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From: gwinn@res.ray.com (Joe Gwinn)
Subject: Re: ada and robots
Date: 1997/06/17
Message-ID: <gwinn-1706972232540001@dh5055155.res.ray.com>#1/1
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References: <338CDA96.53EA@halcyon.com> <338F5D7D.6C03@tiac.net>
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 <gwinn-0506971829240001@smc19.ed.ray.com> <dewar.866303747@merv>
Organization: Raytheon Electronic Systems
Newsgroups: comp.robotics.misc,comp.lang.ada
Date: 1997-06-17T00:00:00+00:00
List-Id: <comp.lang.ada>


In article <dewar.866303747@merv>, dewar@merv.cs.nyu.edu (Robert Dewar) wrote:

> <<Joe said
>                                                                                

> <<As for Ada83 and shared memory, the problem was that the Ada83
compilers      
> all believed that only they changed memory, so it was OK to cache
data          
> items in CPU registers for long periods of time.  For the most part,
there      
> was no reliable (and portable) way to tell the compiler different, so
we        
> performed various dances to ensure that Ada83 never knew the whole
truth.>>     
>                                                                                

>                                                                                

> Well for items that could be kept in registers, e.g. small scalars,
which       
> typically corresponds to the need for messing with IO mapped memory, I
fail    
> to see why the standard feature - pragma Shared - would not be exactly
> what you needed. Please explain why pragma Shared did not do the job. if
> you were using a compiler that did not implement pragma Shared, then it
> was not an Ada 83 compiler, but a compiler for a subset of the language.

The problem was that not all Ada83 compilers implemented pragma shared
correctly, or the same, so we couldn't depend on pragma shared.  It was
simpler, and --oddly-- more portable to just use assembly.  Ada95 is
supposed to have fixed this problem, which was shared by pragma volatile.


> <<abstractions are language independent>>
> 
> That is nonsense. Languages have HUGE differences in abstraction capabilities.
> Anyone who thinks COBOL has the same abtraction capabilities as say, Pascal,
> knows NOTHING about either language.

Ahh ... let's talk only about modern, mainstream languages, like Ada and
C.  Or, we need also to pull in every cat and dog research language that
ever was, and I grant you that many of them are cripples.  Anyway, it
seems to matter more *who* is doing the abstracting than the details of
the language they use.

Joe Gwinn