Optimize Sensor Reads with SensorService

While developing code to read sensors asyncronously in C#, it can be very easy to create a large number of threads because of how simple async Task-based code is to write. On low-resource platforms like Meadow, too many threads can cause excessive CPU cycles as it switches between contexts. You can also exceed the number of available threads on these low-resource platforms. To help with this, Meadow provides the SensorService to help avoid this when you are regularly reading for several sensors every second or more.

What does SensorService provide?

The SensorService provides a shared sensor reading thread that can be used to poll sensors at a regular interval. This allows you to avoid creating a new thread for each sensor, which can be resource-intensive on low-resource platforms like Meadow.

Once you have registered your polling sensors with the SensorService, you continue to read values from them using their respective Read and events. Behind the scenes, the SensorService will manage the polling of the sensors at the regular interval using the shared thread.

SensorService is transparent to the sensor. It doesn't change how you interact with the sensor, it just manages the polling of the sensor, replacing the sensor's internal thread loop with the timer thread built into the service.

Migrate your sensors to SensorService

When you finish initializing your desired sensor, you can register it with the SensorService to have it automatically polled at a regular interval. For example, if your project has an SCD-40 sensor using I2C for carbon dioxide concentration, temperature, and humidity, you can register it with the SensorService after you declare it using the I2C bus.

var scd = new Scd40(I2cBus, (byte)Scd40.Addresses.Default);
Resolver.SensorService.RegisterSensor(scd);

This is how the various sensors are registered by default in the Clima, Project Lab, and GNSS Sensor Tracker boards initialize their onboard sensors.

What sensors can use SensorService?

The SensorService is designed to work with sensors that implement the IPollingSensor interface. This interface is used to define sensors that can be polled at a regular interval, and is used by the SensorService to manage the polling of the sensors.

While they won't benefit from the shared sensor reading thread, you can register other sensors with the SensorService for discovery and management elsewhere in your code.

SensorService polling interval requirements

Even while using the SensorService, you can continue to set the polling period with the StartUpdating method's optional parameter. The SensorService does add an additional contraint to the polling period, requiring that the polling interval be divisible by an even second. If the interval is not divisible by an even second, it will be rounded up to the nearest even second. For example, if you set the interval to 1.5 seconds, you will get a new reading from the service rounded up to every 2 seconds. As an extension of that, the fastest you can poll sensors through the SensorService is every 1 second (1Hz).