Entertainment rides the MOST bus

With a wide-open road, the temptation is to turn up the radio volume, put your foot down, and feel the surge of power as your car accelerates. Unless you’re an automotive engineer, you won’t be thinking about the complicated communications occurring among the various electronic control units (ECUs) that support the driving experience you are enjoying.

Today’s vehicles are very different from older cars that had carburetors and straightforward wiring harnesses. Fuel injection has addressed emissions and performance issues while several electrical networks link as many as 100 ECUs handling everything from power-seat positioning to gear shifting.

Four of the most popular and currently implemented automotive buses are the local interconnect network (LIN), the controller area network (CAN), FlexRay, and the media oriented systems transport (MOST). LIN and low-speed CAN are used to adjust things like power windows and door mirrors. The high-speed version of CAN has been used with anti-lock braking and cruise control. FlexRay offers higher speed and redundancy, making it appropriate for brake- and steer-by-wire safety-critical functions.

MOST is a synchronous network that handles high-speed multimedia streaming and stands out as the only one of the four buses to offer plastic optical fiber (POF) and coaxial physical layers. Being synchronous, MOST has virtually no collisions, benefiting both throughput and determinism. Specifications exist for 25-MHz and 150-MHz POF-based oPHY optical physical layers with an unshielded twisted-pair (UTP)- or STP-based electrical ePHY counterpart for 50 MHz and a special coaxial cPHY 150-MHz version.

As shown in Figure 1, MOST does not just support expensive luxury-car features. At the 16^th International VDI Congress “Electronic Systems for Vehicles” held last October in Baden-Baden, Germany, an economical MOST50 system was demonstrated that eliminated microcontrollers and their associated memory in peripheral nodes. The head unit contains the only microcontroller and remotely controls the other nodes through low-cost UTP connections.¹

Figure 1. MOST50 Demo Configuration
Courtesy of MOST Cooperation

For MOST150, the coaxial and optical network paths neither create EMI nor are they affected by it. In addition, coaxial and glass-fiber connections support the much faster 5-GHz communications rate planned for the next generation of MOST (MOSTng), which is being proposed as a unified bus standard for future vehicles. It’s envisioned by the MOST Cooperation that CAN, LIN, and similar buses won’t disappear, but rather that their communications packets would be encapsulated by MOST much as Ethernet today encapsulates other types of data. And, although MOST networks today are ring structures, a MOSTng network may have a ring, star, daisy-chain, or tree configuration or a mixture.

Players

Notably, the group of companies developing and promoting the MOST standard calls the organization a cooperation rather than a consortium or corporation. At the top level, the partners include Audi, BMW, Daimler, HARMAN, and Microchip Technology. Associate partners are divided between a large number of suppliers and a smaller group of car companies such as Ford, General Motors, Honda, Toyota, and Volkswagen, classified as system integrators. Suppliers include Agilent Technologies, Teledyne LeCroy, RUETZ System Solutions, K2L, and Tektronix on the test side as well as audio/visual vendors such as Bang & Olufsen, Bose, and Visteon.

The capabilities provided by the test companies range from oscilloscope-based protocol decoding to special-purpose MOST test generators and analyzers. Several types of optical-to-electrical converters are available that enable an oscilloscope to be used with an oPHY network. Similarly, the C-O Converter from K2L allows tools developed for an oPHY system to be used with cPHY coaxial-cable networks.

Test solutions

Oscilloscope-based

Tektronix has developed two automotive network software packages. TDSVNM addresses CAN and LIN debug and protocol analysis. You can simultaneously decode CAN and LIN data-link layer information to determine the accuracy of the communications between the buses as well as the message latency. Triggering is selectable for any of the CAN frame types, and decoded messages are displayed along with the bus waveforms.

For MOST50 and MOST150 networks, the company’s DPOJET software with the MOST Essentials Setup Library automates compliance testing and supports flexible and customized test conditions. Scope settings are referred to a network’s four predefined test points for each type of measurement you need to make.

