Building a Stratum 1 NTP Server Using Raspberry Pi

johnpoz · May 28, 2019, 1:56 PM

@tman222 said in Building a Stratum 1 NTP Server Using Raspberry Pi:

is there even a case available out there to protect an SBC and taller double HAT stack like that?

While I have not actually looked into these particular hats your talking about, etc. The typical dogbone cases normally allow for extra spacers to allow for different hats...

Once you get your ntp up and running - let us know the particulars ;)

Maybe this summer when get some free time I will be looking into using the Galileo satellites, from what I have been reading after this thread re perked my interest is that those are disabled by default for use in the hat.. and have to use the gpsctl code that is out there to enable them, etc..

tman222 · May 28, 2019, 2:19 PM

@johnpoz said in Building a Stratum 1 NTP Server Using Raspberry Pi:

@tman222 said in Building a Stratum 1 NTP Server Using Raspberry Pi:

is there even a case available out there to protect an SBC and taller double HAT stack like that?

While I have not actually looked into these particular hats your talking about, etc. The typical dogbone cases normally allow for extra spacers to allow for different hats...

Once you get your ntp up and running - let us know the particulars ;)

Maybe this summer when get some free time I will be looking into using the Galileo satellites, from what I have been reading after this thread re perked my interest is that those are disabled by default for use in the hat.. and have to use the gpsctl code that is out there to enable them, etc..

Thanks @johnpoz - coincidentally, the same thing dawned on me a little bit ago while looking at Odroid cases, i.e. that the dogbone cases (i.e. cases hat just have a top and bottom plate) can we made height variable using multiple standoffs / spacers. For instance, I believe this is essentially the same style of case for the Odroid - would you agree?

https://ameridroid.com/collections/cases/products/odroid-c-series-raspberry-pi-case-black?variant=12363871911970

I think a PoE powered variant will be cool - also gives some flexibility in terms of location around the house (for best satellite signal).

athurdent · May 30, 2019, 8:04 AM

@tman222 I pimped my Pi-hole a week ago. It's on the standard Raspbian OS. Far from an expert, but it works fine I guess.

# ntpq -crv -pn
associd=0 status=0415 leap_none, sync_uhf_radio, 1 event, clock_sync,
version="ntpd 4.2.8p10@1.3728-o Sat Mar 10 18:03:33 UTC 2018 (1)",
processor="armv7l", system="Linux/4.19.42-v7+", leap=00, stratum=1,
precision=-19, rootdelay=0.000, rootdisp=1.045, refid=NMEA,
reftime=e09a0a64.10b97e83  Thu, May 30 2019  9:53:08.065,
clock=e09a0a67.928ebe6a  Thu, May 30 2019  9:53:11.572, peer=43985, tc=4,
mintc=3, offset=0.001561, frequency=-7.225, sys_jitter=0.002188,
clk_jitter=0.002, clk_wander=0.001
     remote           refid      st t when poll reach   delay   offset  jitter
==============================================================================
o127.127.20.0    .NMEA.           0 l    3   16  377    0.000    0.002   0.002

I used the cheapest GPS USB stick I could get and soldered the PPS cable. (https://blog.elektrowolle.de/2017/04/27/gps-pps-basierter-ntp-server-auf-raspberry-pi/)

This is my relevant ntp.conf part, the other examples would not work.

# GPSD
server 127.127.20.0 minpoll 3 maxpoll 4 prefer
fudge 127.127.20.0 flag1 1 refid NMEA

Comparing it to 0.de.pool.ntp.org with Zabbix:

tman222 · Dec 11, 2020, 9:41 PM

Thanks @athurdent for sharing your setup - that looks very cool! I find it interesting that you chose to go with a USB receiver instead of the Pi GPS HAT's that everyone else has been using. Was there any particular reason for that? Are you seeing any adverse effects from using USB (e.g. timing issues, extra jitter, etc.)? I suppose it could also be that using PPS helps offset some of that.

Looking through the link you posted - I did find this interesting part regarding reducing jitter:

http://www.satsignal.eu/ntp/Raspberry-Pi-NTP.html#nohz
https://www.kernel.org/doc/Documentation/timers/NO_HZ.txt

Has anyone tried this and seen noticeable reduction in jitter?

