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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