struct ara::tsync::TimeMasterMeasurementType

The data structure serves to consolidate detailed measurement data for measurement-based validation and runtime monitoring of the time master. For each transmitted synchronization frame, it bundles the transmission timestamp in the global time base via preciseOriginTimestamp [SWS_TS_14140], the network-related egress timestamp syncEgressTimestamp, and the Ethernet frame identifier sequenceId [SWS_TS_14142]. These aggregated measurement values enable downstream analysis instances to perform seamless plausibility checks on jitter and packet sequences. Since the type is declared as a final data container without internal synchronization, concurrent exchange presumably requires additional protection by the caller. Question (open)

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Context

The structure ara::tsync::TimeMasterMeasurementType is part of the time validation in module tsync of the AUTOSAR Adaptive Platform. According to the specification, it bundles detailed measurement data for validating a time master. In distributed systems, the time master provides the time reference for connected network nodes. To ensure compliance with required synchronization accuracies and to detect timing deviations during ongoing operation, measurement metrics are recorded directly at the interfaces of the time master.

The definition of the type is provided in the header file ara/tsync/time_validation_measurement_types.h [SWS_TS_14140]. As a central data transfer object, the structure consolidates three elementary measured quantities that arise when sending synchronization messages (sync frames) via Ethernet:

• preciseOriginTimestamp: The egress timestamp of the sync frame referenced to the global time base in the format ara::tsync::Timestamp [SWS_TS_14140].
• syncEgressTimestamp: The network-level egress timestamp of the sync frame as a 64-bit integer (std::uint64_t) [SWS_TS_14141].
• sequenceId: The sequence identifier of the transmitted Ethernet frame as a 16-bit value (std::uint16_t) [SWS_TS_14142].

The structure thus acts as a standardized interface between the actual synchronization service of the time master and downstream monitoring or validation components.

Lifecycle

It is declared as struct TimeMasterMeasurementType final, designating the class as a final data structure with pure value semantics. Because it does not manage dynamic resources and has no inheritance hierarchy, its creation is lightweight. Typically, an instance is created by the time master immediately after transmitting a sync frame, as soon as the physical egress timestamp and the sequence number are available.

The lifetime of an instance is tightly coupled to the evaluation cycle. The data is likely to be passed to the consuming validation instance as a copy or via move operations and discarded after completion of the plausibility check. Question Q-c09487031c2b5638 (open) The structure does not contain any internal synchronization mechanisms such as mutexes. If an instance is exchanged across thread boundaries in concurrent software architectures, responsibility for thread-safe access presumably lies entirely with the caller.

Usage Path

The typical sequence of usage includes determining the measurement values during frame transmission, encapsulation in the structure, and forwarding for validation:

1. Transmission of the sync frame: The time master transmits a synchronization frame over the Ethernet network, with the frame identifier being recorded in sequenceId [SWS_TS_14142].
2. Measurement value acquisition: The hardware- or driver-level egress timestamp is acquired as syncEgressTimestamp [SWS_TS_14141]. At the same time, the corresponding global time value is determined and stored as preciseOriginTimestamp [SWS_TS_14140].
3. Populating the structure: The recorded values are aggregated in an instance of TimeMasterMeasurementType.
4. Evaluation: The structure is handed over to the validation subsystem, which detects packet losses based on the sequence number and calculates jitter or transmission drifts by comparing the timestamps.

Sequence diagram: Typical sequence of acquisition and forwarding of TimeMasterMeasurementType. Sources: [SWS_TS_14140], [SWS_TS_14141], [SWS_TS_14142].

Interpretation: By jointly acquiring the local egress timestamp [SWS_TS_14141] and the global reference time [SWS_TS_14140], the validation logic can determine whether processing delays have occurred in the protocol stack of the time master. Question Q-7454a019d8b9e764 (open)