Hi Eugene - Which NIC(s) & NVM & OS driver version (default from system? from binary or source?)? If there are updates on any of these they might be worth trying.
Can you try the UHD-4.9 branch and see if that helps? It contains some data transport / networking fixes that are not in a 4.9 release; that will be part of the 4.10 release. These are all useful to try to help debug the issue. Please let us know if you have any success with these & if not we'll dig further. --- Michael L Dickens, PhD Emerson/NI/Ettus SDR RF Principal Application Engineer Teams: +1-512-683-5305 Cell: +1-512-585-1391 [email protected] <[email protected]> [email protected] On Fri, Mar 6, 2026 at 5:52 PM Eugene Grayver <[email protected]> wrote: > I am also seeing this warning: > [WARNING] [RFNOC::GRAPH::DETAIL] Cannot forward action tx_event from > 0/Radio#0:INPUT_EDGE:0, no neighbour found! > ------------------------------ > *From:* Eugene Grayver <[email protected]> > *Sent:* Friday, March 6, 2026 1:17 PM > *To:* usrp-users <[email protected]> > *Subject:* X440 X4_200 image TX underflows > > > - I am trying to send out 16 channels of 40 Msps data from two X440s. > - Getting many underflows (~1/s or more) > - As far as I can tell the X440 are synchronized correctly > - Set time to 0 on next PPS (external) > - Start TX at a future time (5s) using a time_spec in TX metadata > - Each TX streamer is in a separate thread > - Each thread pinned to a different core > - CPU utilization is about 20% > - I am *NOT *reading anything from disk — just sending the same > buffer over and over > - wmem_max size is 25 MB > - MTU is 9000 > - UHD 4.9.0 > > > What could be wrong? > > > Eugene Grayver, Ph.D. > Principal Engineer > 310-336-1274 > _______________________________________________ > USRP-users mailing list -- [email protected] > To unsubscribe send an email to [email protected] >
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