David, You assumed right. I did start with a USB emulated port. The GPS I bought is from U-Blox and it has both USB and serial output. The serial output has the 1PPS signal (with an LED indicator). I thought I would start with the USB output since it's rather hard to find a computer with a serial port. Also I would like to see the accuracy by using the USB port only. I later switched to a machine with a serial port and started using the serial output of the U-Blox GPS device and 1PPS. My objective is to use two of these devices to sync two separate computers to within ms so they can share time-sensitive data (time stamped).
I left the device running overnight and I noticed it computed an offset at one time. It's currently not updating (everything is zero now). I will read carefully what Dave Hart said and follow his advice. Thanks to everyone for your help. Jack On Nov 27, 1:51 am, "David J Taylor" <david-tay...@blueyonder.not-this- bit.nor-this-part.co.uk.invalid> wrote: > "jack" <> wrote in message > > news:9db25657-9837-4ebe-ab32-ce15ae968...@j35g2000vbl.googlegroups.com... > > > > > > > David, > > > I only have the following in the configure file: > > > server 127.127.20.1 minpoll 4 prefer > > > I found the following entry in the log file: > > > Using user-mode PPS timestamp > > > Does it mean NTP reads the GPS strings and sees the 1PPS signal? > > > All the values are still 0 including reach. At one point for about 10 > > minutes, I saw some values after rebooting the machine but they > > disappeared quickly. > > > Thanks. > > > jack > > > ps: I am using the latest NTP from Dave Hart's website. I also > > installed serialpps.sys. > > Jack, > > As Dave Hart has answered you are talking to the expert in this area! > > I had assumed in my first response that you had a GPS receiver with a > serial output connected to a serial-USB convertor, but I see now that this > may not be the case. How well the PPS output is emulated in the > USB-serial port software you will need to check. You need somehow to > "connect" the PPS output from the GPS to the virtual DCD line of the > emulated COM1 port. Not quite sure how you do that. What GPS and > software are you using > > Cheers, > David _______________________________________________ questions mailing list questions@lists.ntp.org https://lists.ntp.org/mailman/listinfo/questions