Home Assistant extensive support

[gamba69]

• Device detected as two different lights, main and back
• Supported on/off, brightness, effects (main and back), color (back)
• Main light clock faces may be named, see clockfaces.txt on SPIFFS
• Supported 12/24 hours and blank zeroes settings switches
• Supported effect's speed change for backlight
• All options are discoverable via Home Assistant MQTT

[eku]

Nice. Please describe all MQTT topics with their function and parameters for users of other HA systems.

[gamba69]

Nice. Please describe all MQTT topics with their function and parameters for users of other HA systems.

A full description would take a lot of time and would be a very long story...
In short:
Interaction with Home Assistant occurs according to the MQTT integration documentation:
https://www.home-assistant.io/integrations/light.mqtt/
https://www.home-assistant.io/integrations/switch.mqtt/
https://www.home-assistant.io/integrations/number.mqtt/
https://www.home-assistant.io/integrations/mqtt/#mqtt-discovery
It is preferable (but not mandatory) to use MQTT Discovery (#define MQTT_HOME_ASSISTANT_DISCOVERY), in which case the device and all entities will be found by the MQTT integration without user intervention. Otherwise, all settings will need to be done manually.
#define MQTT_CLIENT is used as a unique device name (i.e. it should be different if you have several IPS clocks) and is the "root" part of the topic for all entities that will be interacted with via MQTT. Further analysis is easier to perform using, for example, "MQTT Explorer", a common add-on for users who prefer manual configuration.

[aly-fly]

Looks good to me. Thanks for the contributions. Merged.