From: craigselton@... (Craig Selton)
Date: 2003-04-01T06:58:42+09:00
Subject: Re: Announce: RHDL-0.4.2 (Ruby HDL) an agile HDL

Jan Decaluwe <jan@jandecaluwe.com> wrote in message news:<3E8813F1.502D4ED8@jandecaluwe.com>...
> Craig Selton wrote:
> > 
> > This looks interesting.  You've managed to make a standard scripting
> > language look convincingly like an HDL.  I've seen some other similar
> > efforts recently (like one that uses Python) but, while interesting,
> > they don't end up looking like an HDL - in most cases they end up
> > forcing the HDL designer to learn a totally different style.
> 
> At least for MyHDL (my Python HDL attempt that you refer to), this
> should
> not be the case. Just substitute "while 1" for "process" or "always",
> and "yield" for "wait", and you're done :-) Also, see the section
> on RTL modeling in the MyHDL manual.

First off, I didn't mean to dis MyHDL...

But, as an HDL developer I must say that I prefer not having to do
that mental substitution if I don't have to.  RHDL's syntax just looks
more natural, I guess, but I'm sure MyHDL's approach has merits.

> 
> Moreover, I believe emphasis on superficial syntax similarities can
> make things confusing, as the semantics may still be different.
> For example, the very first "process" example in the RHDL manual has
> a global sensitivity list *and* an internal wait statement, something
> which is forbidden in VHDL. It's forbidden for good reasons I believe,
> because if I try to imagine how this is supposed to work, I get
> thoroughly confused .. 
> 

I kind of see your point, but on the other hand after reading the
explanation I can kind of see how that particular process with wait
works.  I'm not sure how you would use that behavior in a real life
model (I would have to think about it) but I suppose it might be nice
to have that option.  So I'm not sure I would disallow the use of wait
inside of a process with a sensitivity list.

-Craig