Re: [MirageOS-devel] NTP implementation for mirageos

[Daniel BÃnzli <daniel.buenzli@xxxxxxxxxxxx>]

Hello Kia,  


Le mercredi, 3 fÃvrier 2016 Ã 00:15, Richard Mortier a Ãcrit :

> "Leap Seconds (considered harmful)" one just now

I also read that. As you notice yourself in the post leap seconds are quite 
useful for humans, so the title sounds a little bit strange.

Just a few remarks about the "proven alternative". Strictly speaking what you 
need is not the timezone database, you only need TAI + the leap second table 
[1] that relates UTC to TAI. Timezones are yet another confusing business.

You also mention GPS as giving you TAI + the current offset to UTC (basically 
the last line of [1]). Note that while this is sufficient for rendering the 
current UTC time it is not enough to convert arbitrary TAI timestamp to UTC and 
vice-versa or to compute the duration in TAI seconds between two arbitrary UTC 
timestamps. In both cases you still need the full leap seconds table for that.  

This table may change every 6 months and updating software systems is annoying. 
So a good time protocol would not only give you TAI + the current offset to 
UTC, but also allow you to retrieve the full current leap seconds table.

Best,  

Daniel

[1] http://maia.usno.navy.mil/ser7/tai-utc.dat

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