doc(location/README):Note how to enable serial port for gpsd

[EVA-2020-02.git] / doc / time / README.org

* Time 
This document was created by Steven Baltakatei Sandoval on
~2020-07-23T22:27Z~ under a [[https://creativecommons.org/licenses/by-sa/4.0/][Creative Commons BY-SA 4.0 license]]. It
was updated by Steven Baltakatei Sandoval on ~2020-07-25T19:34Z~
** Development Task list
*** Set up prototype unit
**** DONE Solder wire for PPS signal
***** 2020-07-25T20:03Z; bktei> Soldered pins to permit accessibility.
     CLOSED: [2020-07-25 Sat 20:03]
**** Follow guide
- [[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.
- [[http://www.satsignal.eu/raspberry-pi/Schmidt-RPZ-NTP-2016.pdf][Schmidt article]] on Raspberry Pi Zero time server.
- [[https://gpsd.gitlab.io/gpsd/gpsd-time-service-howto.html][GPSD dev ref]] page for ~gpsd~ interfacing with ~ntp~.
- [[https://raspberryautomation.com/connect-multiple-ds18b20-temperature-sensors-to-a-raspberry-pi/][Raspberry Autom]] article on specifying custom GPIO pin.
*** Document prototype unit
** Narrative
The ~ninfacyzga-01~ device is equipped with an Ozzmaker BerryGPS-IMU
module which provides time and location data to ~gpsd~. The time is
provided by GPS satellites which themselves are [[https://science.nasa.gov/science-news/science-at-nasa/2002/08apr_atomicclock/][equipped]] with atomic
clocks. This extremely accurate set of clocks are needed since a GPS
receiver calculates its position in space using a General Relativity
calculation that uses the small variations in the time stamps received
from each satellite. This means that ~gpsd~ may be used to set the
system clock without a need for an internet connection to a default
Debian time server; ~ninfacyzga-01~ can be its own time server.
** Description
*** Hardware
Ozzmaker BerryGPS-IMU, Version 3
*** Software
This guide describes steps that may be used to convert a Raspberry Pi
into a time server using ~gpsd~.
** Operating Procedures
*** Initial Startup
**** Install Raspbian 10 (Buster) onto a Raspberry Pi Zero W.
**** Install Hardware
See [[https://ozzmaker.com/forums/topic/connecting-gps-pps-pin/][this]] Ozzmaker forum topic about connecting the BerryGPS-IMU
~T_PULSE~ pin to GPIO 18.

Connect the ~T_PULSE~ connection on the BerryGPS-IMU-3 to GPIO pin 18
(ex: with solder and wire) in order to provide the PPS data signal
generated by the BerryGPS-IMU to the Raspberry Pi. Processing of this
data signal is handled by adding a line to ~/boot/config.txt~ in the
next section ("Install Software").

**** Install Software
These instructions assume that ~gpsd~ has already been setup to
provide NMEA sentences to ~gpspipe~ for location. See the ~README.org~
in ~doc/location~ for details. Basically, ~gpsd~ needs to be told via
its ~/etc/default/gpsd~ configuration file of which ~/dev/ttyS0~ will
provide the raw GPS module data.

***** Install packages via ~apt~
Run the following command to install the required packages.
: $ sudo apt install usbmount eject gpsd gpsd-clients python-gps pps-tools ntp

***** Modify ~/boot/config.txt~
In order to tell the Raspberry Pi to expect PPS data on ~BCM 18~ (pin
number 12; see [[https://pinout.xyz/][RaspPi pinout]]), add the following line to
~/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]]:

: dtoverlay=pps-gpio,gpiopin=18

PPS data can be confirmed by running:

#+BEGIN_EXAMPLE
$ sudo su -
# 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 1595708074.003644641, sequence: 219 - clear  0.000000000, sequence: 0
source 0 - assert 1595708075.003709620, sequence: 220 - clear  0.000000000, sequence: 0
source 0 - assert 1595708076.003779580, sequence: 221 - clear  0.000000000, sequence: 0
source 0 - assert 1595708077.003850580, sequence: 222 - clear  0.000000000, sequence: 0
#+END_EXAMPLE

***** Add udev rule
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~
pointing to the PPS device. This may be performed by creating the file:

: /etc/udev/rules.d/09-pps.rules

with the contents:

#+BEGIN_EXAMPLE
KERNEL=="ttyAMA0", SUBSYSTEM=="tty", DRIVER=="", OWNER=="root", GROUP=="tty", MODE=="0777", SYMLINK+="gps0"
#+END_EXAMPLE

***** Modify ~/etc/modules~
For older versions of Raspberry Pi, it may be necessary to explicitly
require the ~pps-gpio~ module to be loaded by making sure
~/etc/modules~ contains the line:

: pps-gpio

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
forums,

#+BEGIN_QUOTE
rowlandski wrote:
> Hi,
> 
> I want the RPi to load/probe the w1-gpio module on boot.
> 
> I have added:
> 
> sudo modprobe w1-gpio
> 
> To the etc/modules file, but on boot it is not loaded.
> I have checked this by the lsmod command. If i then enter the above line manually and then check it's there loaded.
> 
> What's wrong with my line on code in the modules file?
> 
> Thanks

You no longer need to load modules for some devices. It's handled by devicetree.

Search for "devicetree" on the forum, or start here:
https://www.raspberrypi.org/forums/viewtopic.php?f=28&t=97314
#+END_QUOTE

As of 2020-07-25, using Raspbian Buster 10 with a BerryGPS-IMU v3,
~/etc/modules~ did not need to be modified.

***** Remove DHCP client hooks
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)".

This can be performed by running the following command (shown in
script form for readability):

#+BEGIN_EXAMPLE
if [ -f  "/etc/dhcp/dhclient-exit-hooks.d/ntp" ]; then
    mv /etc/dhcp/dhclient-exit-hooks.d/ntp /etc/dhcp/dhclient-exit-hooks.d/xxxntp-orig;
else
    echo "NTP exit hook does not exist";
fi;
#+END_EXAMPLE

*** Normal Startup
*** Normal Operation
*** Normal Shutdown
*** Unscheduled Shutdown