[LEAPSECS] the big artillery
imp at bsdimp.com
Mon Nov 3 14:19:32 EST 2014
On Nov 3, 2014, at 11:11 AM, Brooks Harris <brooks at edlmax.com> wrote:
> CAUTION about the PTP Epoch. Its not "just nitpicking”.
> We've been advised by PTP experts that A) yes, its confusing, and B) most implementations use a integral-second interpretation, as in Table B.1. I understand the "escape clause" they use to justify this is the "(POSIX) algorithms" phrase in Note 1 of 7.2.2 Epoch. By "(POSIX) algorithms" they mean "gmtime()" and (strict) POSIX "ticks" at 1Hz, so, integral seconds. In any event its really the only interpretation that yields a manageable, practical, implementation that is consistent with TAI and UTC, NTP, and common-use of POSIX.
A few years ago, I had to produce TAI-like data from a measurement system. We defined the value as “seconds since 1970” but the technical definition was "number of SI seconds since 1 Jan 1972 00:00:00 UTC + 10 + #seconds-in-1970&71” to avoid the ambiguity. Given that our chief time scientist suggested this, and they were quite involved in PTP…
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