TinyOS

1
TinyOS

• Session 2, September 16th
• Events, Tasks, and Basic Programming

2
Components

• There are two types of components in nesC
  modules and configurations.
• Modules provide application code, implementing
  one or more interfaces.
• Configurations are used to wire other components
  together, connecting interfaces used by
  components to interfaces provided by others.
• Every nesC application is described by a
  top-level configuration that wires together the
  components used

3
Interfaces

• An Interface is like a function definition,
  similar to an abstract class in C
• Modules can use interfaces to make calls to
  implementations
• Example random number generator component
• (in the module definition note, it still has to
  be wired to implementation)
• uses
• interface Random
• Later on we can call
• call Random.rand()

4
Wiring

• Wiring is the method we use to connect an
  interface we use to an implementation of that
  functionality Example
• Here, our module ExampleMessageM uses the Time
  interface
• It is wired to the implementation of the Time
  interface on the LogicalTime Componen
• ExampleMessageM.Time -gt LogicalTime.Time

5
Modules

• Wiring file is MyCode.nc (sorta like a header
  file in c, but not exactly)
• Module file is MyCodeM.nc (sorta like the .c file
  in c)
• Contains the implementation code for your program

6
Our Module

• module ExampleMessageM
• provides
• interface StdControl
• interface BluSH_AppI as HelloWorld
• interface BluSH_AppI as SendMessage
• uses
• // allows us access to the random number
  generator component in tinyOS
• interface Random
• interface StdControl as TimerControl
• interface Timer
• interface Time // allows us to see elapsed
  time
• interface TimeUtil

7
Tasks

• A task is similar to a function in c programming
• It takes no parameters
• Continues execution until completion, other tasks
  do not execute until it is complete
• Can only be pre-empted by an event

8
Task Example

• task void ExampleTask()
• trace(DBG_USR1," --- ExampleTask Start ---
  \r\n", TOS_LOCAL_ADDRESS)
• .. And then
• post ExampleTask()

9
Events

• Events are method calls made to a component
• Similar to a callback in c programming
• Common event in code is the Timer fired() event
• event result_t Timer.fired()

10
Timers

• In our example code, a basic Timer is wired up
• Allows us to periodically do a function, or post
  a task
• Similar to a thread that wakes up every so often
  in relation to how you are used to thinking about
  programming.

11
Timer Example

• event result_t Timer.fired()
• trace(DBG_USR1, "Timergt Fired!\r\n")
• return SUCCESS

12
The Radio

• The Imote2 employs the CC2420 chipset which is
  fairly standard, similar to your laptop wifi
• Integrated 802.15.4 Radio
• Integrated 2.4GHz Antenna

13
Issues with Physical Mediums

• The wireless physical medium is crazy. Just know
  this.
• Everything in the immediate area can and mostly
  will interfere with your data, and it will drive
  you crazy.
• Radio waves bounce around off everything,
  sometimes distance isnt your only obstacle.
• For a technical reference on how power and
  interference effects this, take a look at
  http//en.wikipedia.org/wiki/Friis_transmission_eq
  uation

14
So How Do We Send a Message?

• Basically, we have a data structure which has a
  data field which is an array of bytes
• We have a packet format, and we write our values
  into the slots designated by the format
• We then pass this data structure on to the
  underlying messaging communication subsystem via
  the Send interface
• call RadioSend.send( radio_msg )

15
Packets at the Bit Level

• // read a field from the packet
• uint16_t Read_ArbitraryField_FromPacket(
  TOS_MsgPtr pMsg )
• uint8_t d0, d1
• d0 (uint8_t) pMsg-gtdata PKT_ARBITRARY_16_FIELD
  _0
• d1 (uint8_t) pMsg-gtdata PKT_ARBITRARY_16_FIELD
  _1
• return d0 d1 ltlt 8
• // write a field to the packet
• void Write_ArbitraryField_ToPacket( TOS_MsgPtr
  pMsg, uint16_t iArbitrary_16bit_Value )
• pMsg-gtdata PKT_ARBITRARY_16_FIELD_0
  iArbitrary_16bit_Value 0xff
• pMsg-gtdata PKT_ARBITRARY_16_FIELD_1
  (iArbitrary_16bit_Value gtgt 8) 0xff

16
The BLuSH Shell

• Basically an easy way to talk to the mote from
  the pc while the mote is running
• You write shell commands that execute on the mote
• Anything that the mote writes to trace will show
  up in your console window
• Imoteconsole.exe brings up the BLuSH shell

17
Our Messaging Codebase

• So now weve taken a look at most of the basic
  concepts on how to structure the code, setup
  parts of the code, etc
• We now want to get our hands dirty and try out a
  few of these new concepts
• Download the ExampleMessage codebase at
  http//jpatterson.floe.tv/tinyOS/ExampleMessage.zi
  p
• Compile the code, flash the mote, and run
  imoteconsole.exe