[USRP-users] GPSDO and B210

Marcus D. Leech mleech at ripnet.com
Sun Jul 5 21:37:37 EDT 2015


On 07/05/2015 09:11 PM, Sharath via USRP-users wrote:
> Hello,
> Reposting an old thread to see if there has been any progress.
> I installed a board mounted GPSDO on my B210. The problem is that this now requires a valid GPS fix to proceed, else I get a "No GPRMC message found".
> Now with an active GPS antenna, outdoors, the GPSDO picks up a signal easily. Indoors it is still iffy. Without the active GPS antenna, there is very little hope indoors even near a window. So my strategy now is to go outdoors, get the GPS fix and then continue my work indoors. Not ideal...
> Now my questions:
> (i) Is there a way to force the B2100 to use the internal clock and not wait for the GPS fix for all applications? For example I don't want to change the uhd_usrp_proble executable, but would like the board to use the internal clock and not wait for GPS fix. Is there a way to toggle the mode from automatic to internal clock for all applications via a jumper or other means? I don't want to recompile other working applications just because I have installed the GPSDO.
Any application can  ask for internal clock:

http://files.ettus.com/manual/classuhd_1_1usrp_1_1multi__usrp.html#a73ed40009d0d3787c183d42423d25026

And an application that  doesn't use that API call, or specifies 
"default" will use the GPSDO, if present, otherwise it will use "internal".

Global, all-application, device-parameter management is rather outside 
the scope of what amounts to a device-driver should be doing, since
  that type of functionality really belongs in the application layer, 
not in the driver layer.


> Separately:
> (ii) Once the GPS actually starts working, how can I use gpsd to get the gps data. That is the web pagehttp://files.ettus.com/manual/page_gpsdo_b2x0.html  says "Other information can be fetched as well. You can query the lock status with the gps_locked sensor, as well as obtain raw NMEA sentences using the gps_gprmc, and gps_gpgga sensors. Location information can be parsed out of the gps_gpgga sensor by using gpsd or another NMEA parser."
> I am able to get some of the data, but it seems that the $GPGSV string is not part of the code currently. Anyway the code can be updated to get these strings also output by default?
> Any suggestions are welcome.
You'd  have to write an interface to GPSD yourself.

I'm not aware of any immediate plans to expand the variety of NMEA 
sentences that are  parsed by the UHD software.  Keep in mind that the 
primary purpose of the GPSDO in USRP hardware is to provide 10Mhz and 
1PPS outputs for purposes of precise system-clock management.
The fact that the modules in use *also* produce NMEA navigation messages 
is rather secondary to their intended purpose in USRP hardware.

>
> Thanks, Sharath
>
>
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