[Raspbian-devel] Confusion and decay around the serial UART - need help

[Eric S. Raymond]

I am the technical lead of NTPsec, a project to improve and
security-harden NTP time service.

Last April I successfully wrote a recipe for equipping a Pi 3 running
the 2016-03-18 Raspbian with a GPS daughterboard and fitting it out
as a Stratum 1  NTPsec time server.  Here it is:

http://www.catb.org/esr/faqs/stratum-1-microserver-howto/

I have four Pi 3s running this build; I use them for long-term
stability testing of NTPsec.

Since then, undocumented or poorly-documented changes to Raspbian have
made this build steadily less viable.  By June I had discovered that I
could not use any Raspbian image later than 2016-03-18 because
undocumented changes in UART handling caused 1PPS to stop working.

Two days ago I tried to replicate the recipe in order to re-image
two Pi 3s that had developed bad sectors on their SDs, and discovered
that I can no longer even start from the 2016-03-18 Raspbian image
and allow a kernel upgrade.  That now breaks too.

I have spent the last two days researching and trying fixes to no
avail.  I can no longer throw a lot more time into this, because I'm
trying to prepare for a 1.0 release of NTPsec.  I really shouldn't
allow the recipe to hang out in public much longer without a big
warning at the top that it doesn't work any more.

Rather than putting up that warning, which would have the inevitable
side effect of making Raspbian look like an unstable toy, I'm asking
for fast help repairing the recipe.

I have three issues when I try to make the build work with a current image.

1. The udev rule to make a /dev/gpsd0 symlink to /dev/ttyAMA0 no
longer works.

2. The dance to disable Bluetooth and map the serial UART back to pins
14 and 15 no longer works.  Symptom: no data visible from the GPS HAT.

3. 1PPS no longer works.  I can't tell whether this is due to breakage
in the pps-gpio driver or some other cause.
-- 
		<a href="http://www.catb.org/~esr/">Eric S. Raymond</a>

Political language... is designed to make lies sound truthful and
murder respectable, and to give an appearance of solidity to pure wind.
                -- George Orwell