Object-oriented techniques applied to real-time systems

We propose a framework for programming real-time and embedded computer systems. The goal of the framework is to provide the programmer with tools so that the application source code can directly express the problem specification. The framework overcomes programming obstacles such as the process-oriented concurrency model exhibited by current real-time operating systems and the lack of real-time constructs in existing programming languages. These obstacles force the application code structure to deviate from that desired by the application programmer. Our programming framework is centred on the object-oriented programming model, in which objects communicate by sending messages. Objects encapsulate state and export only a well-defined set of operations. The object-oriented model is suited to real-time software applications, which interact with entities in the real world. The framework is based on RPL, an object-oriented real-time programming language. RPL supports asynchronous messaging, has a built-in mutual exclusion construct, can express periodic processing and event-triggered message servicing. Programming in RPL allows the application to express timing constraints at the source code level. Using RPL, the programmer can express problem specifications more naturally compared to current real-time programming environments. To support the RPL programming model, the framework also includes RCL, a real-time kernel component library. RCL is a class library from which the programmer constructs real-time executives required by embedded applications. Features of RCL include deadline scheduling, support for devices and a single form of asynchrony which eliminates interrupt level programming.