Differences between Ada and VHDL

Differences between Ada and VHDL

[Bob Sheraga]

Can anyone refer me to a comprehensive discussion of the differences 
between Ada and VHDL (primarily syntactical differences)? 

Thanks in advance.

Bob Sheraga
bob@jrs.com

Re: Differences between Ada and VHDL

[Paul Pukite]

Bob Sheraga  <bob@jrs.com> wrote:
>Can anyone refer me to a comprehensive discussion of the differences 
>between Ada and VHDL (primarily syntactical differences)? 
>
>Thanks in advance.
>
>Bob Sheraga
>bob@jrs.com

I haven't seen one myself (I suppose you could get the two LRMs
and compare page by page. That would be comprehensive!).

Besides the syntactic "surface" similarities, Ada and VHDL have a common 
foundation in that they both emphasize strong typing, hierarchical 
organization, separation of interface from implementation, levels of 
abstraction, and maintainability through readability.  The strong typing 
eliminates at least one class of errors from occurring, the 
hierarchical organization and interface conventions allow large teams 
of developers to work on a project, and the levels of abstraction permit 
either bottom-up or top-down system design techniques (Ada 9X also allows 
full object-orientation). 

With that said, a few syntactical differences do stand out:

   VHDL            Ada
   ~~~~            ~~~
  to, downto       ..          -- range (Ada requires a reverse keyword)
  inout            in out      -- one less keyword required in Ada
  library, use     with, use   -- use clauses have different semantics
  variable X       X           -- need a variable keyword to denote object
  constant X:      X:constant  -- constant declaration
  generic          generic     -- generic in Ada includes types, fxns, etc
  TextIO           Text_IO     -- File objects have different syntax

Many parts of VHDL have no correspondence to Ada, such as:
  signals, entities, components, assert, attribute, physical types, etc.

On the other hand, Ada has the following constructs you don't find in VHDL:
  private and tagged types, tasks, exceptions, delay, etc.

I wouldn't try to compare VHDL concurrency and Ada concurrency as they 
don't have any real common ground (hardware modeling vs. operating system 
threads). However, if you want to compare only the sequential statements, 
flipping back and forth between the LRMs is justifiable if you need 
elaboration on a concept.

--
Paul Pukite (pukite@daina.com)       
DAINA Engineering 612/781-7600       
4111 Central AVE NE, Suite 212       
Minneapolis, MN  55421-2953