1.定义MQTTPacket_connectData 类型的结构体初始化连接协议、版本、心跳包的参数

        2.NewNetwork是网络设置函数，需传入的参数是网络配置的结构体指针和socket号

        3.ConnectNetwork是连接网络函数，需传入的参数是socket号、服务器ip、端口号

        4.MQTTClientInit是客户端初始化函数，需传入mqtt连接配置的结构体指针和网络配置的结构体指针、命令超时时间/ms、发送缓存和发送缓存大小、接收缓存和接收缓存大小。

        5.将得到的数据存入到结构体 MQTTPacket_connectData中

        6.MQTTConnect函数和MQTTSubscrib函数是查看监测是否连接服务器和订阅上主题，如果返回值为0则表示成功

void mqtt_init(void)
{
    int ret;

    MQTTPacket_connectData data = MQTTPacket_connectData_initializer;
    NewNetwork(&n, 1);
    ConnectNetwork(&n, mqtt_params.server_ip, 1883);
    MQTTClientInit(&c, &n, 1000, mqtt_send_buff, MQTT_SEND_BUFF_SIZE, mqtt_recv_buff, MQTT_RECV_BUFF_SIZE);
    data.willFlag = 0;
    data.MQTTVersion = 3;
    data.clientID.cstring = mqtt_params.clientid;
    data.username.cstring = mqtt_params.username;
    data.password.cstring = mqtt_params.passwd;
    data.keepAliveInterval = 30;
    data.cleansession = 1;
    connOK = MQTTConnect(&c, &data);
    printf("Connected:%s\r\n", connOK == 0 ? "success" : "failed");
    printf("Subscribing to %s\r\n", mqtt_params.subtopic1);
    ret = MQTTSubscribe(&c, mqtt_params.subtopic1, mqtt_params.QOS, messageArrived);
    printf("Subscribed:%s\r\n", ret == 0 ? "success" : "failed");
   
    sleep_ms(300);
    MQTTMessage pubmessage={
        .qos=QOS2,
        .dup=0,
        .retained=0,
        .id=0,
    };
    pubmessage.payload="hello mqtt!\r\n";
    pubmessage.payloadlen=strlen(pubmessage.payload);
    MQTTPublish(&c,mqtt_params.pubtopic,&pubmessage);
}

        messageArrived发布消息函数，传入参数是MessageData的结构体，里面主题和消息，函数里面主要是对发布消息的服务等级的判断。
        keep_alive心跳包保活函数，此函数必须放在主循环函数中

void messageArrived(MessageData* md)
{
    unsigned char messagebuffer[512];
    MQTTMessage* message = md->message;
    if (mqtt_params.QOS)
    {
        memcpy(messagebuffer,(char*)message->payload,(int)message->payloadlen);
        *(messagebuffer + (int)message->payloadlen + 1) = '\n';
        printf("%s\r\n",messagebuffer);
    }
    if (mqtt_params.QOS)
        printf("%.*s", (int)message->payloadlen, (char*)message->payload);
    else
        printf("%s%.*s%s%s", "RX:",(int)message->payloadlen, (char*)message->payload, mqtt_params.QOS,"\r\n");
}
void keep_alive(void)
{
    if (!connOK)
    {
        if (MQTTYield(&c, 30))
        {
            mqtt_init();
        }
    }
}
         主函数：主要是对串口和网络还有mqtt进行初始化

int main()                                                          
{   
    struct repeating_timer timer;
    stdio_init_all();
    sleep_ms(2000);
    wizchip_initialize();
    wizchip_setnetinfo(&net_info);
    print_network_information(net_info);
    add_repeating_timer_ms(1, repeating_timer_callback, NULL, &timer);
    mqtt_init();
    while(true)
    {
        // loopback_udpc(SOCKET_ID, ethernet_buf, destip, destport);
        keep_alive();
        sleep_ms(10);
    }
    
}