[LEAPSECS] POSIX and C (Was: Re: ISO Influence)

[Warner Losh]

On 12/23/2010 02:49, Ian Batten wrote:

>

>> Checking, I see that MSF transmits UTC but also encodes DUT1, so you can

>> derive UK legal time by looking at bits 01B to 16B and *58B.

> We used to do that for BT equipment, but they gave up, and now (so far as I know) all the UK telcos tick UTC(GPS).


I know this is the leap second list, and not the time-nuts list, but how 
on earth do you get a good, stable frequency to tick to if you have the 
base frequency provided by the carrier of the signal, but need to do 
phase offsets to keep it in sync (which means frequency skews to steer 
them in/out).  The data is only good to 100ms, so you'd see a lot of 
jumps you'd have to smooth out.  And what's the right time constant for 
steering, etc

I can understand why you just went with ticking to the SI second rather 
than the UT1 second.  All the oscillators are calibrated to the former, 
since none can be calibrated to the latter (since it is not constant).  
You can only steer a derived signal to the latter, but you'd need a lot 
better than 100ms resolution in DUT1 to do that...

Warner