The Contiki Operating System

1
The Contiki Operating System

• Jack Nosek

2
History

• Developed by Adam Dunkels of SICS
• Also developed protothreads and µIP
• First released on March 10, 2003
• Named after Thor Heyerdahl's famous Kon-Tiki raft
• Contiki runs on tiny and prehistoric computers,
  yet is able to do much of what we expect from
  large and modern computers.

3
Who uses it?

• Most common application is as an OS for Networks
  of Embedded Systems
• Hobbyists use it as an OS for older and smaller
  systems
• Ports for Apple II, Atari, Gameboy, NES,
  Commodore 64 and 128
• Screen captures at http//www.sics.se/adam/contik
  i/ports/index.html

4
Features

• Minimalist Event Driven Kernel, even runs on
  8-bit Microcontrollers
• TCP/IP Stack Support
• Dynamic Loading and Unloading of Programs
• Small Memory Requirements
• Optional Preemptive Multithreading through
  Protothreads

5
Event Driven Kernel

• Kernel is event based making it a real time OS
• An event triggers the kernel to call the
  corresponding event handler
• Functions very similar to TinyOS
• Has its drawbacks, i.e. long running computations

6
TCP/IP Stack Support

• Implements Dunkelss own TCP/IP stack called µIP
• Memory Requirements
• Kilobytes of Program Code
• Hundreds of bytes of RAM
• Allows to connect to networks using SLIP (Serial
  Line IP)

7
Dynamic Program Loading

• The Core Code and Program Code are kept separate
  in ROM.
• Program Code loaded at runtime.
• Program code can be loaded from ROM or RAM
• Allows for Over the Air Programming for
  networks of sensors

8
Small Memory Requirements

• The base system, providing multitasking and
  TCP/IP networking, can be compiled in about 32 KB
• Smallest system to date uses about 2000 bytes of
  RAM
• Jack Ganssle praised Contiki for its low memory
  usage in his Embedded Muse newsletter, 113

9
Protothreads

• Implemented as an additional library on top of
  the event based kernel
• Stackless, lightweight thread comprised of a
  single C function using 2 bytes of RAM to record
  its state
• Adds a layer of abstraction to the state-machine
  event based code usually written, to create a
  sequential flow of program code.

10
Event-driven
Handler

• Event-driven (TinyOS)
• Processes do not run without events
• Event occurs kernel invokes event handler
• Event handler runs to completion (explicit
  return)

Handler
Kernel
Handler
Handler
11
Contiki implementing threads on top of an
event-based kernel
Event
Thread
Thread
Event
Kernel
Event
Event
12
Contiki Programs

• Contiki Tool-kit (CTK) GUI
• Virtual Network Computing (VNC) Server
• A Web Server
• A Web Browser
• A command line shell.
• A telnet server.
• An IRC client.
• An FTP client.
• A disk directory file reader.
• A file and disk image downloader utility.
• A simple desktop calculator.

13
End

• Works Cited
• Slides 10 and 11 Taken fromAdam Dunkles
  Presentation Contiki a Lightweight and
  Flexible Operating System for TinyNetworked
  Sensorsfound at http//www.sics.se/adam/slides/c
  ontiki-emnets.ppt