Hi Philipp, thanks for your feedback. You're absolutely right on the latency side, I was not considering this when I wrote my response (it's still true that many people who use PCIe could just as well use Ethernet, and for those, I think Ethernet is a better choice). Regarding the usability, you know, I use the PCIe connection so rarely that I had totally forgotten about this upside. Your comments (and your request!) have been heard!
--M On Thu, Jan 22, 2026 at 5:48 PM Philipp Niedermayer <[email protected]> wrote: > 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]> <[email protected]> > > *Sent:* Thursday, 22 January 2026 at 14:11 > > *To:* [email protected] <[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. > > --M > > On 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: >>> - >>> >>> ni-fpga-interface >>> - >>> >>> ni-rio-mxie >>> - >>> >>> ni-rseries >>> - >>> >>> ni-hwcfg-utility >>> - >>> >>> 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 to [email protected] > >
_______________________________________________ USRP-users mailing list -- [email protected] To unsubscribe send an email to [email protected]
