Re: Preferred OS, processor family for running embedded Ada?

[Stephen Leake <stephen_leake@stephe-leake.org>]

"Dr. Adrian Wrigley" <amtw@linuxchip.demon.co.uk.uk.uk> writes:

> I came to Ada from VHDL.  When I first encountered VHDL, my first though
> was "Wow!  You can say what you mean clearly".  Features like user
> defined types (ranges, enumerations, modular types, multi-dimensional
> arrays) gave a feeling of clarity and integrity absent from software
> development languages.

I had the same feeling when I first met Pascal, after learning APL and
Basic. Then Ada was just more of the same :).

> But I have ever since wondered why the VHDL and Ada communities are
> so far apart. It seems like such a natural partnership for
> hardware/software codevelopment. And there is significant scope for
> convergence of language features - fixing the niggling and
> unnecessary differences too. Physical types, reverse ranges,
> configurations, architectures, defered constants and ultra-light
> concurrency come to mind from VHDL. And general generics, private
> types, tagged types, controlled types from Ada (does the latest VHDL
> have these?)

I haven't actually studied the additions in VHDL 2003, but I don't
think most of these Ada features make sense for VHDL. At least, if you
are using VHDL to program FPGAs.

And reverse ranges make things ambiguous, especially for slices of
unconstrainded arrays. So I don't want to see those in Ada.

One big problem with VHDL is that it was not actually designed for
programming FPGAs; it was designed as a hardware modeling language.
People discovered that you can sort of use it for FPGA programming,
and it was the only standard language available for that purpose.
There are many things that you can say in VHDL that make no sense in
an FPGA, so each compiler vendor picks a slightly different subset of
VHDL to support for FPGAs, and gives things different meanings. 

> Perhaps a common denominator language can be devised which has the
> key features of both, with none of the obsolescent features, and
> can be translated into either automatically?  

Why would you want to translate them into each other? The semantics of
VHDL are _significantly_ different from Ada. A VHDL process is _not_
an Ada task.

Although I suppose if you decided to use VHDL to write code for a CPU
instead of an FPGA, you could decide that they were the same.

-- 
-- Stephe