Function is not defined for values of class embedded.fi when using HDL coder

Hi,

When I am experimenting in converting matlab code into vhdl with hdl coder, I am getting the error such as Function 'log' is not defined for values of class 'embedded.fi' or Function 'exp' is not defined for values of class 'embedded.fi'.

The specific block of code comes from the block:

        f_0 = fi( 0, 0, 1, 0, fm );  % 133.33333;
        f_sp = fi( 200*fi( 1/3, 0, 14, 15 ), 0, 14, 7, fm );  % 66.66667;
        brkfrq = fi( 1000, 0, 11, 0, fm );
        brkpt = fi( fi_div( (brkfrq - f_0), f_sp ), 0, 14, 10, fm );
        logstep = fi( 1.0711703, 0, 14, 13, fm );  
        linpts = (f<brkfrq);
        z = fi( fi( 0, 0, 1, 0 )*f, 0, 6, 0, fm );
        z( linpts ) = fi( fi_div( (f( linpts ) - f_0), f_sp ), 0, 6, 0, fm );
        % error with line below.
        z( ~(linpts~=0) ) = fi( brkpt + (log( fi_div( f( ~(linpts~=0) ), brkfrq ) )) ./ log( logstep ), 0, 6, 0, fm );

The original matlab code is from audspec.m of rastamat. I have tried converting fixed point to double before calling log(), but then another error pops up.

Thanks,

Answer 1

[Tim McBrayer]

As the error message states, there is no fixed-point version of the 'log' or 'exp' commands in MATLAB HDL Coder. The complete list of functions that have fixed point versions and are supported for HDL code generation is at http://www.mathworks.com/help/hdlcoder/ug/fixed-point-run-time-library-support.html.

[Sam]

Thanks for point this out. I think I was looking for that page, but couldn't find it.

[Shubham Kapoor]

Is there any workaround around using expn function?

Answer 2

[Dhananjay Kumar]

Here is the link to check function supported for code generation using fixed point arithmetic

https://www.mathworks.com/help/fixedpoint/ug/functions-supported-for-code-acceleration-and-code-generation-from-matlab.html

Answer 3

[Bharath Venkataraman]

HDL Coder allows you to replace an unsupported function with an equivalent Lookup table. Here is an example on how to do that for exp.