Section: New Software and Platforms

Lopht

Participants : Thomas Carle, Manel Djemal, Dumitru Potop Butucaru [correspondant] .

The Lopht (Logical to Physical Time Compiler) has been designed as an implementation of the AAA methodology. Like SynDEx, Lopht relies on off-line allocation and scheduling techniques to allow real-time implementation of dataflow synchronous specifications onto multiprocessor systems. But there are several originality points: a stronger focus on efficiency, which results in the use of a compilation-like approach, a focus on novel target architectures (many-core chips and time-triggered embedded systems), and the possibility to handle multiple, complex non-functional requirements covering real-time (release dates and deadlines possibly different from period, major time frame, end-to-end flow constraints), ARINC 653 partitioning, the possibility to preempt or not each task, and finally SynDEx-like allocation.

Improved efficiency is attained through the use of classical and novel data structures and optimization algorithms pertaining to 3 fields: synchronous language compilation, classical compiler theory, and real-time scheduling. A finer representation of execution conditions allows us to make a better use of double resource reservation and thus improve latency and throughput. The use of software pipelining allows the improvement of computation throughput. The use of post-scheduling optimizations allows a reduction in the number of preemptions. The focus on novel architectures means that architecture descriptions need to define novel communication media such as the networks-on-chips (NoCs), and that real-time characteristics must include those specific to a time-triggered execution model, such as the Major Time Frame (MTF). Attaining efficiency alse requires a fine-grain description of more classical platform resources, such as the multi-bank RAMs, to allow efficient allocation during scheduling.

Significant contributions to the Lopht tool have been brought by T. Carle (the extensions concerning time-triggered platforms), M. Djemal (the extensions concerning many-core platforms), and Zhen Zhang under the supervision of D. Potop Butucaru. The tool has been used and extended during the PARSEC project. It is currently used in the direct collaboration with Airbus Defence and Space and the CNES, in the IRT SystemX/FSF project, and in the CAPACITES project. It has been developed in OCaml.