Stratum-1 NTP server, part 3

After about 24 hours it has settled down nicely.

# ntpq -c peers
     remote           refid      st t when poll reach   delay   offset  jitter
oPPS(0)          .PPS.            0 l    4   16  377    0.000    0.010   0.002
* .PTB.            1 u   55   64  177   51.291    1.112   1.450      2 u    8   64  377   19.008    3.451   0.819
-time-a.as43289.     2 u   49   64  177   73.242   14.530   4.915    2 u    5   64  377   73.743    7.543   0.509
-hemel-hempstead    2 u   12   64  377   19.829    3.720   0.551    2 u   11   64  377   19.924    0.677   0.491   2 u   40   64  177   62.218    3.616   0.372     4 u   11   64  377   19.365    4.274   0.652
# ntpq -c rv
associd=0 status=011d leap_none, sync_pps, 1 event, kern,
version="ntpd 4.2.6p5@1.2349-o Sat Jul  4 15:08:48 UTC 2015 (1)",
processor="armv7l", system="Linux/3.18.11-v7+", leap=00, stratum=1,
precision=-20, rootdelay=0.000, rootdisp=0.394, refid=PPS,
reftime=d943cdae.7978b6bf  Sun, Jul  5 2015 16:37:18.474,
clock=d943cdb8.e8908274  Sun, Jul  5 2015 16:37:28.908, peer=2027, tc=4,
mintc=3, offset=0.010, frequency=-3.056, sys_jitter=0.002,
clk_jitter=0.000, clk_wander=0.002


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5 responses to “Stratum-1 NTP server, part 3

  1. problemchild68

    Good job Richard, do you have any idea how much if any the Jitter varies depending on the number of satellites that are received at any given time ?

    • rich

      At present I’m not clear on how (or even if) I can get any visibility into the GPS device status. I will have to take a look at the datasheet of the board (which is on a bit of paper at the office, so I can’t reference it right now).

      Edit: I found the datasheet online. It should be possible to read and write to the serial(?) TX/RX data pins of the GPS device. Exactly how you’d do that and what you could read and write needs further investigation.

      Edit #2: Reading this comment and comparing the datasheet to the RPi+ GPIO pins, I see that the GPS device is already connected to GPIO pins 14 & 15 which correspond to the RPi+ UART0. So reading/writing to /dev/ttyAMA0 (which I didn’t actually try yet) would talk to the GPS device directly.

      Edit #3: I connected to the serial port, and I see lots of numbers and interspersed random binary data. Hmm. Maybe gpsd or something else is needed.

      • problemchild68

        yeah gpsd will read the NMEA sentences you can read all sorts from there like relative signal strengths numbers of satellites location accuracy etc. have XGPSD running and you can even watch the sateliites move overhead!

  2. I wonder if an old android phone would do a reasobale job at neing a NFS server. Perhaps the biggest drawback is lack of cabled internet connection.

  3. problemchild68

    I presume you mean NTP, if so yes it would be OK for the purposes of basic dating of files etc. I think you may suffer a bit as the WIFI can have quite a large jitter if you wanted to have the low jitter’s and high accuracies shown above.

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