Re: [Discuss-gnuradio] How do I capture of the time of USRP N210 samples with host computer system time?

[Marcus D. Leech]

> On 01/07/2013 04:46 PM, LD Zhang wrote:
> > Thanks to Josh and Marcus for their comments. The set_time_now command
> > works! After I put it in, the earlier observed 0.5 sec offset between the 2
> > USRP became ~0.1 second. So there is still work to do. I guess my options
> > are:
> >
> > 1. Make the set_start_time command to work. My question is how I can make it
> > work in python. I hand edited the set_time_now command to embed in the
> > initialization part of the top_block.py code generated from GRC (which has
> > worked). Do I just hand edit the set_start_time just following that command?
> > Now the problem is that after set_time_now, the USRP time is sync'd to the
> > system time. But what is the argument I should give to set_start_time?
If you're running this on two different computers, and using the local 
system clock, it'll be hard to make both USRPs really agree on what time
  it is.  Even if the two hosts are synchronized with NTP, you'll have 
to do a fair bit of dancing about to make sure that they both, more-or-less,
  do the set_time_now() with the same value, and at the same time.

This is why for precision synchronized samples, people use a GPSDO with 
a 1PPS output (to allow set_time_next_pps() ), and a 10Mhz
  refclock (so that the clocks on the two-or-more USRPs all step 
together at the same rate and phase).



--
Marcus Leech
Principal Investigator
Shirleys Bay Radio Astronomy Consortium
http://www.sbrac.org