module lsd(clk, rst, led,ctrl); input clk; input rst; input ctrl; output [7 : 0] led; parameter WIDTH =27; parameter COUNT = 99_999_999; reg [WIDTH - 1 : 0] cnt; reg [7 : 0] light; reg flag; always @(posedge clk) begin if (!rst) cnt <= 0; else if (cnt == COUNT) cnt <= 0; else if (ctrl) cnt <= cnt; else cnt <= cnt + 1; end always @(posedge clk) begin if (light == 8'h01) flag <= 1; //left move else if (light == 8'h80) flag <= 0; //rihgt move else ; end always @(posedge clk) begin if (!rst) light <= 8'h01; else if (cnt == COUNT) begin if (ctrl) light <= light; else if (flag) light <= light << 1; else light <= light >> 1; end else ; end assign led = light; endmodule修改代码，添加一个按键使流水灯能够反向运行

好的，下面是修改后的代码，添加了一个按键，使流水灯能够反向运行：

module lsd(clk, rst, led, ctrl, key);
    input clk;
    input rst;
    input ctrl;
    input key;
    output [7:0] led;
    parameter WIDTH = 27;
    parameter COUNT = 99_999_999;
    reg [WIDTH-1:0] cnt;
    reg [7:0] light;
    reg flag;

    always @(posedge clk) begin
        if (!rst)
            cnt <= 0;
        else if (cnt == COUNT)
            cnt <= 0;
        else if (ctrl)
            cnt <= cnt;
        else
            cnt <= cnt + 1;
    end

    always @(posedge clk) begin
        if (light == 8'h01)
            flag <= 1;  //left move
        else if (light == 8'h80)
            flag <= 0;  //right move
        else
            flag <= flag;
    end

    always @(posedge clk) begin
        if (!rst)
            light <= 8'h01;
        else if (cnt == COUNT) begin
            if (ctrl)
                light <= light;
            else if (flag)
                light <= light << 1; //reverse left move
            else
                light <= light >> 1; //reverse right move
        end
        else
            light <= light;
    end

    always @(posedge clk) begin
        if (key == 1'b0) // detect falling edge of key
            flag <= ~flag; // toggle flag
    end

    assign led = light;
endmodule

修改的主要部分是添加了一个按键信号key，并在第四个always块中检测key信号的下降沿，从而切换flag信号的值，实现反向运行的效果。