Date: Sat, 31 Jul 2004 21:38:04 -0700 From: "Kevin Oberman" <oberman@es.net> To: Garrett Wollman <wollman@khavrinen.lcs.mit.edu> Cc: FreeBSD-stable@FreeBSD.org Subject: Re: Looking for ntp/PPS setup guide Message-ID: <20040801043804.800F95D08@ptavv.es.net> In-Reply-To: Your message of "Sat, 31 Jul 2004 21:25:04 EDT." <200408010125.i711P44H056311@khavrinen.lcs.mit.edu>
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> Date: Sat, 31 Jul 2004 21:25:04 -0400 (EDT) > From: Garrett Wollman <wollman@khavrinen.lcs.mit.edu> > > In article <20040731231908.18F485D08@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@es.net Phone: +1 510 486-8634
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