Thanks again everyone.

athurdent · May 30, 2019, 2:25 PM

@tman222 Thanks! :)
I went with a USB receiver, because it's just a little home project and I did not want to spend too much money on it. I wanted to show my son how to disassemble something electronic and (hopefully) not break it, also how to solder without completely melting anything.
I had a good laugh on this one, when it came to configure NTP and compare time sources:
“A man with one watch knows what time it is. A man with two watches is never sure.”

While I am no expert on NTP and did not really dive into all the background info, I think this is important to note:
"/dev/ttyAMA0
The UART device on a Raspberry Pi. Has the side effect of opening /dev/pps0 for RFC2783 1PPS data." (http://www.catb.org/gpsd/gpsd.html)

So, you probably don't need to specify a separate PPS source in ntp.conf because of that. At least here that did not work anyways, maybe because GPSD already uses PPS that way.

Also, on the lastest Raspbian, there is no need to compile NTP yourself, everything is build in already now. You just have to get the symlinks for GPS and PPS in place.
This took care of it here, if I documented it right:

systemctl disable hciuart
systemctl mask serial-getty@ttyAMA0.service

vi /etc/udev/rules.d/09.pps.rules
KERNEL=="pps0", OWNER="root", GROUP="tty", MODE="0660", SYMLINK+="gpspps0"

I have not tried that nohz option. I think jitter is OK and does not vary too much. But then again, I am far from an expert, just the firewall guy trying to play a little with something else :)

q54e3w · Jun 1, 2019, 6:55 AM

I've been meaning to put a quick how-to together for a NTP server based on a pcengine apu2 which offers much better performance at a slightly higher price. You may not need the increased accuracy but its available if you want to join the ranks of time-nuts.

chronyc tracking
Reference ID    : 47505330 (GPS0)
Stratum         : 1
Ref time (UTC)  : Sat Jun 01 06:56:35 2019
System time     : 0.000000004 seconds fast of NTP time
Last offset     : +0.000000004 seconds
RMS offset      : 0.000000008 seconds
Frequency       : 4.568 ppm fast
Residual freq   : +0.000 ppm
Skew            : 0.001 ppm
Root delay      : 0.000000001 seconds
Root dispersion : 0.000000941 seconds
Update interval : 1.0 seconds
Leap status     : Normal

stephenw10 · Jun 1, 2019, 9:02 AM

That 4ns fast? Nice!

tman222 · Jun 1, 2019, 12:53 PM

@q54e3w said in Building a Stratum 1 NTP Server Using Raspberry Pi:

I've been meaning to put a quick how-to together for a NTP server based on a pcengine apu2 which offers much better performance at a slightly higher price. You may not need the increased accuracy but its available if you want to join the ranks of time-nuts.
chronyc tracking
Reference ID    : 47505330 (GPS0)
Stratum         : 1
Ref time (UTC)  : Sat Jun 01 06:56:35 2019
System time     : 0.000000004 seconds fast of NTP time
Last offset     : +0.000000004 seconds
RMS offset      : 0.000000008 seconds
Frequency       : 4.568 ppm fast
Residual freq   : +0.000 ppm
Skew            : 0.001 ppm
Root delay      : 0.000000001 seconds
Root dispersion : 0.000000941 seconds
Update interval : 1.0 seconds
Leap status     : Normal

Hi @q54e3w - those are some very impressive figures! As someone who is a always obsessed with performance and efficiency I just may have to try this too. :) Do you mind sharing with us what parts you used for this setup? In particular, I'm quite curious what you chose for the GPS receiver module in the APU2 box. Also, what OS did you end up running on the machine to get that level of performance (accuracy)? Was it a flavor of Linux (e.g. Debian) or something more custom?

Thanks again!

tman222 · Jun 29, 2019, 7:11 PM

With the Raspberry Pi 4 having just been released, do you guys think it will perform better for this purpose given the improvements to the network on the SoC?

