doc/time/README.org

   1 * Time
   2 This document was created by Steven Baltakatei Sandoval on
   3 ~2020-07-23T22:27Z~ under a [[https://creativecommons.org/licenses/by-sa/4.0/][Creative Commons BY-SA 4.0 license]]. It
   4 was updated by Steven Baltakatei Sandoval on ~2020-07-25T19:34Z~
   5 ** Development Task list
   6 *** Set up prototype unit
   7 **** DONE Solder wire for PPS signal
   8 ***** 2020-07-25T20:03Z; bktei> Soldered pins to permit accessibility.
   9      CLOSED: [2020-07-25 Sat 20:03]
  10 **** Follow guide
  11 - [[https://ozzmaker.com/forums/topic/connecting-gps-pps-pin/][Ozzmaker post]] on ~PPS~ wiring and a [[https://www.satsignal.eu/ntp/Raspberry-Pi-NTP.html][guide]] recommendation.
  12 - [[http://www.satsignal.eu/raspberry-pi/Schmidt-RPZ-NTP-2016.pdf][Schmidt article]] on Raspberry Pi Zero time server.
  13 - [[https://gpsd.gitlab.io/gpsd/gpsd-time-service-howto.html][GPSD dev ref]] page for ~gpsd~ interfacing with ~ntp~.
  14 - [[https://raspberryautomation.com/connect-multiple-ds18b20-temperature-sensors-to-a-raspberry-pi/][Raspberry Autom]] article on specifying custom GPIO pin.
  15 *** Document prototype unit
  16 ** Narrative
  17 The ~ninfacyzga-01~ device is equipped with an Ozzmaker BerryGPS-IMU
  18 module which provides time and location data to ~gpsd~. The time is
  19 provided by GPS satellites which themselves are [[https://science.nasa.gov/science-news/science-at-nasa/2002/08apr_atomicclock/][equipped]] with atomic
  20 clocks. This extremely accurate set of clocks are needed since a GPS
  21 receiver calculates its position in space using a General Relativity
  22 calculation that uses the small variations in the time stamps received
  23 from each satellite. This means that ~gpsd~ may be used to set the
  24 system clock without a need for an internet connection to a default
  25 Debian time server; ~ninfacyzga-01~ can be its own time server.
  26 ** Description
  27 *** Hardware
  28 Ozzmaker BerryGPS-IMU, Version 3
  29 *** Software
  30 This guide describes steps that may be used to convert a Raspberry Pi
  31 into a time server using ~gpsd~.
  32 ** Operating Procedures
  33 *** Initial Startup
  34 **** Install Raspbian 10 (Buster) onto a Raspberry Pi Zero W.
  35 **** Install Hardware
  36 See [[https://ozzmaker.com/forums/topic/connecting-gps-pps-pin/][this]] Ozzmaker forum topic about connecting the BerryGPS-IMU
  37 ~T_PULSE~ pin to GPIO 18.
  38
  39 Connect the ~T_PULSE~ connection on the BerryGPS-IMU-3 to GPIO pin 18
  40 (ex: with solder and wire) in order to provide the PPS data signal
  41 generated by the BerryGPS-IMU to the Raspberry Pi. Processing of this
  42 data signal is handled by adding a line to ~/boot/config.txt~ in the
  43 next section ("Install Software").
  44
  45 **** Install Software
  46 These instructions assume that ~gpsd~ has already been setup to
  47 provide NMEA sentences to ~gpspipe~ for location. See the ~README.org~
  48 in ~doc/location~ for details. Basically, ~gpsd~ needs to be told via
  49 its ~/etc/default/gpsd~ configuration file of which ~/dev/ttyS0~ will
  50 provide the raw GPS module data.
