[time-nuts] In search of ways to improve Raspberry Pi stratum 1 server

[paul swed]

Neil
Welcome to time-nuts. You say that your antenna is less then ideal. OK on
time-nuts your going to find out details matter. So what does that mean?
Typically the antenna needs to be high enough to have a clear view of the
sky and it does matter.
But there have been posts in the past about the Pi and I think there are
internal issues with the Pi itself that may limit its use. Not an expert
and maybe one day I will build a Pi NTP server. To many other things
cooking.
Regards
Paul
WB8TSL

On Mon, Jan 12, 2015 at 7:30 AM, Neil Green <ncguk at hotmail.co.uk> wrote:

> Hi all,
>
> This is my first post to the list. I have a Raspberry Pi B+ and a HAB
> Supplies U-Blox Max-M8Q set in stationary mode connected to a Virgin Media
> Superhub (broadband router) by a 0.5m cat7 ethernet cable. The GPS is
> attached to the Pi's GPIO and has an external active antenna placed on an
> inside window sill. The Pi is running Raspbian on a fast Class10 microSD
> card and has a kernel (Linux raspberrypi 3.12.35 #1 PREEMPT Sun Jan 11
> 17:40:22 GMT 2015 armv6l GNU/Linux) rebuilt to disable tickless, enable PHY
> timestamping and enable all appropriate PPS options, and has NTP
> 4.2.8p1-beta5 compiled with:
>
> ./configure --enable-linuxcaps --enable-ATOM --enable-NMEA --disable-ipv6
> --disable-all-clocks --disable-parse-clocks --disable-debugging
>
> and with my ntp.conf file set up thus:
>
> ----------
> logfile /var/log/ntp.log
> driftfile /var/lib/ntp/ntp.drift
> statsdir /var/log/ntpstats/
> statistics loopstats peerstats clockstats protostats
> filegen loopstats file loopstats type day enable
> filegen peerstats file peerstats type day enable
> filegen clockstats file clockstats type day enable
> filegen protostats file protostats type day enable
> leapfile /home/time/leap-seconds.3629404800
>
> server ntp0.catn.com iburst
> server ntp2c.mcc.ac.uk iburst
> server ntp1.luns.net.uk iburst
> server ntp1.uk.uu.net iburst
> server ntp.colinbarrett.co.uk iburst
>
> server 127.127.20.0 mode 17 minpoll 4 maxpoll 4 prefer
> fudge 127.127.20.0 flag1 0 flag2 0 flag3 0 flag4 0 time1 0.00000 time2
> 0.1137
>
> server 127.127.22.0 minpoll 4 maxpoll 4
> fudge 127.127.22.0 refid PPS time1 0.000 flag2 0 flag3 1
>
> restrict default limited kod nomodify notrap nopeer
>
> restrict 127.0.0.1
> ----------
>
> After an hour or so, "ntpq -crv -pn; ntptime; ntpq -c clockvar" shows:
>
> associd=0 status=011d leap_none, sync_pps, 1 event, kern,
> version="ntpd 4.2.8p1-beta5 at 1.3265-o Sun Jan 11 19:10:22 UTC 2015 (1)",
> processor="armv6l", system="Linux/3.12.35", leap=00, stratum=1,
> precision=-19, rootdelay=0.000, rootdisp=1.015, refid=PPS,
> reftime=d85e39b2.e1489c74  Mon, Jan 12 2015 12:16:50.880,
> clock=d85e39b4.0ea565be  Mon, Jan 12 2015 12:16:52.057, peer=4258, tc=4,
> mintc=3, offset=-0.000466, frequency=-17.209, sys_jitter=0.001907,
> clk_jitter=0.001, clk_wander=0.000, tai=35, leapsec=201507010000,
> expire=201512280000
>      remote           refid      st t when poll reach   delay   offset
>  jitter
>
> ==============================================================================
> *127.127.20.0    .GPS.            0 l    3   16  377    0.000   -1.066
> 2.801
> o127.127.22.0    .PPS.            0 l    2   16  377    0.000    0.000
> 0.002
> -87.124.126.49   195.66.241.3     2 u   34   64  377   29.758    8.186
> 0.977
> -130.88.200.6    130.88.200.4     3 u   14   64  377   17.783    1.952
> 0.580
> +217.114.59.3    158.43.192.66    2 u    7   64  377   15.947    4.033
> 0.814
> +158.43.128.66   193.67.79.202    2 u   15   64  377   10.319    1.873
> 0.553
>  81.174.247.243  .INIT.          16 u    - 1024    0    0.000    0.000
> 0.000
> ntp_gettime() returns code 0 (OK)
>   time d85e39b4.49e7c8d4  Mon, Jan 12 2015 12:16:52.288, (.288693882),
>   maximum error 2000 us, estimated error 1 us, TAI offset 35
> ntp_adjtime() returns code 0 (OK)
>   modes 0x0 (),
>   offset 0.000 us, frequency -17.209 ppm, interval 256 s,
>   maximum error 2000 us, estimated error 1 us,
>   status 0x2107 (PLL,PPSFREQ,PPSTIME,PPSSIGNAL,NANO),
>   time constant 4, precision 0.001 us, tolerance 500 ppm,
>   pps frequency -17.207 ppm, stability 0.004 ppm, jitter 0.507 us,
>   intervals 73, jitter exceeded 45, stability exceeded 0, errors 0.
> associd=0 status=0000 no events, clk_unspec,
> device="PPS Clock Discipline", timecode=, poll=828, noreply=0,
> badformat=0, baddata=0, stratum=16, refid=80.80.83.0, flags=4
>
> I've tried using Banana Pi and Beaglebone Black SBCs and have also used
> u-blox Max-7Q and Trimble Copernicus II GPS breakout boards with no
> improvement (The Banana Pi is the best but is stuck on the Allwinner 3.4
> kernel, which I'm not thrilled about), leading me to believe the roadblock
> to a more precise clock lies in my less than ideal antenna setup, but my
> questions are: can I improve upon this and, if so, how? Have I made any
> obvious errors? I'm relatively new to this and would appreciate any advice
> I can get.
>
> Thanks,
> Neil.
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