NavSpark GPS+GLONASS Stratum-1 NTP Time Source with a Raspberry Pi

Intro

Here are my notes for getting a NavSpark GPS+GLONASS module working with a Raspberry Pi (Model B) for Timing/NTP purposes. They have since come out with a specific timing module that would probably be better suited for this. But alas, it's not what I have right now :)

What is this all about?

For a long time now, I've wanted to setup a Stratum 1 time source. It allows better matching of logs for debugging, and allows a more accurate time source for local network devices.

This page goes over the module, getting it wired up to a Pi, then getting the Pi working with the module. I've also added a i²c TCXO RTC (DS3231) for timekeeping while the unit does not have power. This was added as the Pi does not have an RTC built in, and it may take some time for the Pi to sync with peers and/or GPS to get time set.

This will give me a time source on my network that is extremely accurate for my needs.

I created a custom PCB for attaching the NavSpark module, DS3231, and associated parts to the Pi. This makes it nice and compact to put to the side to just run. Gives it a nice SAF. (Spouse Approval Factor)

What does this page assume?

• You have a NavSpark (or similar) GPS Module that outputs RS232 TTL NEMA GPS code, as well as a 1PPS (Pulse per second) output.
• You have a Raspberry Pi Model B Variant (Original, B+, or Pi 2 Model B should all work. However the B is recommended over the A variant due to the hardwire network.)
• You know how to wire/breadboard to the Pi
• Fresh install of Raspbian (either directly or through NOOBS)

Other

• Logic Level Converter - If your GPS module outputs 5v, as the Pi need 3v in. (Note: The NavSpark outputs 3v)
• Solder
• Soldering Iron
• Materials in BOM below if using custom adapter board
• Pi Case
• Good, solid/stable output, 5v USB Power Supply (a good quality power supply can make a big difference, especially when used in timing situations. I happen to be using a HP TouchPad supply, as I have a few around.)
• Set up a cross-compile environment. Highly recommended for recompiling the kernel.
• Comfortable compiling and installing software/kernel

My Testing Environment

• Raspberry Pi Model B
• GPIO Breadboard Breakout
• NavSpark GPS+GLONASS Module
• Internal GPS/GLONASS Active Antenna
• Maxim DS3231 i²c TCXO RTC (Temperature Compensated Oscillator)

The Code

You'll want to start with a fresh install of Raspbian, Either directly, or from NOOBS. This makes sure you're on a even base. Once you have a fresh install, just follow the steps below.

If you already have a tweaked install that you want to keep, just pick and choose the commands below that suit what you're trying to do.

Random Notes (The building blocks)

http://www.satsignal.eu/ntp/Raspberry-Pi-NTP.html

set user password

Advanced options

-set hostname - NTP1

-Change GPU memory to 16M (not used for NTP, more memory available to the system)

-Enable Kernel i2c

-Disable Kernel/Shell over Serial

finish, reboot.

login as pi

sudo -s

set root password

Update Pi

apt-get update

apt-get dist-upgrade

rpi-update

apt-get install pps-tools snmp libcap-dev i2c-tools

Yay device-Tree -- Reference: http://www.satsignal.eu/ntp/Raspberry-Pi-quickstart.html edit /boot/config.txt: add --

dtoverlay=pps-gpio,gpiopin=23

Custom PCB uses GPIO23

dtoverlay=i2c-rtc,ds3231

Enables the DS3231 i2c clock at boot.

reboot

Upon reboot, you should see things like this toward the end of the kernel messages:

[ 5.401032] pps_core: LinuxPPS API ver. 1 registered [ 5.506199] pps_core: Software ver. 5.3.6 - Copyright 2005-2007 Rodolfo Giometti <giometti@linux.it> [ 5.638198] pps pps0: new PPS source pps.-1 [ 5.741468] pps pps0: Registered IRQ 417 as PPS source [ 5.822304] bcm2708_i2c_init_pinmode(1,2) [ 5.961135] bcm2708_i2c_init_pinmode(1,3) [ 6.260785] rtc-ds1307 1-0068: rtc core: registered ds3231 as rtc0 [ 6.369424] bcm2708_i2c 20804000.i2c: BSC1 Controller at 0x20804000 (irq 79) (baudrate 100000)

