Re: Duration vs. Ada.Real_Time

[Marin David Condic <mcondic.auntie.spam@acm.org>]

Stephen Leake wrote:

> Perhaps it would be more appropriate for Marin to request that type
> Ada.Real_Time.Time_Span (LRM appendix D) match the hardware clock;
> that is more clearly intended to be a "hard real-time" clock type.
>

Oh, I'm not really fussy about how you get there. That might work
reasonably well. And I certainly don't insist that *every*
implementation of Ada go off and do it my way. My point is that when one
is working with an embedded compiler for a specific target that has a
real time clock, one just kind of expects Duration to have some
relationship to that clock. If you do delays, you kind of expect to be
able to get a delay approximately as good as the resolution of the clock
- no more - no less.

An analogy would be, for example, someone implementing the type
Character as a 32 bit word. (Don't know if this is *legal*, but suppose
that it was?) Yes, a 32 bit word will hold a single ASCII character just
fine and provided the compiler is consistent in this, it will mostly be
invisible to the programmer. But if someone declares an object of type
Character (or aray of them) one rather expects to allocate and use a
single byte. Anything else would be regarded as kind of silly. For most
applications, it may not matter, but for embedded work, it could be
quite important because you are so close to the hardware.


>
> > And also, programs do various calculations with Duration, if there
> > is more precision, these calculations are more accurate.
>
> I agree with Marin here; convert to a type that you know or control
> the precision of to do computations.

Thanks. :-)

MDC
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Marin David Condic - Quadrus Corporation - http://www.quadruscorp.com/
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