Verilog -- 并行2bit输入序列检测器

Verilog -- 并行2bit输入序列检测器

@(verilog)

乐鑫2020笔试题：

描述：模块输入口是并行的2bit，实现对((1011001)_2)的序列检测，输入数据顺序为高位2bit先输入，当检测到序列时输出一拍高电平脉冲，用verilg描述。

方法一：状态机

采用状态机描述，先列出状态转移表，跟单bit输入不同的是，这里的输入是并行的2bit：

stateinput	00	01	10	11
0	0	1	10	1
1	0	101	10	1
10	0	1	10	1011
101	0	101	10110	1
1011	101100	101	10	1
10110	0	1011001	10	1011
101100	0	1	10	1
1011001	0	101	10	1

以及输出的状态转移表：

stateinput	00	01	10	11
0	0	0	0	0
1	0	0	0	0
10	0	0	0	0
101	0	0	0	0
1011	0	0	0	0
10110	0	1	0	0
101100	0	0	1	1
1011001	0	0	0	0

通过分析可以发现，1011001和1状态是完全等价的，因此可以归并，并且其他状态的转移也有相同的，也可以放到一起：
状态转移表：

stateinput	00	01	10	11
0101100	0	1	10	1
1	0	101	10	1
1010110	0	1	10	1011
101	0	101	10110	1
1011	101100	101	10	1

输出转移表:

stateinput	00	01	10	11
01101011011	0	0	0	0
10110	0	1	0	0
101100	0	0	1	1

Verilog代码：

`timescale 1ns/1ps

module two_bit_input_seq_detector
(
input                                   clk,
input                                   rst_n,
input        [1:0]                      data,
output reg                              success
);

reg [2:0] current_state;
reg [2:0] next_state;

parameter S0      =  3'b000,
          S1      =  3'b001,
          S10     =  3'b011,
          S101    =  3'b010,
          S1011   =  3'b110,
          S10110  =  3'b111,
          S101100 =  3'b101;

always @(posedge clk or negedge rst_n) begin
    if(!rst_n) current_state <= 3'b0;
    else current_state <= next_state;
  end

always @(*) 
  case(current_state)
    S0,S101100: 
            case(data)
              2'b00: next_state = S0;
              2'b01: next_state = S1;
              2'b10: next_state = S10;
              2'b11: next_state = S1;
            endcase
    S1:     case(data)
              2'b00: next_state = S0;
              2'b01: next_state = S101;
              2'b10: next_state = S10;
              2'b11: next_state = S1;
            endcase
    S10,S10110:
            case(data)
              2'b00: next_state = S0;
              2'b01: next_state = S1;
              2'b10: next_state = S10;
              2'b11: next_state = S1011;
            endcase   
    S101:   case(data)
              2'b00: next_state = S0;
              2'b01: next_state = S101;
              2'b10: next_state = S10110;
              2'b11: next_state = S1;
            endcase
    S1011:  case(data)
              2'b00: next_state = S101100;
              2'b01: next_state = S101;
              2'b10: next_state = S10;
              2'b11: next_state = S1;
            endcase
    default:         next_state = S0;
  endcase

  
always @(posedge clk or negedge rst_n) begin
    if(!rst_n) begin
      success <= 0;
    end else begin
      case(current_state)
        S0,S1,S10,S101,S1011:        success <= 0;
        S10110 : if(data == 2'b01)   success <= 1;
                 else                success <= 0;
        S101100: if(data[1] == 1'b1) success <= 1;
                 else                success <= 0;
        default:                     success <= 0;
      endcase
    end
  end

endmodule

testbench:

`timescale 1ns/1ps

module two_bit_input_seq_detector_tb();


reg         clk;
reg         rst_n;
reg   [1:0] data;

wire     success;
reg [127:0] seq;


always #1 clk = ~clk;
initial begin
  clk = 0;
  data = 0;
  rst_n = 1;
  #4 rst_n = 0; #2 rst_n = 1;

  seq = 0;
  while(1) begin
    @(posedge clk) begin 
      data <= $random%4;
      seq <= (seq<<2) + data;
    end
  end

end



two_bit_input_seq_detector U_2BIT_INPUT_SEQ_DETECTOR_0
(  .clk     ( clk     ),
   .rst_n   ( rst_n   ),
   .data    ( data    ),
   .success ( success ));


initial begin
  $fsdbDumpvars();
  $fsdbDumpMDA();
  $dumpvars();
  #1000 $finish;
end

endmodule

波形图：

放大来看：

可以看到，功能正确。

方法二：移位寄存器

使用移位寄存器解决序列检测问题是真的简单粗暴，直接上代码：

`timescale 1ns/1ps

module two_bit_input_seq_detector_v2
(
input                                   clk,
input                                   rst_n,
input        [1:0]                      data,
output                                  success
);

parameter DETECTOR = 7'b1011001;
reg [7:0] fifo;

always @(posedge clk or negedge rst_n) begin
    if(!rst_n) begin
      fifo <= 8'b0;
    end else begin
      fifo <= {fifo[5:0],data};
    end
end

assign success = (fifo[7:1]==DETECTOR || fifo[6:0]==DETECTOR) ? 1:0;

endmodule

testbench:

`timescale 1ns/1ps

module two_bit_input_seq_detector_v2_tb();


reg         clk;
reg         rst_n;
reg   [1:0] data;

wire     success;
reg [127:0] seq;


always #1 clk = ~clk;
initial begin
  clk = 0;
  data = 0;
  rst_n = 1;
  #4 rst_n = 0; #2 rst_n = 1;

  seq = 0;
  while(1) begin
    @(posedge clk) begin 
      data <= $random%4;
      seq <= (seq<<2) + data;
    end
  end

end




two_bit_input_seq_detector_v2 U_TWO_BIT_INPUT_SEQ_DETECTOR_V2_0
(  .clk     ( clk     ),
   .rst_n   ( rst_n   ),
   .data    ( data    ),
   .success ( success ));


initial begin
  $fsdbDumpvars();
  $fsdbDumpMDA();
  $dumpvars();
  #1000 $finish;
end

endmodule

仿真波形：

功能正确！