[time-nuts] An embedded NTP server

Michael Tharp gxti at partiallystapled.com
Thu Dec 27 21:00:26 UTC 2012


On 12/27/2012 01:41 AM, Michael Tharp wrote:
> The good news is that the disciplining algorithm I lifted from my
> previous GPSDO project works quite well, and I have the gritty details
> of measuring the PPS worked out. If I can get the Trimble working
> tomorrow I might have much better results soon, otherwise I'm traveling
> for a few days so it'll have to wait until the new year.

And here we go, it works. Much more reasonable, tens-of-microseconds 
jitter figures.

[root at rei ~]# ntpq -pn
      remote           refid      st t when poll reach   delay   offset 
  jitter
==============================================================================
-138.236.128.36  216.218.254.202  2 u   21 1024  377   68.819    3.228 
  0.641
+108.59.14.130   209.51.161.238   2 u  298 1024  377   34.920    1.167 
  0.288
+108.61.73.244   96.47.67.105     2 u  300 1024  377   39.524    1.135 
  1.604
-64.6.144.6      128.252.19.1     2 u  772 1024  377   84.329    6.609 
  0.252
*172.24.0.6      .GPS.            1 u    2   16  377    0.320   -0.073 
  0.016
-172.24.0.66     135.34.116.162   3 u  237 1024  377    0.197    0.130 
  0.581
x172.24.0.68     172.24.0.6       2 u  291 1024  377    0.237  113.341 
77.665
-172.24.0.1      172.24.0.6       2 u  287  512  377    0.123    2.382 
  0.876

[root at maruko ~]# ntpq -pn
      remote           refid      st t when poll reach   delay   offset 
  jitter
==============================================================================
-67.18.187.111   129.7.1.66       2 u  965 1024   37   66.695    1.952 
  0.842
+174.129.25.69   131.188.3.221    2 u  753 1024  377   35.926    1.734 
  0.250
*2001:470:1:15b: 132.239.1.6      2 u  513 1024  377  107.240    0.982 
  0.373
-172.24.0.1      172.24.0.6       2 u  786 1024  377    0.187    2.960 
  1.027
+172.24.0.6      .GPS.            1 u   55   16  377    0.356   -0.008 
  0.060
-172.24.0.64     108.59.14.130    3 u  912 1024  377    0.301    0.058 
  0.685
x172.24.0.68     135.6.140.0      3 u  938 1024  377    0.378  243.604 
166.234

[root at hanmyo ~]# ntpq -pn
      remote           refid      st t when poll reach   delay   offset 
  jitter
==============================================================================
*172.24.0.6      .GPS.            1 u   25   64  377    0.399   -2.390 
  0.258
  172.24.0.64     172.24.0.6       2 u    9 1024  377    0.134   -2.273 
   0.708
-172.24.0.66     135.34.116.162   3 u  342  512  377    0.216   -2.607 
  1.728
  172.24.0.68     172.24.0.6       2 u  300  512  377    0.092  245.910 
124.378
-72.251.251.11   62.192.15.212    3 u   22 1024  377  122.988   -0.097 
  1.585
+67.18.187.111   129.7.1.66       2 u  270  512  377   66.916   -1.235 
  3.977
-199.7.177.206   64.147.116.229   2 u  368  512  377   59.035    3.838 
  1.815
+50.97.210.169   131.107.13.100   2 u    8 1024  377  100.003    2.547 
  1.025

hanmyo (172.24.0.1) is a small "digital engine" computer that I use as a 
router; it is pretty much 100% idle, has no fans, and is located in a 
closet where it is temperature stable. At the same time, it shows by far 
the highest jitter figure so I'm guessing its clock is not very good. I 
will have to probe around and see if there is something I can replace, 
because it is the best candidate for characterizing the performance of 
my little NTP server. It's hard to get quality measurements when the 
peer boxes are just ordinary desktops.

I've only been testing this new firmware for ~30m so I will let it soak 
while I'm traveling and when I get back the numbers should look even better.

-- m. tharp




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