fft size in fpga

Hello,

I am implementing a 128 point real Radix-2 fft, data and coefficient widths are 16 bit. I am synthezising it for use in an FPGA. However, it is taking a very long time to synthesize. (approx 3 days using Leonardo on a 2 GHz machine with 512 MByte RAM) I am using a 20K1000 Altera FPGA. The ram required by the fft will be internal to the FPGA

Will this design take up all the space on the device. From past experience, can someone give me an indication of what area of the device the fft will occupy.

Surely if it takes up most of the device, then it will be too big, as I have other features to implement in the FPGA also !!

Thank you PJ

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PJ
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--Ray Andraka, P.E. President, the Andraka Consulting Group, Inc.

401/884-7930 Fax 401/884-7950 email snipped-for-privacy@andraka.com
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Reply to
Ray Andraka

Hiya,

I have noted with some synthesizers that if it cannot infer your RAM "correctly" it will try to build it out of registers (as opposed to the dedicated RAM on the FPGA). This can end up taking a _very_ long time for only reasonably large RAMs.

You might consider synthesizing each module in your design separately until you find the part that causes the problem. If it isn't already structured thus it might be wise to do so as this may also help.

Later,

Andyman.

Reply to
Andyman

Several of the textbooks on FFTs such as Smith & Smith "Handbook of realtime FFTs" describe higher radix FFTs. I believe the Xilinx FFT core data sheet goes into a fair amount of detail on a radix 4 kernel. The easiest way to do hardware sharing is to use one kernel and run the data through it in multiple passes. You'll need to change the twiddle factors (which are really a phase rotation) and the data ordering. The twiddles can be handled by changing the input to a multiplier using a table. The data reordering is doable by permuting the bits of your address counter.

DA is really a technique for do> Hi Ray/Andyman,

--

--Ray Andraka, P.E. President, the Andraka Consulting Group, Inc.

401/884-7930 Fax 401/884-7950 email snipped-for-privacy@andraka.com
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"They that give up essential liberty to obtain a little temporary safety deserve neither liberty nor safety." -Benjamin Franklin, 1759

Reply to
Ray Andraka

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