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Re: [Ntp] Antw: [EXT] Re: Timescales

Martin Burnicki <martin.burnicki@meinberg.de> Wed, 09 December 2020 23:10 UTC

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To: Magnus Danielson <magnus@rubidium.se>, ntp@ietf.org
References: <20201209190210.2408740605C@ip-64-139-1-69.sjc.megapath.net> <ae748c46-a180-1741-c082-4087d21f2995@rubidium.se>
From: Martin Burnicki <martin.burnicki@meinberg.de>
Organization: Meinberg Funkuhren GmbH & Co. KG, Bad Pyrmont, Germany
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Subject: Re: [Ntp] Antw: [EXT] Re: Timescales
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Magnus Danielson wrote:
> Hal,
> 
> On 2020-12-09 20:02, Hal Murray wrote:
>> mlichvar@redhat.com said:
>>> Most computers work primarily in UTC.
>> Most computers work on POSIX pseudo UTC time.
>> (which is why we have this leap-second mess)
> 
> Most computers use one of two interpretations of POSIX Time.
> 
> One variant of UTC to POSIX time_t mapping was provided for a while, but
> later removed from the POSIX documentation, mapping 23:59:60Z into
> 00:00:00, which is what you expect from (omitting date)
> 
> time_t = hours*3600 + min*60 + sec
> 
> and as this is re-interpreted as print-out time
> 
> sec = time_t % 60
> min = (time_t / 60) % 60
> hour = (time_t / 3600) % 24
> 
> reads out as 00:00:00, which next section also labelled 00:00:00. This
> behavior is mimiced by the NTP time-scale for at NTPv3 and NTPv4 as I
> recall it.

The problem is that there is no status flag. For example, if you read a
POSIX-like timestamp from a Meinberg PCI card, there are API calls that
also include a status word, and while one of the status bits tells that
a leap second is approaching, another bit tells that the current second
is a leap second, so you can properly solve the ambiguity if you
evaluate the status flag.

Martin
-- 
Martin Burnicki

Senior Software Engineer

MEINBERG Funkuhren GmbH & Co. KG
Email: martin.burnicki@meinberg.de
Phone: +49 5281 9309-414
Linkedin: https://www.linkedin.com/in/martinburnicki/

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