KERNEL TIME

Reason to compile is default kernel has NO_HZ enabled, and because of that, does not have CONFIG_NTP_PPS, for the kernel to sync to PPS. See: https://support.ntp.org/bin/view/Sandbox/HowtoPpsOnRaspberryPi

Recommend to compile kernel on another system --http://elinux.org/Raspberry_Pi_Kernel_Compilation

Build Machine

crossdev -S -v -t arm-unknown-linux-gnueabi

export CCPREFIX=arm-unknown-linux-gnueabi-

may need gcc-config to set current version if updated

get kernel source: git clone --depth 1 git://github.com/raspberrypi/linux.git pikern

grab default /proc/config.gz from Pi, uncompress and copy to pikern/.config

make ARCH=arm CROSS_COMPILE=${CCPREFIX} oldconfig

modify kernelmake ARCH=arm CROSS_COMPILE=${CCPREFIX} menuconfig

General -> Timers Subsystem -> Deselect "Old Idle Dynticks Config"Device Drivers -> PPS Support -> Enable: PPS Kernel Consumer Support (Will not show up if the timer subsystem options above are not set)

make ARCH=arm CROSS_COMPILE=${CCPREFIX} -j4

mkdir modtmp

make ARCH=arm CROSS_COMPILE=${CCPREFIX} INSTALL_MOD_PATH=./modtmp modules_install

Compress files

tar -cjf modules.tar.bz2 modtmp/

tar -cjf dts.tar.bz2 arch/arm/boot/dts/

Transfer Files

scp modules.tar.bz2 root@ntp1:~/

scp dts.tar.bz2 root@ntp1:~/

scp arch/arm/boot/Image root@10.0.3.14:/boot/Image-3187

Extract and move modules

tar -xjf modules.tar.bz2

mv /lib/modules/<version> /lib/modules/<version>-orig

mv modtmp/lib/modules/<version> /lib/modules

cp -R modtmp/lib/firmware/* /lib/firmware

extract and move DTB's

tar -xjf dts.tar.bz2

cp arch/arm/boot/dts/*.dtb /boot/overlays

mv /boot/overlays/bcm*.dtb /boot

Need to sign kernel: https://github.com/raspberrypi/documentation/blob/master/configuration/device-tree.md (Section 4.1)

grab mkknlimg(https://github.com/raspberrypi/tools/blob/master/mkimage/mkknlimg), and sign the kernel:

mkknlimg /boot/Image-3187 /boot/Image-3187S

grab knlinfo(https://github.com/raspberrypi/tools/blob/master/mkimage/knlinfo) and verify:

knlinfo /boot/Image-3187S

Should show something like:

./knlinfo /boot/Image-3187S Kernel trailer found at 8697996/0x84b88c:

 KVer: "Linux version 3.18.7+ (root@XXXXXXXX) (gcc version 4.8.3 (Gentoo 4.8.3 p1.1, pie-0.5.9) ) #1 PREEMPT Thu Feb 19 20:30:48 EST 2015"
 DTOK: true

Edit /boot/config.txt, add:

kernel=Image-3187S

Configuring NTP

Grab latest NTP from: http://www.ntp.org/downloads.html,

extract

./configure --prefix=/usr --enable-ATOM --enable-NMEA --enable-GPSD --enable-SHM --enable-WWV --with-ntpsnmpd --enable-ipv6 --enable-linuxcaps --enable-clockctl

make && make install

now wait ~20minutes

Configure network:

