Re: SDL-News: Gates and Block Substructure

Subject: Re: SDL-News: Gates and Block Substructure
From: Andreas Prinz (
Date: Tue Nov 15 2005 - 07:25:50 GMT

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-----From Andreas Prinz <> to sdlnews -----

Dear Jose Marķa Parra Sageras,
you wrote:
> I am developing a program (in SDL-92) that requires a substructure
> inside the definition of a Block Type. I have a doubt about the use of
> gates in this case.

Please note that in general it is not recommended to use substructure
any more. In SDL'2000 this concept is even deleted. It is far better to
use the object-oriented constructs, e.g. inheritance and redefinition.

> In my particular programming context, there is a Block Type definition
> that only contents a block substructure. Inside the substructure there
> are several channels connecting some blocks with the substructure
> environment. I have defined the gates I need in the block type boundary
> (I cannot do this in the block substructure) and I have specified the
> name of the appropriate gate in the substructure boundary (as I am
> supposed to do) in order to connect each channel with the block type
> environment but it does not work.

The basic idea behind substructure is that you have *two* definitions of
the same thing. This means, you write the first way to do the things
using an ordinary block type (This one must not be empty!). Then you add
a substructure definition and put the other alternative in there.
Please note that the substructure defines a static alternative. This
means you have to decide which version to use when you simulate it.
I suppose that you start simulation as is, which means your top-level
version is selected (the one with nothing in it). This again means that
nothing happens.

> Is that all correct or it is needed any other element? I have look some
> book but noone tell anything apart from what I am doing.

So the first thing to do is to make sure that your spec makes sense even
without the substructure. The substructure is then an alternative to
this, and the spec should make sense when replacing the block type
definition by the substructure.

Please note that it is a matter of the tool how you select the version
that should be used for simulation. This is not defined within the
language itself.

Best regards,

Andreas Prinz
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