Test points within a MOST network are specified at the output of the transmitter (SP1), at the output of the electrical-to-optical converter (SP2), at the input to the optical receiver (SP3), and at the output of the optical-to-electrical converter following the receiver (SP4). For MOST50’s ePHY, the names of the test points all append an “E,” for example SP1E. The locations of the test points remain the same; in particular, SP2E and SP3E are at the start and end of the UTP link corresponding to SP2 and SP3 at the start and end of the optical fiber link.

For oPHY testing, an optical-to-electrical converter such as the Graviton Model SPD-2 is necessary. The software-supported measurements include eye mask hits, alignment jitter, B0/B1 extinction ratio, overshoot, and undershoot. The application’s report section generates plots showing limits and measured values as well as whether or not the test was passed.

Teledyne LeCroy’s QualiPHY solutions for MOST50 and MOST150 also address compliance testing (Figure 2). The company’s Bob Mart, technical marketing engineer, explained, “Our QualiPHY packages are complete diagnostic tools for finding physical-layer errors and come with the required probes. QualiPHY is designed to reduce the time, effort, and specialized knowledge needed to perform compliance testing on high-speed serial buses.”

Figure 2. WaveRunner 6 Zi with QualiPHY Testing MOST150
oPHY Signals
Courtesy of Teledyne LeCroy

Mart explained that “the software guides the user through each test setup, performs each measurement in accordance with the relevant test procedure, compares each measured value with the applicable specification limits, [and] fully documents all results.” The company has been an associate partner in the MOST Cooperation and provides MOST50 and MOST150 QualiPHY packages free to other members of the organization.

In addition to MOST QualiPHY software, LeCroy offers a variety of automotive trigger/decode solutions for CAN, PSI5, LIN, SENT, and FlexRay networks. Mart said that the trigger, decode, and measurement packages allow you to isolate nodes and error conditions, examine the responses for a given node, and graph them for analysis.

Proprietary Testers

RUETZ System Solutions specializes in car infotainment systems based on the MOST network and serves both as a test lab for products used in these networks as well as a source of MOST-specific test equipment. The company’s TESTERLYZER is a modular test system that includes the TESTERLYZER Pro Compliance software, the hardware TESTERLYZER Box (for MOST25 oPHY), and two OptoLyzer MOST interface modules. With the TESTERLYZER, you can automate MOST device compliance testing.

In addition, the company provides the MOST150 physical-layer stress-test tool (PhLSTT) and the TTsuite graphical software platform for development of TTCN-3-based test programs. According to information on the company’s website, the PhLSTT is used to apply a stress-test pattern to a MOST ECU and check the signal of the responding ECUs for errors. The tool is available with a high-end EOC for compliance testing or alternatively with a standard FOT unit for end-of-line control applications.

Microchip Technology, one of the MOST Cooperation Partners, owns Standard Microsystems Corporation (SMSC) and K2L. The SMSC name has been associated with the OptoLyzer G2 tool chain, a combination of hardware and software elements capable of monitoring and analyzing MOST network data traffic. Following a 2012 management buyout of part of K2L’s business, the decision was announced that SMSC products and newer K2L products would be marketed under the K2L brand.

Several products and combinations of products are available from K2L, all related to automotive networks. The company’s MOCCA compact bus interface unit often is part of these combinations and can be used as an interface for PC-based test and simulation.

As explained by Matthias Karcher, senior manager at K2L, “The OptoLyzer MOCCA compact
(Figure 3) is a crucial component of K2L’s top solutions, which include the Automotive Test System (ATS) and the OptoLyzer MOCCA Bundle. The ATS is a bundle of PC software and the OptoLyzer MOCCA compact hardware, which supports the full extended test and simulation use cases (for example, device simulation, rest bus simulation, test automation) of networked devices and systems using CAN, LIN, FlexRay, MOST, and standard Ethernet or any subset of these communications standards.”

Figure 3. MOCCA Compact Interface Unit
Courtesy of K2L

Karcher continued, “The OptoLyzer MOCCA Bundle …[has] a different compilation, since it comes with the OptoLyzer Suite PC software plus the OptoLyzer MOCCA compact hardware. This solution is designed for deep system analysis of MOST systems, which means tracing, logging, and analysis of all communications on the MOST bus, plus the capability of sending/receiving messages as well as stressing the system.