1. Static IP

Edit /etc/networking/interfaces

iface eth0 inet static

address 10.10.10.10

netmask 255.255.255.0

gateway 10.10.10.1

rm /var/lib/ntp/ntp.conf.dhcp

GPS/UDEV Rules

create /etc/udev/rules/09-gps.rules

file contents:

1. Adds symlink from serial interface to /dev/gps0 for ntpd

KERNEL=="ttyAMA0", SYMLINK+="gps0"

Edit /etc/ntp.conf

enable calibrate

enable kernel

1. GPS Module

server 127.127.20.0 mode 82 minpoll 4 maxpoll 6

fudge 127.127.20.0 time2 +0.1939

1. PPS of GPS Module

server 127.127.22.0 minpoll 4

fudge 127.127.22.0 flag3 1

Add other servers/peers, set one as prefer (needed to get PPS lock, see http://ntpi.openchaos.org/pps_pi/)

Tune the offset http://www.catb.org/gpsd/gpsd-time-service-howto.html

set timezone -

rm /etc/localtime

ln -s /usr/share/zoneinfo/America/New_York /etc/localtime

edit /etc/default/hwclock

HWCLOCKACCESS=YES

HCTOSYS_DEVICE=rtc0

edit /etc/init.d/hwclock.sh, line 64, comment out if statement for udev

The RTC isn't handled by udev, so this check needs to be removed.

1. http://www.raspberrypi.org/forums/viewtopic.php?f=44&t=16218

dpkg --purge fake-hwclock

1. 1. cd /etc/rcS.d

update-rc.d hwclock.sh enable

update-rc.d alsa-utils disable

update-rc.d x11-common disable

1. 1. OLD

apt-get install gpsd gpsd-clients python-gps

edit /etc/defaults/gpsd

start_daemon = true

devices="/dev/ttyAMA0"

flags -b -n

stty -F /dev/ttyAMA0 115200

set base_baud before gpsd starts, scans faster.

service gpsd enable

reboot, confirm with cgps -s

apt-get install libncurses5-dev bc

edit modules, include pps-gpio

Instead of gpsd - symlink /dev/ttyAMA0 to /dev/gps0, use 127.127.20.0 mode 82 in ntp config, adds GPS_NEMA driver

Uninstall existing ntp, compile/install latest ntp

=

-> (*) PPS Client using GPIO

Device Drivers -> Real Time Clock -> (*) Dallas/Maxim DS1307/37/38/39/40, ST M41T00, EPSon RX-8025 (For RTC 3231 option below)

(Optional)Kernel Features -> memory split -> 2G/2G

Preemption Model -> No forced preemption (Server)

CPU Power Management -> CPU Frequency Scaling -> Default CPU Freq Governor -> Performance

OldKernel

Patch Kernel: http://ntpi.openchaos.org/pps_pi/ - https://raw.githubusercontent.com/lampeh/rpi-misc/master/linux-pps/linux-rpi-pps-gpio-bcm2708.diff

Note: Line numbers are different with newer kernel. Provide updated patch....

NewKernel

>=3.18.x?

Use DeviceTable - No patching

===================

1. 1. Cross-compile NTP:

1. 1. mkdir tmpinstall##make -j2##make install

1. 1. tar -cjf ntp.tar.bz2 tmpinstall

1. 1. copy files out cp bin/ntpd bin/ntp-wait bin/ntptime /usr/sbin

1. 1. https://support.ntp.org/bin/view/Dev/Cross-compilingNTP

1. 1. RTC

modules/i2c already enabled in kernel from above

i2c-dev module

i2cdetect -y 1 - verify on 68

echo "ds3231 0x68" > /sys/class/i2c-adapter/i2c-1/new_device

Add after unset TZ in hwclock.sh

modprobe i2c-bcm2708

modprobe i2c-dev

modprobe rtc-ds1307

echo "ds3231 0x68" > /sys/class/i2c-adapter/i2c-1/new_device