Design and Implementation of Maruti-ii 4.1.1 Design Goals

The design and development of integrated systems that support dependable operation of mission-critical applications with real-time requirements poses challenging problems for systems designers and developers. The Maruti system is being designed to address integrated solutions for such applications, from the development of the application to the operating system support for their execution. Maruti has been designed as a time-driven system to provide temporal determinacy. In this chapter, we present the design philosophy of the Maruti system, as well as discuss the design and implementation of Maruti-II. 4.1 Introduction Many complex, mission-critical systems depend not only on correct functional behavior , but also on correct temporal behavior 2, 13]. These systems are called real-time systems. The most critical systems in this domain are those which must support applications with hard real-time constraints, in which missing a deadline may cause a fatal error. Due to their criticality, jobs with hard real-time constraints must always execute satisfying the user-speciied timing constraints, despite the presence of faults such as site crashes or link failures. A real-time operating system, besides having to support most functions of a conventional operating system, carries the extra burden of guaranteeing the execution of its requested jobs satisfying their timing constraints. In order to carry out real-time processing, the requirements of the jobs have to be speciied to the system, so that a suitable schedule can be made for the job execution. Thus, conventional application development techniques must be enhanced to incorporate support for speciication of timing and resource requirements. Further, tools must be made 72 Sec. 4.1 Introduction 73 available to extract these requirements from the application programs, and analyze them for schedulability. Based on the characteristics of its jobs, a real-time system can be classiied as static, dynamic, or reactive. In a static system, all (hard real-time) jobs and their execution characteristics are known ahead of time, and thus can be statically analyzed prior to system operation. Many such systems are built using the cyclic executive or static priority architecture. In contrast, there are many systems in which new processing requests may be made while the system is in operation. In a dynamic system, new requests arrive asynchronously and must be processed immediately. However, since new requests demand immediate attention, such systems must either have \soft" constraints, or be lightly loaded and rely on exception mechanisms for violation of timing constraints. In contrast, reactive systems have certain lead …