[request] Replace polling by event in Matter examples

[rei-vilo]

Summary

In many examples, delay before two consecutive data acquisition is performed by polling.

arduino/libraries/Matter/examples/matter_sensor_multiple/matter_sensor_multiple.ino

Lines 61 to 67 in 65a739a

	if ((last_action_temp + 10000) < millis()) {
	last_action_temp = millis();
	float current_cpu_temp = getCPUTemp();
	// Publish the temperature value - you can also use 'matter_temp_sensor = current_cpu_temp'
	matter_temp_sensor.set_measured_value_celsius(current_cpu_temp);
	Serial.printf("Current CPU temperature: %.02f C\n", current_cpu_temp);
	}

This might not be especially low-power.

How to use instead an event raised by a timer? As SiLabs core for Arduino seems to rely on FreeRTOS, the RTOS elements should be already available.

Thank you!

[silabs-bozont]

Hello @rei-vilo,

Yes, the examples use polling - so they're might not be that power efficient.
We'll look into introducing event callbacks to the library so you can block your user task and wait for Matter events to happen - it's a good idea.

[silabs-bozont]

Hello @rei-vilo,

I just realized what you need here is to replace the busy-looping with a simple delay() - that'll block the user task for the provided amount of time allowing the device to enter a low-power mode and also run the radio stack if necessary. We'll also introduce support for ArduinoLowPower to allow more control.

What I was thinking about is the ability to register a callback for your devices which is called when some property changes. This would allow you to block your user task and go low power until something changes - then only react to it once without constantly polling for changes. This will be very useful, so it'll be definitely coming.

[rei-vilo]

Thank you for the suggestion.

Actually, a delay() fits perfectly if there is only one single task.

As the weather sensor can raise an interrupt, I am considering using events. This is what I did for the Low Power Home Network Weather Monitoring project based on sub-1GHz and TI-RTOS: idle mode required as little as 0.0267 mW.