Hi Tim,
Ah, that's the problem! The sync out pulse will only come once per
input sync, and can be used for resetting downstream logic. However,
after a sync, every N_FFT/N_INPUTS clock cycles represents a new
spectra. You should be able to verify this in simulation by varying
the FFT signal inputs
Jack
I think this may be getting clearer in my murky mind. If I send one and only
one sync pulse into the PFB, conneced to FFT, I get one and only one sync out.
I am assuming that this means that the FFT runs once.
Should I assume that the FFT is still running forever? If this is the case I
n
hi tim,
all casper fft's operate in continuous streaming mode.
there is no way to start and stop them.
if you don't inject in a sync pulse, they continue working anyway.
the data stream into the FFT in time domain, and after you
stream in N samples (the first vector),
you must continue to inject
Hi Tim,
On 2 May 2014 14:16, Madden, Timothy J. wrote:
> Aaron
>
> I thought they were streaming until I tried using simulink.
>
> If I give the FFTs ONE and only ONE pulse, they compute ONE FFT and stop. So
> I have to give a series of pulses.
> So then I must figure out what sync frequency is
Jack
I have a problem then. Because in simulink, if I give ONE and only one sync
pulse, then the FFT stops after one compute. I am not sure what to do about
that, because the simulation seems to disagree with the documentation.
The reason I am trying to give ONE sync pulse in simulation is becau
Aaron
I thought they were streaming until I tried using simulink.
If I give the FFTs ONE and only ONE pulse, they compute ONE FFT and stop. So I
have to give a series of pulses.
So then I must figure out what sync frequency is necessary. It seems to be true
that the FFTs need repeating sync pu
Hi Tim,
>
> Also, if we supply ONE and only ONE sync pulse, should the fft block compute
> indefinately? My simulink seems to require a series of sync pulses to get
> the FFt to work more than once.
>
>
That's right, one and only one sync pulse is sufficient to keep the
FFT operating indefinitely
Dear Tim,
You are aware that the CASPER FFTs are streaming, right? By this, I mean
that they can accept data input at the full clock rate with no pausing
between FFT windows. Everything Dan says is correct about latency, but
historically there have been very few applications that have strict lim
tim,
one more thought:
the PFB FIR in front of the FFT dominates the latency of the PFB/FFT.
the PFB has latency of (Ntaps-1) x FFTlength / Nparallelinputs.
a four tap PFB has about three times the latency of the FFT,
so if you remove the PFB you will cut latency down by about a factor of
three
I appreciate your response Dan.
Tim
From: dan.werthi...@gmail.com [dan.werthi...@gmail.com] on behalf of Dan
Werthimer [d...@ssl.berkeley.edu]
Sent: Friday, May 02, 2014 11:26 AM
To: Madden, Timothy J.
Cc: casper@lists.berkeley.edu
Subject: Re: [casper] FFT comput
hi tim,
the casper fft's are maximized to handle high bandwidths with
low resource utilization, but they are not optimized for low latency,
as astronomers use them in streaming applications where latency
is not important.
there are other FFT architectures - some 512 input FFT's can
convert from t
Folks
I am trying to use a complex fft (the green FFT block) for a spectrum analyzer
application.
I would like to use a 512 point FFT to compute on read time data. I need the
FFT to compute in less than 512 samples. I am using 4 taps in the input, and
running the FPGA at 128MHz. In this case
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