怎样写出这串代码：交通灯; (考察知识: LED， 串口，定时器中断的综合应用) 单片机上电后，红灯亮，高10s,前7秒常高，后3秒闪烁，串口给上位机发送“禁止通行”红灯灭后，绿灯亮8s，前5秒常高，后3秒闪烁，串口给上位机发送“允许通行” 绿灯灭后，黄灯高6s，前3秒常亮，后3秒闪烁，串口给上位机发送“等待通行

以下是基于Arduino平台的代码，实现交通灯功能，需要连接一个LED到引脚13。

const int redPin = 11; //红灯引脚
const int yellowPin = 10; //黄灯引脚
const int greenPin = 9; //绿灯引脚
const int ledPin = 13; //状态指示LED引脚
const int baudRate = 9600; //串口通信波特率

int state = 0; //交通灯状态，0为红灯，1为绿灯，2为黄灯
int timer = 0; //计时器，用于控制闪烁时间
bool blinkState = false; //闪烁状态，用于控制灯的闪烁

void setup() {
  pinMode(redPin, OUTPUT);
  pinMode(yellowPin, OUTPUT);
  pinMode(greenPin, OUTPUT);
  pinMode(ledPin, OUTPUT);

  Serial.begin(baudRate); //初始化串口通信
  Serial.println("禁止通行"); //发送初始状态

  digitalWrite(redPin, HIGH); //初始状态为红灯常亮
}

void loop() {
  switch (state) {
    case 0: //红灯
      digitalWrite(redPin, HIGH);
      digitalWrite(yellowPin, LOW);
      digitalWrite(greenPin, LOW);
      digitalWrite(ledPin, HIGH); //状态指示LED常亮

      if (timer < 7000) { //前7秒常亮
        timer += 10;
      } else if (timer < 10000) { //后3秒闪烁
        if (timer % 1000 == 0) { //每隔1秒切换闪烁状态
          blinkState = !blinkState;
          digitalWrite(redPin, blinkState);
        }
        timer += 10;
      } else { //切换到绿灯状态
        state = 1;
        timer = 0;
        Serial.println("允许通行");
        digitalWrite(redPin, LOW); //红灯灭
        digitalWrite(greenPin, HIGH); //绿灯亮
      }
      break;

    case 1: //绿灯
      digitalWrite(redPin, LOW);
      digitalWrite(yellowPin, LOW);
      digitalWrite(greenPin, HIGH);
      digitalWrite(ledPin, HIGH); //状态指示LED常亮

      if (timer < 5000) { //前5秒常亮
        timer += 10;
      } else if (timer < 8000) { //后3秒闪烁
        if (timer % 1000 == 0) { //每隔1秒切换闪烁状态
          blinkState = !blinkState;
          digitalWrite(greenPin, !blinkState);
        }
        timer += 10;
      } else { //切换到黄灯状态
        state = 2;
        timer = 0;
        Serial.println("等待通行");
        digitalWrite(greenPin, LOW); //绿灯灭
        digitalWrite(yellowPin, HIGH); //黄灯亮
      }
      break;

    case 2: //黄灯
      digitalWrite(redPin, LOW);
      digitalWrite(yellowPin, HIGH);
      digitalWrite(greenPin, LOW);
      digitalWrite(ledPin, HIGH); //状态指示LED常亮

      if (timer < 3000) { //前3秒常亮
        timer += 10;
      } else if (timer < 6000) { //后3秒闪烁
        if (timer % 1000 == 0) { //每隔1秒切换闪烁状态
          blinkState = !blinkState;
          digitalWrite(yellowPin, !blinkState);
        }
        timer += 10;
      } else { //切换到红灯状态
        state = 0;
        timer = 0;
        Serial.println("禁止通行");
        digitalWrite(yellowPin, LOW); //黄灯灭
        digitalWrite(redPin, HIGH); //红灯亮
      }
      break;
  }
}