Hi Eugene, I just tried to reproduce the issue on our end to verify if we have missed something during our release testing. For this I took UHD 4.10, an X440 connected to a switch but from the switch I only have two lanes going to my host computer. So that should be comparable. I didn’t have DPDK configured on the host, so I went without that and used exactly your rate. I could reproduce that we start failing when we reach 8 channels with only one lane, but 7 were still fine. Then I added the second lane and with this, even 8 lanes worked without a single underrun, dropped samples or sequence errors. I could even increase the tx_rate to 61.44 Msps and it still worked fine. I also tried with and without mgmt_addr parameter which made no difference here.
Please check your cables, IP configuration, and MTU config (9000). Best, Martin From: Eugene Grayver <[email protected]> Sent: Thursday, July 2, 2026 8:37 PM To: usrp-users <[email protected]> Subject: [EXTERNAL] [USRP-users] Re: Underflows on X440 TX Responding to martin's question: * Yes, I have a QSFP to 4x SFP breakout cable * The underflows happen even when using just one USRP (i.e. remove all references to the second one from the benchmark) ________________________________ From: Eugene Grayver <[email protected]<mailto:[email protected]>> Sent: Monday, June 29, 2026 1:17 PM To: Peter Jiacheng Gu <[email protected]<mailto:[email protected]>> Cc: usrp-users <[email protected]<mailto:[email protected]>> Subject: Re: [USRP-users] Underflows on X440 TX 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]<mailto:[email protected]>> Sent: Monday, June 29, 2026 12:23 PM To: Eugene Grayver <[email protected]<mailto:[email protected]>> Cc: usrp-users <[email protected]<mailto:[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]<mailto:[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]<mailto:[email protected]> To unsubscribe send an email to [email protected]<mailto:[email protected]>
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