Data sources

SDV Telemetry supports multiple types of data sources. This page provides an overview of these types and what features Telemetry supports per data source type.

Sample code for data source implementations is available in the system/software_defined_vehicle/samples/telemetry directory.

Data source definition in metrics configurations

Metrics configurations define one or more data sources to collect metrics from. Each data source is identified by its source_identifier. The source_identifier format depends on the data source:

Data source	Format	Description	Examples
SDV service	Protobuf message name	The fully qualified protobuf message name. If the service has multiple instances, append the service unit name separated by a pipe (|).	"com.sdv.google.example.TellTale|com-sdv-google-example-tell-tale-status-hibeam"
	Fully Qualified Instance Name (FQIN) with Service Unit Name	The FQIN and service unit name separated by a pipe (|).	"vm-cdc:com.google.android.sdv.pubsub.SomeService/instance1|tire-pressure"
Configurable Publisher Registry-based publisher	Publisher name	The exact serviceName used to register the publisher at the Configurable Publisher Registry.	Any string is valid.

For each data source, you can use the following options to parameterize the message retrieval. You can define the same data source multiple times with different options in the same metrics configuration. For example, you can have some part of your edge processing use a different sub-sampling interval than other parts of your edge processing.

Option	Type	Description
connection_type	SUBSCRIPTION or ON_DEMAND	If set to SUBSCRIPTION, the Telemetry service subscribes to the data source. If set to ON_DEMAND, the Telemetry service fetches messages from the data source only on demand.
configuration	google.protobuf.Any	If set, the Telemetry service passes through the configuration object to the data source when communicating with it.
sub_sampling_interval	google.protobuf.Duration	If set, messages are sub-sampled, so that the Telemetry service processes a message at most every sub_sampling_interval duration.
fetch_last_message	bool	If set, the Telemetry service retrieves the last published message when subscribing to the data source, even if that message was published in the past.

Depending on the type of data source (see the following sections), only a subset of parameters is supported by the Telemetry service. The following table provides an overview.

Option	RPC SDV service	Publish-subscribe (pub/sub) SDV service	Configurable Publisher Registry-based publishers
connection_type: SUBSCRIPTION	Supported 1	Supported	Supported
connection_type: ON_DEMAND	Supported 2	Supported	Supported 3
configuration	Supported	Not applicable	Supported
sub_sampling_interval	Not supported	Supported 4	Not supported
fetch_last_message	Not supported	Supported 5	Not supported

SDV services (through SDV comms stack)

The Telemetry service can collect data from other SDV services. Both RPC and pub/sub SDV services are supported. Since the Telemetry service doesn't know the list of services it will subscribe to at build time, it relies on Protobuf reflection to decode messages received from SDV services.

SDV services don't provide reflection metadata by default. To make an SDV service usable as a telemetry data source, you must enable runtime config generation of the service's VSIDL catalog. For more information, see VSIDL Provider Guide for Service Bundle Developers.

For testing and evaluation purposes only, you can instead set the register_reflection_metadata option to true in the service bundle definition. For more information, see Service bundle.

RPC SDV services

Telemetry has limited support for RPC SDV services. For more information, see Define RPC services. To collect data from an RPC SDV service, the service must expose one or both of the following RPC methods:

• CreateSubscription returns a stream of user-defined responses:

  rpc CreateSubscription(<configuration>) returns (stream <response>)
  

• GetLatestMessage returns a user-defined response:

  rpc GetLatestMessage(<configuration>) returns (<response>)
  

You can use the configuration argument to parameterize the behavior of your data source, for example, to request a different publishing frequency or to select the entity you want to subscribe to (for example, which tire to read tire pressure from).

When defining an RPC SDV service as a data source in a metrics configuration, you can specify a configuration value in the data source definition, which is used as the argument for this RPC. The Telemetry service handles the configuration object transparently and passes through whatever you define.

The type of the configuration argument for both methods can be either google.protobuf.Any or a user-defined type. If you provide both methods, the argument types must be identical. If you don't need a configuration argument for these RPC methods, use google.protobuf.Empty.

Depending on the connection_type specified in the data source definition of the metrics configuration, the Telemetry service calls either CreateSubscription (for connection_type: SUBSCRIPTION) or GetLatestMessage (for connection_type: ON_DEMAND).

Pub/sub SDV services

Telemetry has full support for monitoring pub/sub channels defined in VSIDL exposed by SDV services without any additional configuration required. For more information, see Add a publisher to a service bundle.

In addition to subscribing to pub/sub channels, Telemetry also supports on-demand retrieval of the latest message published to a channel.

Configurable Publisher Registry

In addition to collecting data from SDV services using the SDV comms stack, Telemetry supports collecting data from applications and services that register publishers in the Telemetry service's Configurable Publisher Registry. This capability is most useful on IVI, where the SDV comms stack isn't available.

The Configurable Publisher Registry can also be useful for debugging and prototyping without having to write SDV service bundles. For more information, see Configurable Publisher Registry.