An Introduction to Time-Constrained Automata

Abstract

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.

Method and Tools for Mixed-Criticality Real-Time Applications within PharOS

“…The scheduling algorithm it implements is a variant of EDF for time-constrained automata. We proved this algorithm to be optimal [2]. Optimality means that the proof of feasibility of a set of tasks ensures that EDF will always schedule tasks so that they meet their deadline (provided that they execute for no longer than their allocated timing budgets).…”

“…At the heart of PharOS is a formal model of task, the time-constrained automata model [2], which is based on time. This section gives a short overview of this model and its implementation, which is necessary to understand the design of the temporal isolation in PharOS.…”

“…These informations are used to implement the scheduling algorithm, which is a variant of EDF. Details can be found in [2].…”

A Model of Parallel Deterministic Real-Time Computation

“…We assume that release time and deadline constraints of all instructions in the system are met 6 , i.e. that the execution of the system is temporally correct.…”

“…PharOS [1] is a framework to design, implement and execute safety-oriented embedded real-time applications. It relies on the time-triggered paradigm [5], and implements a multitask model where each task may use a different, dynamically varying time scale [6].…”