refclock 28 gone wacky on me

[Gary E. Miller]

Yo Mike!

On Thu, 9 Jun 2016 20:26:01 -0400
Mike <bellyacres at gmail.com> wrote:

> >> Is seeing NTP0 twice like this typical?  
> > Nope, should be impossible.  Looks to be exactly 500 milliSec apart.
> > Do you have a square wave output?  Or a 2Hz output?
> >
> > How about you put ppstest on it to see.  Except on the Pi you only
> > see one edge, so can not tell square wave from 2 Hz.  Got a scope?
> > What is the GPS again?  
> GPS module is a ST22, SkyTraq Venus 6 chipset.
> 
> http://www.perthold.de/BINARY/gps-st22.pdf Datasheet is here.

Skytraq ships varying firmware, so that is not definitive.

Worse that says this:

    "The 1PPS pin is multiplexed with some debug mode function whose
    mode is to be determined at end of power on reset cycle. To avoid
    incorrect function do not pull-up or pull- down this signal."

What could possibly go wrong there?

And the serial is connected directly to a RasPi?

> It's an oddball corner case I'm sure...

Yes, and the Skytraq are chatty, making 9600 suspect, but unrelated to
the PPS issue.

> If I hook it up to a PC, or with a serial to USB adapter will I be
> able to see more about the edge being seen?

Depends how good you are.  I leave that to you.

> mike at rpi-ticker:~ $ sudo ppstest /dev/pps0
> trying PPS source "/dev/pps0"
> found PPS source "/dev/pps0"
> ok, found 1 source(s), now start fetching data...
> source 0 - assert 1465518012.001419932, sequence: 12052 - clear 
> 0.000000000, sequence: 0
> source 0 - assert 1465518013.001419316, sequence: 12053 - clear 
> 0.000000000, sequence: 0
> source 0 - assert 1465518014.001418700, sequence: 12054 - clear 
> 0.000000000, sequence: 0
> source 0 - assert 1465518015.001418086, sequence: 12055 - clear 
> 0.000000000, sequence: 0
> source 0 - assert 1465518016.001416472, sequence: 12056 - clear 
> 0.000000000, sequence: 0
> source 0 - assert 1465518017.001417858, sequence: 12057 - clear 
> 0.000000000, sequence: 0

No double pulse there.  Looks good.

Hmm, it just occured to me, it is your SHM0 that is sending 2 updates
a second?  Was it the SHM0?  If so, that is not a problem, as long
as the time stamps look right, it just means the NMEA is reporting 2x
a second.  The only thing we care about is the SHM1.

I still need the debug output.  Send me the result of this:
	# gpsd -nND 9 /dev/ttyXX |# fgrep PPS > gpsd.log

RGDS
GARY
---------------------------------------------------------------------------
Gary E. Miller Rellim 109 NW Wilmington Ave., Suite E, Bend, OR 97703
	gem at rellim.com  Tel:+1 541 382 8588
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