【创龙TL3562-MiniEVM开发板试用体验】--MQTT通讯

本篇讲述开发板MQTT通讯。
MQTT（Message Queuing Telemetry Transport，消息队列遥测传输协议），是一种基于发布订阅(Publish/Subscribe)模式的“轻量级”通讯协议。下表是MQTT服务器，使用到HiveMQ。

1.在ubuntu终端安装mosquitto 工具
sudo apt-get install mosquitto-clients

2.代码
这里将开发板作为客户端，发布消息。代码如下

int main(int argc, char **argv)
{
    struct _Params params;
    int ret = -1;
    int status = 0;

    memset(&params, 0, sizeof(params));
    if (parse_parameter(&params, argc, argv) == false) {
        printf("Please try --help to see usage.\n");
        exit(-1);
    }

    /* Ctrl+c handler */
    signal(SIGINT, sig_handle);

    /* Must be called before any other mosquitto functions. */
    ret = mosquitto_lib_init();
    if (ret != MOSQ_ERR_SUCCESS) {
        printf("mosquitto lib init failed!\n");
        exit(-1);
    }

    mosq = mosquitto_new("client1", true, &params);
    if (mosq == NULL) {
        printf("Create new mosquitto client instance failed!\n");
        exit(-1);
    }

    /* Set the connect callback. */
	mosquitto_connect_callback_set(mosq, mqtt_connect_callback);
    /* Set the disconnect callback. */
	mosquitto_disconnect_callback_set(mosq, mqtt_disconnect_callback);
    /* Set the publish callback.  This is called when a message initiated with mosquitto_publish has been sent to the broker successfully. */
	mosquitto_publish_callback_set(mosq, mqtt_publish_callback);
    /* Set the message callback.  This is called when a message is received from the broker. */
    mosquitto_message_callback_set(mosq, mqtt_message_callback);

    /* Connect to an MQTT broker. */
    ret = mosquitto_connect(mosq, params.host, params.port, keepalive);
    if (ret != MOSQ_ERR_SUCCESS) {
        printf("mosquitto connect failed!\n");
        status = -1;
        goto error;
    }

    /* publish */
    if (params.mode == MQTT_PUBLISH) {
        mosquitto_loop_start(mosq);

        while (!g_quit) {
            if (is_connect == false) {
                usleep(100000);
                continue;
            }

            ret = mosquitto_publish(mosq, NULL, params.topic, strlen(params.message), params.message, 0, false);
            if (ret) {
                printf("Error: Publish returned %d, disconnecting.\n", ret);
                mosquitto_disconnect(mosq);
            }

            break;
        }
        
        mosquitto_loop_stop(mosq, false);
    } else if (params.mode == MQTT_SUBSCRIBE) {
        /* subscribe */
        mosquitto_loop_forever(mosq, -1, 1);
    }

error:
    mosquitto_destroy(mosq);
    mosquitto_lib_cleanup();

    return status;
}

工程如下

3.开发板插上网线，连接上网络。前面已有讲过。这里将可执行文件mqtt_client传输到开发板。
scp mqtt_client root@192.168.3.218:/user_app/

4.上位机订阅，开发板发布。
这里在ubuntu订阅MQTT主题。
mosquitto_sub -h broker.hivemq.com -p 1883 -t test/data
开发板发布消息
./mqtt_client -h broker.hivemq.com -p 1883 -M publish -t test/data -m 'www.tronlong.com'
可以看到上位机从MQTT服务器收到订阅的消息。

至此，实现开发板MQTT通讯功能。同上所述，亦可开发板订阅/上位机发布。