The Esterel v5 21 System Manual - Courses

3.3. C CODE FOR DATA HANDLING 33
During its execution, the reaction function can call the user-supplied C
data-handling functions that implement the functions, procedures, and tasks
declared in the Esterel program. It can also read a sensor S1 by calling the
user-supplied sensor C function PROG S S1 that should return the sensor’s
value.
If the Esterel program emits the output signal O1, the generated C code
calls the user-supplied output C function PROG O O1 with the appropriate
output value as argument if the signal O1 is valued.
To summarize, the user must write functions to read sensors, named
PROG S xx, and output functions, named PROG O xx. The reaction function
PROG and the input functions PROG I xx are defined in the generated code.
Notice that all functions related to program input, output, or execution
are prefixed with the program name. On the contrary, the data-handling
function names and the module names are not prefixed. Therefore, it is
unwise to use a name of the predefined C functions as esterel function name
(itoa for example) and a C keyword as module name (main for example).
3.3 C Code for Data Handling
3.3.1 Where to Define the Data-handling Objects
Assume as before that the basename used by Esterel is prog. Then a directive
of the form
#include "prog.h"
is generated in the prog.c file if the Esterel input file declares a type, a
constant, a function, a procedure, or a task.
The prog.h include file must contain the code needed to separately compile
the generated prog.c C file. Therefore, prog.h must at least contain
the C definition of the user-defined types used in the source program. It can
also contain inline constant, function, and procedure definitions by #define
directives.
The constants, functions, and procedures used in the Esterel source program
and not #defined in prog.h are automatically declared to be extern
in the generated file prog.c. They can be defined in any other C file. As
said before, it is often convenient to write them in a file prog data.c.
In all cases, the types, constants, functions, and procedures must be
defined in C with the same name as in the Esterel.