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Using a Checkability Profile to Limit Interactions between Embedded Controllers.

Using a .net Checkability Profile to Limit Interactions between Embedded Controllers. David Greaves, Atif Alvi Tope Omitola, Daniel Gordon. University of Cambridge Computer Laboratory. A myriad of devices connected to the network.

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Using a Checkability Profile to Limit Interactions between Embedded Controllers.

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  1. Using a .net Checkability Profile to Limit Interactions between Embedded Controllers. David Greaves, Atif Alvi Tope Omitola, Daniel Gordon. University of Cambridge Computer Laboratory

  2. A myriad of devices connected to the network. All devices are connected and share a common, all-pervasive, middleware. Devices contain controllable and controlling components. A Vision of Evolution for UbiComp

  3. Rules of the Domain • No rule should issue a command under the same circumstances where another rule issues the counter-rule. • Inlet and outlet valves must not both be open at once. • Fire Alarm must mute all music sources. • The front gates must always be remotely openable by some method or other.

  4. Feature Interaction Detection • Can we define a framework for code management in a UbiComp or Sensor/Actuator network that enables proof of safety and liveness ? • We propose using a .net bytecode framework and evaluate its cost and flexibility.

  5. Component Architecture • We partition all devices and services in to • Pebbles (sensors, actuators, software processes)‏ • Applications (heating control, burglar alarm, CD player control...)‏ • Further, we partition application code so it contains no device drivers, dynamic storage, dynamic binding and uses simple network I/O to all pebbles.

  6. A Device: A collection of Pebbles and a Canned App Lets look at what a modern TV set contains: • 1. The following separate devices, each of which can be individually useful in a networked home: • IR Receiver • Teletext Decoder • MPEG Decoder • Programming Memory • Front Panel User Interface • RF Tuner • Colour Display • Ni-Cam Audio Decoder • Power Amplifier • Surround Sound Decoder • 2. A canned application that joins the components.

  7. Automated Directory Systems Work • Devices register in an ad hoc database • eg. UPnP’s SSDP, INS and O2S Oxygen system • Devices can be found by service offered • eg. A colour printer on floor 3 west. • Retrieval by conjunction of predicates (Few successful deployments. Unexpected behaviours. Load balancing/path finding unsupported.)‏

  8. Controllers Vs The Controlled • API Reflection is now a Mature Technology • It will be further deployed (?)‏ • X-by-wire, Field Busses, Sensor Networks, CAN. • EDDL, XDDL, Embedded Systems • Code Reflection has seen virtually no work! • i.e. how do devices describe their embedded behaviour • and how is reactive behaviour between actuators and sensors captured ?

  9. Code Reflection • A device must expose the proactive behaviour of its canned application(s)‏ • Actual source code (constrained language)‏ • Proof carrying actual source code • Summary of behaviour • E.G. I will not send control messages when I am in standby mode. • E.G. I am always off between 1:00 and 5:00. • Device is banned from full operation within domain unless proof obligations are met.

  10. An Example .net CD player. • We built a CD/DVD player according to our component architecture. • The application code was implemented in a pair of .net code bundles. • The bytecode can be read out by a domain controller and checked, along with the other participating applications in the domain, against the rules of the domain.

  11. Pebbles ProjectGeneral Flow

  12. CD/DVD Player Components

  13. CD/DVD Player Block Diagram

  14. Software Costs • Embedded devices have limited capabilities, especially RAM, but ROM is not so critical. • XML parsing is expensive in RAM use. • We have implemented .net interpreter, HTTP server and XML output all at 'reasonable' cost.

  15. Heap and Stack Ram Use

  16. Checkability Classes ? • We have imposed a checkability profile on the .net bundles. • Current profile is finite-state and strictly limited in IO libraries used. • All participating applications in the domain must correspond to our profile. • In the future, can define a richer class, based on linear integer programming, Presburg and so on.

  17. Conclusions • Running a 'complex' software stack is not a real obstacle, but don't parse too much XML. • Using .net bytecode in embedded systems can be fast and compact enough, otherwise reflect your behaviour in .net while executing something else. • We need to explore incremental model checking. • We need to formally define our checkability class.

  18. The End • David.Greaves@cl.cam.ac.uk • www.cl.cam.ac.uk/Research/SRG/HAN/Pebbles • The Pebbles, AutoHAN and Oxygen O2S Teams

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