DUNEqqiX real-time operating system

Real-time applications need guarantee of response deadline by the computing system, promptness of reflex responses, reliability of application code. The first part of the paper examines the requirements for real-time operating systems and ends with the DuneqqiX basic design decisions. The operating system must be able to provide immediate tasks for reflex reaction to interrupts and autonomous tasks for reacting with a specified deadline to periodic or aperiodic events related to the real-time application. Thus the behaviour of the computing system must be thoroughly controlled. The guarantee of response is provided by a high level real-time scheduler which supervises the priorities given to the tasks, and by a priority-driven, reentrant, preemptive, real-time kernel. In order to provide fast response results, the real-time kernel takes advantage of the symmetric multiprocessor architecture. The reliability of the application code is eased by providing programming tools and allowing code reusability through full Unix compatibility. The second part presents the detailed implementation choices of DuneqqiX which aim at reducing all known kinds of latencies due to processors, resources or I/Os contentions. Immediate task association with an interrupt level and with an autonomous application task context, inter-task shared memory segments, priority inheritance, deadlock prevention, contiguous files are some of the relevant features which are provided. The third part rapidly describes an example of a host architecture for this operating system and the last part gives some performance measures on this host architecture.