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From: Ted Dennison <dennison@telepath.com>
Newsgroups: comp.lang.ada
Subject: Re: Using "delay until" in real-time
Date: Tue, 12 Dec 2000 23:09:46 GMT
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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;

Arg! Slight problem with this. Since 1/60th rounds UP, that means the
first time I enter the else part, the next delay until delays *2* ticks
instead of one. Then when I do the adjustment, it asks to delay until a
time that has already occurred, which misses a tick (or double-ticks,
I'm not sure which). Ug.

Is there a way to specify that a floating-point calculation must round
down? The only other out I see would be to multiply by some largish
power of 10 then do a 'floor and divide that power of 10 back out. Yuck.

--
T.E.D.

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


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