[time-nuts] Lady Heather Server On Raspberry Pi 2 Model B?

Chris Caudle chris at chriscaudle.org
Wed Jan 13 00:20:40 UTC 2016

>> On Jan 12, 2016, at 7:17 AM, Chris Caudle <chris at chriscaudle.org> wrote:
>> Can ntpd using a Thunderbolt as a time source run cooperatively with LH
>> accessing the same Thunderbolt over ser2net?  That seems like the best

On Tue, January 12, 2016 4:01 pm, Nick Sayer via time-nuts wrote:
> I'm going to guess no, because only one thing can connect to the
> ser2net socket at a time.

No, ntpd would be getting time from the serial port, not from the network
socket.  The idea would be that ntpd was getting the clock time from the
serial port, but the time messages would be interleaved with whatever data
the Thunderbolt was sending back in request to the LH commands.

LH would also be seeing the time messages, but it sees those anyway, so I
think the only concern would be the behavior of ntpd when all the data
from LH commands is going by.  Possibly a second concern of whether ntpd
sends any commands to the Thunderbolt that might cause LH to be confused
by responses to commands LH did not send.

> If I were going to do it, what I might do is connect up the PPS output of
> the tbolt to a GPIO pin of the RPi and configure that pin for the pps
> device and set up ntpd for that.

You still have to get wall clock time from somewhere, PPS just delineates
the seconds, it doesn't name the seconds.
For some cases you could have ntpd get the starting time from another
network source and just use PPS to keep track of the seconds after that,
but then you would still have corner cases of knowing when leap seconds
occurred, maybe others.
And of course if you relied on network access to other time servers you
could not operate on an isolated network.

> That way, LH can have the serial
> interface all to itself. I've done this with a far more ordinary GPS
> module to make a public stratum 1 server out of a Pi Zero for the NTP pool
> (ntp.kfu.com).

How did it get the correct time set at startup?  Did it have to query
other network servers to set the time, then the PPS controlled the clock
after that?
Can it be a "stratum 1" server if it has to rely on another server to get
the correct time when it starts up?  I guess it could if it doesn't serve
time until it has checked with other stratum 1 servers to make sure the
time is correct.

Sorry, didn't mean to go off into those weeds, but that isn't the system I
I want a machine which can get the correct current time without reference
to another system, which means that ntpd must get the time information
from somewhere, either by directly reading the serial port, or passed
through from gpsd which is reading the serial port, or some similar setup.
The PPS driver would be connected directly to ntpd.

Chris Caudle

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