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Re: [gpsd-dev] [PATCH] Fixes various flakiness in PPS handling.

From: Gary E. Miller
Subject: Re: [gpsd-dev] [PATCH] Fixes various flakiness in PPS handling.
Date: Wed, 28 Sep 2016 17:16:36 -0700

Yo Fred!

On Wed, 28 Sep 2016 17:03:17 -0700 (PDT)
Fred Wright <address@hidden> wrote:

> > Which one?  Can you just resend it?  
> I just did.  I also BCCed you on it, so you should have received a
> copy that bypassed the listserver.  And it's also an attachment here,
> though there's something fishy about why that should be necessary.

Just pulled and pushed.

> > It solves a real problem for RasPi and BeagleBone users.  Any change
> > now would break a lot of HOWTO's and existing systems.  I'd consider
> > a patch to implement an opt-out option.  
> You still haven't answered the question of what that "real problem"
> was, and neither the comments nor the commit message provide any
> documentation.

I thought is was well documented when Eric added that 'feature'.  Most
users could not figure out how to add /dev/pps0 to the gpsd commandline,
or even worse how to get systemd to do so.

So Eric made that an autodetect.  It solved a huge support issue.  Now
it is documented and referred to in a lot of third party doc.  Not gonna
step that change back, this is way better than before.

> It certainly never helped Beaglebone users using the only
> off-the-shelf GPS cape that's available, since it's incompatible with
> the kernel provided by the vendor.

Well, you'll have to explain that a bit better.  I have no Beaglebone.
If it is ALWAYS a problem on the BeagleBone then maybe scons could
detect the BeagleBone and do something different.

> An opt-out approach makes sense as an interim fix that doesn't break
> existing setups, but everyone should be strongly encouraged to opt
> out and stop depending on it.

No, it solved WAY too many problems.  The decrease in suport requests
was very dramatic.

>  Any HOWTO needs to include a section
> on identifying the correct PPS device, since it can't be assumed to
> be /dev/pps0.

Actually, on the RasPi, it can be assumed.  And is there any harm in opening
any pps?  If /dev/pps0 is not found, you just need to add the
real /dev/ppsXX on the gpsd command line, just as before the
autodetect patch.

> 1) If your GPS serial port is named something other than /dev/ttyAMA0
> or /dev/gpsd0, then include the name of your PPS device on the
> command line in addition to the serial device name.

That breaks on RasPi.

> 2) If your GPS serial port is named /dev/ttyAMA0 or /dev/gpsd0 and
> your GPS PPS device is /dev/pps0, then specify just the serial device
> on the command line, and gpsd will add /dev/pps0 automatically.

Well, it is not automatic if you have to specify it.  And that fact
that people forgot to specify was a huge problem, now gone.

> 3) If your GPS serial port is named /dev/ttyAMA0 or /dev/gpsd0 and
> your GPS PPS device is something other than /dev/pps0, then rebuild
> gpsd with MAGIC_HAT disabled, or create a symlink to the GPS serial
> port that's named something other than /dev/ttyAMA0 or /dev/gpsd0 and
> use that name instead, and specify both the serial device and the PPS
> device on the command line.

Rebuilding is not an option for the vast majority of gpsd users.

> Specify both the serial device and the PPS device for your receiver
> on the command line.

You can do that now.

Gary E. Miller Rellim 109 NW Wilmington Ave., Suite E, Bend, OR 97703
        address@hidden  Tel:+1 541 382 8588

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