This paper introduces the notion of transparent distribution of real time software components. Transparent distribution means that (1) the functional and temporal behavior of a system is the same no matter where a component is executed, (2) the developer does not have to care about the differences of local versus distributed execution of components, and (3) the components can be developed independently. We present the design and implementation of a component model for real time systems that is well suited for transparent distribution. The component model is based on logical execution time, which abstracts from physical execution time and thereby from both the execution platform and the communication topology. 1 The MoDECS project (www.MoDECS.cc) is supported by the FIT-IT Embedded Systems grant 807144 (www.fit-it.at).
We present a framework for command processing in Java/Swing programs based on the model-view-controller (MVC) pattern. In addition to standard approaches our framework supports (1) centralized exception handling, (2) premature command termination, (3) pre-and postprocessing of commands, (4) undo/redo based on event objects and model listeners, and (5) generic undo/redo commands. The framework has been applied successfully in a number of graphical editors as part of a tool chain for real time programming. It proved to increase the quality of the software by eliminating local exception handlers and by confining the impact of undo/redo to a small add-on to the model part of the application.
Oberon simultaneously refers to a modular, extensible operating system and an object-oriented programming language developed for its implementation. Although the original Oberon System had been conceived as the native operating system for a custom-built workstation, further implementations for several commercial platforms were developed later and are described here. All of these implementations are based on an efficient, retargetable Oberon compiler, and each provides a complete Oberon environment and the original library interface. This paper describes the structure of the compiler, summarizes the experience gained in adapting it for various CISC and RISC processors, and presents some empirical performance data. It also sheds light on the task of grafting an operating environment onto a variety of existing operating systems.The front-end is controlled by the module OPP, a recursive-descent parser. Its main task is to check syntax and to call procedures constructing the symbol table and the syntax tree. The parser requests lexical symbols from the scanner (OPS) and calls procedures of OPT, the symbol table handler, and of OPB, the syntax tree builder. OPB also checks for type compatibility.The back-end is controlled by OPV, the tree traverser. It first augments the symbol table with machine-dependent data (using OPM constants), such as the sizes of types, the addresses of variables, or the offsets of record fields. It then traverses the syntax tree and calls procedures of OPC, the code generator, which in turn synthesizes machine instructions using procedures of OPL, the low-level code emitter.This module structure results in a fully portable front-end, as well as a hostmachine independent back-end.
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