## General information

**Starting date.** march 2009.

**Project coordinators**: Robert de
Simone and Jean-Pierre Talpin

**Presentation.**
The design of Real-Time Embedded (RT/E) Systems is currently a field of encounter
between numerous methods and techniques developed independently, for specific purposes
and often in different aims. A current grand challenge is to combine them into a global
coherent design flow, each at its appropriate modeling level. The
overall objective is to best
map complex applications onto heterogeneous architectures, the former comprising latent
(logical) concurrency while the latter offer (physical) intrinsic parallelism with contrived
communication structures.

The TRIADE Collaborative Research Initiatives (in french, Action de
Recherche Collaborative - ARC) of INRIA
aims to tackle these issues using formal model developments and by using techniques
pertaining to Concurrency Theory, Scheduling Theory, Compilation and Optimization
Theories, Model Driven Engineering and Electronic System Level design altogether.
In some cases, the models are currently put forth in the approach, in others they are
somehow buried under some algorithmic treatments. Exhibiting them and making their
relations explicit is the focus of the project.

The models adopted by TRIADE require precise formal semantics and, more specifically, precise mathematical
modeling for logic, temporal and timing aspects. This is required so that the subsequent
transformations, abstractions and refinements are provably sound and
semantic preserving.
This should be opposed to the mainstream model-driven approach, where
(certainly useful) higher-level models are simply put next to a lower-level implementation
counter-parts, as if proximity alone would make them behave "the same".

In this prominent, informal approach the models are sometimes explicitly concurrent
descriptions which correspond to (lower-level) sequential simulation code (as often in UML
or Simulink). On the opposite, they are also sometimes seemingly sequential simulation
descriptions, that are in turn synthesized into (lower-level) parallel hardware (as in TLM
SystemC or High-Performance Computing nested loop code). TRIADE would
like to consider both
kinds of transformations, as well as the general case where models of computations are
refined one into another. Its approach requires a number of formal restrictions on the type of models
dealt with. This, again, can be opposed to the larger setting where
general-purpose programming languages are naively used, but where often hidden synthesizability side conditions
crawl in incidentally at hidden places. The belief in TRIADE is that the clarity of assumptions
(which often match mandatory requirements in the RT/E domain anyway) is a prerequisite
of sound model-based design approach.

TRIADE shall build on techniques and theories that have been for a long-time developed
inside INRIA or in the neighboring French research community, and in fact can often be
traced back to the original C3 (Cooperation, Communication, Concurrency) nation-wide
initiative of the mid-1980s. Typical examples are: Models of Computations and Communications
(MoCCs) such as Process Algebras, Timed Event Graphs and Synchronous
Reactive Languages; model-based scheduling techniques (with periodic steady regimes);
nested loop parallelizing and optimization; distributed real-time scheduling; optimized
compilation onto micro-architectures with instruction- and task-level parallelism, model-based
and platform-based design in the field of embedded systems; high-performance and
grid computing... (list not exhaustive).

Precise links between formalisms on their time aspects, for instance by using formal
semantics concepts of modules systems and type theory, is in our view a necessary condition
for a true component-based approach of design, where the same object can be considered
at various levels of realization, with some amount of confidence that the contract promised
at some external level will be satisfied (in some well-defined sense) by the implementation.
Clear understanding of time is a prerequisite for interoperability in co-simulation. By
contrast, current attempts amount all too often to exercising jointly various simulators
in a step mode, without real concern for established formal coherency of the whole (just
plausibility of results).

Of course, it has to be realized that in "real-life" these approximate practices are
already providing many helps in early system evaluation, improving on most current practices.
But, given that precise comparative semantic links exist at places, we want to push
further the limits of true model-based design for RT/E systems wherever feasible. The
good news is that, but dealing with formal models and semantics, one gets very often rich
automatic optimization techniques (which apply under well-established conditions).