File content as of revision 3:e5716d0d5e36:

/*
    STM32 Nucleo MQTT Ultrasound Demonstration
    Author : Sam Walsh
    Date: 24/10/16
    Platform: STM32F746ZG NUCLEO (ARM Cortex M7 @ 216MHz)
    
    Description: This code exercises the ethernet and digital IO on the F7 Nucleo
    by connecting to an MQTT broker automatically through the ethernet and then
    publishing values from a sensor (ultrasound sensor HCSR04)
    
    Although not fully tested it is publishing values from the sensor to the MQTT broker
    (Raspberry Pi 3 connected on a 100Mb LAN) at a rate of about 10Hz, this is limited
    by the timeout functionality I have added to the default HCSR04 software - it usually
    waits for an echo indefinitely which leads to lags in program, so I added some timeouts (10ms)
    to each echo to stop that. These could be tweaked to gain more time I think.
    
    I have benchmarked the Nucleo to be able to send messages to the Pi at a rate of about 16k per second 
    with a payload of just "0.5", it is the ultrasound limiting the speed of transfer
    
    <samuel.walsh@manchester.ac.uk>
*/

#include "mbed.h"
#include "rtos.h"
#include "EthernetInterface.h"
#include <stdio.h>
#include "hcsr04.h"

#define MQTTCLIENT_QOS2 1
#include "MQTTEthernet.h"
#include "MQTTClient.h"

HCSR04 UltrasonicSensor(D4,D5); //Trigger,Echo 
float distance;
 
EthernetInterface eth;

DigitalOut led1(LED1);

int arrivedcount = 0;

//Callback function for arriving messages
void messageArrived(MQTT::MessageData& md)
{
    MQTT::Message &message = md.message;
    printf("\n\rMessage arrived: qos %d, retained %d, dup %d, packetid %d\n", message.qos, message.retained, message.dup, message.id);
    printf("\n\rPayload %.*s\n", message.payloadlen, (char*)message.payload);
    ++arrivedcount;
}

int main()
{
    printf("\n\n*** Ethernet MQTT Demo for STM32F746ZG***\r\n");
    printf("Starting to connect to Ethernet\r\n");
    
    MQTTEthernet ipstack = MQTTEthernet();
    float version = 0.5;
    char* topic = "ultrasound_front";
    
    printf("HelloMQTT: version is %f\n", version);
              
    MQTT::Client<MQTTEthernet, Countdown> client = MQTT::Client<MQTTEthernet, Countdown>(ipstack);
    
    //This is just my MQTT broker, this could be anything//
    char* hostname = "10.42.0.54";
    int port = 1883;
    printf("Connecting to %s:%d\n", hostname, port);
    int rc = ipstack.connect(hostname, port);
    if (rc != 0)
        printf("rc from TCP connect is %d\n", rc);
 
    MQTTPacket_connectData data = MQTTPacket_connectData_initializer;  
         
    data.MQTTVersion = 3;
    data.clientID.cstring = "mbed-sample";
    data.username.cstring = "testuser";
    data.password.cstring = "testpassword";
    
    
    //Connect to broker
    printf("Connecting to MQTT Broker\r\n");
    if ((rc = client.connect(data)) != 0)
        printf("rc from MQTT connect is %d\n", rc);
    
    //Subscribe to topic
     printf("Subscribing to topic\r\n");
    if ((rc = client.subscribe(topic, MQTT::QOS2, messageArrived)) != 0)
        printf("rc from MQTT subscribe is %d\n", rc);

    //Start building Message
    MQTT::Message message;
    // QoS 0
    char buf[100];
    message.qos = MQTT::QOS0;
    message.retained = false;
    message.dup = false;
    
    //Publish ultrasonic distance
    while(1)
    {
        //I have not fully benchmarked this loop but by eye it seems to be publishing sensor data about 10Hz TODO:Speed it up as much as possible and properly characterise sensor update rates
        distance = UltrasonicSensor.distance();
        wait_ms(50);
        if(distance == 17182){
            //this is just 999999 error code ran through distance calc
            printf("\n\rOut of range ->  echo timed out");
        }
        else{
            printf("\n\rDistance is: %0.2f", distance);
        }
        
        sprintf(buf, " %f\n", distance);
        message.payload = (void*)buf;
        message.payloadlen = strlen(buf)+1;
        rc = client.publish(topic, message);
    }
    //client.yield(100);              
//    if ((rc = client.unsubscribe(topic)) != 0)
//        printf("rc from unsubscribe was %d\n", rc);
//    
//    if ((rc = client.disconnect()) != 0)
//        printf("rc from disconnect was %d\n", rc);
//    
//    ipstack.disconnect();
    

}