Use if-generate structure to define two variations of a function, and call that function in the same tb

Question

Here is a small tb, with some example code, where I am trying to define a function two ways, then call that fn below its definition.

module tryfact;
  
  localparam FUNCTION_IS_STATIC = 1;
  
  generate :mygen
    
  if(FUNCTION_IS_STATIC)
      // static fn
      function  integer factorial (input [31:0] operand);
        factorial = 1;
      endfunction: factorial
    
      else
      // automatic fn
      function automatic integer factorial (input [31:0] operand);
        factorial = 1;
      endfunction: factorial
      
  endgenerate :mygen
    
  // test the function
  begin
  integer result;
  initial begin
    result = mygen.factorial(1);
    $display("%0d factorial=%0d", 1, result);
    end
  end
  
endmodule

If I name the block so that it can be called using mygen.factorial1, simulation errors producing:

generate :mygen
           |
xmvlog: *E,UMGENE (testbench.sv,5|11): An 'endgenerate' is expected [12.1.3(IEEE 2001)].
  generate :mygen
           |
xmvlog: *E,EXPENM (testbench.sv,5|11): expecting the keyword 'endmodule' [12.1(IEEE)].
endmodule

If I remove the block label, its fine with the generate, but now I have no hierarchical reference.

xmelab: *E,CUVUNF (./testbench.sv,25|23): Hierarchical name component lookup failed for 'factorial' at 'tryfact'.

How should the generate be named with a single name so that it can be hierarchicaly referenced by that name when called?

toolic · Accepted Answer · 2024-06-26 15:55:31Z

2

This compiles and runs for me without errors on Cadence and Synopsys simulators:

module tryfact;
  
  localparam FUNCTION_IS_STATIC = 1;
  
  if (FUNCTION_IS_STATIC) begin : mygen

      function  integer factorial (input [31:0] operand);
        factorial = 1;
      endfunction: factorial
    
  end else begin : mygen

      function automatic integer factorial (input [31:0] operand);
        factorial = 1;
      endfunction: factorial
      
  end
    
  // test the function
  begin
    integer result;
    initial begin
        result = mygen.factorial(1);
        $display("%0d factorial=%0d", 1, result);
    end
  end
  
endmodule

I added begin/end keywords on each branch of the if/else, and added the mygen label on each branch.

Refer to IEEE Std 1800-2023, section 27.5 Conditional generate constructs

I removed the optional generate/endgenerate keywords. I don't think adding a label after the generate keyword is legal syntax.

edited Jun 26, 2024 at 15:55

answered Jun 26, 2024 at 15:43

toolic

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1 Comment

Mikef Over a year ago

I did not realize the same label could be used in both branches if the if. It makes sense bc only one branch is elaborated.

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