Databus Test: More than meets the Eye

Fast-evolving databus test technology brings new life to the test, simulation, and analysis of tried-and-true protocols like MIL-STD-1553 and ARINC 429.

Avionics databus technologies change slowly, but databus testers evolve at a much more rapid pace, becoming smaller, denser in circuitry, and more capable.

It’s common for test cards to implement multiple protocols, such as ARINC 429 and MIL-STD-1553, and to fit a large number of channels into a small space. AIM GmbH, for example, squeezes 32 fully programmable 429 channels onto an XMC mezzanine module.

The increasing use of Field-Programmable Gate Arrays (FPGAs) in testers also helps to reduce equipment size, weight and power as well as to increase its versatility and upgradability.

Portability and convenience also account for the popularity of Universal Serial Bus (USB)-linked testers. And Ethernet has come into its own as a medium for test gear.

High-density FPGAs make it easier to host protocol intellectual property from different instruments on the same device. Avionics Interface Technologies (AIT), for example, can provide “a small, ruggedized, flight-test-ready system, which can simultaneously handle 10/100/1000-Mbit/s Ethernet (copper), 1Gb/s Ethernet (optical), 1 Gb/s Fibre Channel (optical) and 10 Gb/s Ethernet (optical),” says Troy Troshynski, AIT’s vice president of marketing and product development. Multi-protocol devices are particularly useful in development and system integration.

Databus test equipment is more about checking the health of the avionics systems attached to the communications medium than about testing the health of the bus or network. This aspect is key as to why you would build and use a databus tester, says Joachim Schuler, AIM’s managing director. The data, for example, could be corrupted or have protocol violations, he says. The tester “acts like a traffic cop in all layers of communication,” down to the physical layer, monitoring and controlling every transaction on the bus.

As the data produced by aircraft systems explodes in volume, databus test/analysis/simulation software is becoming ever more important to help users select the data to be viewed and to display it in human-readable units. The software also helps users understand timing and data integrity issues.

The increasing level of integration in avionics architectures calls for “a simple graphical summary of what is going on at a quick glance,” says Jeff Solberg, marketing manager for Astronics Ballard Technology. “It is further expected that the summary has the ability for users to zoom into details when needed.”

The larger role of test software and hardware is especially true, given the use of legacy buses, says Bill Tilman, field applications engineer with Abaco Systems. College graduates today “never heard of 1553 and 429,” he says. “Take an avionics box that uses an FPGA to format data for the bus. What if engineers design an FPGA that responds too slowly or encodes an extra data word? These devices need to be thoroughly and deeply tested up front, but that doesn’t always happen.”

Multi-Protocol Challenge

In today’s architectures, data traverses different buses and networks. Software helps users to visualize activity across different systems. A box in the wheel well, for example, needs to tell other boxes around the aircraft whether the landing gear is up or down, the gear doors are open or closed, or the lights are on or off, Tilman explains.

System developers and integrators have to know the exact time data is sent and received for all transactions to verify that the boxes are operating correctly. Users need to determine, for example, whether send/receive intervals are within prescribed budgets, the timing is repeatable, the data always gets to its destination, it is correctly formatted, and a box always responds correctly to a given stimulus.

Abaco offers multiple bus analysis packages in its BusTools family. Its BusTools-AFDX-AIL software, for example, supports ARINC 664 — avionics full-duplex switched Ethernet, AFDX — and ARINC 429, with an option for CANbus. “We show the data [for time] together on the same screen,” Tilman says.

The Avionics Interface Technologies Flight Simulyzer, an analyzer/simulator application, can generate, capture, and analyze 1553, 429 and 664 data. The product is used in system integration and avionics development.

The Flight Simulyzer “can help users assess network health by providing quick views of data rates and periodicity per UDP [user datagram protocol] port — the most granular level of addressing — per IP [internet protocol] endpoint and per Ethernet/MAC [media access control] endpoint,” Troshynski says.

AIM’s analyzer software, PBA.pro, allows customers to visualize data flows, error injection, and error detection on multiple protocols simultaneously, Schuler says. “All our interfaces for the different databus protocols can be synchronized for time correlation of captured traffic of all protocols.”

