hi gerry,
we haven't tried this, but i think the largest spectrometer you could fit on a roach2 is 256M points, implemented by a 16K point FFT, followed by DRAM based corner turn and twiddle factors, followed by another 16K point FFT. if you have this many channels in your correlator, you also be running up near the correlator X engine memory limits: for instance, if you cross correlate in a Titan GPU, then you only have 5 or 6 GB of memory on each GPU card. let's assume you have a max of 32 GPU's for your X engine. then max frequency channels = 32 GPU's x 6GB/GPU x 42^2 baselinepols x 4B/baseline = 435M channels max for 32 GPU's (round down to 256M max channels) if you cross correlate in a CPU (eg: DiFX) then you can have more memory, but you'll need a lot more CPU's to keep up with the data rate, so CPU's won't help. be wary of readout rate too - that's a lot of data to read out : 256M channels x 42^2 baselinepols x 4B = 1 TB every integration time best wishes, dan On Mon, Jan 20, 2014 at 7:53 PM, Gerry Harp <[email protected]> wrote: > Hi > > Just for fun, how large of an FFT (filter bank) can fit into one of the > Roach# boards? Has anyone ever successfully compiled a filter bank with > length 2^17? We're interested in building a relatively narrow-band > correlator so we need lots of channels. Any experience at large lengths or > educated guesses are welcome. Also, how fast did it go? Possible to keep up > with 100 MSPS? > > It is proposal time, once more... > > Thanks > > Gerry Harp > > > On 1/17/2014 11:56 AM, Dan Werthimer wrote: > >> >> >> >> >> Dear Casper Collaborators, >> >> >> We hope you can attend this year's Casper Worshop >> >> in Berkeley, California >> >> June 9 throuh June 13, 2014 >> >> >> >> >> We'll have more information later about registration, >> travel, abstracts, etc, but for now, please reserve these dates. >> >> >> Hoping you can participate, >> >> >> Dan and the Scientific and Local Organizing Committees >> >> >> >> >> >> >> > -- > ---------------------- > Gerald R. Harp, Ph.D. > Director, Center for SETI Research > SETI Institute > > >
