RPi GPS/NTP for Dashcam System

This is more notes for my future self in case I ever have to get ntp working using a gps time source. The biggest lesson was to wait for a few minutes before giving up on ntp getting the GPS signal.

This is for an Adafruit Ultimate GPS on my Raspberry Pi 2. GPIO 18 is connected to the PPS pin on the GPS. I'm connected to the GPS using a USB to serial adapter.

/etc/udev/rules.d/09-pps.rules
KERNEL=="ttyUSB0", SYMLINK+="gps0"
KERNEL=="pps0", OWNER="root", GROUP="tty", MODE="0777", SYMLINK+="gpspps0"

/etc/ntp.conf

server 127.127.20.0 mode 16 maxpoll 6 prefer

fudge 127.127.20.0 time2 -0.301 flag1 1 refid GPS

/etc/default/gpsd

START_DAEMON="true"

# Use USB hotplugging to add new USB devices automatically to the daemon

USBAUTO="true"

# Devices gpsd should collect to at boot time.

# They need to be read/writeable, either by user gpsd or the group dialout.

DEVICES="/dev/ttyUSB0"

# Other options you want to pass to gpsd

GPSD_OPTIONS="-n -F /var/run/gpsd.sock"

/etc/modules

pps-gpio

/boot/config.txt

dtoverlay=pps-gpio,gpiopin=18