PPS via USB-based devices - NTP/Chrony

[knaggsy2000]

Hello!

Long time FreeBSD user here, first started with v5.0 and a software and electronics engineer - just for some background.

In the past I've previously used a WRAP board with an Oxford chipset-based RS-232 to provide real hardware-based RS-232 (with a few kernel source changes so it is recognised) to provide NTPD with an GPS-based timesource which also provided PPS via the DCD pin. That setup worked great and I built it with NanoBSD scripts.

Now, moving on at least a decade, things have of course moved on...

I was looking at repurposing my APU2 device as it was expensive (at the time) and I thought that I should bring back my own time server.

I had a Garmin GPS 18 which was wired during the WRAP days and I soldered up the connector to provide both PPS and NMEA. But I noticed (recently-ish) that PPS via either DCD or CTS pin via USB was now actually supported - https://lists.freebsd.org/pipermail/freebsd-usb/2019-August/016078.html

But upon my own research and testing, that doesn't actually seem to true. I even e-mailed the OP of that thread asking for more information but that e-mail bounced back. I've tried to feed in a PPS signal via both DCD and CTS and every app (GPSD, NTPD, and Chrony) via USB and it just ignores it. Tried numerous USB adapters which even provided those pins but it seems that either the app or FreeBSD just ignores PPS by USB-based devices. It ONLY seems to work if it's a REAL hardware-based RS-232 port (ie UART). So why does "Ian" claim that it worked for him?

Can someone help shed some light on this? As that list thread seemed to claim that everything was working but it seems that it isn't. Or did I miss something very obvious?

Additional information available on request.


Thanks in-advance,

Danny.

 

[Sergei_Shablovsky]

Hello!

Long time FreeBSD user here, first started with v5.0 and a software and electronics engineer - just for some background.

If You are electronics engineer, probably You know how to work by hands , because You may doing some work (link would be later in this reply).

In the past I've previously used a WRAP board with an Oxford chipset-based RS-232 to provide real hardware-based RS-232 (with a few kernel source changes so it is recognised) to provide NTPD with an GPS-based timesource which also provided PPS via the DCD pin. That setup worked great and I built it with NanoBSD scripts.

Now, moving on at least a decade, things have of course moved on...

I was looking at repurposing my APU2 device as it was expensive (at the time) and I thought that I should bring back my own time server.

Nice idea, especially if it eating less electricity and have a small form-factor and HAVE A GOOD STABLE POWER SUPPLY UNIT.

I had a Garmin GPS 18 which was wired during the WRAP days and I soldered up the connector to provide both PPS and NMEA.

Recently we bought for one of projects new Garmin GPS 16x-HVS (more robust and stable working, and same or better receiver sensitivity rather 19x-HVS, especially for non-moving objects like rack server).

P.S. May be this thread would be interesting for You
And this one

But I noticed (recently-ish) that PPS via either DCD or CTS pin via USB was now actually supported - https://lists.freebsd.org/pipermail/freebsd-usb/2019-August/016078.html

But upon my own research and testing, that doesn't actually seem to true. I even e-mailed the OP of that thread asking for more information but that e-mail bounced back. I've tried to feed in a PPS signal via both DCD and CTS and every app (GPSD, NTPD, and Chrony) via USB and it just ignores it. Tried numerous USB adapters which even provided those pins but it seems that either the app or FreeBSD just ignores PPS by USB-based devices. It ONLY seems to work if it's a REAL hardware-based RS-232 port (ie UART). So why does "Ian" claim that it worked for him?

Most of modern GPS receivers use one of DB9 pins (CTS) for 1PPS signal.

So NMEA without 1PPS give You precision between 50-100milliseconds, - THAT WAS ABSOLUTELY UNUSABLE even for NTP pool server.

Need to note that 1PPS signal are only if Your GPS-antenna able to see sufficent (in my case 3+ satellite, but depend on satellites network You use (GPS, Galileo, etc ) and GPS-receiver developer) clear view.

Also I suggest You carefully read this thread., this one and this one.

Good luck!

 

[Sergei_Shablovsky]

And consider to use Trimble NetRS instead of SOHO computers: it is MUCH MORE robust, stable at work and useful solution from well-reputable company.

P.S. For now it is ~$160 in great condition, on eBay aftermarket