[opendtv] Re: XDS and ATSC
- From: "John Shutt" <shuttj@xxxxxxxxx>
- To: <opendtv@xxxxxxxxxxxxx>
- Date: Tue, 22 May 2007 20:56:14 -0400
----- Original Message -----
From: "John Willkie" <johnwillkie@xxxxxxxxxxxxx>
You start with UTC January 6, 1980. You add the number of seconds that
have elapsed. You end up with UTC.
Well Hell's Bells, John. There's your problem! You start with UTC 00:00:00
January 6th, 1980. You add up all of the seconds that have elapsed from
that moment to the present moment. That is GPS TIME, NOT UTC TIME. You
then must SUBTRACT the number of UTC leap seconds that have occurred between
then and now to arrive at the number of UTC SECONDS, WHICH INCLUDES 14 LEAP
SECONDS that have been observed since that fateful day in 1980.
What you have drilled into your brain from writing PSIP ENCODERS is that
your software must start with UTC time that is given to your software by the
television station's master clock, your software then has to convert that
to the number of UTC seconds that have elapsed since that fateful day in
1980, then your software has to ADD THE NUMBER OF LEAP SECONDS OBSERVED TO
THE UTC SECONDS TO DERIVE GPS SECONDS that your software then encodes in the
variable <system_time>.
That's why you have mixed up SUBTRACTING LEAP SECONDS from GPS with ADDING
LEAP SECONDS to GPS.
Think about it, John, and stop with the petty insults.
John
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