Resumen de Modelado e implementación de Sistemas de Tiempo Real mediante Redes de Petri con Tiempo

Francisco José García Izquierdo

• The work presented in the thesis must be considered in the context of a more general project, which proposes an unified method, based on the use of the Time Petri Nets formalism (TPN), to deal with the development of Real Time Systems (RTS). This project's objective is to cover the whole development cycle of a RTS with Time Petri Nets, from the requirement specification to the testing phase, including the properties analysis an the implementation.

  The thesis tackles two aspects of the RTS life cycle: the modelling and the implementation, or code generation. After introducing of the RTS modelling concepts using TPN, and the analysis techniques fundamentals, the work focuses on the code generation, taking the Petri Nets implementation techniques as a base and extending them in order to make the techniques able to deal with the special temporal requirements of the RTS.

  The centralized technique is presented in first place. Based on the separation of the functional and control parts of the RTS, the technique proposes the use of a coordinator, which holds the control of the system execution and the supervision of the deadline meeting. This technique has several drawbacks, such as the impact in the performance of the coordinator presence.

  In order to cope with these evidenced drawbacks, the thesis proposes the decentralized implementation technique. Its main aim is to split the net into a set of concurrent subnets, mono-marked p-invariants, which communicate between each other through synchronous or asynchronous primitives. These subnets are called protoprocesses. After this net partition, the technique proposes the identification of a set of execution units (specific place-transition structures) that can be directly translated into Ada-95 statements. This strategy leads to the generation of the skeleton of the code that implements the control part of the RTS. As an additional result, the thesis proposes Time Petri Net based models for the real time Ada-95 statements.

  Finally, in cases where it is not possible to apply the decentralized techniques, the work proposes mixed implementation techniques.