Precise timing for in-vehicle network testing

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

With radar, lidar and camera sensors increasingly present in production vehicles, time sensitivity on networks becomes extremely important, as vast amounts of sensor data needs to be transferred and processed within a few milliseconds. For this reason, test and measurement system supplier Rohde & Schwarz and time-sensitive networks specialist TSN Systems have cooperated on precise timing measurements for in-vehicle networks using automotive Ethernet 100BASE-T1.

The two companies have worked together to provide a comprehensive test solution for engineers who need to perform precise timing measurements on in-vehicle networks with nanosecond accuracy for Layers 1-3. Rohde & Schwarz provides a tailored oscilloscope-based solution while TSN Systems contributes its TSN Box, a hardware interface to the network, and TSN Tools, a measurement and analysis software package.

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 oscilloscope is used in combination with R&S’s RTx-K35 bus measurements statistics option to measure and verify 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 500μs cycle time, resulting in a jitter ranging from 8 ns to 20 ns, which was verified by both the TSN Tools and oscilloscope.

The companies stated that 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 visualization and deep detail analysis, TSN Box serves as an 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 synchronize itself to the gPTP master in the network. This enables powerful applications that need correlation between payload time stamps and TAP time.

Meanwhile, 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. Furthermore, the company’s RT-ZF7 test fixture acts as the link in the middle and allows full monitoring between the transmitter and receiver device in both directions using the oscilloscope.

In combination with a suitable decoding option, the two companies stated that the solution allows for the 100BASE-T1 time data to 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.

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