Ben Stienstra

Linux, Unix, network, radio and more...

User Tools

Site Tools


dragino_lora_gps_hat_ntp

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:

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:
    echo "dtoverlay=pi3-disable-bt" >> /boot/config.txt
  • Disable the HCI UART:
    sudo systemctl disable hciuart
  • Disable getty:
    systemctl mask serial-getty@serial0.service
  • Remove console=serial0,115200 from /boot/cmdline.txt
  • Reboot
  • Test GPS output: cat /dev/serial0

Configure Pulse Per Second (PPS)

  • Install PPS tools:
    apt install pps-tools setserial
  • Configure GPIO for PPS:
    echo "dtoverlay=pps-gpio,gpiopin=18" >> /boot/config.txt
  • Configure udev rules in /etc/udev/rules.d/gps.rules
    KERNEL=="ttyAMA0", RUN+="/bin/setserial /dev/ttyAMA0 low_latency"
    KERNEL=="ttyAMA0", SYMLINK+="gps0"
    KERNEL=="pps0", GROUP="dialout", MODE="0660"
  • Reboot
  • There should be a /dev/pps0 device
  • Check for pulse
    # 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

Configure GPdS

  • Install packages:
    apt install gpsd gpsd-clients
  • Configure devices and options in /etc/default/gpsd
    DEVICES="/dev/ttyAMA0"
    GPSD_OPTIONS="-n"
  • Reboot
  • Test GPS output with cgps or gpsmon.

Configure NTPd

  • Disable systemd timesyncd:
    systemctl stop systemd-timesyncd
    systemctl disable systemd-timesyncd
  • Install required packages:
    sudo apt install libcap-dev
  • Install NTP:
    # 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
    
  • Add to /etc/ntp.conf
    # 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
  • Enable and start ntpd:
    systemctl enable ntp
    systemctl start ntp
  • Comment ntp option in /etc/dhcpcd.conf
    #option ntp_servers
  • Reboot
dragino_lora_gps_hat_ntp.txt · Last modified: 2019/03/18 20:42 by admin