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Re: [gpsd-users] Set up for time sync and separate serial port use

From: Pittman, Randall
Subject: Re: [gpsd-users] Set up for time sync and separate serial port use
Date: Fri, 10 Mar 2017 20:29:04 +0000

Thank you for the response, Gary. I have skimmed over the Time Service howto, as well as the Garmin GPS 18 ntpd recipe [].

Let me try to add a bit more detail.

1. My GPS (Hemisphere Vector V103) starts up at 19200 baud, but can be changed to a max 38400 baud with $JBAUD

2. The V103 starts up with a default set of messages, but I want to turn those off and only enable the messages that I need.

3. It is crucial that I receive the PASHR (heading, pitch, roll, heave) and GPGGA messages at the max 20Hz rate as this unit is being used to geolocate marine radar imagery at long ranges on a boat. These two messages use about 25600 of my 38400 baud budget.

4. I would like to bring GPS timing along for the ride. I'm worried that if I let gpsd talk to my unit it will mess up the message configuration that I need. I'd rather just manually set up whatever messages gpsd needs for timing. It looks like gpsd  can operate in a read-only mode with the -b switch, and the Garmin GPS 18 ntpd recipe uses that switch, so it must not be strictly necessary for gpsd to talk to the unit for it to be able to do timing.


I guess my python app and the splitter are not strictly necessary. I could use the approach in the Garmin GPS 18 ntpd recipe and in the step where he runs “$PGRMO,,4” for the Garmin unit, I could run the commands to set the baud rate, disable default messages, and then enable the messages I want. And then I could use gpspipe to get the data, as you mentioned. So… is it sufficient to enable GPRMC, GPGSA, and GPGSV at 1Hz for timing to work? Would more often be any better?


Also, if I change the baud rate to 38400 with $JBAUD, will gpsd automatically figure that out and switch the baud rate of the serial port?


Thank you,



Randall Pittman

Faculty Research Assistant | School of Civil and Construction Engineering | Oregon State University

Location: 006 Covell Hall | Mailing: 101 Kearney Hall | Corvallis, OR 97331-2132

Office: 541-737-2102 | Mobile: 541-286-7896



-----Original Message-----
From: gpsd-users [mailto:gpsd-users-bounces+address@hidden On Behalf Of Gary E. Miller
Sent: Friday, March 10, 2017 10:04 AM
To: address@hidden
Subject: Re: [gpsd-users] Set up for time sync and separate serial port use


Yo Randall!


On Thu, 9 Mar 2017 18:04:18 +0000

"Pittman, Randall" <address@hidden> wrote:


> I have a python app that connects to my GPS Compass (Hemisphere Vector

> V103), sets it up to send certain messages, and then records the

> messages as they come in and parses them with the pynmea2 library.


You might consider adding that functionality to gpsd.


> However, I'd also like to sync the system clock (CentOS 7) with the

> 1PPS signal from the GPS. Here is how I'm considering doing this, but

> I have no idea if it will work:


Have you read the gpsd howtos?  Like the time service howto?


> serial connection      38400 baud, GPZDA @ 20Hz, PASHR @ 20 Hz, GPGGA

> @ 20 Hz, GPROT @ 5 Hz from V103 with 1PPS

> __   on DCD line

>   \                                   ________

>   |                                  /

>   |==================================|  USB-to-serial adapter >>

>   |    \\                            \________ Used by Python app

> __/     \\

>          \\

>           \\

>            \\                          __

>             \\  Tap RX line,          /

>              \\ Split off DCD line    |

>               \=======================|  Serial port (ttyS0) >>

>                                       |    used by gpsd for time sync

>                                       \__


> Will this work?


The problem is there is no way for gpsd to talk to the GPS.  gpsd will configure the GPS as it needs to be.


> What NMEA messages does gpsd need to work for time-sync? GPZDA only?

> My setup is currently outputting GPZDA at 20Hz


The minimal set of NMEA messages required is not a single unique set.

There are many ways to get the minimum.  You will need the sats used (maybe GPGSV and or GPGSA) and PVT data (maybe GPRMC).


> I guess an alternate approach could be to set up the message sending

> in my app and then is there any easy way to record all the message

> data with gpsd?


gpspipe -r


> Oregon State University Location


Stop by if you get to Bend.





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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