  51
  52 ***** Install packages via ~apt~
  53 Run the following command to install the required packages.
  54 : $ sudo apt install usbmount eject gpsd gpsd-clients python-gps pps-tools ntp
  55
  56 ***** Modify ~/boot/config.txt~
  57 In order to tell the Raspberry Pi to expect PPS data on ~BCM 18~ (pin
  58 number 12; see [[https://pinout.xyz/][RaspPi pinout]]), add the following line to
  59 ~/boot/config.txt~ as described on [[https://ozzmaker.com/forums/topic/problems-with-pps-on-a-pi0w-running-raspian-and-attached-to-a-berrygps-imuv3/][this Ozzmaker page]]:
  60
  61 : dtoverlay=pps-gpio,gpiopin=18
  62
  63 PPS data can be confirmed by running:
  64
  65 #+BEGIN_EXAMPLE
  66 $ sudo su -
  67 # ppstest /dev/pps0
  68 trying PPS source "/dev/pps0"
  69 found PPS source "/dev/pps0"
  70 ok, found 1 source(s), now start fetching data...
  71 source 0 - assert 1595708074.003644641, sequence: 219 - clear  0.000000000, sequence: 0
  72 source 0 - assert 1595708075.003709620, sequence: 220 - clear  0.000000000, sequence: 0
  73 source 0 - assert 1595708076.003779580, sequence: 221 - clear  0.000000000, sequence: 0
  74 source 0 - assert 1595708077.003850580, sequence: 222 - clear  0.000000000, sequence: 0
  75 #+END_EXAMPLE
  76
  77 ***** Add udev rule
  78 As per [[https://www.slsmk.com/how-to-setup-a-gps-pps-ntp-time-server-on-raspberry-pi/][the slsmk.com]] guide, create symbolic links expected by ~ntp~
  79 pointing to the PPS device. This may be performed by creating the file:
  80
  81 : /etc/udev/rules.d/09-pps.rules
  82
  83 with the contents:
  84
  85 #+BEGIN_EXAMPLE
  86 KERNEL=="ttyAMA0", SUBSYSTEM=="tty", DRIVER=="", OWNER=="root", GROUP=="tty", MODE=="0777", SYMLINK+="gps0"
  87 #+END_EXAMPLE
  88
  89 ***** Modify ~/etc/modules~
  90 For older versions of Raspberry Pi, it may be necessary to explicitly
  91 require the ~pps-gpio~ module to be loaded by making sure
  92 ~/etc/modules~ contains the line:
  93
  94 : pps-gpio
  95
  96 According to [[https://www.raspberrypi.org/forums/viewtopic.php?p=757747#p757747][this]] post on 2015-05-13T09:14 by [[https://www.raspberrypi.org/forums/memberlist.php?mode=viewprofile&u=31454][ame]] on the Raspberry Pi
  97 forums,
  98
  99 #+BEGIN_QUOTE
 100 rowlandski wrote:
 101 > Hi,
 102 >
 103 > I want the RPi to load/probe the w1-gpio module on boot.
 104 >
 105 > I have added:
 106 >
 107 > sudo modprobe w1-gpio
 108 >
 109 > To the etc/modules file, but on boot it is not loaded.
 110 > I have checked this by the lsmod command. If i then enter the above line manually and then check it's there loaded.
 111 >
 112 > What's wrong with my line on code in the modules file?
 113 >
 114 > Thanks
 115
 116 You no longer need to load modules for some devices. It's handled by devicetree.
 117
 118 Search for "devicetree" on the forum, or start here:
 119 https://www.raspberrypi.org/forums/viewtopic.php?f=28&t=97314
 120 #+END_QUOTE
 121
 122 As of 2020-07-25, using Raspbian Buster 10 with a BerryGPS-IMU v3,
 123 ~/etc/modules~ did not need to be modified.
 124
 125 ***** Remove DHCP client hooks
 126 As per [[https://www.slsmk.com/how-to-setup-a-gps-pps-ntp-time-server-on-raspberry-pi/][this]] guide, "remove ntp DHCP hook (so that it doesn't override ntp settings)".
 127
 128 This can be performed by running the following command (shown in
 129 script form for readability):
 130
 131 #+BEGIN_EXAMPLE
 132 if [ -f  "/etc/dhcp/dhclient-exit-hooks.d/ntp" ]; then
 133     mv /etc/dhcp/dhclient-exit-hooks.d/ntp /etc/dhcp/dhclient-exit-hooks.d/xxxntp-orig;
 134 else
 135     echo "NTP exit hook does not exist";
 136 fi;
 137 #+END_EXAMPLE
 138
 139 *** Normal Startup
 140 *** Normal Operation
 141 *** Normal Shutdown
 142 *** Unscheduled Shutdown
 143
 144