Dear Simon, it's actually really just a constraint of how RFNoC packages data for transport. It doesn't support fragmenting big vectors (yet), so your vector has to fit one packet. Since the maximum size a packet can carry is 9000B, and a sc16 complex is 8B long, you only get 9000/8-long FFT output, or shorter.
> Ok thanks, so it's a limit in the RFNoC software and not related to Ettus FPGA hardware or something like that? Now, whether our FPGA code having that limitation is a software or an FPGA hardware problem is up for discussion, in my opinion :) A possible workaround would be writing your own wrapper for the Xilinx IP core used to actually do the FFT, which would be able to fragment. But then again, the question is what you want to do with the output afterwards. Best regards, Marcus On 03/03/2016 05:10 PM, Simon Olvhammar wrote: > Ok thanks, so it's a limit in the RFNoC software and not related to > Ettus FPGA hardware or something like that? > I dont see that limit in regular GNURadio and 8192 channels works > fine, isnt the packet size also max 9000 there? > Simon > > On Thu, Mar 3, 2016 at 3:45 PM, Marcus D. Leech <mle...@ripnet.com > <mailto:mle...@ripnet.com>> wrote: > > On 03/03/2016 05:21 AM, Simon Olvhammar wrote: > > Hi, > > I'm wondering what it would take to modify the current FFT > RFNoC block to be able to compute a 8192 channel FFT. Someone > that can guide me in the right direction? I'm a quite > experienced programmer, however not in HDL. > > Best regards > Simon > > > The main current stumbling block to large FFTs in RFNOC is that > the FFT output has to be able to fit into a single transport > packet, and > that is limited to 9000 bytes, which pretty-much limits you to > 2048-bin FFTs. There will be work in the future to allow FFT > outputs in > RFNOC to span multiple packets. > > > > > _______________________________________________ > Discuss-gnuradio mailing list > Discuss-gnuradio@gnu.org <mailto:Discuss-gnuradio@gnu.org> > https://lists.gnu.org/mailman/listinfo/discuss-gnuradio > > > > > _______________________________________________ > Discuss-gnuradio mailing list > Discuss-gnuradio@gnu.org > https://lists.gnu.org/mailman/listinfo/discuss-gnuradio
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