“For in-depth testing of A/V streaming applications, which is the case for devices such as amplifiers, tuners (radio/TV), players (CD/DVD/Blu-ray), displays, and instrument panel clusters, K2L offers the MOST PCI Toolkit.” He concluded, “This is a PCI card that can be plugged into a standard PC or into a PCI extender box connected to a laptop. It operates via PC software and allows designers to easily send/receive audio or video streams of any kind via the MOST bus in order to simulate or intensively test A/V applications.”

Stimulation

RUETZ’s PhLSTT and K2L’s ATS and OptoLyzer MOCCA Bundle include the capability to stress MOST networks. K2L’s Karcher said that his company’s products can create high traffic on the MOST bus to determine how well DUTs cope in this situation. In addition, he said, “[The OptoLyzer MOCCA Bundle] can generate unlocks on the MOST bus, which simulates possible and real scenarios in a car. For example, when a ring breaks, the voltage drops down and, consequently, one certain device stops working. It can even generate cycles of MOST unlocks where the durations of the unlock and the pause between two unlocks are both adjustable in software.”

Agilent Technologies’ Model 81150/60A Pulse Function Arb Generator “is able to simulate various kinds of physical-layer stress,” according to the company’s Dimitri Malsam, business development engineer—pulse pattern generators. He continued, “It can be channel attenuation, signal reflections from connector interfaces, creation of special signal path behavior, amplitude noise, jitter, intermittent glitches, specially designed logical level transitions, any kinds of signal modulations, multilevel signaling, and others. The signal can be formed arbitrarily, and two channels can be internally combined to generate even more comprehensive real-world scenarios.”

With regard to MOST network testing, he said, “Our product allows the loading of the MOST compliance pattern and the injection of various kinds of distortions for signal level detection measurements and all eye-diagram measurements established in the MOST specification.”

Recording

TTTech Automotive and Vector both offer data loggers suitable for use with CAN, LIN, FlexRay, and MOST networks. TTTech’s ^TTXDataLogger provides 12 LIN and 12 CAN inputs—four of which can be switched between low- or high-speed CAN—as well as three FlexRay, one MOST25, one MOST150, 15 analog, and 15 digital inputs. In addition, six RS-232 and two 100-Mb/s Ethernet ports are included along with six digital and three analog outputs. All activity is simultaneously timestamped with 1-µs accuracy.

The ^TTXDataLogger uses a 1.33-GHz Intel Atom microprocessor along with large amounts of memory: 1 GB of DDR2 RAM, a 4-GB internal flash for system data and configuration, and a 64-GB solid-state disk for data recording and as program memory. The device accesses ECU signals via CCP/XCP and optionally transmits acquired data via Wi-Fi. Data capture is controlled through filtering and triggering selections.

Vector’s GL Loggers also handle CAN, LIN, FlexRay, and MOST150 networks. All of the GL loggers provide in-vehicle operation according to the selections you have made via the graphical configuration program. Using the program, you can configure hardware settings for the various buses. This includes filter and trigger conditions and the diagnostic requests for reading ECU internal data.

For work with MOST150 networks, the optional GLA150 module must be added to a GL3000 or GL4000 family logger. The module interfaces to the MOST network and communicates with the logger via Ethernet. The MOST150 control channel data and both MOST data packets and Ethernet packets are recorded. Captured data is output in ASC, BLF, IMG, or CLF format.

Implementation

To facilitate integration of IP-based data into vehicle infotainment networks, MOST150 includes the capability to transport native Ethernet/IP frames. In a recent MOST Cooperation press release about Daimler’s use of MOST150 technology in the Mercedes Benz S-Class cars, Peter Haeussermann, head of telematics electrics/electronics at Daimler AG, said, “We expect that the prevalence of Internet applications in the automotive environment will grow significantly. Consequently, future infotainment platforms have to meet these new requirements.”

The press release continued, “The Ethernet channel can transmit unmodified Ethernet frames (according to IEEE 802.3) with more than 100 Mb/s depending on the network configuration. This permits software stacks and applications from the consumer and IT domains to be seamlessly migrated into the car. TCP/IP stacks or protocol entities utilizing TCP/IP can communicate via MOST without any modifications. Thus, the new generation of MOST provides the automotive-ready physical layer for Ethernet in the car.”²