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From: | Aditya Arun Kumar |
Subject: | Re: Performing a USRP Packet Loopback |
Date: | Wed, 20 Jan 2021 14:48:20 +0530 |
Hi, I realized that in my packet loopback example, I didn't connect any of the QT GUI sinks after the USRP source. The updated flow graph is attached in screenshot0. After I connected them, I ran the packet loopback example on my MacBook Air using one B210 board with TX/RX and RX2 antennas attached and got the results attached in screenshot1, but still received underruns as printed out in the terminal in the bottom left corner. I also ran the example with two B210 boards with a TX/RX antenna on one and a RX2 antenna on the other and got slightly different results. Instead, the third graph was just a straight horizontal line and still ran into underruns. I also ran the same program with a Raspberry Pi 4 with one B210 board and got similar results. So I don't think it's an issue concerning computer power.Also, I was wondering what you meant by "for a loopback flow at low rates you may need to alter the internal buffer sizes in your flow-graph to prevent TX starving for samples because the RX buffers are still filling. But this is not a distinctly USRP problem and has more to do with GnuRadio". How would I alter the internal buffer sizes and what would I need to change it to?Are there any other suggestions you have for me to successfully get this loopback example running?Thanks!On Tue, Jan 19, 2021 at 1:36 PM Marcus D Leech <patchvonbraun@gmail.com> wrote:Keep in mind that the Pi 3b isn’t that powerful. So running a modulate+demodulator loopback flow may be too much for it, even at low rates.Also for a loopback flow at low rates you may need to alter the internal buffer sizes in you flow-graph to prevent TX starving for samples because the RX buffers are still filling. But this is not a distinctly USRP problem and has more to do with GnuRadio.Sent from my iPhoneOn Jan 19, 2021, at 3:37 PM, Jeff Long <willcode4@gmail.com> wrote:The USRP can not operate at a rate of 5k samples/sec. Minimums are usually around 250k or 500k (can't remember for that model).On Tue, Jan 19, 2021 at 2:57 PM Jada Mariano Berenguer <berenguj@uci.edu> wrote:Hi, I've been trying to verify the function of my B210 Ettus board.The first thing I did was use the UHD benchmark, receiving samples, and transmitting samples examples found here. When running these examples, I had overruns (O's) and underruns (U's), even as I tried adjusting the sample rates.Next, I decided to try to find another way to verify the function of the B210. I want to create a simple flow graph that will send a text file to the B210 and have the B210 receive it, and then transmit the same file back out, like a loopback example. I came across the GNURadio digital/packet_loopback_hier.grc example from this message thread. I was able to run the packet loopback example on its own but when I replaced the Channel Model block with USRP Sink and Source blocks, I ran into overruns and underruns. I tried changing the sample rates and gains, but still got O's and U's. I was wondering what I could do to fix this? I've attached an image of the edited packet loopback example with the USRP blocks as well.Thanks in advance!
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