led跑马灯多种方法（移位法，位拼接法，调用模块法，位移及位拼接语法，testbench的理解，源文件的存储路径，计数器的个数，调用模块的方式）

module led_run1(    //移位法
    clk,
    reset,
    led  
    );
    input clk;
    input reset;
    output reg [7:0]led;
    
    reg [5:0]counter1;
    always@( posedge clk or negedge reset )begin
        if( reset == 1'd0)
        counter1 <= 1'd0;
        else if(counter1 == 4 )　　　　这两个虽然赋值语句一样，但是不能把判断语句合并。
        counter1 <=1'd0;
        else
        counter1 <= counter1 + 1'd1;     
    end
    
    always@(posedge clk or negedge reset) begin
        if( reset == 1'd0)
        led <= 8'b0000_0001;
        else if(counter1 == 4 )begin
            if(led == 8'b1000_0000)
            led <= 8'b0000_0001;　　　　　　//最后一位的处理
            else
            led <= led << 1'd1 ;  　　　　//注意左移几位的语法，应该怎么写
        end
    end
endmodule

module led_run2(    //位拼接法
    clk,
    reset,
    led  
    );
    input clk;
    input reset;
    output reg [7:0]led;
    
    reg [5:0]counter1;
    always@( posedge clk or negedge reset )begin
        if( reset == 1'd0)
        counter1 <= 1'd0;
        else if(counter1 == 4 )
        counter1 <=1'd0;
        else
        counter1 <= counter1 + 1'd1;     
    end
    
    always@(posedge clk or negedge reset) begin
        if( reset == 1'd0)
        led <= 8'b0000_0001;
        else if(counter1 == 4 )begin
            led <= {led[6:0],led[7]};　　　　//位拼接的语法，十分注意
end
    end
endmodule

module led_run4(    //调用模块4-16译码器法
    clk,
    reset,
    led  
    );
    input clk;
    input reset;
    output wire [15:0]led;
    
    reg [2:0]counter1;
    reg [3:0]counter4;　　　　一个用来计数，一个用来译码
    always@( posedge clk or negedge reset )begin
        if( reset == 1'd0)
        counter1 <= 1'd0;
        else if(counter1 == 4 )
        counter1 <=1'd0;
        else
        counter1 <= counter1 + 1'd1;     
    end
    
    always@(posedge clk or negedge reset) begin
        if( reset == 1'd0)
        counter4 <= 8'd1;
        else if(counter1 == 4 )begin
        counter4 <= counter4 + 1'b1;
        end
    end
    
    decoder_4_16 decoder_4_16_run(　　　　　　　　//调用的方法类似于仿真时的例化，存储电路与组合逻辑电路相结合。
               .a(counter4[3]),
               .b(counter4[2]),
               .c(counter4[1]),
               .d(counter4[0]),
               .out(led)
        );
        
endmodule