Altera FFT IP-CORE core version 9

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Allo,

I have a small problem with the FFT core!

What is the size of the FIFO in burst mode ?

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Basically I don't know, but my guess is they start the transform before end of the input writes, So with a dual core, if the input buffer is 8k, you could potentially keep running, for up to 3/4ths the second transform before the input buffer is seen as "Full". (I don't think it's a fifo in the classical since.

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Why Sink_ready does not fall down when the FIFO is full?

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My guess again is you are not running enough clocks. If you have your sink_sop and sink_eop, if you don't do a second sink_sop it will never get full since it will no longer be writing data into the input buffer.

If you have the sink_sop and sink_eop in the wrong place, you will get unknown results.

So my guess is you ended the first transform with sink_eop, but never started the second, so there's no new data getting written into the input buffer. Hard to say without the simulation results however. Also make sure you sink_error = 0. If it's non-zero, then you may be off in your counts for sink_sop/sink_eop positions.

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Why Source_valid is never valid even if source_ready is valid?

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Did you give it a sink_sop?

Is sink_error zero?

Have you ran enough clock cycles for it to complete the transform?

Is source_error zero?

Those are my thoughts. Also having the twiddle factor size not equal the data size could potentially expose a bug in the core generator. With an 8k transform I would suggest you keep the twiddle factors at least 16 bits, and maybe larger. Hardware wise, other than the memory for the twiddle ROM you really aren't saving much, and you are loosing accuracy.

If the 3 items above are correct, then I suggest re-trying with 16 bit twiddle rom and seeing if it all of a sudden starts to work, then you can post a bug to altera about the 8 bit twiddle issue (if that's it). It would be the first time a specific configuration of the core had issues. I've found several over the years with the various versions.

Also for simulation you could try the streaming core and see if you have any better luck. Hardware wise it takes some more logic, but you could compare results and see if it's acting better than your "Burst" mode core.

Hope this helps.

Pete