=====Raspberry Pi, Dragino LoRa / GPS hat - NTP PPS=====
Configure NTPd with PPS. Based on Raspbian Stretch.

**Notes:**
  * Could not get PPS to work with the new refclock driver 46, GPSD NG client protocol. Switched to PPS (22) and SHM (28).
  * GPSd did not auto start at boot, added the driver above with ''noselect'' to get GPSd to start.

**Sources:**
  * [[https://www.eecis.udel.edu/~mills/ntp/html/refclock.html]]
  * [[https://www.slsmk.com/how-to-setup-a-gps-pps-ntp-time-server-on-raspberry-pi/]]

{{:lora_gps_hat1.png?400|}}

====Configure Raspberry Pi====
Based on Raspbian Stretch

  * Disable hardware; Wifi, Bluetooth, HDMI.
  * Disable services; avahi, triggerhappy, wpa_supplicant
  * Add user, remove pi user.
  * Set correct timezone.
  * Update packages.
====Configure serial port====
  * Disable Bluetooth:<code>echo "dtoverlay=pi3-disable-bt" >> /boot/config.txt</code>
  * Disable the HCI UART:<code>sudo systemctl disable hciuart</code>
  * Disable getty:<code>systemctl mask serial-getty@serial0.service</code>
  * Remove ''console=serial0,115200'' from ''/boot/cmdline.txt''
  * Reboot
  * Test GPS output: ''cat /dev/serial0''
====Configure Pulse Per Second (PPS)====
  * Install PPS tools:<code>apt install pps-tools setserial</code>
  * Configure GPIO for PPS:<code>echo "dtoverlay=pps-gpio,gpiopin=18" >> /boot/config.txt</code>
  * Configure udev rules in ''/etc/udev/rules.d/gps.rules''<code>
KERNEL=="ttyAMA0", RUN+="/bin/setserial /dev/ttyAMA0 low_latency"
KERNEL=="ttyAMA0", SYMLINK+="gps0"
KERNEL=="pps0", GROUP="dialout", MODE="0660"
</code>
  * Reboot
  * There should be a ''/dev/pps0'' device
  * Check for pulse<code># 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 1552847111.000139273, sequence: 152 - clear  0.000000000, sequence: 0
source 0 - assert 1552847112.000135096, sequence: 153 - clear  0.000000000, sequence: 0
source 0 - assert 1552847113.000135337, sequence: 154 - clear  0.000000000, sequence: 0
source 0 - assert 1552847114.000134886, sequence: 155 - clear  0.000000000, sequence: 0
source 0 - assert 1552847115.000135615, sequence: 156 - clear  0.000000000, sequence: 0
source 0 - assert 1552847116.000137416, sequence: 157 - clear  0.000000000, sequence: 0
</code>
====Configure GPdS====
  * Install packages:<code>apt install gpsd gpsd-clients</code>
  * Configure devices and options in ''/etc/default/gpsd''<code>DEVICES="/dev/ttyAMA0"
GPSD_OPTIONS="-n"
</code>
  * Reboot
  * Test GPS output with ''cgps'' or ''gpsmon''.

====Configure NTPd====
  * Disable systemd timesyncd:<code>systemctl stop systemd-timesyncd
systemctl disable systemd-timesyncd</code>
  * Install required packages:<code>sudo apt install libcap-dev</code>
  * Install NTP:<code>
# Download latest from http://www.ntp.org/downloads.html
curl -OL http://www.eecis.udel.edu/~ntp/ntp_spool/ntp4/ntp-4.2/ntp-4.2.8p13.tar.gz
tar zxvf ntp-4.2.8p13.tar.gz
cd ntp-4.2.8p13
./configure --enable-linuxcaps
make -j4
sudo make install

sudo cp /home/user/ntp-4.2.8p13/scripts/rc/ntpd /etc/init.d/
# Modify ntpd location in /etc/init.d/ntpd, and add lines below above variables.

### BEGIN INIT INFO
# Provides:             ntpd
# Default-Start:        2 3 4 5
# Default-Stop:
# Short-Description:    NTPD
### END INIT INFO


groupadd ntp
useradd -d /var/lib/ntp -g ntp -s /bin/false ntp
printf 'PATH=${PATH}:/usr/local/bin\n' > /etc/profile.d/ntp-path.sh
install -v -o ntp -g ntp -d /var/lib/ntp

systemctl enable ntpd

</code>
  * Add to ''/etc/ntp.conf''<code>
# PPS
server 127.127.22.0 minpoll 4 maxpoll 4 true
fudge 127.127.22.0 flag3 1 refid PPS

# GPS Serial, GPSD SHM
server 127.127.28.0 minpoll 4 maxpoll 4 iburst prefer
fudge 127.127.28.0 flag1 1 time1 0.200 refid SHM0 stratum 1

# PPS, GPSD SHM
server 127.127.28.2 minpoll 4 maxpoll 4
fudge 127.127.28.2 flag1 1 refid SHM2

# GPSD JSON driver, to auto start GPSD
server 127.127.46.0 minpoll 4 maxpoll 4 noselect

# Fix False tickers
tos mindist 0.5
</code>
  * Enable and start ntpd:<code>systemctl enable ntp
systemctl start ntp</code>
  * Comment ntp option in ''/etc/dhcpcd.conf''<code>#option ntp_servers</code>
  * Reboot

{{tag>[lora dragino gps ntp hat]}}