Re: Ada and Automotive Industry

[james@cdac.com (James Thiele)]

In article <EACHUS.96Nov7203951@spectre.mitre.org> eachus@spectre.mitre.org (Robert I. Eachus) writes:
>In article <1996Nov6.210957.3070@ole.cdac.com> James Thiele <james@cdac.com> writes:
>
>  > The language itself was hardly consistent.  Quick, why is
>  >     for i in -1..1 -- illegal in Ada 83?
>
>   Because the call to "-" is ambiguous.  The only reason this was a
>surprise is that Ada 83 had a special rule to resolve the ambiguity
>and choose a type for i in the "most common" cases.  But this didn't
>fit that mold, since users can redefine "-".  However, if you write:
>
>        for I in Integer range -1..1 loop...
>
>   It is legal and compiles fine.  (But you may have wanted some other
>type...that's why you got the error.)

That's not how I remember it.  The ".." operator required that both
of it's arguments be of the same "type" (the Ada LRM probably used
another term) and -1 was considered an expression, but 1 wasn't.
I prefer a language where if I write a statement that looks like
it should be legal it is.  Even PASCAL accepts for i:= 1- to 1 do ...

>  > In Ada 83 you can't schedule a periodic event reliably -- no Ada
>  > task was guaranteed to run at the time requested.  Everyone I knew
>  > who used Ada for avionics in the 80s wrote their own scheduler.
>
>   A HUGE amount of wasted effort because people couldn't be bothered
>to read the reference manual.  What the Ada 83 RM said, and pretty
>plainly at that, was that a critical task would run exactly (within
>the limits of accuracy of the physical clock, etc.) when scheduled,
>unless there was an equal or higher priority task using every
>available processor.  There was even an AI, published as a
>ramification, titled "Preemptive scheduling is required" (AI-32).
>Can it get any clearer?  
>

We didn't find any Ada compiler vendors in the 1986-88 era who
supported preemptive scheduling.  And they all talked to us,
because we were potentially a huge customer.  Do you know any?

Anyway, I saw this on the realtime newsgroup.  If I'd noticed the
crossposting to comp.lang.ada I'd have stayed away.

--
James Thiele
james@cdac.com (work) or jet@eskimo.com (home)
http://www.eskimo.com/~jet