HDLbits: ps2data

这一题在上一题基础上多了一个输出，并且这个输出是不需要像上一题考虑出错的情况的，所以只要把输入in按次序排好就可以。我一开始的想法是在状态切换判断的always块里把in赋给out，但是不正确，代码如下：

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

    parameter byte1=4'b0001, byte2=4'b0010, byte3=4'b0100, byte_fault=4'b1000;
    reg [23:0] out_bytes_reg;
    
    reg [3:0] state,next_state;

    // State transition logic (combinational)
    always@(*)begin
        case(state)
            byte1:  begin
                next_state = byte2; out_bytes_reg[23:16] = in[7:0];
            end
            byte2: begin
                next_state = byte3; out_bytes_reg[15:8] = in[7:0];
            end
            byte3: begin
                next_state = in[3]?byte1:byte_fault;
                out_bytes_reg[7:0] = in[7:0];
            end
            byte_fault: begin
                next_state = in[3]?byte1:byte_fault; 
            end
            default: next_state = byte1;
        endcase
    end

    // State flip-flops (sequential)
    always@(posedge clk)begin
        if(reset)
            state <= byte_fault;
        else
            state <= next_state;
    end
    
    // Output logic
    assign done = (state == byte3);
	assign out_bytes = out_bytes_reg;

endmodule

看了大佬的写法，又改了思路，用一个always块专门实现这部分功能，如下：

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

    // FSM from fsm_ps2

    // New: Datapath to store incoming bytes.
    parameter byte1=4'b0001, byte2=4'b0010, byte3=4'b0100, byte_fault=4'b1000;

    
    reg [3:0] state,next_state;

    // State transition logic (combinational)
    always@(*)begin
        case(state)
            byte1: next_state = byte2;
            byte2: next_state = byte3;
            byte3: next_state = in[3]?byte1:byte_fault;
            byte_fault: next_state = in[3]?byte1:byte_fault; 
            default: next_state = byte1;
        endcase
    end

    // State flip-flops (sequential)
    always@(posedge clk)begin
        if(reset)
            state <= byte_fault;
        else
            state <= next_state;
    end
    
   always@(posedge clk)begin
        if(reset)
            out_bytes <= 24'd0;
        else
            out_bytes <= {out_bytes[15:0],in[7:0]};
    end
    
    // Output logic
    assign done = (state == byte3);


endmodule