Hi everyone, I'm having quite a lot of trouble getting large-ish designs (16k channels) to produce spectra. The spectra that are being produced are quite strange. I've provided links below to a few examples. The first link is the spectrum produced by the unmodified tut3 model (except for the ADC and FPGA clocks increased to 1024 MHz and 256 MHz, respectively). It's pretty much as you'd expect - a bog-standard L-band spectrum full of RFI. The second link is what happens when I try to increase the number of channels to 16k. As you can see, I can pull 16k channels from the board, but there are no actual data in there, beyond the original 2k channels. All the usual blocks were modified to get the model to work at 16k channels: the #PFB and #FFT points increased to 32768, the vector length in the VACC increased to 8192, the sync_gen block (using for now before changing to a PPS-based system) adjusted, and the shared_brams adjusted for longer address length. The third link is a zoomed-in image of the same spectrum, just to show that there is a partial spectrum in there. The fourth link is what comes out when I replace the FFT and PFB blocks with black-boxes... where the pre-compiled PFB and FFT blocks have the same settings as in the previous spectra....! The inconsistency between compiling with "raw" blocks and pre-compiled blocks is another source of concern.
https://dl.dropboxusercontent.com/u/38103354/tut3_spectrum.png https://dl.dropboxusercontent.com/u/38103354/tut3_mod3_correct.png https://dl.dropboxusercontent.com/u/38103354/tut3_mod3.png https://dl.dropboxusercontent.com/u/38103354/tut3_mod2.png I can also make my models available if anyone would like. If I were to list every setting I'd changed to try and get this to work, this email would take about an hour to write.... but I've kept a log of everything I've tested. So, I'd be very grateful for suggestions for what to do next... I really have run out of ideas. I've compared the settings I'm using to the VEGAS models available on the git repo, and have even looked back to the deprecated "million channel spectrometer" model to look at the block settings used there. Nothing seems very different to what I'm doing. I'm going for 16k channels at the moment just because I was having trouble getting timing closure on 32k channels in 2-pols, with all the backend logic. Eventually I need to get a 64k channel model in 1-pol working, with the 5 GS/s ASIAA ADC, so this pre-requisite is essential. Many thanks in advance Michael P.S. I should add that the 1024 MHz ADC clock has to stay fixed because the downconverted 500 MHz L-band signal comes into the ADC at 0.5-1 GHz....
