Instruments, Software Drive Serial Bus Success
When debugging and troubleshooting automotive serial buses, you can choose from a variety of test-system configurations. Products on the market are able to support Controller Area Network (CAN), Local Interconnect Network (LIN), and FlexRay buses as well as the emerging Media Oriented System Transport (MOST) bus supported by the MOST Cooperation, and BroadR-Reach, a technology developed by Broadcom and supported by the OPEN Alliance (One-Pair Ether-Net) Special Interest Group in conjunction with the University of New Hampshire InterOperability Laboratory.1
The tools you can choose range from complete systems configured for automotive test to general-purpose instruments that can be put to automotive bus test and debug tasks. In the first category is National Instruments’ in-vehicle CAN measurement system, based on NI C Series Modules including the NI 9862 C Series NI-XNET High-Speed CAN Interface as well as NI DIAdem software (Figure 1).
|Figure 1. In-Vehicle CAN Measurement System
Courtesy of National Instruments
In the other category are instruments such as the Tektronix DPO and MSO Oscilloscopes (Figure 2). In fact, many oscilloscope vendors offer software options that support a range of serial buses. The Rohde & Schwarz RTO Oscilloscope, for example, supports I2C, SPI, and UART/RS-232 as well as CAN, LIN, and FlexRay.
|Figure 2. DPO70000, DPO7000, and MSO5000 Series Oscilloscopes
Courtesy of Tektronix
In fact, said Farid Akretch, technical marketing manager at Tektronix, “Except for the speeds and the specific protocols, automotive serial buses are tested in a very similar way to other serial buses. But in addition to that, automotive designs—also due to safety requirements in a harsh environment—put an additional emphasis on interoperability between different electronic systems and components. With more complex systems and more analog, digital, and RF functionality in an environment built to safely operate in a wide array of temperature and environments, safe interoperability under all conditions has to be tested.”
Tektronix offers a variety of tools for such testing. Akretch described the MSO/DPO2000 as a low-cost, comprehensive serial-bus analysis solution; it offers trigger, decode, and analysis for CAN and LIN. When working with FlexRay, he added, the MSO/DPO3000 or MSO/DPO4000 Series would be the tools of choice.
Analyzing Mixed Domains
“In addition to the serial buses used in automotive applications,” he said, “more and more designs include wireless and RF functionality or have to deal with EMI.” To address those concerns, he said, the MDO4000 Mixed-Domain Oscilloscope can analyze time-domain and frequency-domain measurements time-correlated on the same screen. “Customers can analyze their CAN, LIN, or FlexRay serial-bus data,” he said, “and at the same time see and analyze data in the frequency domain—all time-correlated.” The MDO4000 essentially includes a mixed-signal oscilloscope with up to four analog and 16 digital channels plus a spectrum analyzer.
Tektronix joined the MOST Cooperation earlier this year.2 “When it comes to MOST,” Akretch said, “Tektronix offers an analysis package that can be used on our lineup of Windows-based oscilloscopes, namely the MSO/DPO5000 Series, DPO7000 Series, and MSO/DPO70000 Series. The Tektronix MOST solution includes coverage of all mandatory compliance tests for 100% of normative tests for MOST50 (mainstream) and MOST150 (early adopter) plus additional informative tests.” MOST testing, he said, also requires the generation of reproducible deterministic and random jitter signals. For that task, the AWG7000 Arbitrary Waveform Generator can create the MOST Cooperation’s official compliance signal pattern.
Akretch said, “Tektronix test-and-measurement instruments are used across the automotive development cycle to design, develop, and debug every component and aspect of automotive electronics”—in digital analysis, for example, to design, develop, and test embedded systems such as electronic control units. Here, he said, “Mixed-signal oscilloscopes help to develop a deeper understanding of complex timing and signal integrity issues.”
He cited several areas in which Tektronix instruments find use:
- In digital RF, where the use of TPMS and RFID systems within a vehicle has created the need to develop and measure real-time RF signals often times time-correlated to other signals and control buses.
- In power system development, where advanced electronic control systems ensure safe and environmentally responsible operation of ever more complex power systems.
- In automotive networks that focus on several technologies and protocols, for which “Tektronix is uniquely positioned with solutions for CAN, LIN, MOST, and FexRay, again for the design, development, and debug of distributed systems such as infotainment, drive-assist systems, car-to-car communications, suspension control, or x-by-wire controls.”
