In the real-time research community, one often distinguishes between hard and soft temporal requirements. If a deadline is violated in a hard real-time computation the logical result is useless. In a soft real-time computation, the logical result could have a meaning even though a deadline is not met. Many real-time applications of today have both hard and soft temporal requirements. For example, in the computer system of a car, a hard requirement involves controlling the brakes, whereas the automatic climate control is an example of a soft requirement.
Real-time applications often have two types of requirements on control: periodic and aperiodic. Periodic control means that an activity is computed repeatedly with a predefined period time, e.g., implementing a cruise control for a car leads to a periodic activity. Aperiodic control means that the application generates events that the computer system must respond to within a certain time, e.g., the brake system in a car. Periodic and aperiodic activities can be either soft or hard.
An important aspect in the design of real-time systems is the integration of methods, architectures, and tools to avoid inconsistency between design and implementation. It is not unusual to find people using a particular method in the design phase of some new system, then working with another tool for the implementation, violating specifications set during the design phase. A classical example of this dilemma is structured analysis and design which aids the specification of the system without considering the runtime environment. With the proper integration of design specification and implementation tools, specifications made in the design phase could be enforced throughout the entire life-cycle of the product.
This paper describes RealTimeTalk (RTT), a framework for the development of applications with both hard and soft real-time requirements. The organization of the paper is as follows. Section 2 highlights the features of RTT; Section 3 presents the programming-in-the-large aspects of RTT, followed by a presentation of the RTT language in Section 4. Section 5 describes the run-time environment; Section 6 describes the prototype system; Section 7 con-