SDL-News: Re: [SDLTF-Members] Rick's confirmation of interfaces

Subject: SDL-News: Re: [SDLTF-Members] Rick's confirmation of interfaces
From: Rick Reed TSE (
Date: Wed Nov 26 2003 - 15:58:04 GMT

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William H. Skelton at wrote on 26/11/2003 14:26:

> As I understand it, the subset of interfaces would be that an interface is
> defined as a list of signals with their parameters.
> Gates would be declared with the name of an interface instead of a signal
> list. In fact, signal lists could be deleted from the subset.
> I assume previous comments about using signal lists as a data-type, then
> would be applicable to interfaces instead. Is this right, Keith?

Dear William, Dear All,

I am surprised that you and your colleague could not find the <interface
definition> syntax that I cut and paste from Z.100, which made me suspect
you were using an out of date, unapproved version. Please make sure you have
the latest one or at least the version posted at:

You are correct that signal lists should not be needed if interface
definitions are used. The penalty of switching to interfaces exclusively
would be that legacy syntax would not be supported.

It is not clear in what contexts an interface (or signal list) would be used
as a data type, but it would have to have the characteristics of a CHOICE
type. However, currently an interface definition defines a a pid sort, so a
variable declared using the interface identifier can only be assigned a
processing identity (that is a pid value).

Hence using my previous example:

DCL v LineOut;

is legal, and allows statements such as:

v := PARENT; /* parent agent must be compatible with the Interface */


It would not (currently) allow the storing of a received signal in v.

But interfaces are new and probably not implemented yet, so maybe so changes
to SDL would be acceptable so that the declaration defines a CHOICE type.

Rick Reed -
Tel:+44 15394 88462 Mob.:+44 7970 50 96 50

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