Hi Martin, there's one metric where PCIe outperforms Ethernet: Latency.
We have a loopback (via host) application where we can see that the signal latency from USRP X310 RX to TX is better for PCIe based connection compared to Ethernet, both in terms of average latency and jitter. To give some numbers, one of our flowgraphs has 1.67±0.15 ms latency over PCIe; with 10G Ethernet-based connection it drops down to 2.3±0.9 ms (1sigma). Especially the jitter is problematic as it means that latency can go up to > 4 ms. I know it's a very specific use case, but the statement "better choice on any metric" is not correct here from our lab's experience ;)
Another nice feature of PCIe: one can specify different FPGA images in flowgraphs and clicking the "Play" button in GNU Radio loads the correct image for whatever flowgraph you are currently working with automatically. For Ethernet there is at least one separate step required to flash the image first. It works, but I would argue it's a downside in terms of usability.
Hope you guys don't just drop PCIe support! Best Philipp *From:* Martin Braun <[email protected]> *Sent:* Thursday, 22 January 2026 at 14:11 *To:* [email protected] <[email protected]>*Subject:* [USRP-users] Re: USRP-2952R (X310) PCIe interface issue with UHD (built from OAI source)on Ubuntu 22.04
Hey Vishwanath, Ok, thanks for updating the issue.The standard workaround we recommend is to use Ethernet, not PCIe. It's generally the better choice on any metrics (throughput, cable management, ease of setup) and really has no downsides.--MOn Wed, Jan 21, 2026 at 10:22 AM Vishwanath <[email protected]> wrote:Hi Martin, Thank you for your message. I have now updated the bug report at the link you shared (Issue #818) with my system details and observations so that the information is available for reference. I would really appreciate it if you could kindly take a look at the report when you get a chance. If you have any suggestions, potential fixes, or known workarounds for this issue, your guidance would be very helpful. Please let me know if any additional logs or information are needed from my side. Thanks again for your support. Regards, Vishwanath On 20/01/26 14:38, Martin Braun wrote:Hi Vishwanath, can you please amend this bug report: https://github.com/EttusResearch/uhd/issues/818 ...with your system details so we can get a bigger picture of what's happening. Thanks! --Martin On Sat, Jan 17, 2026 at 2:32 PM P S Vishwanath Koushik <[email protected]> wrote: Hello community, I am seeking guidance regarding using *USRP-2952R (X310)* over *PCIe* on a Linux host, and I would appreciate any suggestions or known-good configurations. *System and software setup:* * Host OS: Ubuntu 22.04 LTS * USRP: NI USRP-2952R (X310), PCIe (RIO) interface * UHD: Built from source (UHD version bundled with / referenced by OAI source tree) * NI Linux Device Drivers: *NI USRP 2025 Q2 driver linkj <https://www.ni.com/en/support/downloads/drivers/download.ni-usrp.html?srsltid=AfmBOor6EEe0WKBK67bW6htIgwYHrSZHCqjQNjITK3N8gELTv-JB5AbO#565446>* * Installed NI packages: o ni-fpga-interface o ni-rio-mxie o ni-rseries o ni-hwcfg-utility o ni-usrp-rio *Use case:* I am trying to interface the USRP-2952R with an *OAI-based host machine*, using UHD over PCIe (RIO), not Ethernet. *Observed behavior:* * The device is detected correctly using |uhd_find_devices| * [INFO] [UHD] linux; GNU C++ version 11.4.0; Boost_107400; UHD_4.8.0.HEAD-0-g308126a4 -------------------------------------------------- -- UHD Device 0 -------------------------------------------------- Device Address: serial: fpga: HG name: product: X310 resource: RIO0 type: x300 | | * UHD finds and selects the correct FPGA image (|usrp_x310_fpga_HG.lvbitx|) * However, |uhd_usrp_probe| fails during RIO initialization with: |RuntimeError: x300_impl: Could not initialize RIO session. Unknown error. (Error code -63150)| * vishwanath@vishwanath:~$ sudo uhd_usrp_probe [INFO] [UHD] linux; GNU C++ version 11.4.0; Boost_107400; UHD_4.8.0.HEAD-0-g308126a4 [INFO] [X300] X300 initialization sequence... [INFO] [X300] Connecting to niusrpriorpc at localhost:5444... [INFO] [X300] Using LVBITX bitfile /usr/local/share/uhd/images/usrp_x310_fpga_HG.lvbitx Error: RuntimeError: x300_impl: Could not initialize RIO session. Unknown error. (Error code -63150) || This suggests the failure occurs after FPGA image selection, during NI-RIO session initialization. *Questions:* 1. Is *NI Linux Device Drivers 2025 Q2* known to be compatible with UHD (especially when UHD is built from OAI sources) for X310/USRP-2952R over PCIe? 2. Are there any *recommended UHD versions* or commits known to work reliably with USRP-2952R + PCIe on Ubuntu 22.04? 3. Has anyone successfully used *OAI with USRP-2952R over PCIe*, and if so, could you share the software stack versions? 4. Are there additional NI-RIO or kernel requirements that UHD depends on for PCIe-based X310 devices? Any insights, known limitations, or recommended downgrade/upgrade paths would be very helpful. Thank you for your time and support. Regards, Vishwanath _______________________________________________ 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 [email protected]
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