函数调用的简单示范。执行同布时钟触发操作，每个clk计算将在测试模块中执行时钟周期，并通过调用系统任务$display每次计算的结果都显示在时钟的下降边。

1.1 程序语句：

module tryfunction(clk, n, reset, result);  input [3:0]n;  input clk, reset;  output [31:0]result;  reg [31:0]result;   always @(posedge clk)   begin    if(!reset)     result <= 0;    else     begin       result <= n * factorial(n)/((n * 2)   1);     end   end   function [31:0]factorial;   input [3:0]operand;   reg [31:0]index;   begin    factorial = operand ? 1 : 0;    for(index = 2; index <= operand; index = index   1)    factorial = index * factorial;   end  endfunction  endmodule

1.2 testbench语句：

`timescale 1 ns/ 100 ps `define clk_cycle  50  module tryfunction_vlg_tst(); reg clk; reg [3:0] n,i; reg reset;                                               wire [31:0]  result;                      tryfunction i1 (    .clk(clk),  .n(n),  .reset(reset),  .result(result) ); initial                                                  begin   clk = 0;   n = 0;   reset = 1;   #100 reset = 0;   #100 reset = 1;   for(i=0;i<=15;i=i 1)    begin     #200 n=i;    end  end initial  begin   #100000 $stop;  end   always #`clk_cycle clk = ~clk;  endmodule

1.3 仿真波形：

module square_cube_factorial(clk, sel, n, reset, result); output [6:0]result; input clk, reset; input [2:0]n; input [1:0]sel; reg [6:0]result;  always @(posedge clk)  begin   if(!reset)    result <= 0;   else    begin     case(sel)      2'b01: result <= square(n);      2'b10: result <= cube(n);      2'b11: result <= factorial(n);      default: result <= 7'bx;     endcase    end  end  function [6:0]square;  input [2:0]operand;  begin   square = operand * operand;  end endfunction  function [6:0]cube;  input [2:0]operand;  begin   cube = operand * operand * operand;  end endfunction  function [6:0]factorial;  input [2:0]operand;  reg [3:0]index;  begin   factorial = operand ?1:0;   for(index = 2; index <= operand; index = index  1)   factorial = index * factorial;  end endfunction  endmodule

`timescale 1 ns/ 100 ps `define clk_cycle 50 module square_cube_factorial_vlg_tst(); reg clk; reg [2:0] n; reg reset; reg [1:0] sel;                                              wire [6:0]  result;                           square_cube_factorial i1 (  .clk(clk),  .n(n),  .reset(reset),  .result(result),  .sel(sel) ); initial                                                  begin   n = 0;   sel = 0;   clk = 0;   reset = 1;   #100 reset = 0;   #100 reset = 1;   forever    begin     #100 sel = {$random}%3;       n  = {$random}%6;    en
	end
	
initial
	begin
		#10000 $stop;
	end
	
always #`clk_cycle clk = ~clk;

endmodule

2.3 仿真波形：

        factorial模块中，operand和index的代码长度需不同，否则仿真报错（原因暂时我也不知道。