[ntp:questions] OK - You told me so! Amazing Sure gps performance on real serial

[Ron Frazier (NTP)]

Hi all,

I finally got around to attaching a serial cable to the motherboard 
header on my desktop computer and attaching the Sure gps to it.  This 
NTP+GPS has been a long and winding road, and has been much more 
difficult to get a handle on than I anticipated, including ordering a 
number of parts and waiting what felt like eternity to get them.  
Watched pot never boils, etc.

WOW!  I'm blown away as I'm now getting + / - 50 MICROSECOND 
performance.  Yes, I know, old hat to you guys, but still news to me.  I 
can't believe decades old comm technology works so much better than 
modern comm technology.

Still, I wanted to wring out the maximum performance on USB since 3 of 
my 4 computers don't have serial.  I eventually got around + / - 1ms, 
which is pretty good considering the system limitations of USB.

Unfortunately, my poor laptop has now been demoted to running with only 
stratum 2 internet servers.  It's doing ok, and in fact, is better since 
I have interpolation on.  However it's only making + / - approx 20 ms.  
Also, what's bugging me is that there seems to be a continuous 20 ms 
offset from zero.  This is certainly good enough for running from a 
backup time source, but still confusing.  While I wanted to let the 
internet servers be polled as much as 2 hours apart, I eventually 
settled on letting them go back to the default polling intervals of 6 
(64 seconds) to 10 (1024 seconds) to minimize offset fluctuations 
between polling on the computer currently without the gps.  One problem 
with having these intervals on the computer with the gps, is that the 
polling interval gets continuously clamped to 64 seconds, which is 
enough to get me banned from polling some systems.

http://dl.dropbox.com/u/9879631/laptop%20internet%20ntp%202012-03-29.png
http://dl.dropbox.com/u/9879631/ntp.conf%20laptop%20internet%20ntp%202012-03-29

Eventually, I hope to have the desktop computer set up as a local time 
server.  Before I do that, I have to configure all the other systems 
like the laptop I was originally experimenting on, and figure out what 
to do with firewalls and changing ip addresses via dhcp.

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