Re: [gpsd-dev] PPS glitch - Venus chip

[Gary E. Miller]

Yo Hal!

On Sat, 30 Jan 2016 04:03:01 -0800
Hal Murray <address@hidden> wrote:

> I have a SparkFun SkyTraq Venus GPS breakout board connected via USB.
>   https://www.sparkfun.com/products/11058
> 
> The PPS is sometimes off by a second, but only sometimes.  Sometimes
> it is right.

Odd, PPS is supposed to be suppresed by gpsd when off that far.

> What's the right way to debug this?

Sadly if you turn on a lot of debugging that affects timing a lot
making problems hard to see.

I'd spend time staring at the code for why the PPS was not rejected.

Also the serial to USB chip and driver could be doing oddd things to
the timing.  I hope nothing else is on that same USB bus.

> Here is one second from:
>   gpspipe -u -r -P

Also, PPS is in a thread, so the only valid restults out of that thread
are in the shmmem or socket.  Having a thread do character I/O is
problematic.

> Note that there are two TOFF slots with quite different offsets.

The TOFF is for the serial time, so only for course time.  But clearly
a bug as only one TOFF should be output per second.  Historically that
code gets changes by people that do not understand it...

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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