OS installation

I decided to buy a Raspberry Pi5.
I installed this image

2025-12-04-raspios-trixie-arm64-lite.img with unziped file size 2986344448

And the idea was to setup a stratum 1 NTP server.

I used the GPS-hat I already have since years.

As you can see the vendor is M0UPU. I bought this GPS modules at uputronics.com
This is not available anymore. At that time an ublox MAX-M8Q was used as chip on the gps HAT.

I decided to compile GPSD and NTPD by myself and not to use an available package. As it was a brand new installation a lot of packages are needed:

NTPD

For NTP I took NTPsec from https://gitlab.com/NTPsec/ntpsec
As first step I installed the official package from OS with
apt-get install ntpsec ntpsec-doc ntpsec-ntpdate
With this I got the necessary scripts to start which I had to change only slightly for the self compiled version.
Additional the following packages were needed: git, m4, m4-doc, bison, bison-doc

The basic steps to compile are:

git clone https://gitlab.com/NTPsec/ntpsec.git
cd ntpsec/
./waf configure --refclock=gpsd,generic,shm,pps,nmea,local
./waf build
sudo ./waf install

For the further usage it’s important to set $PYTHONPATH correct. In my case

export PYTHONPATH=/usr/local/lib/python3.13/site-packages/

With ntp.conf from the package one can test if ntpd works well, but in the moment not as stratum 1 service.

GPSD

To run a GNSS disciplined stratum 1 NTP server the gpsd package is not necessary. What we need is a 1PPS ( one puls per second ) which we get from the gps HAT with the available drivers from the OS. But the gpsd package with all its tools makes the life easier.

You can find the source here: https://gitlab.com/gpsd/gpsd

But gpsd needs a lot of additional packages:

 scons ncurses-base ncurses-bin ncurses-doc ncurses-term python-matplotlib-data python3-matplotlib
 python3-serial python3-cairo:arm64 python3-gi-cairo libqt6network6 libqt6networkauth6 
 qt6-networkauth-dev libncurses-dev libgtk-3-dev

For testing the following packages are additional useful: minicom , ppstest

For complete documentation I want to refer to the Internet

https://gpsd.io/building.html
https://gpsd.gitlab.io/gpsd/installation.html

But compiling is quite straight forward:

git clone git@gitlab.com:gpsd/gpsd.git 
scons ; scons check ; sudo scons install

If you decide later on to update to the latest version run:

git pull origin master --rebase
scons --config=force

OS configuration

To make it runnable some minor changes are necessary in the system. And this is maybe the most tricky part.

/boot/firmware/cmdline.txt

This was the original content:

console=serial0,115200 console=tty1 root=PARTUUID=e20c853e-02 rootfstype=ext4 fsck.repair=yes rootwait

Strip away which makes troubles. Then it looks like this

root=PARTUUID=e20c853e-02 rootfstype=ext4 fsck.repair=yes rootwait

There is still the console on the HDMI port available.

/boot/firmware/config.txt

Add a line in the global block:

dtoverlay=pps-gpio,gpiopin=18

And add a new block at the end of the file

[all]
enable_uart=1

If your HAT delivers the 1PPS on a different gpiopin then you have to change the number of course.
For a detailed list see bananapi-gpio-wiringbp

modules

Create a new file /etc/modules-load.d/pps-gpio.conf with one line:

pps-gpio

I modified /etc/group to be sure not having permission issues. User nobody is important as gpsd is running as nobody.

dialout:x:20:admin,root,nobody

reboot

Now reboot the Pi5 and check the logs. With

dmesg | egrep 'tty|pps'

you should see something like this:

[    0.000093] printk: legacy console [tty0] enabled
[    0.012546] 107d001000.serial: ttyAMA10 at MMIO 0x107d001000 (irq = 16, base_baud = 0) is a PL011 rev3
[    0.012557] printk: legacy console [ttyAMA10] enabled
[    1.131186] pps_core: LinuxPPS API ver. 1 registered
[    1.136167] pps_core: Software ver. 5.3.6 - Copyright 2005-2007 Rodolfo Giometti <giometti@linux.it>
[    1.594509] 107d50c000.serial: ttyS0 at MMIO 0x107d50c000 (irq = 33, base_baud = 6000000) is a Broadcom BCM7271 UART
[    1.605118] serial serial0: tty port ttyS0 registered
[    2.656325] 1f00030000.serial: ttyAMA0 at MMIO 0x1f00030000 (irq = 125, base_baud = 0) is a PL011 AXI
[    4.337107] systemd[1]: Created slice system-getty.slice - Slice /system/getty.
[    4.400531] systemd[1]: Created slice system-serial\x2dgetty.slice - Slice /system/serial-getty.
[    4.604327] systemd[1]: Expecting device dev-ttyAMA10.device - /dev/ttyAMA10...

