Verilog :此FF/Latch将在优化过程中进行修剪

Question

我正在使用Xilinx ISE项目导航器(P.28d)为自动售货机编写verilog代码。我的代码出了什么问题？这么多警告，但没有错误。

module vend(
    input clk,
    input reset,
    input cancel,
    input sel1,
    input sel2,
    inout [6:0] money,
    input Rs_10,
    input Rs_20,
    output reg product,
    output reg [6:0] change,
    output reg [6:0] returns
    ); 
     wire wait_1,wait_2;
     reg st_1,st_2,st_3,st_4;
     wire pr_1,pr_2;
     reg nx_1,nx_2;
     reg snacks,coffee;
     reg snack_c,coffee_c;
     reg [6:0] money_count;

always @(posedge clk)

begin   : count
if (sel1==1)
    begin
    if(pr_1==1)
          begin
    nx_1<=wait_1;

          if((Rs_10) & ~(Rs_20))
    begin
    nx_1<=st_1;
    money_count=(money_count+7'b0001010);
          if(money_count>=7'b0011110)
    begin
                                    nx_1<=snacks;
    change<=({0,money_count}-7'b0011110);
                                    snack_c<=snack_c-1;
    disable count;
    end
    nx_1<=wait_1;
    if(cancel==1)
    begin
    returns<=({0,money_count});
    disable count;
    end

    end
    if(~(Rs_10) &(Rs_20))
    begin

    nx_1<=st_2;
    money_count=(money_count+7'b0010100);
    if(money_count>=7'b0011110)
    begin
                                    nx_1<=snacks;
    change<=({0,money_count}-7'b0011110);
                                    snack_c<=snack_c-1;
    disable count;
          end
                                    nx_1<=wait_1;
    if(cancel==1)
    begin
          returns<=({0,money_count});
    disable count;
    end
    end

    end
    end 
    else
            begin
                snack_c<=1'd4;
                nx_1<=reset;
                product<=0;
            end


          if (sel2==1)
    begin
    if(pr_2==1)
    begin
    nx_2<=wait_2;

    if((Rs_10) & ~(Rs_20))
    begin
    nx_2<=st_3;
    money_count=(money_count+7'b0001010);
    if(money_count>=7'b0101000)
    begin
    nx_2<=coffee;
    change<=({0,money_count}-7'b0101000);
    coffee_c<=coffee_c-1;
    disable count;
    end
    nx_2<=wait_2;
    if(cancel==1)
    begin
    returns<={0,money_count};
    disable count;

    end

    end
          if(~(Rs_10) &(Rs_20))
    begin

    nx_2<=st_4;
                                money_count=money_count+7'b0010100;
    if(money_count>=7'b0101000)
    begin
    nx_2<=coffee;
    change<=({0,money_count}-7'b0101000);
    coffee_c<=coffee_c-1;
    disable count;
    end
    nx_2<=wait_2;
    if(cancel==1)
    begin
    returns<=({0,money_count});
    disable count;

    end
    end

    end
    end 
        else
            begin
                coffee_c<=1'd4;
                nx_2<=reset;
                product<=0;
            end

end 
endmodule

我收到的一些警告

Xst:1710 - FF/Latch <returns_0> (without init value) has a constant value of 0 in block <vend>. This FF/Latch will be trimmed during the optimization process.
Xst:1710 - FF/Latch <change_0> (without init value) has a constant value of 0 in block <vend>. This FF/Latch will be trimmed during the optimization process.
Xst:2677 - Node <money_count_0> of sequential type is unconnected in block <vend>.

Answer 1

看起来这个错误是指这样一个事实：change和returns的MSB总是为0，所以它不会综合逻辑(因为它会无端浪费门)。

你有没有试过模拟这个？

Answer 2

当我模拟并且只有z值时，这是因为我的模块中没有初始块。一定要记住初始化寄存器和变量。

module foo(
     input a,
     output reg b);

    // Runs on startup.
    initial
    begin
        b = 1'b0;
    end
endmodule