Re: help with setting up NTP on windows with a USB GPS

Hi all,

After reading Dave Hart's message, I realized that I didn't configure
the GPS device to only emit $GPRMC messages. After doing this, the NTP
software starts to function. So that's big progress for me.

Right now, I am using:

server 127.127.20.1 minpoll 4 prefer
server 127.127.22.1 minpoll 4

NTPStatus shows that it's syncing to PPS(1) although the offset and
jitter are still quite big (-3ms and 0.2ms respectively).

I tried the following combination but the offset actually increased.
server 127.127.20.1 minpoll 4 prefer
fudge 127.127.20.1 flag1 1

Right now I am trying to figure out how to switch to kernel mode. I
have
1) serialpps.sys
2) the correspond DLL
3) the environment variable that points to the DLL
I am unclear as to what should be done to switch to kernel mode.

Thanks to all for the help.

Jack

On Nov 27, 9:12 am, jack <j.jack.w...@xxxxxxxxx> wrote:
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...@xxxxxxxxxxxxxxxxxxxx



bit.nor-this-part.co.uk.invalid> wrote:
"jack" <> wrote in message

news:9db25657-9837-4ebe-ab32-ce15ae968af8@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx

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

.

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