| RE: [chrony-users] PPS Synchronization Verification |
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- To: "chrony-users@xxxxxxxxxxxxxxxxxxxx" <chrony-users@xxxxxxxxxxxxxxxxxxxx>
- Subject: RE: [chrony-users] PPS Synchronization Verification
- From: "Chang, Benjamin" <Benjamin.Chang@xxxxxxxxxxxxxxx>
- Date: Mon, 2 Nov 2020 12:24:32 +0000
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- Thread-topic: [chrony-users] PPS Synchronization Verification
The PPS signal is coming from the NTP server (it's a syncserver S650) and is connected via a 232 line. I essentially did this https://www.crc.id.au/2016/09/24/adding-a-pps-source-to-ntpd/ but switched the ntpd kernel with the chrony kernel. Should I set an offset of .00002 for the PPS?
-----Original Message-----
From: Miroslav Lichvar <mlichvar@xxxxxxxxxx>
Sent: Monday, November 2, 2020 4:20 AM
To: chrony-users@xxxxxxxxxxxxxxxxxxxx
Subject: Re: [chrony-users] PPS Synchronization Verification
On Fri, Oct 30, 2020 at 02:38:27PM +0000, Chang, Benjamin wrote:
> Hello,
>
> I am trying to verify that I have my device successfully synced to a PPS. It shows up in my chronyc sources.
>
> From my chronyc sources imagine below, since the NTP is always about ~20us behind while the PPS is about +387ns ahead, does this mean my device is successfully synced to my PPS?
> The PPS's refid is 'NTPS'. I also have an NTP server (the IP address) connected. The PPS is generally .20us after the ntp (by design).
The server in your screenshot is marked with the 'x' symbol, meaning it doesn't agree with the PPS source. I assume the PPS source has the trust option, otherwise both should have the 'x'. The reported +/- value is quite small. That would indicate a HW-based server, or interleaved mode enabled.
At this level, it's difficult to tell which source is more accurate.
How exactly is the PPS signal connected? If it's something using interrupts like serial port, you might need to specifiy an offset for the PPS source.
--
Miroslav Lichvar
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