Automotive Ethernet basics — 100/1000BASE-T1, time sync, and measurement

100BASE-T1 (formerly BroadR-Reach) and 1000BASE-T1 achieve full duplex over a single pair (two wires). The aim is to reduce wiring, cutting weight and cost.

The important point is that the two ends of a link are split into master and slave. If both ends have the same setting, the link will not come up. Check this setting when connecting evaluation equipment.

Some configurations supply power with PoDL (Power over Data Line). Check support and the power class when selecting equipment.

A PC's ordinary Ethernet port cannot connect directly to 100/1000BASE-T1. For evaluation and measurement, a media converter translates between them.

A TAP passes the signal through to the downstream ECU while duplicating the same data to the measurement system. Not having to break the signal path in order to record is the decisive difference in in-vehicle measurement.

Converters and TAPs serve different purposes. Decide first whether you need to receive and process the signal, or observe it while passing it through.

IEEE 802.1AS (gPTP) and IEEE 1588 (PTP) are mechanisms for aligning the clocks of devices on a network.

Where many measurement systems stumble is that aligning clocks and having sensors capture data at the same instant are separate problems. Distributing the same time with PTP does not guarantee that every camera exposes at the same moment.

If strict synchronization is required, you need a two-stage design: distribute a common trigger (FSYNC or similar) to all sensors, and relate capture times to a common time domain. The achievable accuracy also depends on whether timestamps are applied in hardware or software.

In multi-camera setups, the bandwidth of uncompressed RAW data is the biggest constraint. Calculate the required bandwidth from resolution, bit depth, frame rate, number of HDR exposures, and number of cameras, and confirm it fits within the recorder's sustained write bandwidth (not its peak figure).

Converters from SerDes (GMSL2, FPD-Link III, CSI-2) to Ethernet have a fixed number of output ports per unit. Matching the number of converters × outputs per converter to the number of recorder input ports is the starting point for configuration design.

OPEN Alliance TC8 is the test specification for automotive Ethernet ECUs. It defines test items from the physical layer up to the upper layers, and OEMs may require proof of conformance.

Whether to own test equipment in-house or outsource to an accredited lab is, in practice, best decided by test frequency and the number of target products. In some cases, test reports from an ISO/IEC 17025-accredited lab are required.

For automotive and industrial managed switches, transparent-clock support for time synchronization can be a selection criterion in addition to VLAN, QoS, and port mirroring.

For measurement, check that the mirror port's bandwidth can handle the traffic on the main link, and that mirroring does not introduce delay or loss.