For loop Verilog计算错误8位1'；s补码减法器

我正在写一个8位1的补码减法器，它不使用像+或-

我相信它正在工作（在其他值上手动测试），但任务的最后一部分是让测试台迭代所有可能的值，并将它们相加（256*256或65536个可能的值）（不是所有的数字累积起来产生一个非常大的数，而是0+1、0+2、…1+1、1+2等等）与我的其他模块一起检查计算值，并打印正确匹配减法器的值数和不正确的值数

我已经编写了以下代码，并且没有编译错误，但是它仍然没有显示正确或错误计算的数量。它为我这边的每个数字显示一个x

module refonesub (
  output [7:0] subtractionresult ,
  output carryoverflow ,

  input    [7:0] A ,
  input    [7:0] B ,
  input mode 
  );

wire B0; 
wire B1; 
wire B2; 
wire B3; 
wire B4; 
wire B5; 
wire B6; 
wire B7; 

wire C0; 
wire C1; 
wire C2; 
wire C3;
wire C4; 
wire C5; 
wire C6; 
wire C7;  

xor(B0, B[0], mode);
xor(B1, B[1], mode);
xor(B2, B[2], mode);
xor(B3, B[3], mode);
xor(B4, B[4], mode);
xor(B5, B[5], mode);
xor(B6, B[6], mode);
xor(B7, B[7], mode);


onesub U0(A[0],B0,mode,C0,subtractionresult[0]);
onesub U1(A[1],B1,C0,C1,subtractionresult[1]);
onesub U2(A[2],B2,C1,C2,subtractionresult[2]);
onesub U3(A[3],B3,C2,C3,subtractionresult[3]);
onesub U4(A[4],B4,C3,C4,subtractionresult[4]);
onesub U5(A[5],B5,C4,C5,subtractionresult[5]);
onesub U6(A[6],B6,C5,C6,subtractionresult[6]);
onesub U7(A[7],B7,C6,C7,subtractionresult[7]);  

xor (carryoverflow,C6,C7);                

endmodule


module onesub ( A ,B ,Cin ,Cout ,S );

output Cout ;
output  S ;           


input A ;
wire A ;
input B ;
wire B ;
input Cin ;
wire Cin ;    

reg Cout;
reg S;

always @(A or B or Cin) begin
    case ({A,B,Cin})
     0: begin Cout=0; S=0; end
     1: begin Cout=0; S=1; end
     2: begin Cout=0; S=1; end      
     3: begin Cout=1; S=0; end
     4: begin Cout=0; S=1; end
     5: begin Cout=1; S=0; end
     6: begin Cout=1; S=0; end
     7: begin Cout=1; S=1; end
    endcase
    end
endmodule


module testbench;
   
   reg [7:0] A;
   reg [7:0] B;
   reg       mode;
   wire [7:0] subtractionresult;
   reg  [7:0] subtractionresult_expect;
   wire      carryoverflow;
   
   refonesub sub( 
                  .A(A),
                  .B(B),
                  .mode(mode),
                  .subtractionresult(subtractionresult),
                  .carryoverflow(carryoverflow) );

   
    integer    i, j;
    initial begin
        for (A = 0; i < 256; A = A + 1) begin
            for (B = 0; B < 256; B = B + 1) begin
                subtractionresult_expect = A+B;
                if (subtractionresult == subtractionresult_expect) begin
                    i = i + 1;
                end else begin
                    j = j + 1;
                end
            end
        end
        $display("All cases tested; %d correct, %d failed", i, j);
   end

endmodule

---

测试台上有多个bug

您需要初始化i和j（它们默认为x）

您可能想要

A<255

，而不是

i<256

您需要检查255，而不是256

我在显示屏前添加了

#1

，以确保打印了内容

initial begin
    i = 0;
    j = 0;
    for (A = 0; A < 255; A = A + 1) begin
        for (B = 0; B < 255; B = B + 1) begin
            subtractionresult_expect = A+B;
            if (subtractionresult == subtractionresult_expect) begin
                i = i + 1;
            end else begin
                j = j + 1;
            end
        end
    end
    #1 $display("All cases tested; %d correct, %d failed", i, j);   
end

initial begin
    i = 0;
    j = 0;
    for (A = 0; A < 255; A = A + 1) begin
        for (B = 0; B < 255; B = B + 1) begin
            subtractionresult_expect = A+B;
            if (subtractionresult == subtractionresult_expect) begin
                i = i + 1;
            end else begin
                j = j + 1;
            end
        end
    end
    #1 $display("All cases tested; %d correct, %d failed", i, j);   
end

All cases tested;           0 correct,       65025 failed