Ballard’s CoPilot product performs similar functions, supporting multiple interfaces simultaneously. In addition to high-level summaries and zooms, CoPilot enhances data visualization with graphs, knobs, dials, gauges, tables, and moving maps, plus scripting for custom event handling, Solberg says.

Wireless is also available. Ballard is introducing a product called the webFLT — a derivative of its webFB wireless electronic flight bag. The webFLT is a functional tester for aircraft systems using the ARINC 717 flight data acquisition bus. The unit connects to the Flight Data Recorder (FDR) system test plug to access information on either the flight data recorder or the digital flight data acquisition unit and then transfers the data to the test computer via an 802.11 b/g WiFi link. This eliminates cabling in the crowded cockpit that can pose tripping hazards or become damaged, Solberg says.

USB

USB-linked equipment is available from AIM, Abaco, Astronics Ballard Technology, and AIT, among others. As the standard peripheral communications bus, USB technology is found on every computer. It’s especially attractive, in combination with handheld computers, for mobile applications. Although it’s not perfect, USB has become an effective option for test.

“USB is not ideal for all types of applications,” says Bill Wargo, president of AIM USA. “It is not fast enough to do real-time across the bus.” That is why AIM’s architecture is designed to do all the processing locally on the device, minimizing how often you have to go across the USB interface, he says. AIM’s design does not rely on constant interaction with the host. Rather, the USB bus is used “for setup and bulk data transfers only.” AIM calls its line of small USB testers “smart cables” because the small units are embedded in connector housings.

AIT’s Network Data Aggregator.

Abaco’s customers, on the other hand, have sufficient processing capability — via the company’s system-level products — on the host computer test system, Tilman says. This approach has proven to be simpler to work with as it allows data to be controlled in a single software location, he says.

PC operating systems raise larger issues. With Windows, for example, “there is no control over things that must happen for timing control,” Tilman says. Tight timing doesn’t matter in PC applications like word processing. But for 1553 and 429, real-time and deterministic systems timing is critical.

Abaco hardware and software are built to work around some of these issues with Windows and Linux, Tilman says. “We have plenty of extra memory and addressable space internally to help provide the data space on the device to mitigate some of these shortfalls [and] also multiple buffers and automatic switching of data buffers for transmitting on the avionics interfaces, so that good and valid data is always available.”

Abaco provides USB products for both 1553 and 429 that are used in avionics development and field tests. The units run under Windows or Linux, so they can be used with tablet computers like Surface as well as laptops. The 429 box is about 1 inch tall, 5 inches long and 5.4 inches wide.

Another aspect of USB is that it is optimized for a constant flow of data in large packets. But MIL-STD-1553 data packets are very small, and USB involves a lot of transaction overhead. So USB can be said to be inefficient for sending a small amount of data between a computer and the 1553 device.

But you can set up USB transactions to occur at specific intervals, when a large amount of data has been collected, AIT’s Troshynski explains. “You can put a lot of memory on the USB device, buffer up large chunks of data and then stream it off [to the computer].” This works well in bus monitoring, for example. AIT’s USB device hosts a large amount of RAM, he says, “so that we can buffer the data from the bus.” The company has both 429 and 1553 USB products that are designed to support lab test and simulation applications and flight line maintenance applications where portability is key.

Ballard also offers a multi-protocol USB device that can interface to 1553, 429, the ARINC 708 weather radar display databus and more. The number of channels that can be addressed, however, is greater with its single-protocol USB interfaces.

Test Cards

Standard-format cards are well suited to the factory test environment, where many different interfaces may need to be squeezed into a rack or chassis. Among the typical form factors are PCI, PCI Express, Compact PCI Express, and PXI Express. For this environment, channel density is a key consideration because it saves the limited space in test system chassis, Troshynski says.

AIT’s newest 1553, 429, and 664 cards focus on PXI Express. This is because of the timing and synchronization features provided by PXI/PXI Express host systems, Troshynski says. The Inter-Range Instrumentation Group (IRIG) time signal can be converted and distributed to all the instruments in the chassis. High-resolution synchronization enables the correlation of event timing across different databuses.

