Learning Forum

[fdtsaid]

In Scade language referece, these is a code sample illustrate the causality error for variable y:

type T = enum {a, b, c};

node WhenBlkSample(x: T) returns (y: T last = b)

let

  activate when y match

  | a: y = a -> pre(y);

  | b: y = x;

  | c: -- empty

  returns ..;

tel

The output of the scade compiler (kcg) is as the following

*** Causality Error (ERR_400): Causality error

  at file ..., line 5, character 7

  at path whenBlkSample/_:a:y=

 the definition of shared flow y depends on flow y via the control context ;

  at file ..., line 2, character 34

  at path whenBlkSample/y/

 the definition of flow y depends on shared flow y via a control block ;

I still have trouble to understand it. Could anyone give some insight?

[Benjamin Descorps]

Hello,

Actually, in your model, the activate block compute the output y. But activation of the activate block also depends on the variable y. This leads to a causality error.

If you want to resolve this error, you should add a delay. Example:

type T = enum {a, b, c};

node WhenBlkSample(x: T) returns (y: T last = b)

let

  activate when last 'y match

  | a: y = a -> pre(y);

  | b: y = x;

  | c: -- empty

  returns ..;

tel

[fdtsaid]

Hi Benjamn, thank you for your clear illustration!