牛客刷题＜25＞输入序列连续的序列检测

题目：输入序列连续的序列检测_牛客题霸_牛客网

解法一：最容易想到的状态机

`timescale 1ns/1ns
module sequence_detect(
    input clk,
    input rst_n,
    input a,
    output reg match
);
    parameter IDLE = 3'd0;
    parameter s0 = 3'd1;
    parameter s1 = 3'd2;
    parameter s2 = 3'd3;
    parameter s3 = 3'd4;
    parameter s4 = 3'd5;
    parameter s5 = 3'd6;
    parameter s6 = 3'd7;
    
    reg [2:0] state,next_state;
    reg flag;
    always@(*)begin
        if(!rst_n)begin
            state <= IDLE;
            next_state <= IDLE;
        end
        else begin
            case(state)
               IDLE:begin
                   if(a==0)
                       next_state <= s0;
                   else
                       next_state <= IDLE;
               end
                s0: begin
                    if(a==1)
                       next_state <= s1;
                   else
                       next_state <= s0;
                end
                s1: begin
                    if(a==1)
                       next_state <= s2;
                   else
                       next_state <= s0;
                end
                s2: begin
                    if(a==1)
                       next_state <= s3;
                   else
                       next_state <= s0;
                end
                s3: begin
                    if(a==0)
                       next_state <= s4;
                   else
                       next_state <= IDLE;
                end
                s4: begin
                    if(a==0)
                       next_state <= s5;
                   else
                       next_state <= s1;
                end
                s5: begin
                    if(a==0)
                       next_state <= s6;
                   else
                       next_state <= s1;
                end
                s6: begin
                    if(a==1)
                       next_state <= s1;
                   else
                       next_state <= s0;
                end
                default : next_state <= IDLE;
            endcase
        end
    end
    always@(posedge clk or negedge rst_n)begin
        if(!rst_n)
            state <= IDLE;
        else
            state <= next_state;
    end
    always@(posedge clk or negedge rst_n)begin
        if(!rst_n)
            flag <= 1'b0;
        else if(state==s6 && a)
            flag <= 1'b1;
        else
            flag <= 0;
    end
    always@(posedge clk or negedge rst_n)begin
        if(!rst_n)
           match <= 1'b0;
        else
           match <= flag;
    end
endmodule

解法二：同样状态机，三目运算符写法   match <= state==EIGHT;也是三目运算符写法

`timescale 1ns/1ns
module sequence_detect(
	input clk,
	input rst_n,
	input a,
	output reg match
	);
    parameter ZERO=0,ONE=1,TWO=2,THREE=3,FOUR=4,FIVE=5,SIX=6,SEVEN=7,EIGHT=8;
    reg [3:0] state,nstate;
    always@(posedge clk or negedge rst_n)begin
        if(~rst_n)
            state <= ZERO;
        else
            state <= nstate;
    end
    always@(*)begin
        case(state)
            ZERO   :nstate = a? ZERO : ONE;
            ONE    :nstate = a? TWO  : ONE;
            TWO    :nstate = a? THREE: ONE;
            THREE  :nstate = a? FOUR : ONE;
            FOUR   :nstate = a? ZERO : FIVE;
            FIVE   :nstate = a? TWO  : SIX;
            SIX    :nstate = a? TWO  : SEVEN;
            SEVEN  :nstate = a? EIGHT  : ONE;
            EIGHT  :nstate = a? THREE  : ONE;
            default: nstate = ZERO;
        endcase
    end
    always@(posedge clk or negedge rst_n)begin
        if(!rst_n)
            match <= 0;
        else
            match <= state==EIGHT;
    end
endmodule

解法三：使用位拼接运算

`timescale 1ns/1ns
module sequence_detect(
	input clk,
	input rst_n,
	input a,
	output reg match
	);
    reg [7:0] a_r;
    always@(posedge clk or negedge rst_n)begin
        if(!rst_n)begin
            a_r <= 1'b0;
        end
        else begin
            a_r <= {a_r[6:0],a};
        end
    end
    always@(posedge clk or negedge rst_n)begin
        if(!rst_n)begin
            match <= 1'b0;
        end
        else begin
            match <= a_r==8'b01110001;
        end
    end
endmodule

解法四：解法三的简化

`timescale 1ns/1ns
module sequence_detect(
    input clk,
    input rst_n,
    input a,
    output reg match
);
    reg [7:0] a_reg;
    always@(posedge clk or negedge rst_n)begin
        if(!rst_n)begin
            a_reg <= 8'd0;
            match <= 1'b0;
        end
        else begin
            a_reg <= {a_reg[6:0],a};
            if(a_reg == 8'b0111_0001)
                match <= 1'b1;
            else
                match <= 1'b0;
        end
    end
endmodule