Also, @q54e3w - when you have a moment, could you please share some additional details with us what you are using for an APU2 based setup? I'm very curious. Thanks again!

kiokoman · Jul 2, 2019, 1:24 PM

i will tell you in a few days, i'm waiting for the courier ...
raspberry pi 4, but gps is from adafruit.
this will be my first experiment with this toys
...
reviced it today, i just had the time to install raspbian and soldered the gps hat, now i need to find a way to have a gps fix. i don't have the time now to do any test, the only first impression is that the board become very hot, i will probably buy something to cool it down

@johnpoz maybe you know, do you think it will be possible to add a display on top of the gps hat or it will not work ? RX/TX pins are for gps data and pin #4 is used for PPS on my case

kiokoman · Jul 3, 2019, 5:13 PM

and this is how it work here, i have some trouble because the "howto" available are a little outdated, i need to do some research

pi@raspberrypi:~ $ ntpq -crv -pn
associd=0 status=0115 leap_none, sync_pps, 1 event, clock_sync,
version="ntpd 4.2.8p13@1.3847-o Tue Jul  2 16:07:07 UTC 2019 (2)",
processor="armv7l", system="Linux/4.19.50-v7l+", leap=00, stratum=1,
precision=-20, rootdelay=0.000, rootdisp=1938.001, refid=PPS,
reftime=e0c75f48.32187a6c  Wed, Jul  3 2019 19:07:20.195,
clock=e0c75f56.2a9026ff  Wed, Jul  3 2019 19:07:34.166, peer=43403, tc=4,
mintc=3, offset=-0.147120, frequency=-17.048, sys_jitter=0.036991,
clk_jitter=0.118, clk_wander=0.024

     remote           refid      st t when poll reach   delay   offset  jitter
==============================================================================
*172.16.0.100    193.204.114.232  2 u   32   32    3    0.468    0.169   0.027
+31.14.131.188   195.113.144.238  2 u   56   64    1   18.466    0.815   0.075
-213.251.52.250  193.0.0.229      2 u   55   64    1   21.270    4.187  21.794
+85.199.214.99   .GPS.            1 u   54   64    1   35.809   -0.642   0.217
-185.19.184.35   193.204.114.233  2 u   53   64    1   22.388    4.127  23.813
o127.127.22.0    .PPS.            0 l   14   16    7    0.000   -0.147   0.037
 127.127.20.0    .GPS.            0 l    -   64    0    0.000    0.000   0.000

kiokoman · Jul 3, 2019, 8:11 PM

ok this is working now, i found out that on my raspberry pi 4 the gps is not on ttyAMA0 as all the tutorial around is based on, but under ttyS0, took my awhile to find out what was wrong ...

pi@raspberrypi:~ $ ntpq -crv -pn
associd=0 status=0115 leap_none, sync_pps, 1 event, clock_sync,
version="ntpd 4.2.8p12@1.3728-o (1)", processor="armv7l",
system="Linux/4.19.50-v7l+", leap=00, stratum=1, precision=-20,
rootdelay=0.000, rootdisp=7938.582, refid=PPS,
reftime=e0c78921.5335fc30  Wed, Jul  3 2019 22:05:53.325,
clock=e0c7892f.6faf75ea  Wed, Jul  3 2019 22:06:07.436, peer=4517, tc=4,
mintc=3, offset=-0.858325, frequency=-16.929, sys_jitter=0.000954,
clk_jitter=0.406, clk_wander=0.000, tai=37, leapsec=201701010000,
expire=201912280000

     remote           refid      st t when poll reach   delay   offset  jitter
==============================================================================
*172.16.0.100    134.64.19.180    2 u   23   32    1    0.474    0.189   0.167
 it.pool.ntp.org .POOL.          16 p    - 1024    0    0.000    0.000   0.001
x127.127.20.0    .GPS.            0 l   31   64    1    0.000   -1.180   0.001
o127.127.22.0    .PPS.            0 l   14   16    1    0.000   -0.858   0.001
+37.247.53.178   193.204.114.232  2 u   20 1024    1   12.891   -0.781   0.375
-213.251.52.250  193.0.0.229      2 u   14 1024    1   21.182    3.930   0.230
+85.199.214.99   .GPS.            1 u   13 1024    1   36.061   -1.087   7.806
-185.19.184.35   193.204.114.233  2 u   12 1024    1   22.180    3.048   0.105

stephenw10 · Jul 4, 2019, 6:05 PM

Looks like it's marked the GPS as a false ticker. You probably need to adjust the fudge time.

