Looking for ntp/PPS setup guide

[Kevin Oberman]

> Date: Sat, 31 Jul 2004 21:25:04 -0400 (EDT)
> From: Garrett Wollman <wollman at khavrinen.lcs.mit.edu>
> 
> In article <20040731231908.18F485D08 at ptavv.es.net> you write:
> 
> >From what I have seen, the non-kernel PPS software handles jitter more
> >gracefully than the kernel version.
> 
> Which CDMA receiver do you have?  I'm using one from EndRun
> Technologies which emulates a Trimble Palisade and it seems to perform
> fairly well:
> 
>      remote           refid      st t when poll reach   delay   offset  jitter
> ==============================================================================
> *GPS_PALISADE(0) .CDMA.           0 l    1   32  377    0.000   -0.016   0.008
> +NAVOBS1.MIT.EDU .PSC.            1 u   37   64  377    0.836    0.027   0.025
> xtime-b.nist.gov .ACTS.           1 u   49   64  377   15.477   -6.898   9.374
> +ntp2.usno.navy. .USNO.           1 u   10   64  337   40.016   -2.378  83.946
> -gps.freebsd.dk  .GPS.            1 u   51   64  377  115.848    4.315   1.408
> 
> This receiver was recommended to me by Dave Andersen (dga@).
> (Actually, I stole it from him.)  This is using the host-triggered
> timestamp mode of this device rather than PPS.

I am running the EndRun Proesis Ct. It can emulate many different clocks
and, if you don't have PPS, the Palisade is probably the best
choice. Unlike others which send out the time in ASCII every second, the
Palisade sends out the time in binary when polled. But this is not as
accurate as PPS which the unit also provides.

The problem is that polling mode and PPS don't work properly together,
so I have found that the TrueTime format provides the best results.
ctime=off
emul=truetime
ctime=on

I am still looking at the best choice for PPS setup...PPS_SYNC (flag3 1"
or software PPL "flag3 1". Both do very well. I suspect that the absolute
time is closest with PPS_SYNC but the stability is often better with PLL
discipline. If PLL proves the more stable, I will use a fudge of time1
to correct for the offset. (In my last message bnl-owamp was running
PPS_SYNC and the system I queries was running PLL. Note the 51
microsecond offset. I don't know yet if that's real or an artifact of
network delays.
-- 
R. Kevin Oberman, Network Engineer
Energy Sciences Network (ESnet)
Ernest O. Lawrence Berkeley National Laboratory (Berkeley Lab)
E-mail: oberman at es.net			Phone: +1 510 486-8634