The change in time of arrival with B200s is due to phase ambiguity. Do you have a 10MHz reference shared between your devices as well?
Don't know why N210 has that off-by-one timestamp. I'm guessing that there's an extra flop in the logic for the PPS timing chain somewhere -- as in, the clock starts ticking on the first tick after PPS comes in. I've made that error about half a million times, myself. Nick On Fri, Jun 12, 2020 at 2:23 PM Aaron Smith via USRP-users < usrp-users@lists.ettus.com> wrote: > Hello all, > > I have two separate, but related, questions. > > I am trying to trigger an RF transmission every second, and I am receiving > the transmission with a receiver that has very precise time stamps. I am > driving the receiver with the same 1 PPS source as the B200 and N210. For > my simple test, I want the time of arrival at the receiver to register at 1 > PPS + propagation delay of the RF coax cable + the USRP front end delay. In > all cases I am running UHD 3.15.LTS > > With the N210 I can achieve this. However when I call > > usrp->set_time_next_pps(uhd::time_spec_t(0.0)); > > and poll the last pps time, I see that it is consistently 20 ns before a > second. That is, the pps shows at: > > 999999980 ns > 1999999980 ns > 2999999980 ns > > If I call usrp->set_time_next_pps(uhd::time_spec_t(20.0e-9)); then the 1 > PPS registers on the second. It's almost like the clock is biased by 20 ns. > I have observed this across 3 different N210s. What could be causing this? > > With the B200, every time I destroy and recreate the uhd::usrp::multi_usrp > there is a random change in the time of arrival at the receiver that > appears to be uniformly distributed between 0 and 1/master_clock_rate. Is > this expected? The Ettus website says "All functions that directly interact > with the AD93xx (tuning, gain change, etc) are subject to the scheduling of > the AD93xx. The determinism of these operations are not guaranteed. " > > Is this what I am experiencing? > > Thank you for the help! > > _______________________________________________ > USRP-users mailing list > USRP-users@lists.ettus.com > http://lists.ettus.com/mailman/listinfo/usrp-users_lists.ettus.com >
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