Contiki OS preparation usage with kit CC256

Contiki OS instruction

1. ContikiContiki
A Lightweight and Flexible Operating A Lightweight and Flexible Operating
System for Tiny Networked SensorsSystem for Tiny Networked Sensors
Presented by: Jeremy SchiffPresented by: Jeremy Schiff

2. ObjectivesObjectives

LightweightLightweight

Event Driven ModelEvent Driven Model

Has Multi-Threading Support as LibraryHas Multi-Threading Support as Library

Dynamic Loading and Replacement of Dynamic Loading and Replacement of
Individual ServicesIndividual Services

3. Contiki MotivationsContiki Motivations

No memory protection between appsNo memory protection between apps

Kernel very minimalKernel very minimal

CPU multiplexingCPU multiplexing

Loading ProgramsLoading Programs

All other abstractions by librariesAll other abstractions by libraries

Custom ApplicationsCustom Applications

4. DifferentiationDifferentiation

TinyOSTinyOS

Statically linked entire applicationsStatically linked entire applications

MagnetOSMagnetOS

Virtual Machine – byte codeVirtual Machine – byte code

MantisMantis

Pure MultiThreadPure MultiThread

ContikiContiki

Dynamic Linking of binariesDynamic Linking of binaries

Event/Thread HybridEvent/Thread Hybrid

5. Why Loadable ApplicationsWhy Loadable Applications

Smaller file to uploadSmaller file to upload

Less EnergyLess Energy

Less Dissemination Time Less Dissemination Time

6. Why No Threads?Why No Threads?

Thread stacks must be allocated at creation timeThread stacks must be allocated at creation time

Stack Memory Over-ProvisionedStack Memory Over-Provisioned

No Virtual Memory SystemNo Virtual Memory System

No Memory Protection Mechanisms No Memory Protection Mechanisms

Locking for state exclusionLocking for state exclusion

Stack memory is inaccessible to other threadsStack memory is inaccessible to other threads

7. EventsEvents

No lockingNo locking

Only one running at a timeOnly one running at a time

Only one stackOnly one stack

Locking rareLocking rare

Hard to express some things as state machineHard to express some things as state machine

Problem: Cryptography takes 2 seconds, everything Problem: Cryptography takes 2 seconds, everything
else blocked.else blocked.

Solution: Preemptive ThreadsSolution: Preemptive Threads

8. System OverviewSystem Overview

Service – Something that implements Service – Something that implements
functionality for more than one applicationfunctionality for more than one application

Apps have direct access to hardwareApps have direct access to hardware

Single Address SpaceSingle Address Space

Inter-process communication via event postingInter-process communication via event posting

Always Through KernelAlways Through Kernel

9. Core vs. Loaded ProgramCore vs. Loaded Program

Partitioned at compile timePartitioned at compile time

CoreCore

Single Binary Single Binary

Ideally never modifiedIdeally never modified

ProgramProgram

Easily upgradedEasily upgraded

10. KernelKernel

Execution via: Kernel Events or Polling EventsExecution via: Kernel Events or Polling Events

No preemption of scheduled events No preemption of scheduled events

Synchronous vs Asynchronous EventsSynchronous vs Asynchronous Events

Synch: Like Function CallSynch: Like Function Call

Asynch: Like posting new eventAsynch: Like posting new event

Asynch reduces stack spaceAsynch reduces stack space

Debugging issuesDebugging issues

11. Two Level SchedulingTwo Level Scheduling

Events Events

Can’t preempt one anotherCan’t preempt one another

Interrupts Interrupts

Can preempt eventsCan preempt events

Can use “underyling real-time executive” Can use “underyling real-time executive”

