【米尔-全志T113-S3开发板- 极致双核A7国产处理器-试用体验】MQTT使用

首先从https://mqtt.org/上下载基MQTT源码包，我选的是Eclipse Paho C，可以直接使用以下指令下载

git clone https://github.com/eclipse/paho.mqtt.c.git

下载完成后整合到自己工程内，然后编写应用，这里我们使用了来自EMQX的免费的公共MQTT服务器，详见https://www.emqx.com/zh/mqtt/public-mqtt5-broker
详细代码如下：

#include <unistd.h>
#include <fcntl.h>
#include <stdint.h>
#include <stdlib.h>
#include <string.h>
#include "MQTTAsync.h"

#define MQTT_HOST "tcp://broker.emqx.io:1883"
#define CLIENT_ID "abcd"
#define USERNAME  "abcd"
#define PASSWORD  "abcd"

static MQTTAsync g_mqtt_client = NULL;
static int online = 0;

static int connect_to_server(void);
static int pub_topic(const char* topic, void* payload, int len);

static int msgarrvd(void *context, char *topicName, int topicLen, MQTTAsync_message *message) {
    uint8_t *payload = message->payload;
    printf("recv topic: %s %c\n", topicName, payload[0]);
    if(!strcmp(topicName, "/ToT113/led")) {
        if(!payload[0] || payload[0] == '0') {
            system("echo 1 > /sys/class/leds/led-blue/brightness");//led off
            printf("led off\n");
        } else {
            system("echo 0 > /sys/class/leds/led-blue/brightness");//led on
            printf("led on\n");
        }
    }

    MQTTAsync_freeMessage(&message);
    MQTTAsync_free(topicName);
    return 1;
}

static void onConnect(void* context, MQTTAsync_successData* response) {
	printf("Successful connection\n");
	online = 1;
}

static void onConnectFailure(void* context, MQTTAsync_failureData* response) {
	printf("Connect failed, rc %d\n", response->code);
}

static void connlost(void *context, char *cause) {
	printf("Connection lost\n");
	if (cause) {
		printf("\tcause: %s\n", cause);
	}
	connect_to_server();
}

static void onSubscribe(void* context, MQTTAsync_successData* response) {
	printf("Subscribe succeeded\n");
}

static void onSubscribeFailure(void* context, MQTTAsync_failureData* response) {
	printf("Subscribe failed, rc %d\n", response->code);
}

static int subscribe_topic(const char* topic) {
    MQTTAsync_responseOptions opts = MQTTAsync_responseOptions_initializer;
	int rc;
	opts.onSuccess = onSubscribe;
	opts.onFailure = onSubscribeFailure;
	opts.context = g_mqtt_client;
	if ((rc = MQTTAsync_subscribe(g_mqtt_client, topic, 0, &opts)) != MQTTASYNC_SUCCESS) {
		printf("Failed to start subscribe, return code %d\n", rc);
		return -1;
	}
	printf("subscribe topic:%s\n", topic);
	return 0;
}

static void onSend(void* context, MQTTAsync_successData* response) {
    printf("Message send ok\n");
}

static void onSendFailure(void* context, MQTTAsync_failureData* response) {
	printf("Message send failed token %d error code %d\n", response->token, response->code);
}

static int pub_topic(const char* topic, void* payload, int len) {
    MQTTAsync_responseOptions opts = MQTTAsync_responseOptions_initializer;
	MQTTAsync_message pubmsg = MQTTAsync_message_initializer;
	int rc;
	opts.onSuccess = onSend;
	opts.onFailure = onSendFailure;
	opts.context = g_mqtt_client;
	pubmsg.payload = payload;
	pubmsg.payloadlen = len;
	pubmsg.qos = 0;
	pubmsg.retained = 0;
	if ((rc = MQTTAsync_sendMessage(g_mqtt_client, topic, &pubmsg, &opts)) != MQTTASYNC_SUCCESS) {
		printf("Failed to start sendMessage, return code %d\n", rc);
		return -1;
	}
	return 0;
}

static int connect_to_server(void) {
    int rc;
    if(!g_mqtt_client) {
        if ((rc = MQTTAsync_create(&g_mqtt_client, MQTT_HOST, CLIENT_ID, MQTTCLIENT_PERSISTENCE_NONE, NULL)) != MQTTASYNC_SUCCESS) {
            printf("Failed to create client, return code %d\n", rc);
            return -1;
        }
        if ((rc = MQTTAsync_setCallbacks(g_mqtt_client, g_mqtt_client, connlost, msgarrvd, NULL)) != MQTTASYNC_SUCCESS) {
            printf("Failed to set callbacks, return code %d\n", rc);
            return -1;
        }
    }

    MQTTAsync_connectOptions conn_opts = MQTTAsync_connectOptions_initializer;
    conn_opts.keepAliveInterval = 45;
	conn_opts.cleansession = 1;
	conn_opts.onSuccess = onConnect;
	conn_opts.onFailure = onConnectFailure;
	conn_opts.context = g_mqtt_client;
	conn_opts.username = USERNAME;
	conn_opts.password = PASSWORD;

	if ((rc = MQTTAsync_connect(g_mqtt_client, &conn_opts)) != MQTTASYNC_SUCCESS) {
		printf("Failed to start connect, return code %d\n", rc);
		return -1;
	}
	printf("MQTT connecting\n");
	return 0;
}

int main(void) {
    system("echo none > /sys/class/leds/led-blue/trigger");
    connect_to_server();
    while(!online) {
        sleep(1);
    }
    subscribe_topic("/ToT113/led");
    while(1) {
        sleep(1);
        char msg[20] = "";
        int fd = open("/sys/class/gpadc/data", O_RDONLY);
        if(fd < 0) {
            continue;
        }
        read(fd, msg, sizeof(msg) - 1);
        close(fd);
        printf("AD: %s\n", msg);
        pub_topic("/ToApp/ad", msg, sizeof(msg));
    }
    return 0;
}

该代码的作用是定时采集AD口的电压并推送主题，同时接收控制端发送的LED控制指令，实现LED灯的亮灭操作。为了验证该代码，我们先把程序放到开发板，然后让开发板联网，执行该应用，此时开发板会连接MQTT服务器，连上后会不断上报AD电压，如图。

然后通过手机APP Store下载了一个叫MQTTTool的工具，设置参数登录MQTT服务器

接下来订阅/ToApp/AD主题，

当订阅完成后，就可以收到设备上报的电压数据了

然后我们尝试发布主题，将LED灯关闭，如图所示
当Publish后，开发板的蓝灯关闭了

然后我们再去看看控制台，确实收到了手机发来的指令

我们可以看一下开发板上蓝灯确实灭了

至此，整个过程结束