HDLBits 答案之 Fsm ps2data

多加一个数据路径。先用三个寄存器寄存一下输入，然后assign组合一下。

module top_module(
    input clk,
    input [7:0] in,
    input reset,    // Synchronous reset
    output [23:0] out_bytes,
    output done); //

    parameter b1=0,b2=1,b3=2,d=3;
    reg [1:0] state,nstate;
    reg [7:0] m1,m2,m3;
    
    always @(posedge clk) begin
        if (reset)
            state<=b1;
        else
            state<=nstate;
    end
    
    always @(*) begin
        case(state)
            b1: nstate=in[3]?b2:b1;
            b2: nstate=b3;
            b3: nstate=d;
            d: nstate=in[3]?b2:b1;
            default nstate=b1;
        endcase
    end
    
    always @(posedge clk) begin
        if (reset)
            m1<=7'b0;
    else if (nstate==b2)
            m1<=in;
    else
            m1<=m1;
    end
    
    always @(posedge clk) begin
    if (reset)
            m2<=7'b0;
    else if (nstate==b3)
            m2<=in;
    else
            m2<=m2;
    end
    
    always @(posedge clk) begin
    if (reset)
            m3<=7'b0;
    else if (nstate==d)
            m3<=in;
    else
            m3<=m3;
    end
    
    
    
    assign done=(state==d);
    assign out_bytes={m1,m2,m3};
    


endmodule