ARINC-818 TESTING FOR AVIONICS APPLICATIONS. Ken Bisson Troy Troshynski

Transcription

1 ARINC-818 TESTING FOR AVIONICS APPLICATIONS Ken Bisson Troy Troshynski 2007 The ARINC-818 Specification is an industry standard that defines a digital video interface link and protocol that is used for high-speed digital video display data communications. This paper provides an overview of the ARINC-818 link and protocols being used for Avionics. The paper also discusses the practical testing of an ARINC-818 network, and the testing challenges associated with this high-speed/high data rate application.

2 ABSTRACT The ARINC-818 Specification is an industry standard that defines a digital video interface link and protocol that is used for high-speed digital video display data communications. This Specification enables data generation units and display devices working in aerospace applications to utilize a common link and protocols that support high-bandwidth data specifically for digital video applications. Aerospace applications currently use many different video formats. Video formats differ in their Frame Rates, resolution, pixel density, and interlacing techniques. The ARINC-818 Specification defines how all these video formats are built and mapped to the industry standard Fibre Channel. Page 2

3 INTRODUCTION Avionics applications are increasingly using more and more displayed video data. The high-bandwidth video data that comes in large amounts must be integrated into the avionics communications network. To date, most avionics applications rely on proprietary hardware to merge the video display and data that are routed over separate networks. There are commercial standards for avionics data communications like ARINC-429 and ARINC-664, but these are simply not fast enough for video data. A commercial standard called ARINC- 818 has been defined for highbandwidth video data in commercial aircraft applications. The ARINC-818 Specification is based on the Fibre Channel standard (FC). Fibre Channel combines the ability to move large amounts of high-bandwidth data like computer buses with the routing and protocol capabilities found in networks. In addition, Fibre Channel includes redundancy and deterministic behavior that is required for avionics applications. The Fibre Channel standard defines the physical protocol (how to route the data) separately from the application protocol (how the data is organized). The standard identifies layers that are used for moving data. These layers define the physical connections, data encoding, and routing needed to pass data between devices. In addition, Fibre Channel defines an FC-AV (Audio/Visual) Upper Layer Protocol Page 3 (ULP) which maps audio and video data onto a Fibre Channel network. The ARINC-818 Specification refines the FC-AV with specific definition of the amount and types of digital video data for the most common standard video interface types. ARINC-818 has been adopted by Boeing on its 787 commercial aircraft program, and by Airbus on its A400M program. ARINC-818 OVERVIEW There are three reasons why ARINC- 818 is a great fit for avionics applications: Simple to implement Fast and scalable Separate physical and application protocols ARINC-818 defines an application protocol working on a Fibre Channel closed network topology. In order to understand ARINC-818, one must also understand Fibre Channel. Likewise, when testing ARINC-818 applications, it is essential to understand and be able to perform Fibre Channel testing as well.

4 Fibre Channel separates functional areas into layers: FC-4 Mapping of Protocols: Application protocol mapping to Fibre Channel FC-3 Common Services: Frame layout, flow control, class of service FC-2 Protocol: Frame layout, flow control, Class of service FC-1: Transmission Protocol: Encoding, word transmission, error detection FC-0 Physical: Cabling, connectors FC-AV is the ULP defined in layer 4. ARINC-818 further refines the FC-AV definition. SIMPLE TO IMPLEMENT The primary elements of the ARINC- 818 topology are End Systems, which are networked together in a point-topoint connection. The End Systems will either be a data source or a receiver (display unit). The primary elements of the ARINC- 818 topology are End Systems, which are networked together in a point-topoint connection. The End Systems will either be a data source or a receiver (display unit). Fibre Channel data switches can be used for routing if multiple connections are required. But even with a switch for routing, all links are treated as point-topoint connections. The physical interface for a Fibre Channel port is composed of simple, unidirectional, serial connections, using one line for transmit, and another for receive. These are lightweight and easy to maintain, and there are no large multi-pin cable bundles and connectors. Either optical or standard copper cabling can be used. The choice of media type is dependent upon distance, power requirements, and weight. The physical media options, with no degradation of performance, are a real benefit to the avionics design engineer. For testing, the test equipment must be able to simulate End Systems. This means having the flexibility to also accommodate the various Fibre Channel physical interfaces. In addition, the test equipment must be able to insert itself in-line between the End Systems. There are many different splitters and taps available for copper and optical media to do this without affecting signals. FAST AND SCALABLE Fibre Channel is extremely fast. Currently, 1, 2, and 4 Gbps speeds are all in use today, but the Fibre Channel roadmap calls for an increase in speed to 16 Gbps in the next few years. Since each end system has access to the full bandwidth, Fibre Channel links can easily support a multitude of highbandwidth display applications. Avionics applications engineers can choose from a wide variety of display characteristics to meet their needs. ARINC-818 defines the data network to meet these display requirements today, and it includes provisions for future upgrades. Page 4

