[Thumbgps-devel] USB handshake signals and Linux

[Ron Frazier (NTP)]

I have a question about GPSD.  I have nothing against it, but why is it 
necessary to use it at all?  I have NTPD running on both Windows and 
Linux, and reading my GPS.  GSPD isn't available on Windows as far as I 
know.  What does using GPSD get me that running without it does not?

Sincerely,

Ron

On 3/15/2012 10:37 AM, tz wrote:
>
> Skytraq has a number of unique commands that identify the chipsets.  
> So do MTK and Garmin.
>
> Right now the udev for gpsd gets it wrong by including the generic 
> FTDI vendor id for one gps, so plugging in my ftdi arduino/breakout 
> starts up gpsd and it probes (same error in upowerd - I filed a bug 
> report with fedora).   It thought my SkyTraq was this unit.
>
> I have the PPS hooked to the CTS pin, but gpsd has to be recompiled to 
> enable pps or change pins.  This should be configurable at runtime.
>
> You still have the same problem using any other gps for bufferbloat - 
> gpsd will attempt to sync the time via ntpshm based on any NMEA stream 
> at the last sentence in a group.  You will need some tweaking to make 
> it not do this, or reject other gps units, or otherwise indicate that 
> unless you are using one of our 'blessed' units the time won't be 
> accurate.  'Blessed' might mean PPS, but how do we certify it?
>
> How much of an issue will this be?  If we are going to require using 
> one specific hardware combo, it will have the right set for 
> gpsd-ntpd-kernel.  If we allow any configuration of any hardware or 
> software, we have no way of verifying it has precise UTC time - when 
> was the last PPS, has the correction in adjtime caught up, etc. though 
> that applies to ours too.
>
>    

-- 

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Ron Frazier
timekeepingdude AT c3energy.com