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vinodlk123

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01-27-2012 03:33 AM

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Registered:
01-27-2012

FFT CORE INCORRECT RESULTS

Hello....

Im using logic core fft 7.1 in xilinx-12.1, configured it for

burst,

fixed point,

datawidth 32-phase factor(PF) 24,

scaled mode, convergent rounding,

block RAM for data , PF....

when i give inputs in 2's comp format.. output is nowhere the expected output....

i don't know how to solve this issue...

help me in using correct results from IP core

thanks...

8 Replies

rcingham

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01-27-2012 04:30 AM

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Registered:
09-09-2010

Re: FFT CORE INCORRECT RESULTS

------------------------------------------

"If it don't work in simulation, it won't work on the board."

bwiec

Xilinx Employee

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01-27-2012 11:13 AM

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Registered:
08-02-2011

Re: FFT CORE INCORRECT RESULTS

You need to show some data if you expect us to be able to help.

Sim plots, .xco file, instantiation code, testbench, projects, etc...

www.xilinx.com

vinodlk123

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01-28-2012 07:18 PM - edited 01-28-2012 07:48 PM

6,966 Views

Registered:
01-27-2012

Re: FFT CORE INCORRECT RESULTS

yes sir...

im doing simulation...its sowing incorrect outputs..

i have to do 256 point FFT... but when i tried for 8 point FFT core to know their usage, its giving incorrect results...

i'v attached both input & output simulation results...

plz help me to know where i'v done wrong...

in results all the notations are in unsigned decimal.

thank you..

vinodlk123

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01-29-2012 09:16 PM

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Registered:
01-27-2012

FFT CORE 7.1 outputs not understandable----- need attention....

logic core 7.1 FFT core outputs are not correct, or i may be wrong in configuring it properly... i'l specify the config i'v done for IP.

fixed point, inputs are 2's comp inputs.

n=8, R-2, Burest IO

data width 32, Phase factor 24.

scaled, convergent rounding, natural order without cycle prefix insertion.

memory block ram, complex multiplier- 3 multiplier structure,

butterfly arithmetic , use CLB logic.

scale=[111111]

i'v attached outputs of simulation **for forward transform** below..

plz help me in using IP core properly .....

inputs are xn_re=[1 2 3 4 5 6 7 8 ], xn_im=[0 0 0 0 0 0 0 0 ], (unsigned decimal notation in simulation results)

outputs got from simulation are

xk_re=[0, 429496, 429496, 4294961 , 0 ,22 , 23 , 0 ]

xk_im=[0 , 429496 ,9 , 0 , 0 , 23 , 55, 0]

outputs are nowhere near the expected outputs....

whoever knowledged in this IP usage plz help me...

vinodlk123

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01-29-2012 10:48 PM

6,932 Views

Registered:
01-27-2012

Re: FFT CORE INCORRECT RESULTS

sir , i have attached the simulation results....

please go through them & help in getting correct outputs...

bwiec

Xilinx Employee

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01-30-2012 11:52 AM

6,920 Views

Registered:
08-02-2011

Re: FFT CORE INCORRECT RESULTS

Thank you for posting this info.

So what are you comparing these results against to determine that they are incorrect?

www.xilinx.com

vinodlk123

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01-30-2012 10:06 PM

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Registered:
01-27-2012

Re: FFT CORE INCORRECT RESULTS

im unable to get correct outputs in 2's comp format...

output is nowhere near the expected output..

i'v applied xn_re=[1 2 3 4 5 6 7 8]

xn_im=[0 0 0 0 0 0 0 0]

but outputs are not even near the approximation...

also when give constant xn_re with xn_im as zero, than outputs are all zeroes including xk_re..

i may be wrong in configuring or somewhere im doing wrong,

help me to do this in right way & get correct results....

thank you...

ywu

Xilinx Employee

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01-31-2012 04:04 AM

6,911 Views

Registered:
11-28-2007

Re: FFT CORE INCORRECT RESULTS

Your input is too small (you only use the 4 LSbs out of 32-bit input) and the scaling schedule is too big. Try the following values and let's know if the output looks better.

xn_re = [32'h1000_0000, 32'h2000_0000,... 32'h8000_0000]

xn_im = [0 ... 0];

scale_sch = 010101;

@vinodlk123 wrote:

im unable to get correct outputs in 2's comp format...

output is nowhere near the expected output..

i'v applied xn_re=[1 2 3 4 5 6 7 8]

xn_im=[0 0 0 0 0 0 0 0]

but outputs are not even near the approximation...

also when give constant xn_re with xn_im as zero, than outputs are all zeroes including xk_re..

i may be wrong in configuring or somewhere im doing wrong,

help me to do this in right way & get correct results....

thank you...

Cheers,

Jim

Jim