Verilog有限狀態機(5)

HDLBits鏈接

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前言

今天繼續更新狀態機小節的習題。

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題庫

題目描述1：

第一道題目比較容易，題目中的in信號包含了一個起始位（0），8個數據位和一個停止位（1），開始in為1，也就是IDLE狀態，當in為0時，進入START狀態，然后經過8個周期，如果in為1，則進入STOP狀態，接著如果in為0，進入第二輪START狀態，否則進入IDLE狀態。

這里我用了很多個狀態，實際上可以用計數器來代替中間的8個狀態，這里是8個周期，如果是100個、200個周期，那么需要100個、200個狀態，顯然不現實。這道題目是三道題目中的基礎題，大家不用考慮那么多，直接完成就好了。

Solution1：

module top_module(input clk,input in,input reset, // Synchronous resetoutput done ); parameter [3:0] START = 4'd0;parameter [3:0] ONE = 4'd1;parameter [3:0] TWO = 4'd2;parameter [3:0] THREE = 4'd3;parameter [3:0] FOUR = 4'd4;parameter [3:0] FIVE = 4'd5;parameter [3:0] SIX = 4'd6;parameter [3:0] SEVEN = 4'd7;parameter [3:0] EIGHT = 4'd8;parameter [3:0] STOP = 4'd9;parameter [3:0] IDLE = 4'd10;parameter [3:0] WAIT = 4'd11;reg [3:0] state,next_state;always @(*)begincase(state)START:beginnext_state <= ONE;endONE:beginnext_state <= TWO;endTWO:beginnext_state <= THREE;endTHREE:beginnext_state <= FOUR;endFOUR:beginnext_state <= FIVE;endFIVE:beginnext_state <= SIX;endSIX:beginnext_state <= SEVEN;endSEVEN:beginnext_state <= EIGHT;endEIGHT:beginif(in)beginnext_state <= STOP;endelse beginnext_state <= WAIT;endendSTOP:beginif(in)beginnext_state <= IDLE;endelse beginnext_state <= START;endendWAIT:beginif(in)beginnext_state <= IDLE;endelse beginnext_state <= WAIT;endendIDLE:beginif(~in)beginnext_state <= START;endelse beginnext_state <= IDLE;endendendcaseendalways @(posedge clk)beginif(reset)beginstate <= IDLE;endelse beginstate <= next_state;endendassign done = (state == STOP);endmodule

題目描述2：

這道題目是上一道題目的擴展，不僅需要輸出done信號，還需要輸出數據。

Solution2：

/* way 1*/ module top_module(input clk,input in,input reset, // Synchronous resetoutput [7:0] out_byte,output done ); //parameter [3:0] START = 4'd0;parameter [3:0] ONE = 4'd1;parameter [3:0] TWO = 4'd2;parameter [3:0] THREE = 4'd3;parameter [3:0] FOUR = 4'd4;parameter [3:0] FIVE = 4'd5;parameter [3:0] SIX = 4'd6;parameter [3:0] SEVEN = 4'd7;parameter [3:0] EIGHT = 4'd8;parameter [3:0] STOP = 4'd9;parameter [3:0] IDLE = 4'd10;parameter [3:0] WAIT = 4'd11;reg [3:0] state,next_state;reg [7:0] par_in;always @(*)begincase(state)START:beginnext_state <= ONE;par_in[0] <= in;endONE:beginnext_state <= TWO;par_in[1] <= in;endTWO:beginnext_state <= THREE;par_in[2] <= in;endTHREE:beginnext_state <= FOUR;par_in[3] <= in;endFOUR:beginnext_state <= FIVE;par_in[4] <= in;endFIVE:beginnext_state <= SIX;par_in[5] <= in;endSIX:beginnext_state <= SEVEN;par_in[6] <= in;endSEVEN:beginnext_state <= EIGHT;par_in[7] <= in;endEIGHT:beginif(in)beginnext_state <= STOP;endelse beginnext_state <= WAIT;endendSTOP:beginif(in)beginnext_state <= IDLE;endelse beginnext_state <= START;endendWAIT:beginif(in)beginnext_state <= IDLE;endelse beginnext_state <= WAIT;endendIDLE:beginif(~in)beginnext_state <= START;endelse beginnext_state <= IDLE;endendendcaseendalways @(posedge clk)beginif(reset)beginstate <= IDLE;endelse beginstate <= next_state;endendassign done = (state == STOP);assign out_byte = (state == STOP) ? par_in : 8'd0;endmodule/* way 2 */ module top_module(input clk,input in,input reset, // Synchronous resetoutput [7:0] out_byte,output done ); parameter IDLE = 3'd0, START = 3'd1, DATA = 3'd2;parameter STOP = 3'd3, WAIT = 3'd4;reg [3:0] current_state;reg [3:0] next_state;reg [3:0] counter;reg [7:0] par_in;// Use FSM from Fsm_serialalways @(*)begincase(current_state)IDLE:beginif(~in)beginnext_state = START;endelse beginnext_state = IDLE;endendSTART:beginnext_state = DATA;endDATA:beginif(counter == 4'd8)beginnext_state = in? STOP:WAIT;endelse beginnext_state = DATA;endendSTOP:beginnext_state = in? IDLE:START;endWAIT:beginnext_state = in? IDLE:WAIT;enddefault:beginnext_state = IDLE;endendcaseendalways @(posedge clk)beginif(reset)begincurrent_state <= IDLE;endelse begincurrent_state <= next_state;endendalways @(posedge clk)beginif(reset)begindone <= 1'd0;out_byte <= 8'd0;counter <= 4'd0;endelse begincase(next_state)IDLE:begindone <= 1'd0;out_byte <= 8'd0;counter <= 4'd0;endSTART:begindone <= 1'd0;out_byte <= 8'd0;counter <= 4'd0;endDATA:begindone <= 1'd0;out_byte <= 8'd0;par_in[counter] <= in;counter <= counter + 1'd1;endSTOP:begindone <= 1'd1;out_byte <= par_in;counter <= 4'd0;endWAIT:begindone <= 1'd0;out_byte <= 8'd0;counter <= 4'd0;endendcaseendend// New: Datapath to latch input bits.endmodule

