/*  File: seqdet.v
序列監測器——X為輸入碼流，從中檢測出指定序列“10010”（對應狀態A、B、C、D、E），
Z輸出為1。考慮到序列重疊的可能，還有狀態F，G。
*/
module seqdet (x, z, clk, rst);
	input x, clk, rst;
	output z;
	reg [2:0] state;
	wire z;
	
	parameter IDLE = 'd0, A = 'd1, B = 'd2, C = 'd3, D = 'd4,
					E = 'd5, F = 'd6, G = 'd7;
	
	assign z = (state == D && x == 0) ? 1 : 0;
	
	always @ (posedge clk or negedge rst)
		if (!rst)
			begin
				state <= IDLE;
			end
		else
			casex (state)
				IDLE: if (x == 1)
						begin
							state <= A;
						end
				A:	if (x == 0)
						begin
							state <= B;
						end
				B:	if (x == 0)
						begin
							state <= C;
						end
					else
						begin
							state <= F;
						end
				C:	if (x == 1)
						begin
							state <= D;
						end
					else
						begin
							state <= G;
						end
				D:	if (x == 0)
						begin
							state <= E;
						end
					else
						begin
							state <= A;
						end
				E:	if (x == 0)
						begin
							state <= C;
						end
					else
						begin
							state <= A;
						end
				F:	if (x == 1)
						begin
							state <= A;
						end
					else
						begin
							state <= B;
						end
				G:	if (x == 1)
						begin
							state <= F;
						end
				default: state <= IDLE;
			endcase
	
endmodule


//以下為測試代碼
`timescale 1ns/1ns
module test_of_seqdet;
	reg clk, rst;
	reg [23:0] data;
	wire z, x;

	assign x = data[23];
	
	initial
		begin
			clk <= 0;
			rst <= 1;
			#2 rst <= 0;
			#30 rst <= 1;
			data = 'b1100_1001_0000_1001_0100;
		end
	
	always #10 clk = ~clk;
	always @ (negedge clk)
		data = {data[22:0], data[23]};
	
	seqdet m (.x(x), .z(z), .clk(clk), .rst(rst));
	
	//Enter fixture code here
	
endmodule