Verilog 矢量的值为'；t更新

我在verilog系统中有一个32x32乘法器，带有一个fsm风格的机器，基本上可以像在学校一样进行长乘法

我两天前测试过，结果很好。但是，突然之间，甚至没有更改代码，其中一个输出就无缘无故地保持在0。 代码如下：

// 32X32 Multiplier arithmetic unit template
module mult32x32_arith (
    input logic clk,             // Clock
    input logic reset,           // Reset
    input logic [31:0] a,        // Input a
    input logic [31:0] b,        // Input b
    input logic a_sel,           // Select one byte from A
    input logic b_sel,           // Select one 2-byte word from B
    input logic [1:0] shift_sel, // Select output from shifter
    input logic upd_prod,        // Update the product register
    input logic clr_prod,        // Clear the product register
    output logic [63:0] product  // Miltiplication product
);

// Put your code here
// ------------------
logic [15:0] mux2to1a;
logic [15:0] mux2to1b;
logic [31:0] mul;
logic [63:0] shift0;
logic [63:0] shift16;
logic [63:0] shift32;
logic [63:0] mux4to1;
logic [63:0] adder;
always_comb begin
    if(a_sel==1'b1)begin
         mux2to1a=a[31:16];
    end
    else begin
         mux2to1a=a[15:0];
    end
    
    if(b_sel==1'b1)begin
         mux2to1b=b[31:16];
    end
    else begin
         mux2to1b=b[15:0];
    end
    
    mul=mux2to1a*mux2to1b;
    
    shift0=mul;
    
    shift16= mul << 16;
    shift32= mul << 32;
    
    if(shift_sel[0]==1'b0&&shift_sel[1]==1'b0)begin
        mux4to1=shift0;
    end
    else if(shift_sel[0]==1'b1&&shift_sel[1]==1'b0)begin
        mux4to1=shift16;
    end
    else if(shift_sel[0]==1'b0&&shift_sel[1]==1'b1)begin
        mux4to1=shift32;
    end
    else begin
        mux4to1=0;
    end
    
    adder=mux4to1+product;
    
end

always_ff @(posedge clk, posedge reset)begin
                if(reset)begin
                    product<=0;
                end
                
                else begin
                    if(upd_prod==1'b1)begin
                        product<=adder;
                    end
                    else begin
                        product<=product;
                    end     
                    
                    if(clr_prod==1'b1)begin
                        product<=0;
                    end
                    else begin
                        product<=product;
                    end
                end
    end
// End of your code

endmodule

试验台：

// 32X32 Multiplier test template
module mult32x32_tb;

logic clk;            // Clock
logic reset;          // Reset
logic start;          // Start signal
logic [31:0] a;       // Input a
logic [31:0] b;       // Input b
logic busy;           // Multiplier busy indication
logic [63:0] product; // Miltiplication product

// Put your code here
// ------------------

mult32x32 uut(
    .busy(busy),
    .product(product),
    .clk(clk),
    .reset(reset),
    .start(start),
    .a(a),
    .b(b)
);

initial begin
    clk=1'b1;
end
always begin
    #1 clk=~clk;
end

initial begin
    reset=1'b1;
    a=0;
    b=0;
    start=1'b0;
    repeat (4) begin
        @(posedge clk);
    end
    reset=1'b0;
    @(posedge clk);
    a=32'd211578794;
    b=32'd212209639;
    start=1'b1;
    #2;
    start=1'b0;
    @(negedge busy);
end
// End of your code

endmodule

---

你的逻辑有缺陷。你的代码总是至少执行你的2个

产品中的一个是的，但它只是复制粘贴的代码，所以你可以运行tb唯一可能是编码错误而不是错误的东西是在第一部分，但100%我认为这是某种错误，因为它运行得很好，就像2天前一样，非常复杂
// 32X32 Iterative Multiplier template
module mult32x32 (
    input logic clk,            // Clock
    input logic reset,          // Reset
    input logic start,          // Start signal
    input logic [31:0] a,       // Input a
    input logic [31:0] b,       // Input b
    output logic busy,          // Multiplier busy indication
    output logic [63:0] product // Miltiplication product
);
// Put your code here
// ------------------
        
 logic a_sel;       
 logic b_sel;         
 logic [1:0] shift_sel; 
 logic upd_prod;      
 logic clr_prod; 
 
mult32x32_fsm fsm(
    .busy(busy),
    .a_sel(a_sel),
    .b_sel(b_sel),
    .shift_sel(shift_sel),
    .upd_prod(upd_prod),
    .clr_prod(clr_prod),
    .clk(clk),
    .reset(reset),
    .start(start)
    );
mult32x32_arith arith(
    .product(product),
    .clk(clk),
    .reset(reset),
    .a(a),
    .b(b),
    .a_sel(a_sel),
    .b_sel(b_sel),
    .shift_sel(shift_sel),
    .upd_prod(upd_prod),
    .clr_prod(clr_prod)
);

// End of your code
endmodule

// 32X32 Multiplier test template
module mult32x32_tb;

logic clk;            // Clock
logic reset;          // Reset
logic start;          // Start signal
logic [31:0] a;       // Input a
logic [31:0] b;       // Input b
logic busy;           // Multiplier busy indication
logic [63:0] product; // Miltiplication product

// Put your code here
// ------------------

mult32x32 uut(
    .busy(busy),
    .product(product),
    .clk(clk),
    .reset(reset),
    .start(start),
    .a(a),
    .b(b)
);

initial begin
    clk=1'b1;
end
always begin
    #1 clk=~clk;
end

initial begin
    reset=1'b1;
    a=0;
    b=0;
    start=1'b0;
    repeat (4) begin
        @(posedge clk);
    end
    reset=1'b0;
    @(posedge clk);
    a=32'd211578794;
    b=32'd212209639;
    start=1'b1;
    #2;
    start=1'b0;
    @(negedge busy);
end
// End of your code

endmodule

always_ff @(posedge clk, posedge reset) begin
    if (reset) begin
        product<=0;
    end else if (upd_prod) begin
        product<=adder;
    end else if (clr_prod) begin
        product<=0;
    end
end