Steve

kiokoman · Jul 4, 2019, 6:37 PM

yes, indeed, it's still a work in progress

as i say a have trouble because i was unable to find any recent howto, anyway now i have this

pi@raspberrypi:~ $ ntpq -crv -pn
associd=0 status=0115 leap_none, sync_pps, 1 event, clock_sync,
version="ntpd 4.2.8p12@1.3728-o (1)", processor="armv7l",
system="Linux/4.19.50-v7l+", leap=00, stratum=1, precision=-20,
rootdelay=0.000, rootdisp=500.060, refid=PPS,
reftime=e0c8c525.ed3084d9  Thu, Jul  4 2019 20:34:13.926,
clock=e0c8c52a.0f3a2862  Thu, Jul  4 2019 20:34:18.059, peer=42571, tc=4,
mintc=3, offset=0.000149, frequency=-19.939, sys_jitter=0.000954,
clk_jitter=0.001, clk_wander=0.000, tai=37, leapsec=201701010000,
expire=201912280000

     remote           refid      st t when poll reach   delay   offset  jitter
==============================================================================
o127.127.22.0    .PPS.            0 l    5   16  377    0.000    0.000   0.001
*127.127.28.0    .GPS.            1 l    4   16  377    0.000  -146.34  85.899
+193.204.114.232 .CTD.            1 u   41   64  377   30.981    0.240   0.166
+193.204.114.233 .CTD.            1 u   38   64  377   30.653    0.695   0.148
+79.36.117.15    .GPS.            1 u   60   64  377   37.111   -1.756   0.177
+2001:4b20::beef 85.158.25.74     2 u   65   64  377   17.923   -0.204   2.899
+2001:67c:8:abcd .PPS.            1 u   33   64  377   31.323    0.117   6.783
+81.94.123.17    85.158.25.74     2 u    3   64  377   21.208   -2.684   5.947

kiokoman · Jul 7, 2019, 8:39 PM

ok i'm putting here what i have done so far, if someone can check and give feedback pls

inside /boot/config.txt :

dtoverlay=pi3-disable-bt
force_turbo=1
init_uart_baud=9600
dtoverlay=pps-gpio,gpiopin=4

inside /boot/cmdline.txt

dwc_otg.lpm_enable=0 console=tty1 root=PARTUUID=b55c365b-02 rootfstype=ext4 elevator=deadline fsck.repair=yes rootwait quiet splash plymouth.ignore-serial-consoles nohz=off

inside /etc/modules

# /etc/modules: kernel modules to load at boot time.
#
# This file contains the names of kernel modules that should be loaded
# at boot time, one per line. Lines beginning with "#" are ignored.

i2c-dev
pps-gpio

i have created /etc/udev/rules.d/99-gps.rules :

KERNEL=="pps0",SYMLINK+="gpspps0"
KERNEL=="ttyAMA0",SUBSYSTEM=="tty",MODE=="0777", SYMLINK+="gps0"

sudo apt update
sudo apt dist-upgrade
sudo systemctl disable hciuart
sudo systemctl disable serial-getty@ttyAMA0.service
sudo apt-get install pps-tools ntp dnsutils setserial

inside /etc/rc.local

systemctl stop ntp #otherwise the next command will not work
stty -F /dev/ttyAMA0 raw 9600 cs8 clocal -cstopb #set to 9600bps as per adafruit spec
setserial /dev/ttyAMA0 low_latency # improve latency.. maybe
#we need only GPMRC out
/bin/echo -e '$PMTK314,0,1,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0*29\r\n' > /dev/ttyAMA0 
systemctl start ntp

inside /etc/ntp.conf

# /etc/ntp.conf, configuration for ntpd; see ntp.conf(5) for help

driftfile /var/lib/ntp/ntp.drift

# Leap seconds definition provided by tzdata
leapfile /usr/share/zoneinfo/leap-seconds.list

# Enable this if you want statistics to be logged.
#statsdir /var/log/ntpstats/

statistics loopstats peerstats clockstats
filegen loopstats file loopstats type day enable
filegen peerstats file peerstats type day enable
filegen clockstats file clockstats type day enable

# By default, exchange time with everybody, but don't allow configuration.
restrict default kod notrap nomodify nopeer noquery limited
restrict -6 default kod notrap nomodify nopeer noquery limited

# Local users may interrogate the ntp server more closely.
restrict 127.0.0.1
restrict -6 ::1

# Needed for adding pool entries
restrict source notrap nomodify noquery

# Clients from this (example!) subnet have unlimited access, but only if
# cryptographically authenticated.
restrict 192.168.1.0 mask 255.255.255.0

# If you want to provide time to your local subnet, change the next line.
# (Again, the address is an example only.)
#broadcast 192.168.123.255

