Test & Measurement

Nanosecond-precision latency for automotive Ethernet

20th July 2020
Alex Lynn

Advanced driver assistance systems (ADAS) require high bandwidth and low latency communications. Automotive Ethernet is becoming the de-facto communication solution to handle these requirements by offering higher data rates as well as time-sensitive network capabilities.

Together, Rohde & Schwarz and TSN Systems provide a test solution for engineers who need to perform precise timing measurements on in-vehicle networks with nanosecond accuracy for Layers 1-3. In the collaboration, Rohde & Schwarz provides a tailored oscilloscope solution based on the R&S RTO, while TSN Systems contributes TSN Box, a hardware interface to the network and TSN Tools, a measurement and analysis software.

The test setup monitors an automotive Ethernet 100BASE-T1 communication link consisting of TSN Box 3.0 acting as talker, listener and test access point (TAP) device. The TSN Box 3.0 TAP device provides information to a PC with TSN Tools based on Layers 2 and 3. The TAP introduced 2x PHY delay for 100BASE-T1 at around 1.5 μs ±10 ns.

The R&S RTO oscilloscope was used along with the R&S RTx-K35 bus measurements statistics option to measure and verify this timing accuracy in the physical layer of the automotive Ethernet signal (Layer 1). The mean time delay was measured to be precisely 1.5μs with a max deviation of ±10.2 ns. In addition, the Qbv traffic (IEEE802.1) was generated by the TSN Box 3.0 with 500 μs cycle time resulting in a jitter ranging from 8 to 20 ns, which was verified by both the TSN Tools and the R&S RTO.

The combination of TSN Tools and TSN Box provides a broad range of functions to address validation and testing for time sensitive automotive Ethernet. While TSN Tools is a PC based analysis software performing visualisation and deeo detail analysis, TSN Box serves as a precise interface to the link. Based on its configuration, it can act as a generic TSN Talker/Listener device with nanosecond precision. The TAP can transparently synchronise itself to the gPTP master in the network. This allows very powerful applications that need correlation between payload time stamps and TAP time.

The R&S RTx-K35 software option for the R&S RTO oscilloscope enables high precision latency measurements, for example monitoring the communication between two devices for a long period, and provides statistics on error rates as well as frame timing on the packets. The R&S RT-ZF7 test fixture acts as the link in the middle and allows the full monitoring between the transmitter and receiver device in both directions using the oscilloscope.

In combination with the suitable decoding option, the 100BASE-T1 time data can be measured frame-to-frame, and engineers can get full bus error statistics such as frame error rate and rate of consecutive errors. Moreover, they can perform precise timing measurements for all automotive serial bus protocols such as automotive Ethernet, CAN, CAN-FD, LIN, I2C and more.

Dr Nik Dimitrakopoulos, Automotive Market Segment Manager at Rohde & Schwarz said: “Our product portfolio has a strong focus in the automotive industry. With the addition of the R&S RTx-K35 option to our oscilloscope family, precise time measurements using various automotive communication standards are possible. We are very proud to assist TSN Systems to validate their timing information for their TSN Box 3.0 devices.”

Juergen Scheuring, Managing Director at TSN Systems, added: “The advent of time sensitive communication in next generation EE-Architectures raises some serious challenges for the test and validation teams at OEM and Tier1. We are happy to cooperate with Rohde & Schwarz and to benefit from their class-leading products providing Layer 1 analysis and expert level knowledge on time sensitive networking.”

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