For power analysis, he said, Tektronix offers tools like oscilloscopes, high-voltage and high-current probes, and power application software to enable automation of standard power measurements, analysis of circuit operation, and generation of reports in industry-accepted formats, thereby saving time and efforts as well as speeding development times.
Akretch said that for digital analysis, “Tektronix oscilloscopes and logic analyzers can provide a representation of a large number of signals, allowing customers to make precise timing measurements, identify signal integrity issues, perform margin testing, and time-correlate multiple system buses providing total system visibility.” And with the MDO4000 Series, he said, “Customers now can gain time-correlated system visibility across the time and frequency domain for analog, digital, and RF signals.”
“And for RF,” he said, “where applications such as keyless entries and immobilizer systems are triggered by external events that are intermittent in nature, Tektronix real-time spectrum-analysis tools with DPX technology enable fast discovery, triggering, capture, and analysis of time-varying signals that often are difficult to discover and measure with traditional spectrum analysis tools.”
Protocol Decoding and Triggering
Agilent Technologies addresses automotive bus test applications with its oscilloscopes. Johnnie Hancock, applications engineer at the company, said, “Agilent provides a variety of oscilloscopes with protocol decoding and triggering on the most common serial buses utilized in automotive applications including CAN, LIN, and FlexRay. The most popular Agilent scopes for these applications are the InfiniiVision 3000 X-Series (Figure 3) and the InfiniiVision 7000 Series.”
|Figure 3. Eye-Diagram Test of CAN Signals Using a 3000 X-Series Oscilloscope
Courtesy of Agilent Technologies
He explained, “Agilent oscilloscopes with the CAN, LIN, and FlexRay trigger and decode options primarily are used for physical-layer characterization. The key advantage of a scope over a dedicated serial bus protocol analyzer is that you can observe the quality of your signals (signal integrity) with a scope. Although dedicated serial bus protocol analyzers provide a higher application level of decoding and detect communications errors, they can’t tell you if the error was caused by noise, a low amplitude bit, or a slow rise time. This is what the scope can show.”
Hancock said, “Agilent’s InfiniiVision Series Oscilloscopes provide the fastest waveform update rates (up to 1,000,000 waveforms/s) in the oscilloscope industry. Fast waveform update rates help to uncover random and infrequent signal problems.
“In addition, serial bus decoding in Agilent InfiniiVision Series Oscilloscopes is based on hardware technology to provide a near real-time update of protocol decoding,” he continued. “Most scopes that utilize software-based decoding slow down significantly when decoding is turned on. This is especially true when deep memory also is turned on. With Agilent’s hardware-based decoding technology, waveform update rates are not impacted, and serial-bus decoding is virtually real time. Not only does a fast rate update enhance the usability of the scope, but it more significantly enhances the probability of capturing serial bus communications errors.
“Agilent InfiniiVision scopes also provide eye-diagram mask testing for both CAN and FlexRay,” Hancock said. “No other scope vendor currently offers CAN eye-diagram testing. Eye-diagram mask testing provides a single/composite measure of the overall integrity of the bus by overlaying all bits from all frames based on a unique clock-recovery algorithm for the particular protocol (CAN or FlexRay). Oscilloscope eye-diagram displays show both timing and amplitude errors in one picture. When combined with industry-standard masks based on baud rate and test plane, automatic pass/fail testing can be performed quickly.
“Serial buses in an automobile operate in a naturally harsh environment,” Hancock said. “In other words, noise and signal disturbances can couple onto the bus causing signal-integrity problems. In addition, long serial buses in the automobile can exhibit reflections and ringing due to improper terminations. A scope is required to properly characterize the integrity of the bus.”
CAN, LIN, and FlexRay Interfaces
Noah Reding, automotive product manager at National Instruments, said, “For testing automotive networks and validating ECU communications, we provide both hardware and software tools. From a hardware perspective, we offer our NI-XNET high-performance CAN, LIN, and FlexRay interfaces (Figure 4) in a variety of form factors to allow users to test their networks in different environments and settings. With regard to software, we offer a number of tools that integrate seamlessly with our NI-XNET interfaces to address different application needs.”
|Figure 4. NI-XNET CAN Interfaces
Courtesy of National Instruments
For developing a custom application, Reding added, “NI LabVIEW system design software is a tool that can be used to develop applications that do exactly what a user needs using a high-level, easy-to-use, NI-XNET API included with the hardware. Here, [users] can set up the network communications for their project by taking advantage of the flexibility introduced by LabVIEW. In addition, we offer add-on packages for LabVIEW to simplify the development for users who want to test network communications using higher-level protocols for either diagnostic or calibration applications.”
