1. Esterel
By: Sam Weinberg

2. Basis of Esterel Imperative deterministic language
For finite state complex reactive systems
Dual hardware/software language
Can generate C-code to be used as a reactive kernel in other programs
Esterel has been
used in such things as fuel ignition and other before, after, during items.

3. Criterion for an Esterel Program
Only simultaneity and precedence of events matter
The notion of time is of all events being instantaneous
Has a synchronization that is similar to and compliments hardware
Relies on start and stop signals as well as other modules for more complex interaction

4. Primitive Signals

5. Derived Esterel Statements

6. Example one
module ABRO:
input A, B, R;
output O
loop
[ await A || await B ];
emit O
each R
End module - takes a series of pre-built modules and states run in parallel and
When terminated/reached immediately make O present/outputted until R is received
This code is not wholly atypically simple and programs can occur in near instantaneous time

7. Example two The above causes an indirect emission of A
abort
pause;
emit B
when A ||
present B then emit A end.
The above causes an indirect emission of A
One propagating issue of the above point is causality and contradictory programs are very easy to write

8. Flaws
Since Esterel is a dedicated, somewhat inflexible and reliable means to program reactive systems, it has a number of shortcomings
Esterel code is highly simplistic and while the potential for variables does exist, they cannot be shared
There is no dynamic memory allocation or dynamic creation of processes

9. Esterel Compiler
Since Esterel is not widely used, compilers are often not up to date
Available on Windows and Linux as v5_92
links to Esterel Compilers
Was experimentally being used by the Polis group
This is now known as the Center for Electronic Systems Design
The language has been more or less defunct since 2001

10. References
“The Synchronous Language Esterel” Stephen A. Edwards, Columbia University 2002
“An Introduction to Esterel” Embedded.com, 2001.