Information AboutEsterel |
| CATEGORIES ABOUT ESTEREL | |
| synchronous programming languages | |
| hardware description languages | |
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The development of the language started in the early 1980 s, and was mainly carried out by a team of Ecole Des Mines De Paris and INRIA lead by Gérard Berry . Current compilers take Esterel programs and generate C Code or hardware (RTL) implementations ( VHDL or Verilog ). The language is still under development, with several compilers out. The commercial version of Esterel is the development environment Esterel Studio . The company that develops it ( Esterel Technologies ) has initated a normalization process with the IEEE . The Esterel v7 Reference Manual Version v7 30 – initial IEEE standardization proposal is publicly available. THE ESTEREL FRAMEWORK Ontology: Components are states Epistemology: Active states, presence and values of signals Protocols: Components interact via instantaneous broadcast Lexicon: Interaction is via signals THE MULTIFORM NOTION OF TIME The notion of time used in Esterel differs from that of non-synchronous languages in the following way: The notion of physical time is replaced with the notion of order. Only the simultaneity and presence of events are considered. This means that the physical time does not play any special role. This is called multiform notion of time. An Esterel program describes a totally ordered sequence of logical instants. At each instant, an arbitrary number of events occur (including 0). Event occurrences that happen at the same logical instant are considered simultaneous. Other events are ordered as their instances of occurrences. There are two types of statements: Those that take zero time (execute and terminate in the same instant) and those that delay for a prescribed number of cycles. SIGNALS Signals are the only means of communication. There are valued and non-valued signals. They are further categorized as being input, output, or local signals. A signal has the property of beeing either present or absent in an instant. Valued signals also contain a value. Signals are broadcast across the program, that means any process can read or write a signal. The value of a valued signal can be determined in any instant, even if the signal is absent. The default status of a signal is absent. Signals remain absent until they are explicitly set to present using the emit statement. Communication is instantaneous, that means that a signal emitted in a cycle is visible immediately. Note that one can communicate back and forth in the same cycle. Signal Coherence rules
Thus present A else emit A end is an erroneous program. BASIC ESTEREL STATEMENTS ; emit S : Make signal ''S'' present in the current instant. A signal is absent unless it is emitted. ; pause : Stop and resume after the next cycle after the pause. ; present S then stmt1 else stmt2 end : If signal ''S'' is present in the current instant, immediately run stmt1, otherwise run stmt2. ; await S : Waits for the next cycle in which S is present. await normally waits for a cycle before beginning to check. await immediately also checks the initial cycle.; loop p end : This repeates body ''p'' infinitely often. As a rule, the loop body cannot terminate instantly. (Needs at least one pause, await, etc. | ||
| "await" class="copylinks" target="_blank">Aawait B |
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