Performance debugging of Esterel specifications

Abstract

Synchronous languages like Esterel have been widely adopted for designing reactive systems in safety-critical domains such as avionics. Specifications written in Esterel are based on the underlying hypothesis, where the computation/communication associated with the processing of all events occurring within the same clock tick are assumed to happen instantaneously (or in zero time). In reality, Esterel specifications get compiled to implementations (such as C code) which do not satisfy the perfect synchrony assumption. Hence, platform-specific timing analysis of such implementations is an important research topic. Interest in this area has lately been renewed with the recent advances in Worst-case Execution Time (WCET)analysis techniques. In this paper we perform WCET analysis on sequential C code and exploit the structure of the code generated from Esterel specifications to obtain tight WCET estimates. Such estimates can validate Esterel-level assumptions on the instantaneous processing of signals or events that occur together. More importantly, they can be used to identify parts of the specification which might pose as timing/performance bottlenecks with respect to the underlying platform. This is done by exploiting traceability links between Esterel specifications and the generated C code, which map the time-critical computations at the C-level back to the Esterel-level. This not only allows a designer to optimize or simplify Esterel specifications, but also choose/configure suitable implementation platforms. We show the results of our WCET analysis on a set of standard Esterel benchmarks and illustrate the utility of our model-code traceability technique using an Esterel specification of a reflex game application.