On 3/24/2012 7:05 AM, David J Taylor wrote:
I now have the PPS circuit working on the Sure board. I have not
soldered it yet. I just taped a jumper wire between the PPS test
point at the edge of the board and the DCD pin 1 on the RS-232 port.
The serial data is coming in through the Trendnet TU-S9 serial - USB
converter, which is passing DCD. I'm getting + .5 / - 1.5 ms
offsets. The PPS is nowhere to be seen on the statistics screen, but
it is obviously working. I don't know why it's not more centered
around zero, and maybe that will change. However, my total peak to
peak range of offset variance is 2 ms, and that's coming through
USB. If I can maintain that level of accuracy, and it's consistent
with UTC, then I'm very happy. That's plenty good for my purposes.
I still may try to run it through a real serial port on another
machine just for kicks.
Sincerely,
Ron
Ron,
Yes, those were the sorts of figures I was seeing.
http://www.satsignal.eu/ntp/NTP-on-Windows-serial-port.html#usb
The jitter I saw was about 45 microseconds for the USB/PPS against 2.3
- 3 microseconds for various serial-port/PPS. All figures from
Windows XP. If the graphs there are anything to go by it seems that
the offset varied between -0.15 to +0.3 milliseconds (very
approximately).
Hi David,
You appear to be up early. I'm curious to know what time this email
says it arrived. If it says it arrived at about 1030, then that's my
time. If it says it arrived at about 14:30, then that's your time.
Since I wrote that, it seems to have centered itself around zero. I now
have a very nice + 1.2 ms / - 1.2 ms offset pattern. Since I've been
struggling to get anything under 50 ms with other technology, this looks
really sweet to me.
http://dl.dropbox.com/u/9879631/Sure%20board%20first%20night%20pt1.jpg
http://dl.dropbox.com/u/9879631/Sure%20board%20first%20night%20pt2.jpg
Conversion of these images to jpeg reduced the clarity a bit, but you
can still see what's happening.
MICROSECONDS, did you say? I'm nowhere near that territory with
everything going through a serial - USB converter. However, I'm quite
happy with 1.2 ms under the circumstances.
I am NOW assuming that my clock is more accurate than the internet
clocks. I am NOW hoping that neither will appear to be drifting away
and that nothing in the system will be having routine heart attacks.
I notice there is a difference between my clock and the average internet
clock reading. Hypothetically, even though mine is probably closer to
UTC than those readings, if I wanted to shift my offset to match them,
so NTP won't clockhop, how as long as the GPS is working, how would I do
that?
Here are my config lines:
# COM5 57600 windows lines for testing gps selected as main source -
gpgga 57600 baud
server 127.127.22.5 minpoll 3 maxpoll 3
# PPS
fudge 127.127.22.5 flag2 0 refid PPS
# PPS standard polarity
server 127.127.20.5 prefer minpoll 3 maxpoll 3 mode 66
# NMEA
fudge 127.127.20.5 time2 0.0000 refid GPS1
# use WITH PPS
Also, why doesn't the PPS show up in my status screen anywhere? I know
it's working, based on the graphs.
Sincerely,
Ron
--
(PS - If you email me and don't get a quick response, don't be concerned.
I get about 300 emails per day from alternate energy mailing lists and
such. I don't always see new messages very quickly. If you need a
reply and have not heard from me in 1 - 2 weeks, send your message again.)
Ron Frazier
timekeepingdude AT c3energy.com
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