Params ex-server

If you implement a server (autopilot or simulator), you can use IParamsServerEx for high-level parameter management with metadata, type-safe handling, and reactive updates.

First, register the params service during server device build:

var serverDevice = ServerDevice.Create(
    new MavlinkIdentity(config.SystemId, config.ComponentId),
    core,
    builder =>
    {
        // register other services...
        
        // IStatusTextServer has to be registered as well
        config.RegisterStatus();
        
        // Register base params service first
        builder.RegisterParams();
        
        // Then register ex-version with parameter descriptions
        var paramDescriptions = new List<IMavParamTypeMetadata>
        {
            new MavParamTypeMetadata("BARO_PRIMARY", MavParamType.MavParamTypeUint8)
            {
                DefaultValue = new MavParamValue((byte)0),
                MinValue = new MavParamValue((byte)0),
                MaxValue = new MavParamValue((byte)2),
                ShortDesc = "Primary barometer selection"
            },
            new MavParamTypeMetadata("WPNAV_SPEED", MavParamType.MavParamTypeInt32)
            {
                DefaultValue = new MavParamValue(500),
                MinValue = new MavParamValue(10),
                MaxValue = new MavParamValue(2000),
            }
        };
        
        builder.RegisterParamsEx(paramDescriptions, new MavParamCStyleEncoding());
    });

As you can see, some parameter metadata must be provided during server registration. You can read more about metadata here.

After building, you can get the service and work with parameters:

var paramsEx = serverDevice.GetParamsEx();

// Get parameter value
var value = paramsEx["BARO_PRIMARY"];
Console.WriteLine($"Value: {value}");

// Set parameter value
paramsEx["BARO_PRIMARY"] = new MavParamValue((byte)1);

// Subscribe to all parameter changes
using var allChanges = paramsEx.OnUpdated.Subscribe(evt =>
{
    Console.WriteLine($"Parameter {evt.Metadata.Name} changed from {evt.OldValue} to {evt.NewValue}");
});

// Subscribe to specific parameter changes
using var specificChange = paramsEx.OnChange("BARO_PRIMARY").Subscribe(evt =>
{
    Console.WriteLine($"BARO_PRIMARY changed to {evt.NewValue}");
});

You can also set up reactive callbacks for specific parameter types:

// React to float parameter changes
await paramsEx.OnR32(
    myFloatParam, 
    disposeCancel, 
    logger, 
    async (value, firstChange, cancel) =>
    {
        if (firstChange)
        {
            Console.WriteLine($"Initial value: {value}");
        }
        else
        {
            Console.WriteLine($"Parameter changed to: {value}");
            // Apply the new value to your system...
        }
    });

// React to uint8 parameter as boolean
await paramsEx.OnU8Bool(
    myBoolParam,
    disposeCancel,
    logger,
    async (value, firstChange, cancel) =>
    {
        Console.WriteLine($"Boolean parameter: {value}");
        // Apply the boolean value...
    });

// Command-style parameter (triggers action when changed from 0 to non-zero)
paramsEx.OnU8Command(
    myCommandParam,
    disposeCancel,
    logger,
    async (cancel) =>
    {
        Console.WriteLine("Command triggered!");
        // Execute command action...
    });

IParamsServerEx (source)

Represents a high-level parameter server with metadata support, type-safe handling, and reactive updates.

Property	Type	Description
`OnError`	`Observable<Exception>`	Gets the observable sequence of exceptions that occur in the source sequence.
`OnUpdated`	`Observable<ParamChangedEvent>`	Gets an observable sequence of `ParamChangedEvent` events that represents updates to the property.
`AllParamsList`	`IReadOnlyList<IMavParamTypeMetadata>`	List of all parameter metadata.
`AllParamsDict`	`IReadOnlyDictionary<string,(ushort,IMavParamTypeMetadata)>`	Dictionary of parameter metadata by name.

Indexer	Type	Description
`this[string name]`	`MavParamValue`	Gets or sets parameter value by name.
`this[IMavParamTypeMetadata param]`	`MavParamValue`	Gets or sets parameter value by metadata.

