How to set the user defined function in MATLAB to have 8-bit integer datatype

I have simulated a sine pwm in simulink which works well in the model. This model converted to HDL code (verilog code) using HDL Coder tool in the simulink. I have used quartus synthesis tool from Altera (ver 9.1). While simulating the quartus project the following error reported:

Error (10172): Verilog HDL unsupported feature error at Modulation_Subsystem.v(42): real variable data type values are not supported.

The "Modulation_Subsystem.v" is a user defined function. That accepts three switch inputs and based on this boolean input output is defined.

The code for the user defined function is attached:

    function  [y,z] = fcn(u,x1,x2,x3)
    %#codegen
   uint8 z;
  %c=12*u
  if x1==0 && x2==0 && x3==0
          y = u/1.4;
          z = 0;

elseif x1==1 && x2==0 && x3==0
        y = u/2;
        z = 1;
elseif x1==0 && x2==1 && x3==0      
        y = u/2.8;
        z = 2;
elseif x1==1 && x2==1 && x3==0
        y = u/3.6;
        z = 3;
elseif x1==0 && x2==0 && x3==1
        y = u/4.2;
        z = 4;
elseif x1==1 && x2==0 && x3==1
        y = u/5;
        z = 5;
elseif x1==0 && x2==1 && x3==1
        y = u/5.6; 
        z = 6;
else
      y = u/6.4;
      z = 7;

end

Hoping to get reply..

Thanks and Regards,

Roy

Answer 1

[Tim McBrayer]

Ultimately, you need to figure out where the doubles are creeping in; what is the first signal or value in your dataflow that is a double in Simulink? This will get emitted as a real. Looking at your code, you have a lot of constants embedded in it; recall that in MATLAB code all data is by default a double. So, you need to type your constants, which will entail learning about fixed point typing, since you are trying to divide by decimal values. Type "web(fullfile(docroot, 'fixedpoint/index.html'))" to access the fixed point help.

Typed constants may look something like:

 fi(1.4, 0, 8, -5)
 uint8(0)

The input and output data types to your function can be set via the Model Explorer (Tools->Model Explorer via menu, or ^H in the model diagram).

The final problem you will run into is your use of the division "/" operator. In general this is not synthesizable. If you intend to synthesize your design you will need to replace this with some other numeric operation. Since you are dividing by a constant you can change the divisions into multiplies by the reciprocal values.