Check if the pps_gpio module is loaded

pi5# lsmod | grep pps_gpio
pps_gpio               49152  0

modinfo pps_gpio gives also some information

There are new devices

pi5# ls -ld /dev/serial? /dev/pps0
crw-rw---- 1 root root 250, 0 Dec 18 18:01 /dev/pps0
lrwxrwxrwx 1 root root      7 Dec 18 18:01 /dev/serial0 -> ttyAMA0

Checking pps0 is useable. It could also be that it is pps1. Of course a GPS-hat must be connected now.

pi5# ppstest /dev/pps0
trying PPS source "/dev/pps0"
found PPS source "/dev/pps0"
ok, found 1 source(s), now start fetching data...
source 0 - assert 1766270742.000503580, sequence: 9871 - clear  0.000000000, sequence: 0
source 0 - assert 1766270743.000502921, sequence: 9872 - clear  0.000000000, sequence: 0
source 0 - assert 1766270744.000502632, sequence: 9873 - clear  0.000000000, sequence: 0
source 0 - assert 1766270745.000502269, sequence: 9874 - clear  0.000000000, sequence: 0

If this is the result then it’s fine.

To see if data are received run

minicom -b 9600 -o -D /dev/serial0

You should see a lot of clear text data coming from the GPS module. Of course the speed could be a different. If you see some wired character then it’s the wrong speed. In my case it’s working with 9600 bd. Typical baud rates are: 9600, 38400 or 115200 bd.

Now it’s time to start gpsd and see if it is working

/usr/local/sbin/gpsd -n -s 9600 /dev/serial0 /dev/pps0

Now the following test should bring some results:

pi5# ntpshmmon
ntpshmmon: version 3.27.2~dev
#      Name  Seen@                 Clock                 Real                 L Prc
sample NTP0  1766270978.149410814  1766270978.148436931  1766270977.999800704 0  -1
sample NTP0  1766270979.149198025  1766270979.148583713  1766270978.999803051 0  -1
sample NTP0  1766270980.149027698  1766270980.148546201  1766270979.999805398 0  -1

To verify the working daemon run cgps -s -u m. You should see some satellite information.

To start next time successfully with systemctl modify file /etc/default/gpsd like this:

OPTIONS=/dev/serial0
DEVICES="/dev/pps0"
GPSD_OPTIONS="-G -n -s 9600"
USBAUTO="false"

Now it’s time for ntpd

The relevant part in /etc/ntpsec/ntp.conf is the following

# pps needs at least one server to get the time
# for easy start I take another stratum-1 in my network
server 192.168.241.190 minpoll 4 maxpoll 4 prefer

# Enabling PPS/ATOM support
server 127.127.22.0 minpoll 4 maxpoll 4
fudge 127.127.22.0 refid PPS time1 0.000500
fudge 127.127.22.0 flag3 1 flag4 1  # enable kernel PLL/FLL clock discipline and clockstats

# gpsd shared memory clock, if 192.168.241.190 fails this will jump in
server 127.127.28.0 minpoll 4 maxpoll 4 # PPS requires at least one preferred peer
fudge 127.127.28.0 refid GPS
fudge 127.127.28.0 time1 +0.15 flag4 1 # coarse processing delay offset

The time parameter “time1” you have to adjust for your situation. And of course several other configuration lines are necessary to start the deamon.

After some time you should see:

pi5# ntpq -pn 
     remote                                   refid      st t when poll reach   delay   offset   jitter
=======================================================================================================
oPPS(0)                                  .PPS.            0 l    8   16  377   0.0000   0.0002   0.0004
+SHM(0)                                  .GPS.            0 l   15   16  377   0.0000  -2.0118   1.7784
*192.168.241.190                         .GPS.            1 u   13   16  377   0.7064   0.2019   9.8784

GPSD and NTP on Raspberry Pi5 with Debian OS 13 trixie