# If you want to listen to time broadcasts on your local subnet, de-comment the
# next lines.  Please do this only if you trust everybody on the network!
#disable auth
#broadcastclient
logfile /var/log/ntp.log

server 127.127.20.0 mode 17 minpoll 4 maxpoll 4 iburts prefer
fudge 127.127.20.0 flag1 1 time2 0.350 refid GPS

pool 0.it.pool.ntp.org
pool 1.it.pool.ntp.org
pool 2.it.pool.ntp.org
pool 3.it.pool.ntp.org

result is:

pi@raspberrypi:~ $ ntpq -crv -pn
associd=0 status=0418 leap_none, sync_uhf_radio, 1 event, no_sys_peer,
version="ntpd 4.2.8p12@1.3728-o (1)", processor="armv7l",
system="Linux/4.19.50-v7l+", leap=00, stratum=1, precision=-19,
rootdelay=0.000, rootdisp=1.180, refid=GPS,
reftime=e0cb6dbc.b9fa8540  Sat, Jul  6 2019 20:58:04.726,
clock=e0cb6dc9.863ed46d  Sat, Jul  6 2019 20:58:17.524, peer=65419, tc=4,
mintc=3, offset=-0.000335, frequency=-18.876, sys_jitter=0.001907,
clk_jitter=0.002, clk_wander=0.000, tai=37, leapsec=201701010000,
expire=201912280000

     remote           refid      st t when poll reach   delay   offset  jitter
==============================================================================
o127.127.20.0    .GPS.            0 l   13   16  377    0.000    0.000   0.002
 0.it.pool.ntp.o .POOL.          16 p    -   64    0    0.000    0.000   0.002
 1.it.pool.ntp.o .POOL.          16 p    -   64    0    0.000    0.000   0.002
 2.it.pool.ntp.o .POOL.          16 p    -   64    0    0.000    0.000   0.002
 3.it.pool.ntp.o .POOL.          16 p    -   64    0    0.000    0.000   0.002
-213.251.52.250  193.0.0.229      2 u   21   64  377   20.446    3.853   0.146
-94.177.187.22   193.204.114.233  2 u   14   64  377   16.930   -0.241   0.118
-147.135.207.213 85.199.214.99    2 u   17   64  337   28.742   -0.525   0.150
-212.45.144.3    193.204.114.232  2 u   18   64  377   11.872    0.162   0.148
-188.213.165.209 193.204.114.232  2 u   19   64  377   17.956    0.459   0.136
-80.211.52.109   85.199.214.99    2 u   22   64  377   21.608   -1.141   0.134
#5.158.71.217    94.177.187.22    3 u   17   64  377   30.960   -3.933   0.626
+85.199.214.99   .GPS.            1 u   13   64  377   35.659   -0.337   0.172
+37.247.53.178   193.204.114.233  2 u   16   64  377   12.341    0.191   0.159
+185.19.184.35   193.204.114.233  2 u   21   64  377   22.090    3.996   0.139
-80.211.178.99   194.146.251.100  2 u   10   64  377   18.669   -2.758   6.145

pi@raspberrypi:~ $ sudo lsof /dev/pps0 /dev/gps0
COMMAND   PID USER   FD   TYPE DEVICE SIZE/OFF NODE NAME
ntpd    11340  ntp    4u   CHR 204,64      0t0 1165 /dev/ttyAMA0
ntpd    11340  ntp    5u   CHR  242,0      0t0 1495 /dev/pps0

from what i understand there is no need for gpsd as it was causing alot of offset/jitter
plus from what i have read around ntp now bind to /dev/pps0 and /dev/ttyAMA0 (GPS) automatically. mode 17 is 16+1 so 9600bps + GPMRC
rif. https://www.eecis.udel.edu/~mills/ntp/html/drivers/driver20.html
fudge 127.127.20.0 flag1 1 this flag tell ntp to use PPS, i can set flag1 0 and eventually add 127.127.0.22 back and adjust offset, but i don't see why if ntp do the work for me?
my score on pool.ntp.org si now 20 and identified as stratum 1

pi@raspberrypi:~ $ iperf -c 192.168.1.90
------------------------------------------------------------
Client connecting to 192.168.1.90, TCP port 5001
TCP window size:  232 KByte (default)
------------------------------------------------------------
[  3] local 192.168.1.89 port 52616 connected with 192.168.1.90 port 5001
[ ID] Interval       Transfer     Bandwidth
[  3]  0.0-10.0 sec  1.08 GBytes   931 Mbits/sec

tman222 · Jul 4, 2020, 2:14 PM

Hi @kiokoman - thanks for posting your experience using a Raspberry Pi 4. I'm looking to give this project another go this summer and catching up again on the instructions/advice in this thread and the equipment I would need to purchase. Do you mind listing what exact equipment you ended up using and any steps you took that weren't detailed in your prior posts? At this point, I'm looking to generally follow this guide I found, however, using a Raspberry Pi 4 B instead of the Odroid C2 board.

