SIGNAL (programming language)

SIGNAL is a programming language based on synchronized data-flow (flows + synchronization): a process is a set of equations on elementary flows describing both data and control.

The SIGNAL formal model provides the capability to describe systems with several clocks (polychronous systems) as relational specifications. Relations are useful as partial specifications and as specifications of non-deterministic devices (for instance a non-deterministic bus) or external processes (for instance an unsafe car driver).

Using SIGNAL allows to specify an application, to design an architecture, to refine detailed components down to RTOS or hardware description. The SIGNAL model supports a design methodology which goes from specification to implementation, from abstraction to concretization, from synchrony to .

SIGNAL has been mainly developed in INRIAEspresso team since the 1980s, at the same time as similar programming languages, Esterel and Lustre.

The SIGNAL language was first designed for signal processing applications in the beginning of the 1980s. It has been proposed to answer the demand of new domain-specific language for the design of signal processing applications, adopting a dataflow and block-diagram style with array and sliding window operators. P. Le Guernic, A. Benveniste, and T. Gautier have been in charge of the language definition. The first paper on SIGNAL was published in 1982, while the first complete description of SIGNAL appeared in the PhD thesis of T. Gautier. The symbolic representation of SIGNAL via z/3z (over [-1,0,1]) has been introduced in 1986. A full compiler of SIGNAL based on the clock calculus on hierarchy of Boolean clocks, was described by L. Besnard in his PhD thesis in 1992. The clock calculus has been improved later by T. Amagbegnon with the proposition of arborescent canonical forms.

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