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From: Simon Wright <simon@pushface.org>
Newsgroups: comp.lang.ada
Subject: Re: Ada and linux real time
Date: Mon, 19 Mar 2012 13:01:22 +0000
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Date: 2012-03-19T13:01:22+00:00
List-Id: <comp.lang.ada>

Georg Bauhaus <rm.dash-bauhaus@futureapps.de> writes:

> On 18.03.12 23:03, slos wrote:
>
>>          delay until Next_Time;
>> 
>>          MyDuration := To_Duration (Clock - Next_Time);
>
> I haven't looked very closely, but if, say, Next_Time has a value of
> 12 o'clock, then
>
>    delay until Next_Time;
>
>    -- (it is now 12 o'clock)
>
>    My_Duration := Clock - Next_Time;
>
> will likely measure 12 o'clock - 12 o'clock, unless performing "-"
> takes time, or (parts of) the assignment statement is (are) put on
> hold by the scheduler, interrupting the task.  I think that's unlike
> Simon's program, which subtracts a starting time, not next_time, from
> the current time.

I think the point of slos's code is that the delay is supposed to finish
at Next_Time, but may (if the OS isn't very 'RT') finish later; the code
measures this.

I tried this on the same machine as my last report, but got the same
result using 'chrt 1 ./rt_test' as plain './rt_test' (running
   grep -r 'an unlikely phrase' .
 in another window).