Distributed computing paradigm proposes a high performance solution thanks to advances in network technologies. Different programs located on several computers interact all together in order to achieve a global common goal. However, designers and developers of distributed software applications have to face several problems such as heterogeneity of the various hardware components as well as both operating systems and communication protocols. Development of middleware standards allows to consistently face these problems. Modern flight simulators techniques and implementations often result in many sophisticated and complex calculations that require a high level of computing power. Several flight simulator applications often require their services to be delivered with respect to a given period of time (deadline). This issue constitutes the problematic of real-time systems, which are defined as systems in which the correctness of the system not only depends on the logical results of computation, but also on the time at which these results are produced. Real-time systems are broadly classified into two categories based on the nature of the deadline, namely, hard real-time systems, in which the consequences of not executing a task before its deadline may be catastrophic and soft real-time systems, in which the utility of results produced by a task with a soft deadline decreases over time after the deadline expires. The main objective of our work is to use the HLA IEEE 1516-2000 standard in order to develop, to interconnect and to maintain a flight simulator. For years, the French Aerospace Laboratory (ONERA) has been developing his own Open-Source middleware RTI compliant with HLA standard called CERTI, running under several operating systems including Linux and Windows. We will use this RTI for interconnecting each part of our simulator. This RTI is recognizable through its original architecture of communicating processes. It is a distributed system involving two processes, a local one (RTIA) and a global one (RTIG), as well as a library (libRTI) linked with each federate. Each federate process interacts locally with an RTI Ambassador process (RTIA) through a Unix-domain socket. The RTIA processes exchange messages over the network, in particular with the RTIG process, via TCP (and also UDP) sockets, in order to run the distributed algorithms associated with the RTI services. Our work takes place in a global project named PRISE (Plate-forme de Recherche et d'Ingénierie des Systèmes Embarqués). The main focus of this project is to study new embedded systems concepts and techniques through a special hardware and software environment. However, works to include real-time specifications and properties to HLA standard are less advanced than other ones. This presentation explains how we proceed to implement and to test this flight simulator and how we validate real-time behavior on our computing platform. In our case, a key benefit of this architecture is to master the implementation of RTI used and thus facilitate the integration of changes in the source code to ensure temporal predictability of CERTI. Initial results, providing some answers about the suitability of CERTI to face with real-time constraints, came from ONERA/CNES satellites formation flying studies. These studies have shown that CERTI (in its original version) is able to manage multiple real-time federates with short period of time
