Re: [gpsd-dev] GPSd on FreeBSD

[Gary E. Miller]

Yo Daniel!

On Tue, 10 Sep 2019 12:54:52 +0930
"O'Connor, Daniel" <address@hidden> wrote:

> > On 10 Sep 2019, at 12:13, Gary E. Miller <address@hidden> wrote:  
> >> 
> >> My reading of the NTP NMEA refclock code suggests that it will
> >> attempt to use /dev/gpspps0 to go with /dev/gps0 since flag1 is 1.
> >>  
> > 
> > Uh, that is NTP, this is gpsd.  Different projects.  
> 
> Yes I know, I wanted to demonstrate (to myself mostly) that the GPS
> engine & PPS capture are working properly before adding GPSd into the
> mix.

It is hard to follow you if you are not saying when you jump from
project to project...

> >> [ Note that I forgot to mention in my original email that I have a
> >> symlink from /dev/gpspp0 to the device capture device /dev/dmtpps
> >> ]  
> > 
> > None are device names that I recognize.  Why did you do that?  
> 
> That's what ntpd wants.

Luckily gpsd is beyond magic names and numbers.

> >>>> And it all looks good:    
> >>> 
> >>> Not really.  Your NTP is not using the SHM(0).  Which is a good
> >>> thing. It should be using your SHM(1), your PPS.    
> >> 
> >> I think NTP must be using PPS otherwise the jitter would be much
> >> higher.  
> > 
> > Your ntpmon showed that you were NOT using the local time from
> > gpsd!  
> 
> Yes, as above.

The ntpmon showed your system was not using local NTP either.  So you
still have not shown your PPS works with NTP.

> >> Sure, it was done to produce logging to demonstrate the issue, and
> >> given it should be using the kernel for PPS edge capture I think it
> >> wouldn't have an effect.  
> > 
> > Well, the logging demonstrated it was NOT using KPPS.  Nor
> > TIOMCIWAIT PPS.  So no PPS at all.  
> 
> You seem to be missing the point that it is trying to do
> time_pps_create on a file descriptor set to -2 which is not a valid
> FD.

You are missing the point the -2 is not an FD, it is an error code from
an eariler failure.

> > You misunderstand the failure.  Always look at the First Failure
> > (FF).  
> 
> The "first failure" I can see in GPSd output is:
> gpsd:INFO: KPPS:/dev/pps0 time_pps_create(-2) failed: Bad file
> descriptor

Nope.  See above. -2 is not a legal file descriptor, so the error
is earlier when the error code was not caught.

> The "Bad file descriptor" is because it is trying to do an ioctl on
> -2.

Yes!  But the First Failure, the thing that returned an FD of -2, is
the root problem.

> >> I don't have ppscheck and I am not sure what it does. ppsapitest
> >> just opens the given device and captures edges and logs the
> >> result.  
> > 
> > ppscheck check comes with gpsd.  We are talking about gpsd, so you
> > must have it.  If not, your gpsd install is bad.  
> 
> ppscheck doesn't build:

And, looking at it, scons knows that.  I thought that had been fixed...

> >> http://www.dons.net.au/~darius/gpsd-build.log  
> > 
> > Checking for C header file sys/timepps.h... yes
> > Checking if sys/ioctl.h supplies TIOCMIWAIT... no
> > 
> > As expected, you have KPPS, but not TIOCMIWAIT.  But when you ran
> > gpsd the KPPS failed.  
> 
> It failed to do either TIOCMIWAIT or time_pps_create because FreeBSD
> doesn't support the former and it called the later on an FD of -2.

Yes, no need to keep mentioning TIOMCIWAIT, we all know it does not
work on the *BSDs.  And the FD of -2 is after the first failure.

> My question remains: Why is it setting that FD to -2 then trying to
> do operations on it?

Because -2 is an error return to an earlier system call.  That is the
first failure.  Look at the code that returned the FD.

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

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    "If you can't measure it, you can't improve it." - Lord Kelvin

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