MQTTPubService

MQTTPubService is a practical PUBLISH service FB that makes it easy to use MQTT Publish in a program using the MQTT communications Library (SYSMAC-XR020) published by OMRON. Check out this article for more details and here for usage examples.

MQTTPubSerivce FB has a simple structure with only one MQTT connection, one Publish worker, automatic ping check, and minor monitoring. If necessary, it can be combined with an inter-POU messaging mechanism to create a pan-POU service, and a fallback mechanism can be built to increase the degree of data loss avoidance.

As far as I have confirmed, the MQTT client of the MQTT communications Library can avoid data loss with simple buffer management even if there are slight speed fluctuations in the network, as long as the transmission speed per connection is around 1 Mbps. 1 Mbps is a 4 millisecond periodic task containing 500 bytes of information per cycle. Also, if your broker allows it, you can connect up to three at the same time.

Usage environment

Using MQTTPubService requires the following environment.

Controller	NX1 or NX5
Sysmac Studio	I always recommend the latest version.
MQTT broker	You are free to choose any broker that complies with MQTT Version 3.1.1. Unless the broker is running on very constrained hardware, the traffic will not be such that processing power becomes an issue. Avoid using public brokers.
MQTT client	There is no problem with your favorite MQTT client.
Network	Avoid networks with large delays between the localer and controller. A ping value of about 30 ms is recommended.

Built environment

The project was built in the following environment.

Controller	NX102-9000 Ver 1.64
Sysmac Studio	Ver.1.60
MQTT broker	Mosquitto on Docker on local PC (eclipse-mosquitto:2.0.20)
MQTT client	MQTTX
Network	There was an average delay of 10 ms in Ping values ​​between the broker and the controller.

Procedure for using the sample program

This project has a sample program (NotifyStats) for MQTTPubService. You can use it by modifying the project and setting up the environment using the following steps.

1. Check the project file hash
   Nothing can be done if the project file is corrupted.
2. Match the project's controller format to the controller you use
   Older NX1 cannot use MQTT communications Library. Please check the MQTT communications Library manual for available versions.
3. Change settings for "POU/Program/NotifyStats"
   Match the broker address, port number, and client ID to your environment.

   iMqttSettings.BrokerAdr := 'YOUR_BROKER_ADR'; // '192.168.250.2';
   iMqttSettings.BrokerPort := YOUR_BROKER_PORT; // 1883;
   iMqttSettings.ClientID := 'YOUR_CLIEN_ID';
   

4. Change configuration/settings/controller settings/built-in EtherNet/IP port settings
   Change the settings so that you can reach the broker.
5. Set up and start MQTT broker
   Start the broker and check if you can connect with a suitable MQTT client. Also check if you can subscribe to the broker's system status.
6. Adjust controller clock
   If the clock of the connected terminal running Sysmac Studio is appropriate, it will be reflected. If you use NTP, make sure it is synchronized.
7. Download project to controller
   Run the program in run mode and check the event log for errors.
8. Subscribe to "machine/stats" with MQTT client
   Verify that you can subscribe to messages and that the content is reasonable.

How to use MQTTPubService

MQTTPubService can monitor the state and perform necessary control by referring to the State variable (MQTTPubService.State). The state includes follows.

State	Description
STOP	The service is stopped.
INACTIVE	The service is running but not available.
ACTIVE	Able to issue messages.
NO_CONNECTION	Lost connection with broker.
PUBLISHING	Publish a message.
PUBLISHED	The message has been published.
SHTDOWN	Shut down the service.
ERROR	An exception has occurred. Please check ErrorID, ErrorIDEx.

The state transits as follows.

---
title: MQTTPubService state transition
---
stateDiagram-v2
    [*] --> STOP
    STOP --> INACTIVE : Enable=True
    STOP --> [*]

    INACTIVE --> ACTIVE : MqttClient.Connected=True
    INACTIVE --> STOP : Busy=False
    INACTIVE --> SHUTDOWN : Enable=False

    ACTIVE --> NO_CONNECTION : MqttClient.Connected=False
    ACTIVE --> SHUTDOWN : Enable=False
    ACTIVE --> ERROR : MqttClient.Error=True or MqttPing.Error=True
    ACTIVE --> PUBLISHING : Publish=True and start publishing.

    NO_CONNECTION --> ACTIVE : MqttClient.Connected=True
    NO_CONNECTION --> ERROR : MqttClient.Error=True
    NO_CONNECTION --> SHUTDOWN : Enable=False

    PUBLISHING --> PUBLISHED : PubWorkerContext.State = PUBLISHED
    PUBLISHING --> ERROR : An error occures in any MQTT FB.
    
    PUBLISHED --> ACTIVE : [1 cycle]
    PUBLISHED --> ERROR : [1 cycle] MqttClient.Error=True or MqttPing.Error=True

    ERROR --> SHUTDOWN : [1 cycle] An error occurres in the MQTT connection
    ERROR --> ACTIVE : [1 cycle] Faile to publish message
    ERROR --> ERROR : If errors occur continuously

    SHUTDOWN --> INACTIVE : [1 cycle]

Loading

Control using state uses the CASE statement as follows.

CASE iMqttPubService.State OF
    MQTT_PUB_SRV_STATE_STOP:
        // If the service is stopped, it will start immediately.
        iMqttPubService.Enable := TRUE;

    MQTT_PUB_SRV_STATE_ERROR:
        // If an error occurs, the service will be stopped
        // regardless of the content.
        iMqttPubService.Enable := FALSE;
        iMqttPubService.Publish := FALSE;

    MQTT_PUB_SRV_STATE_INACTIVE,
    MQTT_PUB_SRV_STATE_NO_CONNECTION:
        DO_FALLBACK();
        
    MQTT_PUB_SRV_STATE_ACTIVE:
        IF DO_PUBLISH THEN
            iMqttPubService.Request := iPubRequest;
            iMqttPubService.Publish := TRUE;
        END_IF;
        
    MQTT_PUB_SRV_STATE_PUBLISHED:
        // After sending the message, drop the flag.
        iMqttPubService.Publish := FALSE;
END_CASE;
iMqttPubService();

File hash

I recommend checking the hash value of the acquired Sysmac Studio project.

file	sha256
MQTTPubServiceNoBuffer.scm2	1d93296918962a32a01d3c23611ab3dfa7c2f77221b86d89d183f1bb3aeb93e6