module liushui(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，使按键为1时流水灯能够单向运行

可以添加一个输入端口 button，用来输入按键信号。当 button 为 1 时，流水灯单向循环运行；否则，流水灯双向循环运行。修改后的代码如下：

module liushui(clk, rst, led, button);
    input clk;
    input rst;
    input button;
    output [7:0] led;
    
    parameter WIDTH = 27;
    parameter COUNT = 99_999_999;
    
    reg [WIDTH - 1:0] cnt;
    reg [7:0] light;
    reg [1:0] dir; // 0: right, 1: left
    
    always @(posedge clk) begin
        if (!rst)
            cnt <= 0;
        else if (cnt == COUNT)
            cnt <= 0;
        else if (button)
            cnt <= cnt;
        else
            cnt <= cnt + 1;
    end
    
    always @(posedge clk) begin
        if (light == 8'h01) // left move
            dir <= 1;
        else if (light == 8'h80) // right move
            dir <= 0;
    end
    
    always @(posedge clk) begin
        if (!rst)
            light <= 8'h01;
        else if (cnt == COUNT)
            if (button)
                if (dir)
                    light <= light << 1; // left move
                else
                    light <= light >> 1; // right move
            else
                if (dir)
                    light <= light << 1; // left move
                else if (light == 8'h80)
                    light <= 8'h01; // reset to 8'h01
                else
                    light <= light >> 1; // right move
    end
    
    assign led = light;
    
endmodule