pc_engines_apu_ublox_6_timing_gps

PC Engines APU / u-blox 6 Timing receiver / NTP

[hardware, apc, gps, ntp, u-blox, ublox, timing]

PC Engines APU / u-blox 6 Timing receiver / NTP

Prerequisites:

PC Engines APU
Additional serial port(s)
u-blox 6 timing receiver (evaluation kit)

Documentation:

Install and configure OS

Install Voyage linux using PXE (network) or USB.
After installation, log in as root (password voyage) and remount read/write.
```
# remountrw
```
Create non root user.
```
useradd username
passwd username
```
Change hostname /etc/hosts /etc/hostname, configure network.
Change apt mirrors in /etc/apt/…
Install prerquisites.
```
apt-get install dialog setserial
```
Update.
```
apt-get update
apt-get upgrade
```
Configure time zone.
```
dpkg-reconfigure tzdata
```

Configure locale.

apt-get install locales
dpkg-reconfigure locales

Edit Voyage Linux config to enable writing to ntp drift file. Edit /etc/default/voyage-util
```
VOYAGE_SYNC_DIRS="var/lib/ntp"
```

Install and configure gpsd

Install gpsd.
```
apt-get install gpsd gpsd-clients
```

Reconfigure gpsd, add the -n option:

dpkg-reconfigure gpsd

# GPS device /dev/gps0
# Add -n option

Install and configure NTPd

We need to compile NTP to enable ATOM PPS support.

(apt-get remove ntp ntp-doc)

cd /root
apt-get install dpkg-dev dialog devscripts fakeroot pps-tools
  
apt-get source ntp && apt-get build-dep ntp
  
cd ntp-4.2.6.p5+dfsg
debuild -us -uc

cd ..  
dpkg --install ntp_4.2.6.p5+dfsg-2+deb7u1_amd64.deb
dpkg --install ntp-doc_4.2.6.p5+dfsg-2+deb7u1_all.deb

Configure NTPd to run at the highest priority. Edit /etc/default/ntp
```
NTPD_OPTS='-g -N'
```

Create PPS device and set low_latency. Add udev rules. Create /etc/udev/rules.d/gps.rules.

KERNEL=="ttyS2", SYMLINK+="gps0"
KERNEL=="ttyS2", RUN+="/bin/setserial -v /dev/%k low_latency"
KERNEL=="ttyS2", RUN+="/usr/sbin/ldattach pps /dev/%k"

Configure /etc/ntp/conf.

# Allow more distance between GPS (USB) and Serial PPS.
# Stratum level 12 when no ref source available
tos mindist 0.100 orphan 12

driftfile /var/lib/ntp/ntp.drift
leapfile  /var/lib/ntp/leap-seconds
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

# Local servers
server ntp1.polaire.nl

# ATOM PPS (/dev/pps0)
server 127.127.22.0 minpoll 4 maxpoll 4
fudge  127.127.22.0 refid PPS

# GPS (USB /dev/ttyACM0)
server 127.127.28.0 minpoll 4 maxpoll 4 prefer
fudge 127.127.28.0 refid GPSd
fudge 127.127.28.0 time1 0.063

# By default, exchange time with everybody, but don't allow configuration.
restrict -4 default limited kod notrap nomodify nopeer noquery
restrict -6 default limited kod notrap nomodify nopeer noquery

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

Remove /var/lib/ntp/ntp.conf.dhcp
Disable automatic update of ntp package. Remember to update it yourself in case of security updates!
```
sudo apt-mark hold ntp ntp-doc
```
Reboot and check results.

Leap second file

Automatic download of new leap second file.

Install lftp.
```
apt-get install lftp
```
Create leap second download script: /usr/local/bin/get_leap.sh
Change executable mode
```
chmod +x /usr/local/bin/get_leap.sh
```
Download new file weekly. Create /etc/cron.weekly/leapsecond
```
#!/bin/bash

/usr/local/bin/get_leap.sh
```
Change executable mode
```
chmod +x /etc/cron.weekly/leapsecond
```

Verify

Make sure gpsd and ntpd start at boot. If not, enable it.
```
update-rc.d ntp enable
update-rc.d gpsd enable
```

Test PPS reception.

