[time-nuts] NAVSTAR proteus GPS time and frequency unit
cfharris at erols.com
Mon Nov 9 23:37:38 EST 2015
Thanks for the detailed reply. I haven't had a need (read: no customer
has paid me to do so...) to wallow through the GPS ICD, so that document
is foreign to me.
Your explanation clarifies the situation... Now it makes sense.
Magnus Danielson wrote:
> Because all the leap-second info is kept in GPS-calender form, and essentially
> indicating current leap-second difference and which GPS week (modulo 256). Check out
> the ICD for yourself, IS-GPS-200H:
> 184.108.40.206.2.4 Coordinated Universal Time (UTC).
> Page 18 of subframe 4 includes: (1) the parameters needed to relate GPS time to UTC,
> and (2) notice to the user regarding the scheduled future or recent past (relative to
> NAV message upload) value of the delta time due to leap seconds (ΔtLSF), together
> with the week number (WNLSF) and the day number (DN) at the end of which the leap
> second becomes effective. "Day one" is the first day relative to the end/start of
> week and the WNLSF value consists of eight bits which shall be a modulo 256 binary
> representation of the GPS week number (see paragraph 6.2.4) to which the DN is
> referenced. The user must account for the truncated nature of this parameter as well
> as truncation of WN, WNt, and WNLSF due to rollover of full week number (see
> paragraph 3.3.4(b)). The CS shall manage these parameters such that, when ΔtLS and
> ΔtLSF differ, the absolute value of the difference between the untruncated WN and
> WNLSF values shall not exceed 127.
> Depending upon the relationship of the effectivity date to the user's current GPS
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