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| 1 | +# System.Device.Model - attributes for device bindings |
| 2 | + |
| 3 | +**This library is experimental, it may change and it may be moved to a different package in the future. Avoid taking direct dependency on it.** |
| 4 | + |
| 5 | +This library provides a set of attributes which allow to annotate devices. |
| 6 | + |
| 7 | +They can be used for: |
| 8 | + |
| 9 | +- implementation of Azure Plug & Play |
| 10 | +- providing extra metadata about sensors (we can i.e. generate some parts of the README file or add extra checks) |
| 11 | + |
| 12 | +Model is representing language independent description of the device. The attributes represent a C# mapping from C# types into the model. |
| 13 | + |
| 14 | +## InterfaceAttribute |
| 15 | + |
| 16 | +Every class producing telemetry or exposing some commands should put a telemetry attribute on it |
| 17 | + |
| 18 | +```csharp |
| 19 | + [Interface("LPS25H - Piezoresistive pressure and thermometer sensor")] |
| 20 | + public class Lps25h : IDisposable |
| 21 | +``` |
| 22 | + |
| 23 | +- if class derives from class annotated with `[Interface(...)]` attribute: |
| 24 | + - class will inherit all annotations from the base class(es) |
| 25 | + - if class provides extra telemetry/command/properties it should add another InterfaceAttribute on itself |
| 26 | + - if class doesn't provide any extra annotations it should not have extra interface |
| 27 | +- display name must be provided to the InterfaceAttribute |
| 28 | + |
| 29 | +## TelemetryAttribute |
| 30 | + |
| 31 | +Every method or property producing telemetry should have `[Telemetry]` attribute on it. |
| 32 | +For properties providing name of the `Telemetry` is optional as it can be deduced from the property name. |
| 33 | + |
| 34 | +Telemetry can be put on: |
| 35 | + |
| 36 | +- properties |
| 37 | +- methods returning value but not taking any arguments |
| 38 | +- methods returning bool and taking one `out` argument |
| 39 | + - multiple `out` arguments are currently out of scope but are considered |
| 40 | + |
| 41 | +```csharp |
| 42 | + [Telemetry] |
| 43 | + public Temperature Temperature => Temperature.FromDegreesCelsius(42.5f + ReadInt16(Register.Temperature) / 480f); |
| 44 | + |
| 45 | + [Telemetry("Humidity")] |
| 46 | + public bool TryReadHumidity(out RelativeHumidity humidity) => TryReadHumidityCore(out humidity); |
| 47 | + |
| 48 | + [Telemetry("Pressure")] |
| 49 | + public Pressure ReadPressure() { /*...*/ } |
| 50 | +``` |
| 51 | + |
| 52 | +- if telemetry is not producing typed unit (i.e. `Vector3`) it should have additional `displayName` provided |
| 53 | +- optional arguments are treated as if they were not there |
| 54 | +- it's not allowed to have more than one `Telemetry` attribute with the same name on the same `Interface` |
| 55 | + |
| 56 | +## PropertyAttribute |
| 57 | + |
| 58 | +Properties should be put on properties or methods which describe the device or change its functioning. |
| 59 | +They should only be used on things which don't change value between calls (unless it's been written to or a command has been executed on the device). |
| 60 | +Specifially reading (telemetry) from the device should not change the state of the property. |
| 61 | + |
| 62 | +Usage is similar to Telemetry with some additions: |
| 63 | + |
| 64 | +- they can be writable |
| 65 | + - if same name (i.e. `PowerMode`) is used on i.e. `SetPowerMode` and `ReadPowerMode` they will be merged into a single model property |
| 66 | +- they can be put on methods without return value taking one argument (it must not be be passed by reference) |
| 67 | +- it's not allowed for more than one writers or readers with the same name to be present on the same interface |
| 68 | + |
| 69 | +```csharp |
| 70 | +[Property] |
| 71 | +public Sampling HumiditySampling { get { /*...*/ } set { /* ... */ } } |
| 72 | + |
| 73 | +[Property("PowerMode")] |
| 74 | +public void SetPowerMode(Bme680PowerMode powerMode) { /*...*/ } |
| 75 | +[Property("PowerMode")] |
| 76 | +public Bme680PowerMode ReadPowerMode() { /*...*/ } |
| 77 | +``` |
| 78 | + |
| 79 | +## ComponentAttribute |
| 80 | + |
| 81 | +Components represent references to other (instances) of interfaces. |
| 82 | +They can only be put on the properties, the return type of the property or its ancestor class should have an `Interface` attribute. |
| 83 | + |
| 84 | +```csharp |
| 85 | +[Component] |
| 86 | +public SenseHatTemperatureAndHumidity TemperatureAndHumidity { get; private set; } |
| 87 | + |
| 88 | +// ... |
| 89 | +public class SenseHatTemperatureAndHumidity : Hts221.Hts221 { /* ... */ } |
| 90 | +// ... |
| 91 | +[Interface("HTS221 - Capacitive digital sensor for relative humidity and temperature")] |
| 92 | +public class Hts221 : IDisposable { /* ... */ } |
| 93 | +``` |
| 94 | + |
| 95 | +## CommandAttribute |
| 96 | + |
| 97 | +Commands can be something which can be executed on the device and they can be put only on methods. |
| 98 | + |
| 99 | +```csharp |
| 100 | +[Command] |
| 101 | +public void PlayTone(double frequency, int duraton) { /* ... */ } |
| 102 | +[Command] |
| 103 | +protected override void SetDefaultConfiguration() { /* ... */ } |
| 104 | +``` |
| 105 | + |
| 106 | +## Type serialization |
| 107 | + |
| 108 | +Only simple types can be serialized: |
| 109 | + |
| 110 | +- enums (without Flags attribute) |
| 111 | + - values out of enum range are not permitted (i.e. bitwise combination) |
| 112 | +- UnitsNet units |
| 113 | +- basic C# types |
| 114 | +- System.Numerics.Vector2, System.Numerics.Vector3, System.Numerics.Vector4 |
| 115 | +- System.Drawing.Color |
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