Real-time DSP operating systems have recently appeared in several commercial products that integrate multimedia processing into PCs. The DSP OSs, which run on DSP subsystems integrated on PC adapter cards, include admission control capabilities to ensure that timing guarantees are met and sufficient resources are available to handle the processing demands of a given mix of applications. Admission control is possible because the timing characteristics of the kernels are fully understood and real-time scheduling is used for all kernel resources. If a real-time approach is to be successful in host OSs, a similar approach must be followed. We compare the performance of the DSP OS and host OS approaches. We describe the DSP OS architectures and their admission control algorithms. We describe a general framework we have developed which models OSs for the purpose of admission control.

This paper develops formal scheduling models for several common system bus architectures used in PC and workstation systems. The scheduling models include fixed priority, round robin, and hybrid bus scheduling policies. The models provide a quantitative means to explore the real-time design space for each of the buses. This paper provides a simple approach for the creation of bus scheduling models which can be used effectively by a bus designer or system user to improve real-time bus performance. The step by step process of model development is presented. In addition, an application modeling methodology is described which separates the application requirements from the bus model. The utility of the scheduling models is demonstrated by analyzing several common system buses.

Real-time scheduling theory attempts to guarantee that a real-time task set will always meet its deadlines. Real-time systems are typically implemented via real-time operating systems (RTOSs). However, there currently exists a wide gap between real-time scheduling theory and the reality of RTOS implementation. Bridging the gap requires effort on two fronts. First, real-time scheduling theory must be extended such that implementation realities may be correctly incorporated. Second, the high level of sophistication required to apply real-time scheduling theory to RTOSs bars practitioners from creating scheduling (timing) models of their operating systems. This paper summarizes recent work on developing an engineering methodology that allows novice users and developers to accurately model and evaluate RTOSs. Specifically, we recount the experiences of a CMU undergraduate class's experience in modeling and analyzing three commercial Digital Signal Processor (DSP) operating systems.>