Date: Tue, 28 Feb 2017 15:13:43 +0400 (+04) From: Hrant Dadivanyan <hrant@dadivanyan.net> To: Ian Lepore <ian@freebsd.org> Cc: Konstantin Belousov <kostikbel@gmail.com>, freebsd-hackers@freebsd.org Subject: Re: system time instability Message-ID: <E1cifiy-0003hg-1B@pandora.amnic.net>
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> [ Charset ISO-8859-1 converted... ] Dear Ian, Two months are passed, everything works fine and this is status report. > > > 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 ! > There was the load of 1kOhm that I forgot about. But cable was the issue, there was no a single jump in frequency after replacement and jitter is below 1-2us all the time. The second node (the servers are anycasted for redundancy) is upgraded to 11.0 and also works pretty stable. Thank you and Konstantin for great help and sorry for this off-topic thread. Hrant > > -- Ian > > -- > Hrant Dadivanyan (aka Ran d'Adi) hrant(at)dadivanyan.net > /* "Feci quod potui, faciant meliora potentes." */ ran(at)psg.com -- Hrant Dadivanyan (aka Ran d'Adi) hrant(at)dadivanyan.net /* "Feci quod potui, faciant meliora potentes." */ ran(at)psg.com
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