Uniform Driver Interface (UDI) reference implementation and determinism

This paper briefly discusses the technology and standardization activities that are in progress in Project UDI (Uniform Driver Interface) and INCITS (InterNational Committee for Information Technology Standards) Technical Committee R1, Real-time Computing Systems. Project UDI has an open source reference implementation that runs in several operating systems. The design of this implementation is discussed and real time issues identified. The focus of this paper is to discuss the changes that can be made to the Project UDI reference implementation to develop a deterministic UDI reference implementation suitable for real-time needs. These changes are fairly significant, but affect the operating system only, allowing the same UDI drivers to be used in the deterministic implementation as in the time-sharing implementations. The effects of these changes are evaluated in terms of the benefits to, or impacts on, different categories of users. Some of these changes are suitable for real-time safety critical systems; others make sense for other types of realtime systems. The types of issues discussed include allocation of data buffers and control structures, interrupt processing, scheduling, multiprocessors, I/O processors, etc. UDI also introduces a fundamental concept of execution "regions." Regions allow I/O drivers or protocol modules to live in different protection domains. These regions may in fact be on different processors. There are real-time trade-offs to be made in transitioning between regions. These trade-offs are discussed. Finally the paper discusses the status of the real-time standardization activity, the standardization decisions that have been made and the reasons for these decisions.