Method	Return Type	Description
`OnChange(string name)`	`Observable<ParamChangedEvent>`	Filters parameter changes for a specific parameter.
`OnChange(IMavParamTypeMetadata param)`	`Observable<ParamChangedEvent>`	Filters parameter changes for a specific parameter.
`OnRemoteChange(string name)`	`Observable<ParamChangedEvent>`	Filters remote parameter changes for a specific parameter.
`OnRemoteChange(IMavParamTypeMetadata param)`	`Observable<ParamChangedEvent>`	Filters remote parameter changes for a specific parameter.
`OnLocalChange(string name)`	`Observable<ParamChangedEvent>`	Filters local parameter changes for a specific parameter.
`OnLocalChange(IMavParamTypeMetadata param)`	`Observable<ParamChangedEvent>`	Filters local parameter changes for a specific parameter.
`SetOnChangeReal32(IMavParamTypeMetadata param, Action<float> setCallback)`	`IDisposable`	Sets callback for `float` parameter changes (invokes with initial value then on each change).
`SetOnChangeInt32(IMavParamTypeMetadata param, Action<int> setCallback)`	`IDisposable`	Sets callback for `int32` parameter changes (invokes with initial value then on each change).
`SetOnChangeUint32(IMavParamTypeMetadata param, Action<uint> setCallback)`	`IDisposable`	Sets callback for `uint32` parameter changes (invokes with initial value then on each change).
`SetOnChangeUint16(IMavParamTypeMetadata param, Action<ushort> setCallback)`	`IDisposable`	Sets callback for `uint16` parameter changes (invokes with initial value then on each change).
`SetOnChangeInt16(IMavParamTypeMetadata param, Action<short> setCallback)`	`IDisposable`	Sets callback for `int16` parameter changes (invokes with initial value then on each change).
`SetOnChangeUint8(IMavParamTypeMetadata param, Action<byte> setCallback)`	`IDisposable`	Sets callback for `uint8` parameter changes (invokes with initial value then on each change).
`SetOnChangeInt8(IMavParamTypeMetadata param, Action<sbyte> setCallback)`	`IDisposable`	Sets callback for `int8` parameter changes (invokes with initial value then on each change).
`OnR32(IMavParamTypeMetadata param, CancellationToken disposeCancel, ILogger logger, ParamValueCallback<float> setCallback)`	`Task`	Async callback for `float` parameter changes.
`OnU8(IMavParamTypeMetadata param, CancellationToken disposeCancel, ILogger logger, ParamValueCallback<byte> setCallback)`	`Task`	Async callback for `uint8` parameter changes.
`OnS8(IMavParamTypeMetadata param, CancellationToken disposeCancel, ILogger logger, ParamValueCallback<sbyte> setCallback)`	`Task`	Async callback for `int8` parameter changes.
`OnU16(IMavParamTypeMetadata param, CancellationToken disposeCancel, ILogger logger, ParamValueCallback<ushort> setCallback)`	`Task`	Async callback for `uint16` parameter changes.
`OnS16(IMavParamTypeMetadata param, CancellationToken disposeCancel, ILogger logger, ParamValueCallback<short> setCallback)`	`Task`	Async callback for `int16` parameter changes.
`OnU32(IMavParamTypeMetadata param, CancellationToken disposeCancel, ILogger logger, ParamValueCallback<uint> setCallback)`	`Task`	Async callback for `uint32` parameter changes.
`OnS32(IMavParamTypeMetadata param, CancellationToken disposeCancel, ILogger logger, ParamValueCallback<int> setCallback)`	`Task`	Async callback for `int32` parameter changes.
`OnU8Bool(IMavParamTypeMetadata param, CancellationToken disposeCancel, ILogger logger, ParamValueCallback<bool> setCallback)`	`Task`	Async callback for `uint8` parameter as boolean.
`OnU8Enum<TEnum>(IMavParamTypeMetadata param, CancellationToken disposeCancel, ILogger logger, ParamValueCallback<TEnum> setCallback)`	`Task`	Async callback for `uint8` parameter as enum.
`OnU8Command(IMavParamTypeMetadata param, CancellationToken disposeCancel, ILogger logger, Func<CancellationToken, Task> onEvent)`	`void`	Command trigger on 0 to non-zero transition.
`OnInt32Command(IMavParamTypeMetadata param, CancellationToken disposeCancel, ILogger logger, Func<CancellationToken, Task> onEvent)`	`void`	Command trigger on 0 to non-zero transition.

`ParamValueCallback<T>` Delegate

A callback delegate used for parameter value change handlers.

public delegate Task ParamValueCallback<in T>(T value, bool firstChange, CancellationToken cancel);

Parameter	Type	Description
`value`	`T`	The parameter value.
`firstChange`	`bool`	True if this is the initial value, false for subsequent changes.
`cancel`	`CancellationToken`	Cancellation token.

OnChange* Methods

With name:

Parameter	Type	Description
`name`	`string`	Parameter name to filter for.

With param:

Parameter	Type	Description
`param`	`IMavParamTypeMetadata`	Parameter metadata to filter for.

SetOnChange* Methods

Parameter	Type	Description
`param`	`IMavParamTypeMetadata`	Parameter metadata.
`setCallback`	`Action<T>`	Callback invoked with parameter value on each change.

On* Async Methods

Parameter	Type	Description
`param`	`IMavParamTypeMetadata`	Parameter metadata.
`disposeCancel`	`CancellationToken`	The cancellation token.
`logger`	`ILogger`	Logger for error reporting.
`setCallback`	`ParamValueCallback<T>`	Async callback invoked on parameter changes (initial and updates).

On*Command Methods

Parameter	Type	Description
`param`	`IMavParamTypeMetadata`	Parameter metadata.
`disposeCancel`	`CancellationToken`	The cancellation token.
`logger`	`ILogger`	Logger for error reporting.
`onEvent`	`Func<CancellationToken, Task>`	Async handler triggered on 0→non-zero parameter change.

Last modified: 31 October 2025