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Re: [gpsd-users] How to get 10Hz Device Readings

From: Gary E. Miller
Subject: Re: [gpsd-users] How to get 10Hz Device Readings
Date: Wed, 12 Jul 2017 14:55:28 -0700

Yo Jamie!

On Wed, 12 Jul 2017 09:34:55 -0400
Jamie Dixon <address@hidden> wrote:

> I am also using the Adafruit Ultimate GPS (

I also have one Adafruit handy.

> The adafruit forum suggested that if I send:
> $PMTK300,100,0,0,0,0*2C <cr><lf>
> to the GPS breakout
> Is there a method already in the GPSD Api that I can do that?

Your question is very similar to another one also asked today.  I thought
I knew the answer for when gpsd already owns the GPS device:

pi3 ~ # gpsctl -x '$PMTK300,100,0,0,0,0'
gpsctl:ERROR: device must be specified for low-level access.
pi3 ~ # gpsctl -x '$PMTK300,100,0,0,0,0' /dev/ttyAMA0
gpsctl:ERROR: SER: /dev/ttyAMA0 already opened by another process
gpsctl:ERROR: initial GPS device /dev/ttyAMA0 open failed

But as you can see that does not work.  '-x' sets '-f'.  And '-f'
means direct access, so gpsd can not be owning the device.

So then this works:

pi3 ~ # killall gpsd
pi3 ~ # gpsctl -x '$PMTK300,100,0,0,0,0' /dev/ttyAMA0
/dev/ttyAMA0 identified as a NMEA0183 at 9600 baud.

But when gpsd is restarted the GPS is sent new configuration commands that
override that.  That happens in drivers.c on line 1860.  You could change
the PMTK300,1000 to PMTK300,100 and recompile.

Probably too advanced for most people to do, I'll ponder this one a bit.

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

            Veritas liberabit vos. -- Quid est veritas?
    "If you can’t measure it, you can’t improve it." - Lord Kelvin

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