Great! Thanks Josh for the answers to my last email. Please see my comments and questions below.
============================================================================ ======== If you want to use the PC clock, I recommend calling set time now with the current PC time before scheduling streaming. This will make the USRP tick counter roughly match the PC clock. python: usrp_source.set_time_now(uhd.time_spec_t(time.time()) c++ usrp_source->set_time_now(uhd::time_spec_t(secs, micros, long(1e6)); This way, your only time-ambiguity is the variance in ethernet control packets and the difference in time between the different PCs. That should satisfy referenced to PC's time anyway... >>> I will try it in Python to set the USRP time. My generated top_block.py is doing as: self.uhd_usrp_source_0.set_....... I suppose I will just do: self.uhd_usrp_source_0.set_time_now(uhd.time_spec_t(time.time()) There is however a question of how often one needs to set the USRP time. It would depend on how fast the USRP clock drifts with respect to host computer system time. I remember a number of 2 ppm accuracy of the TCXO frequency reference. How does this translate to rate of clock drift (in say micro-seconds drift per hour)? >>> -------------------------------------- The next step would be to schedule when a stream begins for each device so they send RX samples to the host at the "same time" (according to the USRP anyway). I think the USRP source block supports setting the time, and streaming at a specific time, but there isnt a way to do this at the GRC level. So you might need some hand coded python added to the generated flowgraph, if you are using GRC. >>> OK, I want to do this. But what is the command to do in python? Something like: self.uhd_usrp_source_0.rx_sample_time??? Or .schedule_time??? I do need to pass the sample gather start time as a variable to the top_block.py script. How do I do that (I am a matlaber who is still clumsy with python)? Thanks and Regards, LD _______________________________________________ Discuss-gnuradio mailing list Discuss-gnuradio@gnu.org https://lists.gnu.org/mailman/listinfo/discuss-gnuradio _______________________________________________ Discuss-gnuradio mailing list Discuss-gnuradio@gnu.org https://lists.gnu.org/mailman/listinfo/discuss-gnuradio
