chore(doc/time):Update README

diff --git a/doc/time/README.org b/doc/time/README.org
index b346b3b312365d0739dd1da037a08b9bfffa31f3..7f845587978e3541eac623ebe170305caec3118b 100644 (file)
--- a/doc/time/README.org
+++ b/doc/time/README.org
@@ -4,11 +4,14 @@ This document was created by Steven Baltakatei Sandoval on
 was updated by Steven Baltakatei Sandoval on ~2020-07-25T19:34Z~
 ** Development Task list
 *** Set up prototype unit
-**** Solder wire for PPS signal
+**** 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
@@ -34,19 +37,105 @@ See [[https://ozzmaker.com/forums/topic/connecting-gps-pps-pin/][this]] Ozzmaker
 ~T_PULSE~ pin to GPIO 18.
 
 Connect the ~T_PULSE~ connection on the BerryGPS-IMU-3 to GPIO pin 18
-in order to enable ~gpsd~ to read the PPS signal for forwarding to
-~ntp~.
+(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
-Run the following command to install the required packages.
-: $ sudo apt install usbmount eject gpsd gpsd-clients python-gps pps-tools ntp
-
 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/tty???~ will
+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