Problem with subscription to MQTT Broker



  • Hi all!
    I added a subscribtion to my MQTT Broker (Mosquitto on a RPi3) to receive some timing settings. Did it all straight forward like in the example, no fancy things.
    Unfortunately, the callback function is only triggered once, right after subscribe. Here's a little snippet:

    def cb_Get_Settings(topic, msg):
        print("+++++++++++++++++++++++++++++++++\n" * 2)
        print(topic, ' : ', msg)
        print("+++++++++++++++++++++++++++++++++\n" * 2)
    
    def start_wlan():
        global wlan
        global mqtt
        wlan = WLAN(mode=WLAN.STA, power_save=False)
        wlan.connect(config.WIFI_SSID, auth=(WLAN.WPA2, config.WIFI_PASS), timeout=5000)
        print("Try to connect to Wifi...", end='')
        wifi_ok = False
        for _ in range (10):
            if wlan.isconnected():
                wifi_ok = True
                break
            else:
                time.sleep(1)
    
        if wifi_ok:
            #pycom.rgbled(0x550000)
            print("Done!!!")
            wifiaddress = "IP Address is: " + ((str(wlan.ifconfig()[:1]))[2:])[:-3]
            print(wifiaddress)
            print("Connect to MQTT Broker at " + config.MQTT_BROKER + "...", end='')
            mqtt = MQTTClient(config.UNIQUE_ID, config.MQTT_BROKER, keepalive=1, port=config.MQTT_PORT)
            mqtt.settimeout = settimeout
            mqtt.set_last_will(config.LAST_WILL_TOPIC,  config.LAST_WILL_MSG,  retain = True,  qos = 1)
            mqtt.set_callback(cb_Get_Settings)
            mqtt.connect(clean_session=False)
            mqtt.publish(config.LAST_WILL_TOPIC, config.LAST_WILL_BACK, retain=True, qos=1)
            print("Done!!!")
            print("Subscribe to Settings Topic...")
            subTopic = config.MQTT_DEVICE_NAME +"/settings/get"
            mqtt.subscribe(topic=subTopic, qos=1)
            print("Done!!!")
        else:
            maschine.reset()
    

    When ever I send I message to the topic I subscribed to, I get nothing.
    I tried to use mqtt.check_msg() on top my main loop. Then I receive the messages, but check_msg blocks the main loop, so everything inside the main loop is only executed if I publish a message to the subscribed topic.
    What I now wondering is something in the official Pycom MQTT library.
    Snipp---------

    # Checks whether a pending message from server is available.
    # If not, returns immediately with None. Otherwise, does
    # the same processing as wait_msg.
    def check_msg(self):
        self.sock.setblocking(False)
        return self.wait_msg()
    

    Is there really any check done? For me, it just runs wait_msg(), isn't it?

    Cheers,
    Thomas



  • Ok, some news:
    If I publish something to any of my topics with QoS set to 1, I can receive the message from the topic I subsrcibed to, but, unfortunately, only one time. The callback function runs fine, but then, the main loop is blocked.
    I can see, that the sensor threads are still running fine, but there are no more data published, because of the blocked main loop.

    Cheers,
    Thomas


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