From mboxrd@z Thu Jan  1 00:00:00 1970
X-Spam-Checker-Version: SpamAssassin 3.4.4 (2020-01-24) on polar.synack.me
X-Spam-Level: 
X-Spam-Status: No, score=-1.9 required=5.0 tests=BAYES_00
	autolearn=unavailable autolearn_force=no version=3.4.4
Path: 
 eternal-september.org!reader01.eternal-september.org!reader02.eternal-september.org!news.eternal-september.org!mx02.eternal-september.org!feeder.eternal-september.org!aioe.org!.POSTED!not-for-mail
From: Emanuel Berg <embe8573@student.uu.se>
Newsgroups: comp.lang.ada
Subject: Re: how to analyze clock drift
Date: Wed, 19 Nov 2014 23:12:41 +0100
Organization: Aioe.org NNTP Server
Message-ID: <87k32qet5y.fsf@debian.uxu>
References: <6uun6alsp3jh1pob6g9qgcg85etqgenmd0@4ax.com>
	<m4h061$oct$1@speranza.aioe.org> <87zjbn3nss.fsf@debian.uxu>
	<1nvfhit2csxr5.41v36jksch28$.dlg@40tude.net>
NNTP-Posting-Host: feB02bRejf23rfBm51Mt7Q.user.speranza.aioe.org
Mime-Version: 1.0
Content-Type: text/plain
X-Complaints-To: abuse@aioe.org
User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/24.4 (gnu/linux)
X-Notice: Filtered by postfilter v. 0.8.2
Cancel-Lock: sha1:+V1Ii7gYSmzEbC88PQ/s82zIwg0=
Mail-Copies-To: never
Xref: news.eternal-september.org comp.lang.ada:23557
Date: 2014-11-19T23:12:41+01:00
List-Id: <comp.lang.ada>

"Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de>
writes:

> You certainly can use OS services from C++, instead
> of them.

What I use is the <chrono> stuff, e.g.:

    std::chrono::system_clock::now()
    std::this_thread::sleep_until(re_sched_time)

> You need a reference clock [big cut]

Thank you for that post, it is a bit too advanced to
me, so I'll print it and read it again and probably be
back with some questions.

I got a mail from my teacher - it sounds like a lot of
what you said (?):

    You could [...] calculate with the offsets from
    the desired values [...]

    o0 = t1 - t0 - DESIRED_TICK
    o1 = t2 - t1 - DESIRED_TICK
    o2 = t3 - t2 - DESIRED_TICK
    ...

    where DESIRED_TICK is the tick lengths you were
    aiming for. [...]

    From these points you can easily calculate the
    average, minimum and maximum values and their
    standard deviation. The average will be a measure
    of the drift, the min/max the worst-case
    (observed) behaviors and the standard deviation a
    measure of the stability.

    > Also, you mention the short trace. How long a
    > trace is needed (like a rule-of-thumb) to cover
    > all or most patterns?

    It's difficult to say. As a rule-of-thumb I
    suppose one can say that when the values you are
    calculating don't change significantly with longer
    traces, the trace is long enough. But by the
    nature of the problem you can never know, for
    example, if a larger maximum value would be seen
    if the trace was just a little longer.

-- 
underground experts united