SDL-News: Re: Clarification of Interfaces

Subject: SDL-News: Re: Clarification of Interfaces
From: Rick Reed TSE (
Date: Fri May 14 2004 - 14:11:53 GMT

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William H. Skelton at wrote on 14/05/04 12:01:

> Anyway we can put interface declarations in a package, which is what we do
> at SOLINET... :-)
> I suspect that Andreas feels we have misunderstood what an interface is
> supposed to be. For clarification, I have understood from Rick that
> interfaces can be used to contain a signal list or the signals declarations
> themselves, and that gates can be declared with an interface instead of a
> signal list.
> In our case we want to limit the scope of signals, so we just put them in
> interfaces, get rid of signal lists and limit interfaces to only containing
> signals.
> There is scope for misunderstanding, so I would appreciate comments from
> anyone on this, especially Andreas.

Dear All,

In SDL-2000 it is correct that an interface definition can contain one or
more signal definitions. In fact most interfaces are used to define just a
set of signal definitions. Some advantages of an interface over the older
signallist construct are:
1. It is a type, therefore can be parameterised and inherited;
2. It can be used to name a gate (an "interface gate definition") that has
the signals (etc.) defined by the interface.
However, (at least currently) an interface definition cannot contain a
signallist definition, though it can include signallists via a use clause.

I have proposed that the signallist construct is treated as an alternative
syntax for defining an interface. This proposal has not yet been either
accepted or rejected as far the Z.100 standard is concerned.

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

[[Aside - it is not clear why William sent this to the list. Maybe it was sent to the <> list - I don't know because I was excluded from that list. Anyway I have used the sdlnews list to reply because some previous discussion related to the SDL Task Force took place on that list.]]

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