Removing Cycles in Esterel Programs

Programs written in the synchronous programming language Esterel may contain statically cyclic dependencies of signals, which inhibits the application of certain compilation approaches that rely on static scheduling. This talk proposes an algorithm which, given a constructive synchronous program, performs a semantics-preserving source-level code transformation that removes cyclic signal dependencies. The transformation exploits the monotonicity of constructive programs, and is illustrated in the context of Esterel, but should be applicable to other synchronous languages as well

Removing cycles in esterel programs

Esterel belongs to the family of synchronous programming languages, which are affected by cyclic signal dependencies. This prohibits a static scheduling, limiting the choice of available compilation techniques for programs with such cycles. This work proposes an algorithm that, given a constructive synchronous Esterel program, performs a semantics-preserving source-level code transformation that removes cyclic signal dependencies. The transformation is divided into two parts: Detection of cycles and iterative resolution of these cycles. It is based on the replacement of cycle signals by a signal expression involving no other cycle signals, thereby breaking the cycle. This transformation of cyclic Esterel programs enables the use of efficient compilation techniques, which are only available for acyclic programs. Furthermore, experiments indicate that the code transformation can even improve code quality produced by compilers that can already handle cyclic programs

Efficient Compilation of Cyclic Synchronous Programs

Synchronous programs may contain cyclic signal interdependencies. This prohibits a static scheduling, which limits the choice of available compilation techniques for such programs. This paper proposes an algorithm which, given a constructive synchronous program, performs a semantics-preserving source-level code transformation that removes cyclic signal dependencies, and also exposes opportunities for further optimization. The transformation exploits the monotonicity of constructive programs, and is illustrated in the context of Esterel; however, it should be applicable to other synchronous languages as well. Experimental results indicate the efficacy of this approach, resulting in reduced run times and/or smaller code sizes, and potentially reduced compilation times as well. Furthermore, experiments with generating hardware indicate that here as well the synthesis results can be improved

Removing Cycles in Esterel Programs

Esterel belongs to the family of synchronous programming languages, which are affected by cyclic signal dependencies. This prohibits a static scheduling, limiting the choice of available compilation techniques for programs with such cycles. This work proposes an algorithm that, given a constructive synchronous Esterel program, performs a semantics-preserving source code level transformation that removes cyclic signal dependencies. The transformation is divided into two parts: detection of cycles and iterative resolution of these cycles. It is based on the replacement of cycle signals by a signal expression involving no other cycle signals, thereby breaking the cycle. This transformation of cyclic Esterel programs enables the use of efficient compilation techniques, which are only available for acyclic programs. Furthermore, experiments indicate that the code transformation can even improve code quality produced by compilers that can already handle cyclic programs

An Esterel Processor with Full Preemption Support and its Worst Case Reaction Time Analysis

The concurrent synchronous language Esterel allows programmers to treat reactive systems in an abstract, concise manner. An Esterel program is typically first translated into other, non-synchronous high-level languages, such as VHDL or C, and then compiled further into hardware or software. Another approach that has been proposed recently is the direct execution of Esterel-like instructions with a customized processor, which promises the flexibility of a software solution with an efficiency close to a hardware implementation. However, the instruction sets and implementations of the processor architectures proposed so far still have some limitations regarding their completeness, efficiency, and adherence to the original Esterel semantics. This paper presents a novel reactive processor architecture, the Kiel Esterel Processor, which addresses these shortcomings. In particular, it provides a complete, semantically accurate implementation of the Esterel preemption primitives, most of which can be expressed directly with a single machine instruction. One advantage of the reactive processors—in addition to their high execution speed compared to traditional software implementations—is that control-flow is preserved while compiling Esterel into machine code, and that the execution platform has a very predictable timing behavior. This paper presents a precise and very efficient Worst Case Reaction Time (WCRT) analysis, which is geared towards the Kiel Esterel Processor, but which could be adapted to other reactive processors as well