A few comments here: I have almost the exact same setup. After extensively debugging dropped samples on Tx, I concluded that there just wasn't very much on-fabric buffering on the X4_200 image, meaning it's very sensitive to host latency jitter which was causing the sample drops. Using DPDK, isolating some CPUs (isolcpus), and putting all DPDK fast-path sender threads on the isolated cores completely solved my problems.
I would check your network interfaces and make sure the packets are going where they should be. You can "watch -n 0.5 ifconfig" or something like that on your host machine while you run your tests and watch the Tx/Rx packet counters tick up. Make sure when the test starts, the management interface does some small amount of communication and when the test is running the 100G ports do the high speed comms. Also, it would be awesome to get a prebuilt image with RAM buffering and DUC/DDC enabled. I assume some resource limitation prevented an image like this from already shipping with UHD? On Mon, Jun 29, 2026 at 4:18 PM Eugene Grayver <[email protected]> wrote: > I have not tried the X4_400 image because I need many channels at > relatively low (50 MHz) bandwidth. This issue must be solved — I've been > able to use older USRPs for TX at rates up to 200 Msps. There is no reason > for the X440 to behave this way. > ------------------------------ > *From:* Peter Jiacheng Gu <[email protected]> > *Sent:* Monday, June 29, 2026 12:23 PM > *To:* Eugene Grayver <[email protected]> > *Cc:* usrp-users <[email protected]> > *Subject:* [EXTERNAL] Re: [USRP-users] Underflows on X440 TX > > > *Do not open links or attachments unless you recognize the sender. If > unsure, click the Report Phish button or forward the email to OPSEC. * > Hi Eugene, > > I also encountered this issue. I’m currently investigating the X4_400 > image since it supports the replay block. Have you already tried this? > > Best, > Peter > > Am 29.06.2026 um 21:02 schrieb Eugene Grayver <[email protected]>: > > > Hello, > > I am returning to the problem reported a few months ago: > > I have two X440s with X_200 image connected to a Threadripper 24 core. I > am using two 10 GbE direct connect cables for each USRP (total of 4x 10 > GbE). > > I was able to get RX working, but TX is getting continuous underflows. > > > - Using the benchark_rate example. > - Underflows observed both w/ DPDK and w/out DPDK > - Underflows observed with 4, 8 channels and 16 channels > - Fewer underflows with 4 channels, but still get a few per minute > - Priority high/normal does not make a difference (usually) > > > IMPORTANT: If I use only one interface ( > —args=addr=192.168.10.2,mgmt_addr=192.168.1.10) there are no underflows > with up to 7 channels (max to fit in 10 GbE). > > ./benchmark_rate > --args=addr0=192.168.10.2,second_addr0=192.168.11.2,mgmt_addr0=192.168.1.10,addr1=192.168.15.2,second_addr1=192.168.16.2,mgmt_addr1=192.168.1.20,clock_source=external,use_dpdk=1,type=x4xx,product=x440 > --tx_channels 0,1,2,3,4,5,6,7 --tx_rate 40.96e6 --tx_cpu sc16 > --multi_streamer --duration 120 > > This should be trivial for such a powerful machine! > > I am suspecting an issue with handling of packets across multiple network > interfaces. Are the TX flow control packets not getting to the right place? > > This is a critical failure — not something I expect for a $35k box 🙂 > > > > Eugene Grayver, Ph.D. > Principal Engineer > 310-336-1274 > _______________________________________________ > USRP-users mailing list -- [email protected] > To unsubscribe send an email to [email protected] > > _______________________________________________ > USRP-users mailing list -- [email protected] > To unsubscribe send an email to [email protected] >
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