有限状态机问题，组合逻辑部分

Question

第一种写法为什么会出问题

module top_module(
    input in,
    input [9:0] state,
    output [9:0] next_state,
    output out1,
    output out2);

    parameter S0 = 10'b0000000001,
        S1 = 10'b0000000010,
        S2 = 10'b0000000100,
        S3 = 10'b0000001000,
        S4 = 10'b0000010000,
        S5 = 10'b0000100000,
        S6 = 10'b0001000000,
        S7 = 10'b0010000000,
        S8 = 10'b0100000000,
        S9 = 10'b1000000000;
    always @(*) begin
        case(state)
            S0: next_state = in?S1:S0;
            S1: next_state = in?S2:S0;
            S2: next_state = in?S3:S0;
            S3: next_state = in?S4:S0;
            S4: next_state = in?S5:S0;
            S5: next_state = in?S6:S8;
            S6: next_state = in?S7:S9;
            S7: next_state = in?S7:S0;
            S8: next_state = in?S1:S0;
            S9: next_state = in?S1:S0;
        endcase
    end
    
    assign out1 = (state == S8) || (state == S9);
    assign out2 = (state == S7) || (state == S9);
    
endmodule

module top_module(
    input in,
    input [9:0] state,
    output [9:0] next_state,
    output out1,
    output out2);
    
    parameter S0 = 4'd0;
    parameter S1 = 4'd1;
    parameter S2 = 4'd2;
    parameter S3 = 4'd3;
    parameter S4 = 4'd4;
    parameter S5 = 4'd5;
    parameter S6 = 4'd6;
    parameter S7 = 4'd7;
    parameter S8 = 4'd8;
    parameter S9 = 4'd9;
    
    assign next_state[0] = ~in & (state[S0] | state[S1] | state[S2] | state[S3] | state[S4] | state[S7] | state[S8] | state[S9]);
    assign next_state[1] = in & (state[S0] | state[S8] | state[S9]);
    assign next_state[2] = in & state[S1];
    assign next_state[3] = in & state[S2];
    assign next_state[4] = in & state[S3];
    assign next_state[5] = in & state[S4];
    assign next_state[6] = in & state[S5];
    assign next_state[7] = in & (state[S6] | state[S7]);
    assign next_state[8] = ~in & state[S5];
    assign next_state[9] = ~in & state[S6];
    
    assign out1 = (state[S8] | state[S9]);
    assign out2 = (state[S7] | state[S9]);
    
endmodule

Answer 1

手机上看的费劲，没仔细分析第一种的逻辑。但是有个错误需要你更正。
组合逻辑下 case 条件要写全，你的代码中没有写全。需要加个 default 。

 
module top_module(
    input in,
    input [9:0] state,
    output [9:0] next_state,
    output out1,
    output out2);
 reg [3:0] i;

    parameter S0 = 10'b0000000001,
        S1 = 10'b0000000010,
        S2 = 10'b0000000100,
        S3 = 10'b0000001000,
        S4 = 10'b0000010000,
        S5 = 10'b0000100000,
        S6 = 10'b0001000000,
        S7 = 10'b0010000000,
        S8 = 10'b0100000000,
        S9 = 10'b1000000000,
        S10 = 10'b0000000000;
    always @(*) begin
       next_state=S10;
       for(i=0;i<10;i=i+1)begin
        case(state&(1<<i))
            S0: next_state = next_state|(in?S1:S0);
            S1: next_state = next_state|(in?S2:S0);
            S2: next_state = next_state|(in?S3:S0);
            S3: next_state = next_state|(in?S4:S0);
            S4: next_state = next_state|(in?S5:S0);
            S5: next_state = next_state|(in?S6:S8);
            S6: next_state = next_state|(in?S7:S9);
            S7: next_state = next_state|(in?S7:S0);
            S8: next_state = next_state|(in?S1:S0);
            S9: next_state = next_state|(in?S1:S0);
            default:next_state = next_state|S10;
        endcase
        
     end
    end

    assign out1 = (state & S8) == S8 || (state & S9) == S9;
    assign out2 = (state & S7) == S7 || (state & S9) == S9;
    
    //assign out1 = (state == S8) || (state == S9);
    //assign out2 = (state == S7) || (state == S9);
    
endmodule