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SoftwareArchitecture

General Overview

The software is designed to have a loosely coupled architecture making it possible to add new home automation functionality without the need to worry about the MQTT communication to much. This results in a task for the main home automation logic and a seperate task to handle the MQTT communication to the broker. A global variable list is used to share memory objects between the two tasks enabling communication.

SoftwareArchitecture

Main Task (PLC_PRG_MAIN)

The main task is build using a SFC (Sequential Function Chart) with the following actions:

PLC_PRG_MAIN_SFC

  1. MAIN_INIT: action ran once at startup to init FB's with static values/references.
  2. READ_PUSHBUTTONS: action ran continously to read out digital inputs (FB's used in this action assume usage of pushbutton).
  3. WRITE_SWITCHES: action ran continously after READ_PUSHBUTTONS to switch outputs using the results from READ_PUSHBUTTONS.

Each of the Function Blocks (FB's) used to read inputs and switch outputs has a reference to a MQTTPublishQueue which is used to queue events to send to the MQTT broker. The events are sent towards the broker in the MQTT Task which has a lower priority so it never interferes with the main task which does the critical work.

MQTT Task (PLC_PRG_MQTT)

The main task is build using a SFC (Sequential Function Chart) with the following actions:

PLC_PRG_MQTT_SFC

  1. MQTT_INIT: action ran once at startup to init FB's with static values/references.
  2. MQTT_PUBLISH: action ran continously to read the events to publish from the MQTTPublishQueue. Has a number of MQTTPublishWorkers who are able to send MQTT events simultanously.
  3. MQTT_SUBSCRIBE: action ran continously after MQTT_PUBLISH to handle subscriptions.

Global Variable list MQTT (MQTTVariables)

Contains function blocks to enable communication between the main task and the MQTT task. For example:

  • MQTTPublishQueue FB where the main task queue's messages to be published.
  • Callbackcollectors FB's so FB's can register for a callback event in case a message is received on a topic.