david s, it sounds like you are clocking your adc's very slowly for one or more of your aps, which typically means you will be clocking the fpga slowly.
beware that there are minimum clock frequencies for the fpga. if you need to go below these frequencies, then i recommend running the adc sample rate higher than you need, and then decimating the data. eg: run the adc sample clock at 4X what you really want to sample at, and only process every fourth sample from the adc. there are some casper emails archived about minimum clock rates. best wishes on your correlator, dan On Wed, Jun 19, 2013 at 11:08 AM, David MacMahon <[email protected]>wrote: > Hi, David, > > The CASPER PFB has a streaming interface which means that you just keep > giving it samples. For every N time domain samples in (where N is a power > of 2), you get N frequency domain samples out. > > To build an FX correlator, one typically follows the PFB with a quantizer > (quantizing to 4 bits real and 4 bits imaginary is common) and a "corner > turner" that distributes the frequency channel from multiple inputs to > multiple X engines. The key point is that each F engine produces all > channels from some inputs while each X engines consume some channels from > all inputs. The choreography of the F-to-X data transfer is directed by > the "corner turner". In contemporary FX correlators spanning multiple > boards, this is often accomplished by using a 10 GbE switch. The X engines > correlate and integrate the corresponding data samples from each pair of > antennas. > > Because the PFB produces 2**N channels and you have 38 inputs, you will > need to either add (or at least pretend to add) some dummy channels or drop > some actual channels so that you end up with a number of channels that is > divisible by 38. > > Rurik Primiani has written a memo that discusses various PFB resource > requirements. You can probably find a pointer to it in the mailing list > archive. For more details on packetized correlator development, you can > read the following CASPER memo (which confusingly is number 18 on the Memos > list, but has "Memo017" in its name): > > > http://casper.berkeley.edu/memos/Memo017_PacketizedCorrelatorArchitectures.pdf > > Hope this helps, > Dave > > On Jun 18, 2013, at 6:42 PM, David Saroff wrote: > > > Casper folks, > > > > When using a PFB/FFT combination, I get the static picture in figure 3 of > > https://casper.berkeley.edu/wiki/The_Polyphase_Filter_Bank_Technique > > > > So what happens next? Do you slide along N samples or M*N samples, or do > > you just slide one sample, and get one sample out the other end? > > > > I want to make correlation products from the PFB/FFT of 19 antennae. I > > think I fill up a buffer with N complex numbers for each of the 19 > > channels, and do the products in pipeline while the next buffer is > > filling. I think this is equivalent to sliding the M*N tap windows along > > the string of samples by N or Z^-N. > > > > Has to be a slide by N doesn't it? > > > > The project is an FX correlator for a 19 (x2 polarizations) = 38 channels > > on a virtex-6 for low and medium bandwidth. 0.4 MHz and 20 MHz, 2.5 MSPS > > and 50 MSPS respectively, using the 64ADC12. I think I can do it for the > > 0.4 MHz case. > > > > David > > > > > > >