上述第一種解法雖然正確，但是會生成鎖存器，并且這里只有1個字節數據還好，用8個狀態是可以的，如果換成了10個字節、100個字節，難道要80、800個狀態嗎？這是不可能的，于是便誕生了方法二博主最想讓大家使用的方法。大家可以好好看一下，這里將8個數據狀態定義成了一個DATA狀態，不用定義S1、S2、S3什么的了，在狀態機的第三段，將除了DATA狀態的其他狀態時的counter都清零，只有到了DATA狀態時開始計數，順便將par_in中的位數用counter代替，這樣只需要增加counter和out_byte的位寬，就可以實現任意寬度數據的輸出，實用性強。

題目描述3：

較上題添加了奇偶校驗位。

module top_module(input clk,input in,input reset, // Synchronous resetoutput [7:0] out_byte,output done ); //parameter IDLE = 3'd0,START = 3'd1,DATA = 3'd2;parameter STOP = 3'd3,WAIT = 3'd4;reg [2:0] current_state,next_state;reg [3:0] counter;reg [8:0] data_in;reg odd_temp;wire Isdone;// Modify FSM and datapath from Fsm_serialdataalways @(*) begincase(current_state)IDLE:beginif(~in)beginnext_state = START;endelse beginnext_state = IDLE;endendSTART:beginnext_state = DATA;endDATA:beginif(counter == 4'd9)beginnext_state = in ? STOP : WAIT;endelse beginnext_state = DATA;endendSTOP:beginnext_state = in ? IDLE : START;endWAIT:beginnext_state = in ? IDLE : WAIT;enddefault:beginnext_state = IDLE;endendcaseendalways @(posedge clk) beginif(reset)begincurrent_state <= IDLE;endelse begincurrent_state <= next_state;endendalways @(posedge clk) beginif(reset)begindone <= 1'd0;out_byte <= 8'd0;counter <= 4'd0;endelse begincase(next_state)IDLE:begindone <= 1'd0;out_byte <= 8'd0;counter <= 4'd0;endSTART:begindone <= 1'd0;out_byte <= 8'd0;counter <= 4'd0;endDATA:begindone <= 1'd0;out_byte <= 8'd0;counter <= counter + 1'd1;data_in[counter] <= in;endSTOP:begindone <= odd_temp ? 1'd1 : 1'd0;out_byte <= odd_temp ? data_in[7:0] : 8'd0;counter <= 4'd0;endWAIT:begindone <= 1'd0;out_byte <= 8'd0;counter <= 4'd0;endendcaseendend// New: Add parity checking.assign Isdone = (next_state == START);parity u0(clk,Isdone,in,odd_temp);endmodule

該題答案與上題類似，這里我將奇偶校驗位數據也計算在DATA狀態內，判斷起來相對較容易，大家可以借鑒一下。

注意作者在題目中給了奇偶校驗的模塊，大家直接調用即可。

結語

好久沒更新HDLBits了，寒假在家閑來無事，希望勉勵自己把HDLBits刷完吧，加油！有問題的地方歡迎大家與我討論交流。

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