Verilog状态机实现交通灯控制

状态机

在一些应用中，通常希望产生任意的状态序列，并且每个状态停留任意时间。采用状态机的设计思想实现。
举例：交通灯

状态表

状态图

输出

代码实现

lights[5:0]：GYR_GYR
哪个亮，对应位置1

功能模块

  module traffic_fsm (lights, clk, rst);
    input clk, rst;
    output [5:0] lights;
    wire clk, rst;
    reg [5:0] lights;
    
    // define reg
    reg [2:0] curr_st;
    reg [2:0] next_st;
    reg [3:0] count;
    // define state
    parameter s0 = 3'b000;
    parameter s1 = 3'b001;
    parameter s2 = 3'b010;
    parameter s3 = 3'b011;
    parameter s4 = 3'b100;
    parameter s5 = 3'b101;
    // define lights
    parameter light0 = 6'b100_001;
    parameter light1 = 6'b100_010;
    parameter light2 = 6'b100_100;
    parameter light3 = 6'b001_100;
    parameter light4 = 6'b010_100;
    parameter light5 = 6'b100_100;
    // define time delay
    parameter delay5 = 5;
    parameter delay1 = 1;
    
    // 产生一个可能的状态变化
    always @ (posedge clk or negedge rst) begin
      if (!rst) begin
                 curr_st <= s0;
                 count <= 0;
               end
      else      
 //                curr_st = next_st;  
          begin
            if (curr_st == s0 | curr_st == s3)
              if (count < delay5 - 1) 
                  count <= count + 1;
              else begin
                     curr_st <= next_st;
                     count <= 0;
                   end
            else if (curr_st == s1 | curr_st == s2 | curr_st == s4 | curr_st == s5) begin
                     curr_st <= next_st;
                     count <= 0;
                   end
          end
    end
    // 产生下一个状态的组合逻辑 
    always @ (curr_st) begin
        case (curr_st)
          s0:
                next_st <= s1;
          s1: 
                next_st <= s2;
          s2: 
                next_st <= s3;
          s3: 
                next_st <= s4;
          s4: 
                next_st <= s5;
          s5: 
                next_st <= s0;
          default: begin
                next_st <= s0;
              end
      endcase
    end
    // 产生输出lights的组合逻辑
    always @ (posedge clk or negedge rst) begin
      if (!rst) lights = light0;
      else
        case (curr_st)
          s0: lights = light0;             
          s1: lights = light1;
          s2: lights = light2;
          s3: lights = light3;
          s4: lights = light4;
          s5: lights = light5;
          default: lights = light0;
        endcase
    end          
  endmodule

测试模块

// testbench of 'traffic_fsm'
module traffic_fsm_tb;
  reg clk, rst;
  wire [5:0] lights;
  traffic_fsm u1 (.lights(lights), .clk(clk), .rst(rst));
  initial begin
    clk = 0;
    rst = 0;
    #10 rst = 1;
    #80 rst = 0;
    #20 rst = 1;
  end
  always #5 clk = ~clk;
endmodule

仿真波形

在第一个always块中产生下一个状态，写的不简洁