3.1.7.2 MQTT Service

The MQTT service API example is as follows:

RNWF_RESULT_t RNWF_MQTT_SrvCtrl( RNWF_MQTT_SERVICE_t request, void *input)

It handles following services and reports the result to application over the return code or through the registered callback:The following list captures the MQTT callback event codes and their arguments

The sequence chart below explains this process.

User application can publish to the MQTT broker by creating the MQTT frame and then sending the frame using the API. The sequence chart is illustrated below.

RNWF_MQTT_SrvCtrl(RNWF_MQTT_PUBLISH, (void *)&mqtt_pub)

The sequence for subscribing to a topic from the MQTT Broker is illustrated below. The user application needs to use the API to subscribe to the topic with the appropriate QoS value.

RNWF_MQTT_SrvCtrl(RNWF_MQTT_SUBSCRIBE_QOS0, buffer) 

An example of the MQTT application provided below showcases the use of MQTT service API's:

/*
    MQTT application
*/
bool isMqttConnected = false;

/* Application buffer */
uint8_t app_buf[APP_BUFFER_SIZE_MAX];
static uint8_t subCnt;
/* MQTT Subscribe Topic Name List */
static const char *subscribe_list[] = {"$iothub/twin/PATCH/properties/desired/#", "$iothub/methods/POST/#", "$iothub/twin/res/#", NULL, NULL};

/* TLS Configuration details */
const char *cloud_tls_cfg[] = {"DigiCertGlobalRootG2", "test-node-rnwf02", "test-node-rnwf02", 0, 0, 0};

RNWF_MQTT_CFG_t mqtt_cfg = {
    .url = "g2-cert-dps.azure-devices-provisioning.net",
    .username = "0ne00ABD7D1/registrations/test-node-rnwf02/api-version=2019-03-31",
    .clientid = CLIENT_ID,
    .password = "",
    .port = 8883,
    .tls_conf = cloud_tls_cfg,
    .tls_idx = RNWF_NET_TLS_CONFIG_2,
    .azure_dps = 1
};

RNWF_RESULT_t APP_MQTT_Publish(const char *top, const char *msg)
{    
    RNWF_MQTT_FRAME_t mqtt_pub;    
    mqtt_pub.isNew = NEW_MSG;
    mqtt_pub.qos = MQTT_QOS0;
    mqtt_pub.isRetain = NO_RETAIN;
    mqtt_pub.topic = top;
    mqtt_pub.message = msg;        
    return RNWF_MQTT_SrvCtrl(RNWF_MQTT_PUBLISH, (void *)&mqtt_pub);              
}   

void APP_MQTT_Telemetry(uint32_t counter)
{            
    snprintf(app_buf, sizeof(app_buf), "{Counter: %d}", counter);
    printf("Telemetry ->> Counter %d\r\n", counter);
    APP_MQTT_Publish(MQTT_PUB_TOPIC, app_buf);
}

void APP_MQTT_SUBACK_Handler(void)
{    
    if(subscribe_list[subCnt] != NULL)
    {
        sprintf(app_buf, "%s", subscribe_list[subCnt++]);
        RNWF_MQTT_SrvCtrl(RNWF_MQTT_SUBSCRIBE_QOS0, app_buf);            
    }
}

void APP_MQTT_Task(void)
{     
    /* Implement app specific MQTT_Task() method here */  
    
    /* Call periodically at telemetry rate */
    APP_MQTT_Telemetry(counter++);     

    if(!subCnt && subscribe_list[subCnt] != NULL)
    {
        sprintf(app_buf, "%s", subscribe_list[subCnt++]);
        RNWF_MQTT_SrvCtrl(RNWF_MQTT_SUBSCRIBE_QOS0, app_buf);            
    }        
                 
}
void APP_MQTT_SUB_Handler(char *p_str)
{
   /* Handler to receive the subscribed topics*/
}  

RNWF_RESULT_t APP_MQTT_Callback(RNWF_MQTT_EVENT_t event, uint8_t *p_str)
{   
    switch(event)
    {
        case RNWF_MQTT_CONNECTED:
        {   
            isMqttConnected = true;   
        }
        break;
        case RNWF_MQTT_SUBCRIBE_ACK:
        {
            APP_MQTT_SUBACK_Handler();           
        }
        break;
        case RNWF_MQTT_SUBCRIBE_MSG:
        {
            APP_MQTT_SUB_Handler(p_str);
        }
        break;
        case RNWF_MQTT_DISCONNECTED:
        {   
            printf("MQTT - Reconnecting...\r\n");
            isMqttConnected = false;             
            RNWF_MQTT_SrvCtrl(RNWF_MQTT_CONNECT, NULL);            
        }
        break;
        case RNWF_MQTT_DPS_STATUS:
        {
            if(*p_str == 1)
            {
                printf("DPS Successful! Connecting to Azure IoT Hub\r\n");
            }
            else
            {   
                RNWF_MQTT_SrvCtrl(RNWF_MQTT_CONFIG, (void *)&mqtt_cfg);                                                           
            }
            RNWF_MQTT_SrvCtrl(RNWF_MQTT_CONNECT, NULL);                
        }
        break;
        default:
        break;
    }
    return RNWF_PASS;
}   

void APP_WIFI_Callback(RNWF_WIFI_EVENT_t event, uint8_t *p_str)
{
    switch(event)
    {
        case RNWF_SNTP_UP:
        {            
            if(g_isMqttConnected)
            {            
                printf("SNTP UP:%s\n", &p_str[2]);             
                printf("Connecting to the Cloud\r\n");
                RNWF_MQTT_SrvCtrl(RNWF_MQTT_SET_CALLBACK, APP_MQTT_Callback);
                RNWF_MQTT_SrvCtrl(RNWF_MQTT_CONFIG, (void *)&mqtt_cfg);
                RNWF_MQTT_SrvCtrl(RNWF_MQTT_CONNECT, NULL);
            }
            break;
        }
        case RNWF_CONNECTED:
        {
            printf("Wi-Fi Connected\n");
            break;
        }
        case RNWF_DISCONNECTED:
        {
            printf("Wi-Fi Disconnected\nReconnecting... \n");
            RNWF_WIFI_SrvCtrl(RNWF_STA_CONNECT, NULL);
            break;
        }
        case RNWF_DHCP_DONE:
        {
            printf("DHCP IP:%s\n", &p_str[2]); 
            break;       
        }
        default:
        {
            break;
        }
    }
}
void RNWF_APP_Initialize(void)
{    
    const char sntp_url[] =  "0.in.pool.ntp.org";    
    RNWF_SYSTEM_SrvCtrl(RNWF_SYSTEM_SET_SNTP, sntp_url);              
    /* Wi-Fii Connectivity */
    RNWF_WIFI_PARAM_t wifi_sta_cfg = {RNWF_WIFI_MODE_STA, HOME_AP_SSID, HOME_AP_PASSPHRASE, HOME_AP_SECURITY, 1};    
    printf("Connecting to %s\r\n", HOME_AP_SSID);
    RNWF_WIFI_SrvCtrl(RNWF_WIFI_SET_CALLBACK, APP_WIFI_Callback);
    RNWF_WIFI_SrvCtrl(RNWF_SET_WIFI_PARAMS, &wifi_sta_cfg);

    /* RNWF Application Callback register */

    while(1)
    {  
        if(isMqttConnected)    
        {                
            APP_MQTT_Task();                                                              
        }
        RNWF_EVENT_Handler();
    }    
}