Add check bison version in configure.ac file.
To build correctly matiec we need bison greater or equals than 2.4 version.
Now the "configure" script is able to check if system has correctly requirements.
FUNCTION_BLOCK DIFFEQ
VAR_INPUT
RUN : BOOL ; (* 1 = run, 0 = reset *)
XIN : REAL ;
A : ARRAY[1..] OF REAL ; (* Input coefficients *)
M : INT ; (* Length of input history *)
B : ARRAY[0..] OF REAL ; (* Output coefficients *)
N : INT ; (* Length of output history *)
END_VAR
VAR_OUTPUT XOUT : REAL := 0.0 ; END_VAR
VAR (* NOTE : Manufacturer may specify other array sizes *)
XI : ARRAY [0..128] OF REAL ; (* Input history *)
XO : ARRAY [0..128] OF REAL ; (* Output history *)
I : INT ;
END_VAR
XO[0] := XOUT ; XI[0] := XIN ;
XOUT := B[0] * XIN ;
IF RUN THEN
FOR I := M TO 1 BY -1 DO
XOUT := XOUT + A[I] * XO[I] ; XO[I] := XO[I-1];
END_FOR;
FOR I := N TO 1 BY -1 DO
XOUT := XOUT + B[I] * XI[I] ; XI[I] := XI[I-1];
END_FOR;
ELSE
FOR I := 1 TO M DO XO[I] := 0.0; END_FOR;
FOR I := 1 TO N DO XI[I] := 0.0; END_FOR;
END_IF ;
END_FUNCTION_BLOCK