用Verilog HDL设计一个交通灯故障告警电路，HDL描述方法不限

以下是一个简单的Verilog HDL描述交通灯故障告警电路的例子：

module traffic_light_fault_alarm(
  input red_light,
  input yellow_light,
  input green_light,
  output alarm
);

// 定义灯的状态枚举类型
typedef enum {RED, YELLOW, GREEN, OFF} light_state_t;

// 定义当前灯的状态
light_state_t current_light_state;

// 定义故障标志
reg fault;

// 定义状态机
always @ (red_light or yellow_light or green_light or fault) begin
  // 灯的状态转移逻辑
  case (current_light_state)
    RED: if (green_light) current_light_state = GREEN;
         else if (yellow_light) current_light_state = YELLOW;
         else if (fault) current_light_state = OFF;
         else current_light_state = RED;
    YELLOW: if (red_light) current_light_state = RED;
            else if (green_light) current_light_state = GREEN;
            else if (fault) current_light_state = OFF;
            else current_light_state = YELLOW;
    GREEN: if (yellow_light) current_light_state = YELLOW;
           else if (red_light) current_light_state = RED;
           else if (fault) current_light_state = OFF;
           else current_light_state = GREEN;
    OFF: if (red_light or yellow_light or green_light) current_light_state = RED;
         else if (fault) current_light_state = OFF;
         else current_light_state = OFF;
  endcase
  
  // 检测故障
  if (red_light and yellow_light and green_light) fault = 1;
  else fault = 0;
end

// 如果有故障则触发警报
assign alarm = fault;

endmodule

这个电路包含一个状态机，用于控制交通灯的状态。如果在任何时候，红、黄、绿三种灯都亮起来，则表示故障。在这种情况下，故障标志会被设置为 1，告警输出会被触发。状态机的逻辑在 always 块中实现，如果需要添加其他的功能，只需要在这里添加相应的逻辑即可。