One such package, Reding said, is the Automotive Diagnostic Command Set, which abstracts the user from the low-level details of the diagnostic protocols such as OBD-II, KWP2000, and Diagnostics over IP. “Diagnostics are a critical part of ECU communications, and being able to understand these protocols built on top of networks like CAN is essential.”
Reding said another add-on for LabVIEW suitable for testing automotive network communications is the ECU Measurement and Calibration Toolkit. “When ECUs are being developed and need to be calibrated for how they operate in situations like providing the right air-to-fuel mixture, protocols such as CCP and XCP are used to read and write directly to memory to tweak parameters for optimization. The ECU Measurement and Calibration Toolkit serves a similar purpose as the Automotive Diagnostic Command Set because it abstracts the user from the low-level details of protocols and simplifies the user experience for rapid application development, except that it is designed for the calibration protocols like CCP and XCP.”
In addition, Reding said, “Automotive network communications are essential in many real-time testing applications like hardware-in-the-loop simulation and test-cell control. These applications share many commonalities like the need for deterministic I/O, importing and executing simulation models, and real-time stimulus generation. NI VeriStand is a configurable software package designed for these types of applications and has a large amount of built-in functionality for interfacing with our NI-XNET CAN, LIN, and FlexRay interfaces. NI VeriStand can greatly reduce the overall test time of automotive networks by providing this framework and starting point for real-time testing applications.”
From Development to End-of-Line Test
As for specific application areas, Reding said, “Due to the fact that National Instruments has a wide variety of customers spanning the entire automotive industry, we find our tools being used in many different areas. Our hardware and software tools can be used for testing throughout the ECU development cycle due to their inherent flexibility.
“For example, customers use our products in the different stages of development because they need to perform different types of testing, prototyping, and simulation,” he said. “The types of testing they can perform include model-in-the-loop simulation, ECU prototyping, hardware-in-the-loop simulation, test-cell measurement and control, in-vehicle logging, and even end-of-line test on the manufacturing line. The integration and openness of our hardware and software platforms allow users to get maximum reuse of their test components throughout their development and customize the tools for their own needs.”
He said NI VeriStand is suited for these applications “…because it a configurable software package designed specifically for real-time testing applications like hardware-in-the-loop simulation. Its built-in capabilities include simulation model import, real-time I/O, stimulus profile generation, and integration with automotive networks.” NI VeriStand, he said, provides a framework that can be extended by users importing their own functionality using software like LabVIEW or by incorporating their own needs with third-party hardware.
As for NI LabVIEW, he described it as “fully customizable system-design software that can be used to develop an application to interface with the automotive networks like CAN, LIN, and FlexRay using the intuitive NI-XNET API. Our customers often tell us that they have an application they need to test and would like to do only what they need and not pay for functionality they don’t need. LabVIEW provides users the capability to do that in a quick and efficient way.”
The NI-XNET API, he said, not only is intuitive, but it also is a single, common API for use with different networks. “The key and unique feature is that the same essential function calls in the API can be used across networks to simplify the user’s testing. It essentially provides a single automotive network driver for use across CAN, LIN, and FlexRay communications.”
The Automotive Diagnostic Command Set and ECU Measurement and Calibration Toolkit, he added, are specifically designed to simplify the communications with diagnostic and calibration protocols. “These tools allow the user to get and provide the information they need quicker without requiring them to be protocol experts. They are abstracted from the protocol details, and the toolkits also are easily incorporated into LabVIEW so there is built-in flexibility for customization.”
Key Hardware Features
Reding said, “A key trend in the automotive industry is that embedded software inside of the vehicle continues to grow. As a result of this growth, it is even more important for ECUs to be able to communicate efficiently and ensure that a high amount of traffic is being processed appropriately. To ensure that this takes place, we designed our NI-XNET products to be high-performance interfaces that make them ideal for testing network communications. Some of the key features of the interfaces include dedicated per-port processors—onboard processors on the hardware to manage network communications and reduce the overall host system load and software complexity.”
