Hi Luca, I haven't used a recent UHD version with an FFT RFNoC block (probably 4.2 is the latest that I have used), but I have successfully used FFT lengths up to 4096. In order to do this, I had to create my own Xilinx FFT IP and I also had to separate the concepts of streaming packet length from the FFT length. If you want to do this, I can provide additional info. However, using the "stock" FFT block provided by Ettus, I believe that you should be able to stream with FFT length up to 1024 using the N310.
You mentioned in a previous post that your SPP is 2048. I think that this is an invalid SPP for the radio because of the need for the radio to insert "packet header" bytes which reduces the max num samples per packet to <=2000 (or about that). So, my suggestion is to use SPP=1024. Another suggestion is to try the Ettus example "rfnoc_rx_to_file" which will allow you to specify an arbitrary block - in this case the FFT block - to create an RFNoC graph that looks like "rx_radio => DDC => FFT => rx_streamer". This eliminates gnuradio from the equation. This example will capture samples to a file that you can then plot to see the results. You could run this example initially without the FFT block (rx_radio => DDC => rx_streamer) and make sure it is working as you expect. Then you could try again with the FFT block inserted. Rob On Mon, Sep 11, 2023 at 5:30 AM Bachmaier, Luca < luca.bachma...@iis.fraunhofer.de> wrote: > Hi Rob, > > > > thanks for your reply. What I originally wanted to bring across with my > message was that I cannot run the flowgraph with fft_sizes larger than 256, > no matter whether the maximum possible limit is 1024 or 2048. E.g. if I set > the fft_size to just 512, I also get the error about the atomic item size > mentioned below. I keep wondering why that is. > > > Regards > > Luca > > > > *Von:* Rob Kossler <rkoss...@nd.edu> > *Gesendet:* Mittwoch, 6. September 2023 21:29 > *An:* Marcus D. Leech <patchvonbr...@gmail.com> > *Cc:* Bachmaier, Luca <luca.bachma...@iis.fraunhofer.de>; > usrp-users@lists.ettus.com; Nieland, Michael < > michael.niel...@iis.fraunhofer.de> > *Betreff:* Re: [USRP-users] Re: RFNoC: strange behavior of FFT block > > > > Hi Luca, > > A couple of things. The largest FFT size might be limited to 1024 - even > with MTU=9000. I think that the maximum packet length is often 2000 or > 2048 such that when you add a few header bytes, you can no longer achieve > an FFT packet of 2048. > > > > Additionally, if you look in fft_block_control.cpp, you will see that > there is a constant that limits the max size to 1024. This also matches the > parameter "C_NFFT_MAX=10" which you will find in "axi_fft.xci" which is the > Xilinx IP file that is implemented. You can change these in order to build > different sizes, but these are the defaults. > > > > If you search the mailing archive, you may find discussion of this topic > and the need to divorce the concepts of 'fft length' and 'packet length' in > order to achieve FFT lengths greater than 1024. > > Rob > > > > > > On Tue, Sep 5, 2023 at 10:06 AM Marcus D. Leech <patchvonbr...@gmail.com> > wrote: > > On 05/09/2023 04:38, Bachmaier, Luca wrote: > > Hello Marcus, > > > > Thank you for your detailed explanation. I was able to fix the problem > now: I updated GNU Radio from 3.10.5 (installed over apt) to 3.10.7 > (installed from source). With the newer version the FFT block now correctly > displays a noise floor. > > > > So far so good, the FFT resolution is still low as I cannot set the size > higher than 256 (Error “samples per package must not be smaller than atomic > item size”). As far as I understood, the size should be able to go as high > as 2048 when using 10Gbit streaming. > > My current configuration should enable that: > > - MTU on my interface is set to 9000 > > - Parameter spp of RFNoC RX Radio is set to 2048 > > - Current FPGA image is of XG type > > > > In case it’s helpful, here’s the relevant output of `ip a` of my devices: > > Host: > > 4: enp9s0f1np1: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 9000 > qdisc mq state UP group default qlen 1000 > > link/ether 9c:6b:00:16:8e:96 brd ff:ff:ff:ff:ff:ff > > inet 192.168.10.3/24 scope global enp9s0f1np1 > > valid_lft forever preferred_lft forever > > > > USRP: > > 3: sfp0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 9000 qdisc > pfifo_fast qlen 1000 > > link/ether 00:80:2f:31:28:42 brd ff:ff:ff:ff:ff:ff > > inet 192.168.10.2/24 brd 192.168.10.255 scope global sfp0 > > valid_lft forever preferred_lft forever > > > > I think in the "RFNOC Graph" block, you can specify the SPP in the "Device > Args" parameter. > > _______________________________________________ > USRP-users mailing list -- usrp-users@lists.ettus.com > To unsubscribe send an email to usrp-users-le...@lists.ettus.com > >
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