GPSD and NTP on Raspberry PI4 with Debian OS 11.3 Bullseye
OS installation
After 6 years running a GPS disciplined NTP server on old hardware I thought it’s time to setup a new system. I took a Banana PI4 and I installed this image
2022-04-04-raspios-bullseye-arm64.img
I used the GPS-hat I already have since about 6 years.
As you can see the vendor is M0UPU. You can buy the GPS modules at uputronics.com
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 a possible available package. To do so a lot of packages are needed:
scons libncurses5 libncurses5-dev ncurses-doc python3-matplotlib python3-matplotlib-dbg pps-tools libusb-1.0-0 libusb-1.0-0-dev libusb-1.0-doc asciidoctor asciidoctor-doc cu minicom libgtk-3-dev gtk+-3.0 python3-gi-cairo libcap-dev ksh
GPSD
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:
scons ; scons check ; scons install
If you decide later on to update to the latest version run:
git pull origin master --rebase
scons --config=force
NTPD
For NTP I took the tar ball from ntp.org http://www.ntp.org/downloads.html. Currently the latest version is 4.2.8p17 With the following commands compilation was easy
export CC=gcc
./configure '--with-sntp' '--enable-RAWDCF' --enable-SHM --enable-ATOM -enable-NMEA '--enable-autokey' '--enable-simulator' --with-crypto --enable-clockctl --enable-linuxcaps
make
OS configuration
To make it runnable some minor changes are necessary in the system. And this is maybe the most tricky part.
/boot/cmdline.txt
This was the original content:
console=serial0,115200 console=tty1 root=PARTUUID=09abe25e-02 rootfstype=ext4 fsck.repair=yes rootwait quiet splash plymouth.ignore-serial-consoles
Strip away which makes troubles. Then it looks like this
root=PARTUUID=09abe25e-02 rootfstype=ext4 fsck.repair=yes rootwait quiet splash
/boot/config.txt
Add two lines:
dtoverlay=pps-gpio
enable_uart=1
/etc/modules
Add one line:
pps-gpio
I also stoppped hciuart
systemctl disable hciuart
I modified /etc/group to be sure not having permission issues:
dialout:x:20:admin,root,nobody
reboot
Now reboot the PI4 and check the logs. With
dmesg | egrep 'gpio|pps|AMA|serial|gps'
you should see something like this:
[ 0.172164] pps_core: LinuxPPS API ver. 1 registered
[ 0.172177] pps_core: Software ver. 5.3.6 - Copyright 2005-2007 Rodolfo Giometti <giometti@linux.it>
[ 1.288574] gpiomem-bcm2835 fe200000.gpiomem: Initialised: Registers at 0xfe200000
[ 1.415873] uart-pl011 fe201000.serial: there is not valid maps for state default
[ 1.416154] uart-pl011 fe201000.serial: cts_event_workaround enabled
[ 1.416301] fe201000.serial: ttyAMA0 at MMIO 0xfe201000 (irq = 19, base_baud = 0) is a PL011 rev2
[ 1.424233] bcm2835-aux-uart fe215040.serial: there is not valid maps for state default
[ 1.424976] fe215040.serial: ttyS0 at MMIO 0xfe215040 (irq = 20, base_baud = 62500000) is a 16550
[ 3.209970] pps pps0: new PPS source pps@12.-1
[ 3.210095] pps pps0: Registered IRQ 65 as PPS source
[ 9.483539] pps_ldisc: PPS line discipline registered
[ 9.485867] pps pps1: new PPS source serial0
[ 9.485911] pps pps1: source "/dev/ttyS0" added
Check if the pps_gpio module is loaded
pi4:root# lsmod | grep pps_gpio
pps_gpio 16384 2
modinfo pps_gpio gives also some information
There are new devices
pi4:mayer# ls -ld /dev/serial? /dev/pps0
crw-rw---- 1 root root 250, 0 Jun 19 13:28 /dev/pps0
lrwxrwxrwx 1 root root 5 Jun 19 13:28 /dev/serial0 -> ttyS0
lrwxrwxrwx 1 root root 7 Jun 19 13:28 /dev/serial1 -> ttyAMA0
Checking pps0 is useable. It could also be that it is pps1. Of course a GPS-hat must be connected now.
pi4:root# 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 1655239442.996967522, sequence: 49 - clear 0.000000000, sequence: 0
source 0 - assert 1655239443.996906114, sequence: 50 - clear 0.000000000, sequence: 0
source 0 - assert 1655239444.996843175, sequence: 51 - clear 0.000000000, sequence: 0
source 0 - assert 1655239445.996787475, sequence: 52 - 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.
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:
pi4:root# ntpshmmon
ntpshmmon: version 3.24.1~dev
# Name Seen@ Clock Real L Prc
sample NTP0 1655647858.246635278 1655647858.161288573 1655647858.000016114 0 -1
sample NTP2 1655647858.246747648 1655647858.000497546 1655647858.000000000 0 -20
sample NTP2 1655647859.000767703 1655647859.000496185 1655647859.000000000 0 -20
sample NTP0 1655647859.152066030 1655647859.151809902 1655647859.000018310 0 -1
sample NTP2 1655647860.001379136 1655647860.000496214 1655647860.000000000 0 -20
To verify the working daemon run cgps -s -u m. You should see some satellite information.
Now it’s time for ntpd
The relevant part in /etc/ntp.conf is the following
# pps needs another server as peer
# 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
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. If ntp.conf is ready start the deamon.
After some time you should see:
pi4:root# ntpq -pn
remote refid st t when poll reach delay offset jitter
==============================================================================
o127.127.22.0 .PPS. 0 l 5 16 377 0.000 +0.001 0.001
+127.127.28.0 .GPS. 0 l 3 16 377 0.000 +5.908 2.857
*192.168.241.190 .GPS. 1 u 10 16 377 0.712 +0.243 21.012
That’s it.
Just a word about NTP classic.
As you can see the current and latest version of NTP is very old. I am not sure how long it will be available. There are alternatives, for example ntpsec.
But there is one reason. For this see my other blog https://blog.mayer.tv/2022/06/20/NTP-classic-with-.ntprc-file.html