AIT provides PXI testers with 429 and AFDX test instruments to manufacturers of data concentrators, the aircraft nodes that bridge between 429 and 664 protocols, for example. The 429 instrument would send a message to the data concentrator and then the AFDX instrument would capture what comes out on the AFDX side. The user can tell exactly when messages are sent and received and whether messages are arriving at the right locations.

ATI’s eDAQ-1553.

Abaco is offering a 1553/ARINC 429 Mini PCI Express card line with a high-retention, “hard tie screw-in rugged connector,” the company says. Aimed at field test and simulation applications, the units are about 1.2-by-2.0-by-0.2 inches in size. The 1553 card has two fully capable, dual-redundant buses, while the 429 card includes four transmit and eight receive channels.

Ballard also offers modular test cards. Its OmniBus II PXI Express module, for example, enables computers to interface with multiple databuses for the testing, validation, and simulation of commercial and military avionics systems. Databus I/O — added via interchangeable modules — includes 1553, 429, 708, 717, serial, and discretes, the company says.

Ethernet Boxes

Ethernet-based equipment is also popular. Ethernet technology is ubiquitous, fast, and fundamental to IP networks, making it a good choice for distributing bus data around a network.

AIT’s eDAQ 1553 in its current implementation uses Ethernet to make 1553 data accessible to multiple users simultaneously for bus monitoring in a lab. The device reads data off of the 1553 bus, encodes it into Ethernet or AFDX, and sends it out on an Ethernet network. This is much more efficient and cost-effective than having each user connect independently to the bus, Troshynski says.

A successor product, the eDAQ-1553-FQ, expected in 2017, will be flight-qualified for use in flight test scenarios, he says. The data acquisition unit will be able to stream captured 1553 data over Ethernet to flight-test recorders and telemetry gateway systems.

AIM differentiates its ANET Ethernet-based avionics bus interfaces from the competition in its ability to host the Linux operating system. So an embedded version of the company’s PBA.pro bus analyzer software minus the graphical user interface can be employed without an external computer. This standalone capability could come in handy in flight test, for example, where the box could be programmed to automatically carry out certain scheduling and monitoring functions. ANET products currently handle 429, 1553, and 429/1553.

ANET can be used as a traditional instrument (with a PC to visualize and store the data and to control the transactions), standalone instrument, data server or client, or user-customized instrument. AIM argues that this allows more flexibility than earlier products that are connected to a host using a PCI bus, PXI chassis or USB. ANET boxes also can be put into a dock with an Ethernet switch that can interface them to a common computer or network. The units also come in ruggedized packages.

Alta Data Technologies provides an Ethernet appliance/converter. The ENET-MA4 is a small, lightweight, rugged device that the company says can function as a data server “for remoting 1553 and ARINC 429/717 operations on Ethernet local area networks.” The device provides real-time User Datagram Protocol (UDP) connectivity to one or two dual-redundant 1553 buses and eight ARINC channels.

Another Ethernet-enabled product, AIT’s Network Data Aggregator, is a flight-certified system designed to monitor, select, and aggregate Fibre Channel and Ethernet data from multiple input streams to verify the operation of systems in flight. “It can also be configured to capture selected data to forward to flight data recorders over Ethernet and to telemetry transmitters via PCM [pulse code modulation] links,” Troshynski explains.

Ask the Readers

Databus test gear is a perennial requirement for everyone involved in avionics, not just for MROs. This comes out loud and clear in a recent Avionics magazine survey. Readers who are operators, avionics manufacturers, systems integrators, and OEMs, as well as maintenance firms, express a keen interest in the technology, which is used across the board in avionics development, integration, and factory and field environments.

Almost two-thirds of respondents say they are looking to buy new test equipment or upgrade test equipment components. They say they are looking for flexibility, which conforms well to our research. Half or almost half of the respondents say they want legacy as well as next-generation system test capability (45.5 percent), multifunction capability (50 percent), and flexible hardware and software architectures (40.9 percent). AVS

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