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 resetoutput [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@(*)begincase(state)byte1:  beginnext_state = byte2; out_bytes_reg[23:16] = in[7:0];endbyte2: beginnext_state = byte3; out_bytes_reg[15:8] = in[7:0];endbyte3: beginnext_state = in[3]?byte1:byte_fault;out_bytes_reg[7:0] = in[7:0];endbyte_fault: beginnext_state = in[3]?byte1:byte_fault; enddefault: next_state = byte1;endcaseend// State flip-flops (sequential)always@(posedge clk)beginif(reset)state <= byte_fault;elsestate <= next_state;end// Output logicassign 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 resetoutput 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@(*)begincase(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;endcaseend// State flip-flops (sequential)always@(posedge clk)beginif(reset)state <= byte_fault;elsestate <= next_state;endalways@(posedge clk)beginif(reset)out_bytes <= 24'd0;elseout_bytes <= {out_bytes[15:0],in[7:0]};end// Output logicassign done = (state == byte3);endmodule