Issues synchronizing USRP B210s with GNURadio using Octoclock-G

Question

Relevant System Information: 2 USRP B210s, 1 Octoclock-G purchased within the last year, UHD version: UHD_003.010.003.HEAD-0-gef157678, GNURadio version: 3.7.14.0, OS version: Ubuntu 18.04.5 LTS, Cables Used: https://www.ettus.com/all-products/sma-sma/

Hi all,

I am wanting to synchronize multiple USRP B210s using the Octoclock-G. The SDRs are connected to the octoclock with the same type cables on their PPS and 10 MHz inputs. The Octoclock switch is flipped to Internal and is powered on. I followed the steps in https://kb.ettus.com/Synchronizing_USRP_Events_Using_Timed_Commands_in_UHD. I have run 3 tests to attempt to connect them and verify that they are connected.

Test 1: When I connected the two SDRs to GNURadio and sent a sine wave pulse over a splitter to the two SDRs (time and clock source set to "external"), the cross-correlation showed they were misaligned by about 20-30 samples at a sampling rate of 100kHz (so about 0.2-0.3 ms).

Test 2: I tried using the recorder.py and recorder_grc.py (from the mailing list issue http://lists.ettus.com/pipermail/usrp-users_lists.ettus.com/2018-February/055745.html), but that did not seem to help except for confirming that the times were off by about 0.2-0.3ms.

Test 3: When I run the unmodified test_clock_synch program in the examples folder, the two SDRs are in sync in full_secs, although the clock time does not seem to change for some reason. I also tried running the modified test_clock_synch.cpp (from the mailing list issue http://lists.ettus.com/pipermail/usrp-users_lists.ettus.com/2015-January/040293.html) with the two lines:

    usrp1->set_time_next_pps(uhd::time_spec_t(double(0)));
    usrp2->set_time_next_pps(uhd::time_spec_t(double(0)));

uncommented out. It showed the full seconds agreeing and the tick counts remain at a constant 0 for all tests. If I leave the two lines commented, then the tick count and full secs are both off by a constant amount over all tests.

I suppose my overall question is are the SDRs really synchronizing (I suspect not) and if they are, is there something additional I need to do in GNURadio to make them synchronize? Sorry if this question has been asked before or not worded well. Thank you for your time and any assistance you can give. This is something I need to get done as soon as possible so thank you for any help you can provide.

question from:https://stackoverflow.com/questions/66055747/issues-synchronizing-usrp-b210s-with-gnuradio-using-octoclock-g

Answer 1

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