traffic_light_fsm.v Source

1	// SPDX-License-Identifier: MIT
2	// A small finite-state machine. Each tick advances the light state.
3	module traffic_light_fsm (
4	input wire clk,
5	input wire rst,
6	output reg red,
7	output reg yellow,
8	output reg green
9	);
10	localparam S_RED = 2'd0;
11	localparam S_GREEN = 2'd1;
12	localparam S_YELLOW = 2'd2;
13
14	reg [1:0] state;
15	reg [3:0] timer;
16
17	always @(posedge clk) begin
18	if (rst) begin
19	state <= S_RED;
20	timer <= 4'd0;
21	end else begin
22	timer <= timer + 1'b1;
23
24	case (state)
25	S_RED:
26	if (timer == 4'd4) begin
27	state <= S_GREEN;
28	timer <= 4'd0;
29	end
30	S_GREEN:
31	if (timer == 4'd7) begin
32	state <= S_YELLOW;
33	timer <= 4'd0;
34	end
35	S_YELLOW:
36	if (timer == 4'd2) begin
37	state <= S_RED;
38	timer <= 4'd0;
39	end
40	default: begin
41	state <= S_RED;
42	timer <= 4'd0;
43	end
44	endcase
45	end
46	end
47
48	always @(*) begin
49	red = 1'b0;
50	yellow = 1'b0;
51	green = 1'b0;
52
53	case (state)
54	S_RED: red = 1'b1;
55	S_GREEN: green = 1'b1;
56	S_YELLOW: yellow = 1'b1;
57	default: red = 1'b1;
58	endcase
59	end
60	endmodule