add fsm_traffic

fsm_traffic/fsm_traffic.v

@@ -0,0 +1,48 @@
+/*
+    fsm_traffic
+*/
+module fsm_traffic (
+    input clk,
+    input rst,
+    output red_led,
+    output green_led,
+    output yellow_led
+);
+    localparam RED      = 2'b00;
+    localparam GREEN    = 2'b01;
+    localparam YELLOW   = 2'b10;
+
+    reg[1:0] state, next_state;
+    reg[7:0] timer;
+
+    always @(posedge clk or posedge rst) begin
+       if (rst) begin
+        state <= RED;
+        timer <= 3;
+       end
+       else if (timer == 0) begin
+            state <= next_state;
+
+            case (next_state)
+                RED:     timer <= 3;
+                YELLOW:  timer <= 1;
+                GREEN:   timer <= 2;
+                default: timer <= 3;
+            endcase
+       end
+       else timer <= timer - 1; 
+    end
+
+    always @(*) begin
+        case (state)
+            RED:     next_state = GREEN;
+            YELLOW:  next_state = RED;
+            GREEN:   next_state = YELLOW;
+            default: next_state = RED;
+        endcase
+    end
+
+    assign red_led = state == RED;
+    assign green_led = state == GREEN;
+    assign yellow_led = state == YELLOW;
+endmodule