[TangerineSDR] Magnetometer/Grape Raspberry Pi Image

[Rob Wiesler]

Hi, all.

On Sun, Oct 31, 2021 at 21:00:42 -0400, Jonathan via TangerineSDR wrote:
> If I remember correctly, you used a GPS hat for the Raspberry Pi on
> the Magnetometer/Grape system. Is this true? If so, which one do you
> use?
>
> The reason I ask is that there was a bug in gpsd that caused the GPS
> date to be erroneously reported as March of 2002 once October 23th
> 2021 has passed.

To the best of my understanding, this is not exactly true.  The bug
affects test cases (Gary refers to them as "regressions"), not live
code.  Live code uses the current time and date to disambiguate
rollover, but the regressions run on old NMEA captures and do not have
that luxury.  So, if you were to take a buggy version of gpsd and run
the regressions with "scons check", you would encounter the bug then,
but not in normal operation.

(If you're running gpsd on a RPi with no RTC and no guarantee that ntp
-g steps the time *before* gpsd starts, you have a buggy installation
regardless of which version of gpsd you're using.)

>                  This has been fixed and you are encouraged to update
> to gpsd version 3.23.1. To do so, do a git pull of the gpsd
> repository, then type "git checkout release-3.23.1", then "scons -c &&
> scons && scons install".

Please don't do this.  This bug report is months old, and has been
addressed.  The maintainer of the gpsd package in your operating system
should have backported this fix if it's relevant to the packaged
version.  For Debian and Raspian (and likely Ubuntu), this patch is
included in 3.22-4 (the -4 suffix is the Debian revision of the
packaging), and a simple system update is sufficient to bring it in for
bullseye and buster-backports (and bookworm, but I doubt you're running
that).  Older versions of the package (in buster and older) are not
patched, as this bug was caused by a commit first seen in version 3.20 .

The Debian packaging also includes several fixes that are pertinent for
Debian installations.  If you do end up installing from source, I
recommend pulling in the patches from Debian.

> Details about the bug can be found at:
> https://gitlab.com/gpsd/gpsd/-/issues/144 or LWN, El Reg, or CERT
> write ups.

I recommend reading Gary's comment in that bug report that starts with
"GPS, by design, is a 1024 week time warp waiting to happen.".  This is
the best place to start reading to verify if my initial statement in
this email is correct or not.

(It's a good thread in general.  I was absolutely floored to learn that
there was a bug in (a test case of) production software due to global
warming causing a scheduled/expected leap second to be rescinded.)

> As of this email, version 3.32.2 is the most current, but there is a
> bug that prevents using the GPIO PPS with another serial device than
> /dev/ttyAMA0. Most GPS hats use /dev/ttyAMA0, so you can do a git
> checkout and build/install of gpsd, but since I use /dev/ttyAMA0 for a
> serial console (I still believe in out-of-band access), I utilize
> /dev/ttyUSB0 from a FT230 USB serial interface IC that my GPS serial
> port connects to, which then connects to the Pi USB port. In this
> configuration, version 3.23.2 of gpsd cannot use the /dev/ttyUSB0
> /dev/pps0 runtime option and capture PPS asserts/clears from the
> pps_gpio driver. But, most GPS hats and users don't use this
> configuration very often, so you won't be affected. A fix for this
> issue will be pushed to the gpsd repository soon.

3.22 should be unaffected by this.  In general, when an upstream
maintainer recommends jumping straight to the bleeding edge, you might
want to take that with a grain of salt.

-- AC8YV