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From: dennison@telepath.com
Subject: Re: delay until and GNAT - expand
Date: 1999/05/12
Message-ID: <7hc4vu$7k9$1@nnrp1.deja.com>#1/1
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Date: 1999-05-12T00:00:00+00:00
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In article <rracine.17.0007DA28@draper.com>,
  rracine@draper.com (Roger Racine) wrote:
> In article <7h9nal$9dr$1@nnrp1.deja.com> Robert Dewar
<robert_dewar@my-dejanews.com> writes:
> >In article <7h9j77$61l$1@nnrp1.deja.com>,
> >  dennison@telepath.com wrote:
> >> What I am seeing is that "interrupt 0", the clock interrupt,
> >takes about
> >> 11 micro seconds. Then the slighly misnamed "idle" task
> >continues to
> >> execute for about 11 micros. Then my Ada task begins. Where in
> >there my
> We are obviously talking about different metrics.  The original
message (as
> expanded) asked about the "delay 0.0" case, not a positive value.  So
your
> clock interrupt goes away, as does the idle task execution (which is
all of
> your measured time).
>
> All that is needed (not necessarily all that is done) is a check for
positive,
> and, if not, a call to "sched_yield" (POSIX interface), which puts the
task at
> the end of the ready queue and performs a context switch.


Well, it appears that Windview reports the work of a context switch in
the context of the currently running task (yikes, what a sentence!). So
I think it can be reasonably well assumed that the entire period of time
I reported for the "idle" task is being taken up by an attempt to change
the task context from that of the idle task to that of the newly-readied
60hz task. What we *don't* know is how much, if any, task switch
overhead occurrs after Windview reports the context switch. But I think
we can resonably take 11 micros as a lower bound for the amount of time
it takes to perform a context switch in vxWorks (on a PII-400, with the
cache invalidate instruction disabled, etc, etc.).

--
T.E.D.


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