The main focus of this paper is the problem of ensuring timeliness in safety critical systems. First, we introduce a method and its associated technique to model both real-time tasks and the timeliness ensuring concern when tasks are executed in parallel. This approach is based on formal aspects of our real-time tasks model and on the definition of the synchronized product operator on the tasks. Real-time tasks are equivalent to their statetransition diagrams and the operator allows us to compose the diagrams of a set of tasks to represent their interactions. The operator is then used to map the tasks to a system of linear constraints to determine the schedulability of the tasks and deduce a system load upper bound. An illustration of our technique on a safety critical study case is presented in which the timeliness property can be achieved for the real-time set of tasks executed in parallel on the same processor. We also introduce how this work can be applied to the multiprocessor case.

We present time-constrained automata (TCA), a model for hard real-time computation in which agents behaviors are modeled by automata and constrained by time intervals.TCA actions can have multiple start time and deadlines, can be aperiodic, and are selected dynamically following a graph, the time-constrained automaton. This allows expressing much more precise time constraints than classical periodic or sporadic model, while preserving the ease of scheduling and analysis.We provide some properties of this model as well as their scheduling semantics. We show that TCA can be automatically derived from source-code, and optimally scheduled on single processors using a variant of EDF. We explain how time constraints can be used to guarantee communication determinism by construction, and to study when possible agent interactions happen.

Multiprocessor scheduling problems are hard because of the numerous constraints on valid schedules to take into account. This paper presents new schedule representations in order to overcome these difficulties, by allowing processors to be fractionally allocated. We prove that these representations are equivalent to the standard representations when preemptive scheduling is allowed. This allows the creation of scheduling algorithms and the study of feasibility in the simpler representations. We apply this method throughout the paper.Then, we use it to provide new simple solutions to the previously solved implicit-deadline periodic scheduling problem. We also tackle the more general problem of scheduling arbitrary time-triggered tasks, and thus in particular solve the open multiprocessor general periodic tasks scheduling problem. Contrary to previous solutions like the PFair class of algorithms, the proposed solution also works when processors have different speeds.We complete the method by providing an online schedule transformation algorithm, that allows the efficient handling of both time-triggered and event-triggered tasks, as well as the creation of online rate-based scheduling algorithms on multiprocessors.

This paper presents the design and some aspects of implementation of a highly dependable, safety-oriented kernel for real-time applications. It is specifically designed as an execution facility for a deterministic semi-formal model -the OASIS model-which allows to express and verify temporal behaviors and communications of a safety critical real-time application.This paper shows specifically how, from a formalism, and a Domain Specific Language, we achieved to build a generic execution layer that conforms to the highest levels of safety, how the safety is implemented thank to the interaction between the kernel and the compilation tools, and how performance was optimized within these constraints.

No abstract