Dear USRP Community, I am currently working with OpenAirInterface (OAI) 2026.w06 and using a NI/Ettus USRP-2952R (X310 class device, XG FPGA image, reported type as x300) for 5G NR gNB experiments.
I am attempting to configure a 100 MHz NR carrier (273 PRB, 30 kHz SCS, band 77). Based on 3GPP numerology, the expected sampling rate is 122.88 MSps. However, when configuring the device, UHD reports: "[WARNING] [MULTI_USRP] Could not set RX rate to 122.880 MHz. Actual rate is 184.320 MHz" "[WARNING] [MULTI_USRP] Could not set TX rate to 122.880 MHz. Actual rate is 184.320 MHz" The device is therefore running at 184.32 MSps instead of the requested 122.88 MSps. System Details: • SDR: USRP-2952R (X310 class, XG FPGA image) • Master clock observed: 184.32 MHz • UHD version: 4.8.0 • OAI version: 2026.w06 • Host CPU: Intel i7-7700 (4 cores / 8 threads) • CPU governor: performance (all cores locked to max frequency) • NIC: Single 10G interface • MTU of 10G Interface : 9000 • Network buffers configured as: net.core.wmem_max=33554432 net.core.rmem_max=33554432 net.core.wmem_default=33554432 net.core.rmem_default=33554432 • Using single 10G link Observed behavior: When operating at 273 PRB (100 MHz), I see continuous sequences of: *LLLLLLLLLLLL* along with: *L[HW]* *Buffer overflow, count_write = 10, start = 4 end = 4, resetting write package.* It appears that because 122.88 MSps does not satisfy the integer MCR/decimation requirement (184.32 / 122.88 = 1.5), UHD forces the sampling rate to 184.32 MSps (decimation = 1). This significantly increases host data throughput and processing load, possibly contributing to the buffer overflows and late processing. I would appreciate clarification on the following: 1. Is 122.88 MSps fundamentally unsupported with MCR = 184.32 MHz on the X310 architecture? 2. Is there a recommended master clock configuration for stable 100 MHz NR operation? OAI gNB Logs are attached for your reference. Thank you for your guidance. Regards, Vishwanath
oaigNBlog_Sample
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