Hi Mark, I'm not sure if this is your problem, but I had a similar issue. After some debugging, I found that for some reason, with the OOT RFNoC Block inserted, the total size of the CHDR packet plus the Ethernet header that gets added on in the FPGA would slightly exceed the MTU size (mine was set to mtu=8000 for the E320). I never figured out why this happens, since this isn't the case if the OOT block is not inserted (just like the flowgraph you described). Maybe just increasing the MTU size would help?
Anyhow, my solution was just to set the "spp" argument in the RFNoC_RX_Radio. I found that setting spp to a maximum of 1987 keeps the total packet size (after the Ethernet header is appended) to be less than the MTU of 8000. FYI, for spp means 1987 samples per packet. So, for 32-bit samples, 1987*4=7948. This leaves enough room for the Ethernet header. It seems like there should be a better "fix", but you can try setting spp manually to see if that helps. Jim ________________________________ From: USRP-users <usrp-users-boun...@lists.ettus.com> on behalf of Mark D via USRP-users <usrp-users@lists.ettus.com> Sent: Wednesday, February 17, 2021 10:35 AM To: 'usrp-users@lists.ettus.com' <usrp-users@lists.ettus.com> Subject: [USRP-users] OTT Gain Block stopping samples flowing from RFNoC Digital Down Converter I’m working with an E320 using UHD 4.0. I’ve been working through the video ”RFNoC 4 Workshop - GRCon 2020” to install my own custom signal processing block into the RFNoC on the FPGA. I’ve also been following the guide AN-121 “Debugging FPGA images” and have added Chip Scope probes to the payload and context stream signals. I have got to the point where I have the block instantiated in the FPGA. Running the example GNU radio code that streams samples from the host computer through the gain block and pack to the PC works as expected. I am also able to capture the payload and context stream signals in Chip Scope. However if I reconfigure the GNU radio to “RFNoC RX Radio”->”RFNoC Digital Down Converter”->”RFNoC Gain”->”RFNoC Rx Streamer”->”QT GUI Time Sink” the system no longer works. The Time Sink appears but the GNU Radio console is saying rfnoc_rx_streamer0 – UHD.recv() call timed out. Removing the gain block from the GNU radio design restores operation, so it appears that the gain block is in some way blocking the streaming data. I’ve also rebuilt the FPGA with the gain block connected between the DDC and Stream Endpoint but the results are the same. I’ve tried reverting the gain block code back to that generated rfnocmodtool, which just loops the context and payload data straight through. Does anybody have any idea why this block would be stopping data internally generated within the USRP from streaming out, whereas it works Ok when data is flowing from and back to the host? Any help would be greatly appreciated, Mark ________________________________ This email and any files transmitted with it are confidential and intended solely for the use of the individual or entity to whom they are addressed. If you have received this email in error please notify the system manager.
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