Update GPS docs for Adadfruit Ultimate GPS to be more reliable time source

hardware/gps.md

@@ -12,15 +12,36 @@ Location fun. Tracking, logging, etc
 - [http://www.catb.org/gpsd/gpspipe.html](http://www.catb.org/gpsd/gpspipe.html)
 - [http://www.catb.org/gpsd/gpsd-time-service-howto.html#_feeding_chrony_from_gpsd](http://www.catb.org/gpsd/gpsd-time-service-howto.html#_feeding_chrony_from_gpsd)
 - [http://thomasloughlin.com/gpspipe-gps-client/](http://thomasloughlin.com/gpspipe-gps-client/)
+- [http://robotsforroboticists.com/chrony-gps-for-time-synchronization/](http://robotsforroboticists.com/chrony-gps-for-time-synchronization/)
+- [https://forum.armbian.com/topic/4944-opi-zero-gps-ntpserver/](https://forum.armbian.com/topic/4944-opi-zero-gps-ntpserver/)
+- [http://darethehair.net/gps_time_server.html](http://darethehair.net/gps_time_server.html)
+- [https://forum.armbian.com/topic/7033-solved-orangepi-one-1-pps-ntp-server/
+](https://forum.armbian.com/topic/7033-solved-orangepi-one-1-pps-ntp-server/
+)
+- [https://www.satsignal.eu/ntp/Raspberry-Pi-NTP.html](https://www.satsignal.eu/ntp/Raspberry-Pi-NTP.html)
 
 ## Hardware
 
 The author chose the [Adafruit Ultimate GPS Breakout (link)](https://www.adafruit.com/product/746) for this guide. YMMV with other boards.
 
+### Pinout
+
+- Connect vcc to a 3v source on the main expansion header
+- Connect gnd to a gnd on the main expansion header
+- Connect tx to rx pin of uart2 on the main expansion header
+- Connect rx to tx pin of uart2 on the main expaions header
+- Connect pps to the PA6 pin on the main expansion header
+
 ## Setup
 
 ``` bash
-armbian-config # enable hardware uarts
+
+armbian-config # Enable hardware uart2 and pps-gpio
+    # System
+    # Hardware
+    #   Enable uart2 option
+    #   Enable pps-gpio option
+    # Save/reboot
 apt install gpsd gpsd-clients python-gps gpsbabel # necessary software
 systemctl stop gpsd # stop gpsd to help with testin
 gpsd -n -N -D 2 /dev/ttyS2 # run gpsd by hand
@@ -37,6 +58,19 @@ Edit ```/etc/default/gpsd```
 
 ## Chrony
 
+Setup PPS for chrony
+
+``` bash
+
+cat >> /boot/armbianEnv.txt <<EOF
+param_pps_pin=PA6
+
+EOF
+systemctl reboot
+demsg | grep -i pps # Verify pps is enabled and shows in the kernel
+
+```
+
 Add GPS as a time source to chrony
 
 ``` bash
@@ -45,12 +79,14 @@ cat >> /etc/chrony/chrony.conf <<EOF
 # set larger delay to allow the NMEA source to overlap with
 # the other sources and avoid the falseticker status
 refclock SHM 0 refid GPS precision 1e-1 offset 0.9999 delay 0.2
-refclock SOCK /var/run/gpsd.sock refid PPS
+refclock PPS /dev/pps0 lock NMEA
+
 EOF
 
 systemctl restart chrony
 cgps # look for ```Status:     3D FIX```
-chronyc sources # Should see GPS and SOC1 with times for recent samples
+chronyc sources -v # Should show PPS and GPS time sources as having a recent reading
+chronyc tracking # Further details
 
 ```