Provides realtime guaranteesProvides realtime guarantees

Non-hardwareNon-hardware

Can’t post eventsCan’t post events

Use polling flag insteadUse polling flag instead

Prevent race conditionsPrevent race conditions

12. Loading ProgramsLoading Programs

Relocation Information in BinaryRelocation Information in Binary

Check for space before loadingCheck for space before loading

Call Initialization FunctionCall Initialization Function

Replace or Starts new ProgramReplace or Starts new Program

13. Power Save ModePower Save Mode

No explicit Kernel assistanceNo explicit Kernel assistance

Access to event queue size Access to event queue size

14. ServicesServices

ApplicationApplication

Service LayerService Layer

Service InterfaceService Interface

Service ProcessService Process

15. ApplicationApplication

Must dynamically linkMust dynamically link


Interact via Service StubInteract via Service Stub

Compiled inCompiled in

Version numberVersion number

Caches Service ProcessIDCaches Service ProcessID

16. Service LayerService Layer

Works with KernelWorks with Kernel

Provides lookup for specific serviceProvides lookup for specific service

Returns a Service InterfaceReturns a Service Interface

Has pointers to all functions service providesHas pointers to all functions service provides

Contains a version NumberContains a version Number

Interface description implemented by Service ProcessInterface description implemented by Service Process

Version numbers must matchVersion numbers must match

Failure Support? MANTIS thinks about this better.Failure Support? MANTIS thinks about this better.

17. Service ExampleService Example

18. Service ReplacementService Replacement

Process ID must be preservedProcess ID must be preserved

Kernel supportedKernel supported

Kernel instructs service to remove itselfKernel instructs service to remove itself

Could lead to problemsCould lead to problems

Kernel provides mechanism to transfer state Kernel provides mechanism to transfer state

Service state also versionedService state also versioned

Service state must be stored in a shared space during Service state must be stored in a shared space during
swap due to reallocations of old version’s spaceswap due to reallocations of old version’s space

Is there a better way to do this - SOS?Is there a better way to do this - SOS?

19. LibrariesLibraries

Application optionsApplication options

Static link with coreStatic link with core

Static link with librariesStatic link with libraries

Single binarySingle binary

Call a serviceCall a service

Memcpy() vs Atoi()Memcpy() vs Atoi()

MemCpy in CoreMemCpy in Core

20. CommunicationCommunication

Architecture makes easy to replace Communication Architecture makes easy to replace Communication
Stack Stack

A service like any otherA service like any other

Enables multiple communication stack for comparisonEnables multiple communication stack for comparison

Comm Services use Service Mechanism to call one Comm Services use Service Mechanism to call one
anotheranother

Comm Services use Synchronous events to Comm Services use Synchronous events to
communicates with applicationscommunicates with applications

No copying of buffers because Synch events can’t be No copying of buffers because Synch events can’t be
preemptedpreempted

21. Communication StackCommunication Stack

22. Multi-ThreadingMulti-Threading

Optional Library linked inOptional Library linked in

Kernel interactionKernel interaction

Platform IndependentPlatform Independent

Stack Switching / Preemption primitivesStack Switching / Preemption primitives

Platform DependentPlatform Dependent

23. Multi-Thread APIMulti-Thread API

24. Over the air ProgrammingOver the air Programming

1 node took 30 seconds1 node took 30 seconds

40 nodes took 30 minutes40 nodes took 30 minutes

1 component for 40 nodes took 2 minutes1 component for 40 nodes took 2 minutes

Used naïve protocolUsed naïve protocol

25. Code SizeCode Size

Bigger than TinyOS, Smaller than MantisBigger than TinyOS, Smaller than Mantis

Polling Handlers and Increase FlexibilityPolling Handlers and Increase Flexibility

Less compiler optimization possibleLess compiler optimization possible

26. Preemption DemoPreemption Demo

Start 8 second Start 8 second
process at 5 Seconds process at 5 Seconds
and continually pingand continually ping

~.1 ms latency ~.1 ms latency
increaseincrease

Poll handler caused Poll handler caused
spikesspikes

Mainly Radio Packet Mainly Radio Packet
driverdriver

27. PortabilityPortability

Custom Code in a portCustom Code in a port

Boot up codeBoot up code

Device DriversDevice Drivers

Architecture specific parts of program loaderArchitecture specific parts of program loader

Stack switching code of the multithreading libraryStack switching code of the multithreading library

Kernel and Service layer need no changesKernel and Service layer need no changes

28. Questions?Questions?