Re: [Gumstix-users] GPS setting time.

[mike a. <all...@gm...>]

Hi,

I am assuming you're happy just to set the time through ntpd with the
NMEA messages, and aren't too bothered about PPS? PPS is possible, but
it's more of a hassle, because of how the gps is wired to the gpsstix
(i.e. not on the usual lines gpsd would expect it to be on, ie. RTS or
CTS, it's actually on a gpio) - I managed to come up with a solution
by patching/hacking the gpsd source code and using gpio-event, but
it's not that pretty. I am hoping to write a guide when I have some
time free, which I can put on the wiki.

There are three things I can think of off the top of my head:

1. you need to make sure your /etc/ntp.conf file is set-up correctly -
this means you must add a line to tell ntpd where your gps is. For
NMEA messages, you need the line:

server 127.127.28.0 minpoll 4 maxpoll 4
fudge  127.127.28.0 time1 0.185 refid GPS

to understand more about these lines, I would suggest looking at:

http://www.eecis.udel.edu/~mills/ntp/html/index.html
http://www.eecis.udel.edu/~mills/ntp/html/clockopt.html
http://www.sput.nl/time/garmin.html (has some interesting insights,
but the gps is a different unit - information from 'Configuring NTPD'
is useful)

2. GPSD is run with the -n flag, so that the data is always being
streamed from the device. If this is not done, then you won't get data
being put into the nptd shared memory unless you're actually
contacting the gps unit (for example, using cgps). See
(http://linux.die.net/man/8/gpsd) for more information.

3. the system clock is set somewhere near the actual time that will
start coming from the gps messages. If it's not, then ntpd will ignore
the gpsd times that are fed to it through the shared memory. This
problem bit me for a long time, and is to do with the fact that the
clock on the gumstix is reset every time the power is removed. The
easiest way to do this is use ntpdate to set the system clock before
ntpd starts, although this only works if you have a network
connection! It is possible to try and set the clock using the gps, but
it's not very reliable, especially with the alamanac problems that
happen when a gps unit is 'cold booted' (see here:
http://docwiki.gumstix.org/index.php/Frequently_asked_questions/GPSstix_and_Audiostix2).
If you desperately need to do this, I can provide some pointers.

Hope this points you in the right direction.

Mike

2009/10/15 Juan Osuna <jma...@ci...>:
>
>  Hi to All.
>
>  I need to get date/time from GPS in order to set the Verdex date/time, The
> GPS module is working properly and there is data at /dev/ttyS2.   An example
> of my data below using "gpspipe -r" :
>
> $GPRMC,005754.00,A,3152.18981,N,11639.89319,W,0.031,344.52,151009,,,A*7F
> $GPVTG,344.52,T,,M,0.031,N,0.057,K,A*39
> $GPGGA,005754.00,3152.18981,N,11639.89319,W,1,08,2.55,55.3,M,-36.9,M,,*5F
> $GPGSA,A,3,10,15,29,05,12,02,30,18,,,,,3.46,2.55,2.34*04
> $GPGSV,3,1,10,10,43,051,44,21,34,271,,15,16,133,18,29,61,341,40*7D
> $GPGSV,3,2,10,05,52,056,34,31,02,286,14,12,31,176,24,02,14,062,29*79
> $GPGSV,3,3,10,30,52,211,35,18,16,207,33*73
> $GPGLL,3152.18981,N,11639.89319,W,005754.00,A,A*72
> $GPZDA,005754.00,15,10,2009,00,00*6B
>
> I have installed gpsd, ntpd and ntpq properly, and I can read data from GPS
> using the SW mentioned.
> I can read the right UTC time fro GPS using "cgps" also.
> My question is: How can I set my Verdex time using the GPS date/time?
>
>  I have a verdex XL6P with GPSstix and OE,
>  Thank you in advance for your help.
>  Regards.
>
> --
> View this message in context: http://www.nabble.com/GPS-setting-time.-tp25900847p25900847.html
> Sent from the Gumstix mailing list archive at Nabble.com.
>
>
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