LMS implementation in LabVIEW fpga (High throughput personality)

Question

Have to say surprised with the limitations of labVIEW FPGA in array implementation. I am not experienced enough in labview to make this comment but I found it very difficult to work with arrays !!. I am working on Active Noise Cancellation project. I need to collect audio data from two microphones @40k Sample rate and 100 samples per frame (at least) and output the audio through loud speaker @40k sample rate. For this purpose, I am using myRIO 1900 in FPGA High throughput personality.

Right now, I am trying to implement LMS algorithm in LabVIEW FPGA platform. I have attached the MATLAB code below, what I want to implement !

Till array intializations are fine but when it comes to temporary vector manipulations. like :

x_temp(1:nr_c-1)=x_temp(2:nr_c);
x_temp(nr_c)=x(i);

I am going mad ! How to do this ? LabVIEW doesnt allow us to index the 1D arrays properly ( we can only extract one particular element of array not part of array, I can extract x_temp(1:nr_c) with sub array function but how to extract x_temp(2:nr_c) ??)

Please help me how to do the manipulation of 'x_temp' vector with the above basic statements.

PS: 1.LabVIEW FPGA supports only one dimensional array operations.

2. Even though Adaptive Filter Toolkit pallettes are available in myRIO FPGA High throughput personality, I cannot install Adaptive Filter Toolkit on myRIO Target.!!!

   3.In MyLMS program : x : input vector(Array) , y: Desired Signal, nr_c : number of filter coefficients ,step: step size. I hope you understood the rest program :)

MyLMS.m :

function [y_hat,e,w] = MyLms(step, nr_c, x, y)
%intializing all vectors
coeffs=zeros(1,nr_c);
x_temp=zeros(1,nr_c);
y_hat=zeros(length(x),1);
e=zeros(length(x),1);

for i=1:length(x)
  %temporary vector formation
  x_temp(1:nr_c-1)=x_temp(2:nr_c);
  x_temp(nr_c)=x(i);
  %LMS algorithm iterations
   y_hat(i) = x_temp * coeffs';      
  e(i)= y(i) - y_hat(i);       
  coeffs = coeffs+step*e(i)*x_temp;     
 end

Answer 1

I am by no means a LabVIEW FGPA expert, but I think you would encounter very similar limitations in VHDL.

At any rate, the typical technique for accessing subarrays is using rotate and replace subset (see Joel_G's post). For more information about the FPGA constraints and capabilities, see the help document: Array Palette Details (FPGA Module).