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From: Ted Dennison <dennison@telepath.com>
Newsgroups: comp.lang.ada
Subject: Re: Using "delay until" in real-time
Date: Wed, 20 Dec 2000 03:17:41 GMT
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Date: 2000-12-20T03:17:41+00:00
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I finally did get a solution to this that worked to my satisfaction.

In article <915jl7$jt5$1@nnrp1.deja.com>,
  Ted Dennison <dennison@telepath.com> wrote:

>   o  Figure out what the denominator is (60 in this case), and redo
> the calculation every time that number of runs have happened.
>
> For instance, in the above code, I'd add something like:
>       Runs := Runs + 1;
>       if Runs >= Natural(Iteration_Hz) then
>          -- Adjust for drift due to rounding errors.
>          Runs := 0;
>          Run_Time := Run_Time + Ada.Real_Time.To_Time_Span (1.0);
>          Next_Time := Run_Time;
>       else
>          Next_Time := Next_Time + Iteration;
>       end if;

This was close to my final solution, but not quite. Instead, it ended up
causing *more* problems with missed clocks. The solution was to use the
above code, except that all calls to "To_Time_Span" are replaced by
calls to "Ada.Real_Time.Nanoseconds", which gives better accuracy.
Real_Time.Microseconds would probably have been sufficient, but this
works too, and is a bit more portable.

--
T.E.D.

http://www.telepath.com/~dennison/Ted/TED.html


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