https://nguvu.org/pfsense/network%20time%20protocol%20(ntp)/ntp-server/

At the time this was written the Pi 4 had not been released yet and the Odroid presented a better option over the Pi 3 given true gigabit network support. I also like the PoE hat integration which helps simplify cabling.

Thanks in advance for any help and advice you can provide.

kiokoman · Jul 4, 2020, 2:52 PM

Raspberry PI 4
Memory Card with raspian
GPS Adafruit ultimate GPS hat
battery cr1220
external active antenna
uFL to SMA converter

https://www.kiokoman.eu.org/index.php/per-non-dimenticare/24-howto-raspberry-pi-4-headless-ntp-stratum-1-gps-pps

https://www.ntppool.org/scores/ntp.kiokoman.eu.org

tman222 · Nov 28, 2020, 10:09 PM

Thanks @kiokoman for sharing your setup and instructions, I really appreciate it. I wanted to bring this thread back up because I'm looking into this again as a small tinkering project and was also curious to learn more about the alternative APU2 based Stratum 1 NTP server setup @q54e3w mentioned above. @q54e3w - could you share some more details on your setup? Thanks in advance.

q54e3w · Nov 28, 2020, 10:30 PM

I had a half finished build and setup guide I was in the process of putting finishing touches to but didn't get to. I'll push it to the top of the list.
The downside of the PTP protocol is that the accuracy isn't preserved across the LAN unless you have hardware that supports it and because of the clients who typically care about this level of accuracy, its seems to be only available in more expensive switches etc, take a look here for a starter and please follow up if you find any more home lab friendly pieces.
https://en.wikipedia.org/wiki/List_of_PTP_implementations
My hardware solution that data came from was a Intel i210 based SBC that supports IEEE1588 and a regular GPS received running stock debian with mild kernel optimization.

I've migrated from using NTP to Chrony which syncs up quicker especially from a cold start which was one of the drawbacks of the NTP implementation. I tried the Odroid C4 which is an updated C2 but the earlier kernels didn't have PPS deciding included and I didn't have the time to build a custom kernel. Im sure things have evolved since then.

All of this is perhaps irrelevant though as Ive had great success with a LeoNTP server, unbelievably accurate and consistent across the year through temperature fluctuations etc and outperforms a non temperature controlled Pi substantially.
http://leobodnar.com/shop/index.php?main_page=product_info&products_id=272
When I update that guide I'll include some performance graphs etc.

tman222 · Nov 28, 2020, 10:46 PM

@q54e3w said in Building a Stratum 1 NTP Server Using Raspberry Pi:

I had a half finished build and setup guide I was in the process of putting finishing touches to but didn't get to. I'll push it to the top of the list.
The downside of the PTP protocol is that the accuracy isn't preserved across the LAN unless you have hardware that supports it and because of the clients who typically care about this level of accuracy, its seems to be only available in more expensive switches etc, take a look here for a starter and please follow up if you find any more home lab friendly pieces.
https://en.wikipedia.org/wiki/List_of_PTP_implementations
My hardware solution that data came from was a Intel i210 based SBC that supports IEEE1588 and a regular GPS received running stock debian with mild kernel optimization.

I've migrated from using NTP to Chrony which syncs up quicker especially from a cold start which was one of the drawbacks of the NTP implementation. I tried the Odroid C4 which is an updated C2 but the earlier kernels didn't have PPS deciding included and I didn't have the time to build a custom kernel. Im sure things have evolved since then.

All of this is perhaps irrelevant though as Ive had great success with a LeoNTP server, unbelievably accurate and consistent across the year through temperature fluctuations etc and outperforms a non temperature controlled Pi substantially.
http://leobodnar.com/shop/index.php?main_page=product_info&products_id=272
When I update that guide I'll include some performance graphs etc.

Thanks @q54e3w, I really appreciate the response. If you don't mind me asking, where did you purchase the LeoNTP server? Is there a US distributor or did you purchase directly from the UK? Thanks again.