  components inside
• All hardware resources are abstracted as
  components, i.e., calling getData() command on a
  sensor component will cause it to later signal a
  dataReady() event when the hardware interrupt
  fires

48
Life Cycle of a Sensor Program

• Main is a component that is executed first in a
  TinyOS application
• All the sensor programs need to connect with Main
  Program
• init() can be called multiple times, but will
  never be called after either start() or stop are
  called
• It is an event driven model. You need to specify
  what to do when an event arrives

Main.StdControl.init()
Main.StdControl.start()
Main.StdControl.stop()
49
Example Blink

• Blink causes the red LED on the mote to turn on
  and off at 1Hz
• Blink application is composed of two components
  a module, called BlinkM.nc and a configuration
  called Blink.nc
• Blink.nc configuration Blink implementation
    components Main, BlinkM, SingleTimer,
  LedsC  Main.StdControl -gt BlinkM.StdControl 
  Main.StdControl -gt SingleTimer.StdControl 
  BlinkM.Timer -gt SingleTimer.Timer  BlinkM.Leds
  -gt LedsC

User
Connect the Blink Program to Main program
Provider
50
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51
Example Blink

• BlinkM.nc module BlinkM   provides    
  interface StdControl    uses     interface
  Timer    interface Leds  // Continued
  below...

Used by Main
Blink Program uses the component Timer and Leds
52

• implementation command result_t
  StdControl.init()     call Leds.init()   
  return SUCCESS    command result_t
  StdControl.start()     return call
  Timer.start(TIMER_REPEAT, 1000)     command
  result_t StdControl.stop()     return call
  Timer.stop()  event result_t
  Timer.fired()      call Leds.redToggle()   
  return SUCCESS 

Executed by Main program, as it is connected with
Main.stdControl.init() Main.stdControl.start() Mai
n.stdControl.stop()

Handle the event Timer.fried() i.e. to blink the
red led
53

• StdControl.nc interface StdControl   command
  result_t init()  command result_t start() 
  command result_t stop()
• Timer.nc interface Timer   command result_t
  start(char type, uint32_t interval)  command
  result_t stop()  event result_t fired()

54
The Future of Sensors

• Further smaller in size
• Larger in number
• Cheaper in price
• Fixed and mobile
• Greater in capability
• Better connectivity
• More tools for development and debugging
• Better real-time supports and scheduling
• BUT, energy is still a concern

55
References

• RFID
• Tom Polizzi, RFID in the Enterprise, pp. 4-13,
  pp.42-55.
• Christine Legner and Frederic Thiesse,
  RFID-Based Maintenance at Frankfurt Airport,
  Pervasive Computing, Jan-Mar 2006, pp. 34-39.
• Sensors
• www.xbow.com
• www.tinyos.net
• http//www.tinyos.net/tinyos-1.x/doc/tutorial/less
  on1.html
• http//www.xbow.com/Products/Product_pdf_files/Wir
  eless_pdf/MICA.pdf