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From: Simon Wright <simon@pushface.org>
Newsgroups: comp.lang.ada
Subject: Re: Ada.Execution_Time
Date: Sat, 01 Jan 2011 16:01:45 +0000
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Date: 2011-01-01T16:01:45+00:00
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Simon Wright <simon@pushface.org> writes:

> Niklas Holsti <niklas.holsti@tidorum.invalid> writes:
>
>> The question is then if the compiler/system vendors will take the
>> trouble and cost to customise Ada.Execution_Time for a particular
>> board/computer, or if they will just use the general,
>> lowest-denominator but portable service provided by the kernel. Dmitry
>> indicates that GNAT on VxWorks takes the latter, easy way out.
>
> The latest supported GNAT on VxWorks (5.5) actually doesn't implement
> Ada.Execution_Time at all (well, the source of the package spec is
> there, adorned with "pragma Unimplemented_Unit", just like the FSF
> 4.5.0 sources and the GNAT GPL sources -- unless you're running on
> Cygwin or MaRTE).

Actually, Dmitry's complaint was that time (either from
Ada.Calendar.Clock, or Ada.Real_Time.Clock, I forget) wasn't as precise
as it can easily be on modern hardware, being incremented at each timer
interrupt; so if your timer ticks every millisecond, that's your
granularity.

This could easily be changed (at any rate for Real_Time), but doesn't I
believe necessarily affect what's to be expected from delay/delay until,
or Execution_Time come to that.