Hi Jim,
Thank you so much for your quick reply. Your finding is very interesting and I
believe it is very related to my problem.After some thinking, I am still having
some confusion:Because N320 and X310 USRPs are using different pulse edges,
their time 0s are actually different by 200ms in universal time, but their
internal timers should be similar. When querying their time respectively, we
should get similar time - the responses are their internal times. But I am
seeing 200ms difference.
Could you please give some comments on this?
Thanks a lot,
Hongwei
On Monday, 20 December 2021, 11:04:09 GMT, Jim Palladino
<j...@gardettoengineering.com> wrote:
Hi,
We had the exact same issue a couple months ago between an N320 and an X310.
The issue is that the N320 (and I'm guessing the N310) detects the 1PPS pulse
on the rising edge, as expected. The X310 detects the 1PPS edge on the falling
edge. Note that the 1PPS pulse from the Octoclock stays high for about 200ms,
so I'm guessing this is the issue you are seeing.
We ended up making our own custom FPGA build for the X310. We modified the file:
"uhd/fpga/usrp3/lib/rfnoc/utils/timekeeper.v".
Originally, the PPS edge detection looked like:
pps_edge<= pps_del & ~pps;
We changed it to:pps_edge<= ~pps_del & pps;
It would be good if this could get "fixed" in UHD, as it would be nice to not
have to maintain a custom FPGA build. I'm not sure what effect this change will
have on other USRP FPGA builds that use the same timekeeper.v file.
In any case, I'm guessing this is your problem.
Jim
From: zhou via USRP-users <usrp-users@lists.ettus.com>
Sent: Monday, December 20, 2021 5:31 AM
To: usrp-users@lists.ettus.com <usrp-users@lists.ettus.com>; Marcus Müller
<marcus.muel...@ettus.com>
Subject: [USRP-users] Time different between X310 and N310 USRPs using UHD4.1.0
Hi,
I am using mixed types of USRPs in my applications, namely, X310 and N310. The
signals are timed. I find 0.2-second time difference between these two
USRPs.Details:Each USRP is controlled by a Linux server;
The same Linux version in all PCs;All USRPs are connected to the same Octoclock;
UHD version is 4.1.0 in Linux servers;All Linux servers are connected to a
control PC which is the client;The sampling rates are different: 184.32MHz in
X310 USRP and 245.76MHz in N310 USRP
Control PC sends command to set time 0 after PPS in all USRPs, then query the
time in each of them.The time difference between USRPs of the same type is
small, ~2ms, but the time difference between different types of USRP is much
bigger, ~0.2s.Times should be impacted by sampling rate; when setting timers,
no signal is transmitted.
2ms time difference between USRPs could be due to network delay; 200ms can't be
because of network. It seems to be due to HW in USRPs. Does this mean that X310
and N310 are not synchronized?
Thanks for any comment,
Hongwei
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