Other features, he said, incorporate a NI-XNET device-driven DMA engine. “NI-XNET interfaces combine the performance of low-level microcontroller programming with the speed and power of Windows and LabVIEW Real-Time OS development,” he explained. “The patent-pending NI-XNET device-driven DMA engine reduces system latency, a common pain point for PC-based CAN interfaces, from milliseconds to microseconds. The engine enables the onboard processor to move CAN frames and signals between the interface and the user program without CPU interrupts, freeing host processor time for processing complex models and applications.”
Another feature is the capability to automatically translate CAN, LIN, and FlexRay frames to engineering-level signals, a feature often found in turnkey applications. “The NI-XNET API works with the interface processors. Featuring integrated support for industry-standard signal databases including FIBEX, DBC, LDF, and NI-CAN (.NCD), NI-XNET simplifies building custom applications to work with other tools in complex embedded design workflows.”
“Testing the electronics of a vehicle isn’t just about the network communications,” Reding said. “We hear from different automotive engineers that they need to perform network communications while also reading and measuring signals from a variety of analog and digital signals at the same time. To get an accurate representation of the system in the vehicle they are interested in, we often see them add instrumentation for acquiring additional data that will help them in their development. By having our automotive-network-communications products part of the NI product family, this is very easy to do. Having a single system that can communicate with CAN, LIN, or FlexRay networks while acquiring many types of data like temperature, vibration, and noise can provide key information to developers with all of this synchronized data.
“Network communications,” Reding said, “can take place in a variety of settings: in the lab with a PC, in the garage with a laptop, in a vehicle without driver interaction, or on a manufacturing line. We have designed our NI-XNET products in a number of form factors to help our customers for all of these use-cases. We provide PCI interfaces for the PC use-case; USB, Ethernet, or wireless for portable communications with our NI CompactDAQ platform; a headless, embedded form factor with our NI CompactDAQ or CompactRIO platforms; or even a PXI form factor for the end-of-line test use-case. In addition, we have designed the software to be easily reused across all of these settings to save the amount of time for testing their devices.”
Driving the Future
As for the emerging BroadR-Reach standard, LeCroy announced at the beginning of the year that it was releasing new test packages to address the automotive segment—specifically, two new QualiPHY automated compliance test packages are available for emerging BroadR-Reach and MOST. In addition, LeCroy said its Vehicle Bus Analyzer test solution has been expanded to operate on the WaveRunner 6 Zi, WavePro 7 Zi, and WaveMaster 8 Zi oscilloscope platforms. As the OPEN Alliance and UNH-IOL gear up to assist, initially, semiconductor companies, and subsequently, subsystems and systems makers and finally auto manufacturers themselves, you can expect test-and-measurement companies to extend their support as well.
1. “OPEN Alliance and UNH-IOL Address Evolution of Connected Car,” Industry Update, EE-Evaluation Engineering Online, Aug. 20, 2012, bit.ly/PryGWZ
2. “Tektronix Debuts MHL Test, Joins MOST,” EE-Evaluation Engineering Online, March 7, 2012, bit.ly/Nvl1jc
For Further Reading
CAN Eye-Diagram Mask Testing, Agilent Technologies, Application Note, May 20, 2012.
CAN, LIN, and FlexRay Interfaces for NI VeriStand, National Instruments, Tutorial, March 11, 2011.
FlexRay Physical Layer Eye-Diagram Mask Testing, Agilent Technologies, Application Note, Oct. 20, 2011.
Getting Started with the NI-XNET API for LabVIEW, National Instruments, Tutorial, May 9, 2012.
Measurement, Debug and Analysis for Embedded Automotive Designs, Tektronix, How-to Guide, 2012.
MOST50, MOST150, CAN, LIN Compliance Solution, Tektronix, Datasheet, June 28, 2012.
NI-XNET CAN, LIN, and FlexRay Platform Overview, National Instruments, Tutorial, Nov. 3, 2011.
Oscilloscope Measurement Tools to Help Debug Automotive Serial Buses Faster, Agilent Technologies, Application Note, May 24, 2012.
View a Demo of Configuring Your CAN, LIN, or FlexRay Application with NI-XNET, National Instruments, Webcast on Demand, May 18, 2012.
For More Information