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!
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