FPGA: Basic Getting Started Button Controlling LED Lights

题目概述：
使用按键控制LED灯亮灭.
无按键按下——LED全灭
按下KEYO——Flowing water light effect from right to left
按下KEY1——Flowing water light effect from left to right
按下KEY2——LED闪烁
按下KEY3——LED全亮
编程：

`timescale 1ns / 1ps

module key_led(
    input sys_clk,
    input sys_rst_n,
    input [3:0] key,
    output reg [3:0] led
    );
    
 //定义0.2s计数器 0.2s/20ns=10^7
reg [23:0] cnt; 

[email protected](posedge sys_clk or negedge sys_rst_n)
begin
     if(!sys_rst_n)
     cnt<=0;
     else if(cnt<24'd999_9999)
     cnt<=cnt+1'b1;
     else
     cnt<=0;
end    

reg [1:0] led_control;//4个LED 00 01 10 11

//State transition and state assignment
 [email protected](posedge sys_clk or negedge sys_rst_n)
 begin
        if(!sys_rst_n)
        led_control<=4'b0;
        else if(cnt==24'd999_9999)
        led_control<=led_control+1'b1;
        else
        led_control<=led_control;
 end  
 
 
 [email protected](posedge sys_clk or negedge sys_rst_n)
  begin
  
       if(!sys_rst_n)
       led<=4'b0000;
       
       else if(key[0]==0)
       case(led_control)
       2'b00:led<=4'b1000;
       2'b01:led<=4'b0100;
       2'b10:led<=4'b0010;
       2'b11:led<=4'b0001;
       endcase
       
       else if(key[1]==0)
       case(led_control)
       2'b00:led<=4'b0001;
       2'b01:led<=4'b0010;
       2'b10:led<=4'b0100;
       2'b11:led<=4'b1000;
       endcase
       
       else if(key[2]==0)
       case(led_control)
       2'b00:led<=4'b0000;
       2'b01:led<=4'b1111;
       2'b10:led<=4'b0000;
       2'b11:led<=4'b1111;
       endcase
       
       else if(key[3]==0)
       led<=4'b1111;
       
       else
       led<=4'b0000;     
end   
endmodule

上机实践：

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