The Esterel v5 21 System Manual - Courses

3.4. THE REACTION INTERFACE 43
3.4.3 Output Signals
For each output signal OS, the user must write a void output C function
PROG O OS that takes an argument of the appropriate type if the signal OS
conveys a value. This function is automatically called by the reaction function
if the signal is emitted.
WARNING: The order of the output function calls performed
by the reaction function is arbitrary and unspecified 1 .
Assume that a reaction causes the output of a pure signal OS1 and of an
integer signal OS2 with value 4. Then PROG calls the user-defined C functions
PROG O OS1 and PROG O OS2 with the appropriate arguments; the following
calls will be executed (in arbitrary order) in the body of PROG:
PROG_O_OS1 ();
PROG_O_OS2 (4);
The C functions PROG O OS1 and PROG O OS2 must do whatever is necessary
to communicate with the actual environment.
3.4.4 Inputoutput Signals
For an inputoutput signal IOS, an input C function PROG I IOS is automatically
generated as for an input signal, and the user must write an output
C function PROG O IOS as for an output signal.
An inputoutput signal IOS received by the reactive program behaves as if
it was internally emitted by it, and is therefore re-emitted outside whenever
received in a reaction:
• if IOS is a pure inputoutput signal, then PROG O IOS is called if IOS is
received or emitted by the program. Therefore, PROG O IOS is always
called by the reaction function if PROG I IOS was called before.
• If IOS is a single signal, then there are two cases:
– If IOS is received by the program, it cannot be emitted by it
in the same reaction, which is detected by the Esterel compiler
when option -Icheck is set. The function PROG O IOS is called
with argument the value received by PROG I IOS.
1 According to the Esterel semantics, this ordering cannot be specified