RaspbPi HOWTO

[Mike]

On 05/03/2016 06:16 PM, Eric S. Raymond wrote:
>
> == Initial configuration in the GUI (Pi only) ==
>
> Plug in a monitor, a mouse, and keyboard, and a live Ethernet cable;
> power up the Pi. Go through your normal configuration - hostname,
> keyboard layout, timezone, locale, etc.
I'm gathering here the user has aquired a Pi with some distro already on 
a card?
With the references here to having a gui, does this imply NOOBS?  I 
started with the
latest image from here https://www.raspberrypi.org/downloads/raspbian/
specifically Rasbian Jessie Lite.  Console only already, just dd to a 
card and boot...

Followed mostly from here on except as noted.
> ------------------------------------------------------------------------
> # rpi-update
> ------------------------------------------------------------------------
I'm on a Pi, this command isn't found, see references to it all over.
Perhaps it is obsolete?
> === Configure the 1PPS GPIO pin ==
> In all versions, you force the driver to be loaded by
> editing /etc/modules to contain the line "pps-gpio"
> footnote[Alternatively, you can build your own kernel with pps-gpio
> hardwired in.].
With recent changes in overlays I have found that one doesn't need
to modify /etc/modules.  The module will be loaded if the overlay is
written well.  This works for other devices also.  Forcing it with
the addition to /etc/modules doesn't appear to change anything, just
another change for someone to screw up.  Finger pointing back at me!

> # apt-get install libreadline-dev asciidoc
> ------------------------------------------------------------------------
asciidoc pulls in a shit ton of dependancies!  500+ Mb that filled /
and caused me some hair pulling.  Docs are online :)  I am using a 
smaller SD card than recommended above though.
> ------------------------------------------------------------------------
> KERNEL=="ttyAMA0", SYMLINK+="gps0"
> KERNEL=="pps0", OWNER="root", GROUP="tty", MODE="0660", SYMLINK+="gpspps0"
> ------------------------------------------------------------------------
I have the above, just question tty as group.  I'm running ntpd as ntp:ntp.
Guessing things works as nptd gets the pps device before dropping 
permissions.
> According to <<NEVILL>>, "[dhcpcd5] has a nasty habit of interfering where
> it's not wanted. Specifically, in this instance, if your DHCP server
> specifies an NTP server, it will start ntpd with its own version of
> ntp.conf."
#dpkg --purge dhcpcd5
mike at ticker:/var/log $ cat /etc/rpi-issue
Raspberry Pi reference 2016-03-18
Generated using Pi-gen, https://github.com/RPi-Distro/Pi-gen, stage2

With this release I did find before I purged dhcpcd5 that it ignores 
/etc/networks/interfaces.
After a bit a digging turns out you need to modify /etc/dhcpcd.conf to 
add static entries.
> ------------------------------------------------------------------------
> # /etc/ntp.conf, configuration for ntpd; see ntp.conf(5) for help
>
> # Local
> server 127.127.1.0
> fudge 127.127.1.0 stratum 10
Local refclock shows "D" in the refclocks chart and we didn't build it in
by the above instructions.

# PPS
server 127.127.22.0 minpoll 4 maxpoll 4 iburst
fudge 127.127.22.0 flag2 0 flag4 1 refid PPS
> # GPS with PPS enabled
> server 127.127.20.0 mode 17 minpoll 4 maxpoll 4 iburst true prefer
> fudge 127.127.20.0 flag1 1 refid GPS
Shouldn't 22.0 be the preferred refclock?  My experience is slim to none 
here and built on the work of others.  I've always thought that we 
wanted the pps signal for the precision not the NMEA.  Have I be 
misunderstanding this?
> # By default, exchange time with everybody, but don't allow configuration.
> restrict default kod nomodify notrap nopeer noquery
kod needs "limited" from log messages.
> # Drift file etc.
> driftfile /var/lib/ntp/ntp.drift
The drift file location from example configs in the src pulled from git 
bit me.
Most of them reference /etc/ntp.drift which DOES NOT work when running 
as ntp:ntp...
> == Edge-detection issues and new HATs ==
>
> As the pps-gpio module is in April 2016 it has a flaw. It catches only
> one edge of the PPS. You have a 50/50 chance you are seeing the
> trailing edge rather than the leading edge (which is the actual top of
> second).  A patch to fix this has been submitted to the Linux kernel
> maintainers but not merged.
I've tried to figure out just how one determines exactly which edge is 
being seen.
I'm at a loss on this one with software.  Using ppstest shows me 
atypical output
from nearly every example I'm seen online.  What is the definetive way 
to determine this?

The GPS device I'm using isn't a hat.  In the past I've had it working 
with gpsd and ntp classic.  I haven't a clue which edge is actually 
being seen though.

Mike


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