Re: [Discuss-gnuradio] read GPSDO data with GRC

[Marcus Müller]

Hi Francois,

actually, not by itself. You must set the USRP's time source to the GPSDO; 
please refer to the usrp source GRC block or to the doxygen documentation for 
reference.

Hope that helped,

Marcus

On 09/03/2013 05:17 AM, fquitin wrote:
> Hi Marcus,
>
> So, if I understand right, when the GPSDO is connected and I read the time tags 
> with GRC, I will get the time in GPS time (rather than in time since the USRP 
> was turned on)?
>
> Thanks a lot,
> Francois
>
> On 02.09.2013 11:09, Marcus Müller wrote:
> > Hi Francois,
> >
> >  I think you answered your question yourself:
> >  There are ways to query the GPS module; however, these are queries
> > and do not behave like sample streams or messages. Therefore,
> > integration with the GRC does not really make much sense.
> >  The GPSDO is just a device that is connected by serial line (and the
> > clock and pps cables) to your USRP; it does not add any tags. Tags are
> > a GNU Radio concept that neither the USRP nor UHD know about; your
> > time, tune and rate tags are attached by the usrp_source GNU Radio
> > block.
> >  However, if you look into what the GPSDO does (e.g. synchronize your
> > USRP's clock rate and internal real time clock to GPS),
> >  you will find that reading the rx_time stream tags yield exactly the
> > information that you could get if there was a pps tag attached to a
> > sample every second by just counting the samples that you processed
> > (which GNU Radio does for you), converting the number to an absolute
> > time (which time_spec_t::from_ticks does for you), and subtracting you
> > first samples' time.
> >
> >  So, basically, there's an easy way to add your own "every second
> > there's a tag"-block. But since that seems to be application-specific,
> > you're bound to write it yourself, which raises the question why you
> > would do something like that when you can infer the time of each
> > sample by just looking at its number.
> >
> >  So: Happy hacking,
> >  Marcus
> >
> >  On 09/02/2013 03:10 AM, Francois Quitin wrote:
> >
> > > Hi all,
> > >
> > > I'd like to know if it's possible to read the GPSDO data (more specifically the 
> > > GPS time) with GNURadio-companion. I understand there are simple commands to 
> > > read this data in C++ or python, and I'd like to know if it's possible in GRC.
> > >
> > > I'm familiar with programming GRC blocks and working with time-tags. Does the 
> > > GPSDO attach some tag on a sample when sending it's pps signal that I could 
> > > retrieve in GRC?
> > >
> > > Thanks,
> > >
> > > Francois
> > >
> > > --
> > >
> > > Francois Quitin, Ph.D.
> > >
> > > Research Fellow
> > >
> > > School of Electrical & Electronic Engineering
> > >
> > > Nanyang Technological University
> > >
> > > Singapore
> > >
> > > Phone: +65-8502-3690
> > >
> > > Email: address@hidden
> > >
> > > _______________________________________________
> > > Discuss-gnuradio mailing list
> > > address@hidden
> > > https://lists.gnu.org/mailman/listinfo/discuss-gnuradio [1]
> >
> >
> >
> > Links:
> > ------
> > [1] https://lists.gnu.org/mailman/listinfo/discuss-gnuradio
> >
> > _______________________________________________
> > Discuss-gnuradio mailing list
> > address@hidden
> > https://lists.gnu.org/mailman/listinfo/discuss-gnuradio