From owner-freebsd-hackers@freebsd.org Tue Dec 13 19:52:10 2016 Return-Path: Delivered-To: freebsd-hackers@mailman.ysv.freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:1900:2254:206a::19:1]) by mailman.ysv.freebsd.org (Postfix) with ESMTP id 289EAC764C8 for ; Tue, 13 Dec 2016 19:52:10 +0000 (UTC) (envelope-from hrant@dadivanyan.net) Received: from pandora.amnic.net (pandora.amnic.net [IPv6:2001:67c:21c:a610::11]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (Client did not present a certificate) by mx1.freebsd.org (Postfix) with ESMTPS id DCF1B1D60; Tue, 13 Dec 2016 19:52:09 +0000 (UTC) (envelope-from hrant@dadivanyan.net) Received: from ran by pandora.amnic.net with local (Exim 4.87 (FreeBSD)) (envelope-from ) id 1cGt7P-0006W1-8E; Tue, 13 Dec 2016 23:52:07 +0400 Subject: Re: system time instability In-Reply-To: <1481654211.1889.346.camel@freebsd.org> To: Ian Lepore Date: Tue, 13 Dec 2016 23:52:07 +0400 (AMT) From: Hrant Dadivanyan CC: Konstantin Belousov , freebsd-hackers@freebsd.org X-PGP: https://amnic.net/pgpkeys/hrant.asc X-NCC-RegID: am.isoc X-Mailer: ELM [version 2.4ME+ PL127 (25)] MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Content-Type: text/plain; charset="UTF-8" Message-Id: X-BeenThere: freebsd-hackers@freebsd.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: Technical Discussions relating to FreeBSD List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Tue, 13 Dec 2016 19:52:10 -0000 [ Charset ISO-8859-1 converted... ] > > The server did run for almost a day without PPS and looks stable. I > > start > > to believe, to my shame, that I did a mistake when testing this > > previously. > > Then the whole post is wrong and cable seems to be most suspected > > part again. > > Even now it's hard to understand this wrong behaviour, but anyway ... > > > > Just replaced the cable with shielded one where each pair has > > separate > > shield, used dedicated pair for PPS and ground; grounded the shields. > > > > Thank you Konstantin, thank you Ian ! > > Hrant > > > > A bad PPS signal could definitely lead to frequency trouble, if the way > the signal is bad involves ringing, or the electrical level floating > around the cutoff points for detecting low vs. high level -- you'd get > false pulses, and some of them would be close enough to the time of the > real pulse that they would make it through the spike/median filters in > ntpd.  An early or late pulse looks like a phase step, and several > consistant-enough phase steps in the same polling period looks like a > frequency step. > > You mentioned using a 74LS245 bus driver... that can lead to ringing if > the load is light, maybe the rs232 port on this new hardware has a much > higher input impedance than your old system.  It might be worth adding > a series resistor at the computer end to soak up reflections, something > in the 30-100 ohm range should work. > Wow, thank you, will try ! > -- Ian -- Hrant Dadivanyan (aka Ran d'Adi) hrant(at)dadivanyan.net /* "Feci quod potui, faciant meliora potentes." */ ran(at)psg.com