Hi Tim
I think the number of "simultaneous streams" refers to how many signals you
want to process in parallel in the FFT. I think it makes multiple parallel FFTs that
share twiddle factors.
I could have maybe used 'simultaneous polarisations' to be more
astronomy specific. Also, the way the data input ports are labelled can
be ambiguous. I will try to neaten this up. (I am sure Dan will mention
documentation on the wiki too at some point)
As Dave mentions, the streams share twiddle factors. They also share
sync signals and the shift input. If you are using it asynchronously i.e
put in valid data flagged with the 'en' port, then the enable signal is
also shared. All the sharing makes things more efficient.
The sync_out lets you know when the output spectrum starts. sync_out hoes high
for one cycle preceding the first channel of the output spectrum. sync_out
need not go high for every output spectrum. Since the FFT is streaming, the
spectra come out one right after the other so you only really need the first
sync_out pulse to make sense of the output spectra.
Please note that when using the FFT asynchronously, the sync must
coincide with the last valid data word of the previous spectrum. The
first sample of the first spectrum must thus be preceded by a pulse on
'en' and 'sync' when in asynchronous mode.
Feel free to send questions/problems to the list, user feedback is
always useful.
Regards
Andrew
Regards
Andrew
