There's support in "over the air" ATSC digital TV signals for DST info,
but most TV stations aren't known for keeping their time information up
to date. There's a system time packet that has the GPS time, the number
of seconds difference between GPS time and UTC (and a lot of stations
don't get that right either), and then a day and hour indicator saying
when a DST to standard time (or vice versa) is supposed to happen. That
indication is supposed to be present soon after it is unambiguous, i.e.
the transition is less than 28 days away. But I believe it is up to the
local station to program most of that, and some stations get it really
wrong.
Regardless, you are trusting someone to configure DST information
somewhere. Obviously it's easier to trust the folks at NIST to get it
right, rather than your local TV station. If you go with static DST
configuration rules then you have to trust yourself to update the
information as appropriate.
Someone suggested scraping the NIST time service website for this
information. The NIST website specifically says "Also, it is
inappropriate to generate your own software to use the functionality of
this site. Contact us for details."
It might be interesting to send an email to [email protected]
and ask them what they would suggest for getting accurate DST
information, but I doubt they will suggest anything that hasn't already
been proposed.
Regards,
John
8/24/2018 11:18 AM, Mark Sims wrote:
Lady Heather has DST support code in it (in file heathmsc.cpp). It supports
the current standard settings for several areas (US, Europe, Australia, New
Zealand) or you can specify a custom DST rule. The code is around 200 lines
long... some of that is Heather-specific requirements. It can also be
simplified by not parsing the ASCII rule string and using hard coded values.
Implementing and testing seamless DST adjustment is a bit of a pain...
particularly keeping the time correct during the hours before/after the switch.
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