MATLAB: Simulink “Find block” HDL Coder

code generationdigital image processingdigital signal processinghdlHDL CoderMATLABsignal processingsimulink

How can I use HDL compatible blocks to portray the "find block" functionality. http://uk.mathworks.com/help/simulink/slref/find.html#bsdkmvh-8

Unfortunately the find block is not HDL compatible, so there must be other ways to output an index based on a condition. I have the Matlab code:

idx = find(gs >= g, 1, 'last')

that I need to simulate in Simulink with HDL coder and I don't think a user defined function block will work as it will just contain find() which is not HDL compatible. Thanks for your help in advance.

Best Answer

I believe this is answered with the other question you posed on the break command. See how idx is a persistent value - that means it stores its value across calls. If you choose to update only when idx is 0, you get the the first value of gs >= g. If you update all the time you get the last value.

You can make this work for a 2D case as well.

In general, you should avoid having all these comparisons in a for loop. The entire for loop will run in one "clock", so your FPGA code will run very slowly. You are better off streaming the gs values in one at a time and taking one "clock" to compare one value of gs to g (the second code example in my answer to your other question ).

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In this case, since you are passing in the 80x1 matrix, here's what you do:

% returns last index that matches gs >= g
for ii = fi(1:80)
  if gs(ii) >= g
     idx = ii;
  end
end

To use the first/smallest index of gs that is >= g, do the following:

% returns smallest index of gs that is >= g
  for ii = fi(80:-1:1)
    if gs(ii) >= g
       idx = ii;
    end
  end

In both these cases, you are trying to loop over all 80 indices in one clock cycle, which means 80 comparisons in one cycle. If instead, you were able to pass in the 80x1 matrix one value at a time to the function, that would help compare one value of gs at a time.

MATLAB: Problem with simulink and HDL coder

It sounds as if the HDL data associated with your Stateflow.MATLAB Function block may have become damaged. I don't know if this will work, but please try it out.

Find each MATLAB Function block or Stateflow chart
Right click on the block, choose HDL Code > HDL Block Properties...
Change any property (e.g. InputPipeline), Apply the change, change it back to the original value, and Apply the reverted value.

This should have the effect of rewriting the HDL data associated with each potentially affected block, which should correct whatever issue you are having.

Best Answer

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