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Why do i get an error in the Fixed Point Conversion Step?

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Error: The function 'HDLIFFT128' contains persistent variables 'ifft128' and has specialization 'HDLIFFT128_s1' associated with it. Function specializations containing persistent variables are not supported for fixed-point conversion. Consider rewriting your algorithm such that it does not use persistent variables within functions that require specialization.
I am trying to generate HDL Code from this main function.
function [out1,out2] = main(x,y,z)
%call subfunction 1
out1 = sub1(x);
%call subfunction 2
out2 = sub2(y,z);
Sub-function 2 code:
function [yOut,validOut] = HDLIFFT128(yIn,validIn)
% Processes one sample of data using the dsp.HDLIFFT System object(TM)
% yIn is a fixed-point scalar or column vector.
% validIn is a logical scalar.
% You can generate HDL code from this function.
persistent ifft128;
if isempty(ifft128)
ifft128 = dsp.HDLIFFT('FFTLength',128);
[yOut,validOut] = step(ifft128,yIn,validIn);

Accepted Answer

Walter Roberson
Walter Roberson on 13 Jul 2016
I would suggest breaking it up into two pieces, one of which constructs the ifft128 object, and the other of which expects that object to be always input.
Walter Roberson
Walter Roberson on 13 Jul 2016
function ifft128 = init_HDLIFFT128
ifft128 = dsp.HDLIFFT('FFTLength',128);
function [yOut,validOut] = HDLIFFT128(yIn, validIn, ifft128)
[yOut,validOut] = step(ifft128,yIn,validIn);
The init function would be outside of any loop, and you would route its output to be an input of HDLIFFT128 that might be in a loop.
Pablo Medina
Pablo Medina on 14 Jul 2016
Thanks that solved the fixed point generation error.

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More Answers (1)

Bharath Venkataraman
Bharath Venkataraman on 13 Jul 2016
Pablo, splitting the function into a main function and calling the IFFT function from it resulted in HDL code generation. Here are the functions split up. Please replace the testbench and design files as needed.


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