# ppswatch /dev/pps0
trying PPS source "/dev/pps0"
found PPS source "/dev/pps0"
timestamp: 1403289214, sequence: 11, offset:  81613988
timestamp: 1403289214, sequence: 11, offset:  81613988
timestamp: 1403289215, sequence: 12, offset:  81607583
timestamp: 1403289215, sequence: 12, offset:  81607583
timestamp: 1403289216, sequence: 13, offset:  81609303
timestamp: 1403289216, sequence: 13, offset:  81609303
timestamp: 1403289217, sequence: 14, offset:  81601958
^C

Check ntpq status. The 'o' means, PPS is working.

$ ntpq -p
     remote           refid      st t when poll reach   delay   offset  jitter
==============================================================================
 ntp1.polaire.nl .PZF.            1 u   47   64    1    0.270   12.367   0.001
 ntp2.polaire.nl 95.97.208.29     2 u   48   64    1    0.293   12.720   0.001
 ntp3.home.polai .DCF.            1 u   47   64    1    0.300   13.941   0.001
oPPS(0)          .PPS.            0 l    -   16    7    0.000   12.355   0.102
*SHM(0)          .GPSd.           0 l    2   16    7    0.000    1.188   1.431

# After a while...

     remote           refid      st t when poll reach   delay   offset  jitter
==============================================================================
+ntp1.polaire.nl .PZF.            1 u   56   64  377    0.292   -0.099   0.075
-ntp2.polaire.nl 95.97.208.29     2 u   50   64  377    0.289    0.638   0.086
+ntp3.home.polai .DCF.            1 u   41   64  377    0.237    1.656   0.048
oPPS(0)          .PPS.            0 l   15   16  377    0.000    0.027   0.003
*SHM(0)          .GPSd.           0 l   16   16  377    0.000   -8.657   2.708

Show connected clients:
```
ntpdc -c monlist
```

Verify leap variables:

ntpq -c "rv 0"
associd=0 status=0118 leap_none, sync_pps, 1 event, no_sys_peer,
version="ntpd 4.2.6p5@1.2349-o Tue Jan  6 09:09:39 UTC 2015 (1)",
processor="x86_64", system="Linux/3.10.11-voyage", leap=00, stratum=1,
precision=-22, rootdelay=0.000, rootdisp=85.497, refid=PPS,
reftime=d8562b21.98df89e1  Tue, Jan  6 2015 10:36:33.597,
clock=d8562b2d.36477b48  Tue, Jan  6 2015 10:36:45.212, peer=27238, tc=4,
mintc=3, offset=0.000, frequency=0.000, sys_jitter=8.116,
clk_jitter=65.587, clk_wander=0.000, leapsec=201207010000,
expire=201506280000

Configure, firmware update ublox 6 module

The module is attached to an embedded device and you cannot run Windows on the APU system board. The following directions will let you pass through the serial device to a Windows computer over the network. Then you will be able to run the u-center GNSS evaluation software for Windows.

APU config

Install socat.
```
apt-get install socat
```

Connect serial to TCP port.

socat file:/dev/ttyACM0,raw,echo=0 tcp-l:3006,fork&

Windows config

I'm using Windows 7 in this example.

The com0com.sys is a test-signed kernel-mode driver that will not load by default. NOTE: Enabling test signing will impair computer security. To enable test signing, enter command:
```
bcdedit.exe -set TESTSIGNING ON
```
Reboot
Download and install com0com and com2tcp http://sourceforge.net/projects/com0com/files/?source=navbar
Launch setup to determine virtual com port pair. In my case it's COM5 ⇔ COM6

Start cmd.exe, run:

com2tcp.exe --ignore-dsr \\.\COM6 1.2.3.4 3006

Download and install u-center http://www.u-blox.com/en/evaluation-software/u-center.html
Run u-center, go to Receiver → Port → COM5
Receiver → Generation → u-blox 6

Screenshot

Recommended settings for timing applications

SBAS → Subsystem: Disabled.
TMODE2 → Fixed location. As a rule of thumb the position should be known with an accuracy of better than 1 m for a timing accuracy in the order of nanoseconds. If an accuracy is required only in the order of microseconds, a position accuracy of roughly 300 m is sufficient. If the position is known, the receiver can provide an accurate time solution by tracking only one satellite. For an unknown position, the receiver needs a minimum of four satellites to calculate a position fix and to solve for a timing solution. This is known as survey-in and can be chosen using the UBX-CFG-TMODE2 message. It is recommended to use survey-in only for non-moving platform applications. For optimal performance a known fixed position of the antenna should be used.
NAV5 → Dynamic Model: Stationary
TP5 → Active, 1Hz, 0, Lock to GNSS, Other setting, 1Hz, 100000us, Align Pulse to TOW, 0-UTC time, clear invert pulse.

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