5 Figure 1 shows the relationship between the various display resolutions and data bandwidth. Figure 1 called the frame. For Fibre Channel, a frame has 24 bytes of control information (header) and anywhere from 0 to 2,112 bytes of payload (pure data containing the user information). If a packet of user information us too large to send in one frame, then multiple frames must be grouped together, forming a sequence. Figure 2 Fibre Channel Frame Format SEPARATE PHYSICAL AND APPLICATION PROTOCOLS The Fibre Channel standard defines the protocol (how to route the data) separately from the ARINC-818 application protocol (how the display data is organized). Each has its own unique characteristics. The ARINC-818 Specification only defines the ULP that is mapped onto Fibre Channel. In fact, it would be possible to route multiple types of protocols (for example ARINC- 818 and IP) simultaneously over the same Fibre Channel network. FIBRE CHANNEL As stated previously, in order to understand ARINC-818, one must also understand Fibre Channel. Fibre Channel, like a network architecture, transmits blocks of user information called packets. Before sending the data over the physical link, additional Fibre Channel-specific control information is added to the packet. The combination of the control information and the data is an IDLE. Page 5 In addition to frames of data, Fibre Channel also specifies another type of data to be sent over the link. These are called ordered sets. Ordered sets are Fibre Channel s mechanism to perform control and signaling functions over the simplex transmission link. There are three types of Ordered Sets: Frame delimiters: identify start/end of frames Signals: indicate events or actions Primitive Sequences: indicate states transmitted until something changes Preceding any frame of data is a start of frame (SOF) delimiter. Likewise, every frame is followed by an end of frame delimiter (EOF). Lastly, there must be a minimum of six ordered sets (most likely fill words) between the transmissions of frames. The most common fill word is

6 ARINC-818 ARINC-818 maps the display video data format onto the payload of the Fibre Channel frames. In order to understand the mapping protocol, one must understand a little about digital video frames. A digital frame is a two dimensional image made up of multiple rows of individual pixel data that display horizontally in a visible display. Digital display formats vary by the number of rows and the number of bits per pixel. For example, an SVGA PC display is 1280 rows by 800 pixels in a row. The bits per pixel usually identifies the color resolution. Therefore, the amount of data needed to generate a single 1280 by 800 frame with 16-bits per pixel color is 1.6 MB. Digital displays are also generally scanned vertically; which means that data starts from the top and progressively scans to the bottom. Frames delivered to the digital display must be ordered in the same fashion. In addition to the data, there are timing elements that must be met. digital displays must be synchronized vertically and horizontally. There must be an identifiable, consistent timing pattern associated with the display of each consecutive row (synchronized horizontally); also, every time the display data reaches the bottom of the display it starts again at the top. high-bandwidth, low latency network is required. In the ARINC-818 Specification, each digital display frame is called a container. The container is made up of a header and objects. Objects are the data elements of the container. There are four types of objects: Object 0: Ancillary data Object 1: Audio data Object 2: Video data (progressive scan) Object 3: Video data (for interlaced displays) Since the container is larger than what a single Fibre Channel frame can hold, the container is transferred as multiple data objects. In addition, most single digital display lines will also exceed the payload of a single Fibre Channel frame, so multiple data objects may be used to transmit one digital display line. Figure 3 shows how a single container and its objects are defined. Figure 3 Single Container and Objects For example, a common vertical synchronization is a 30Hz display. By adding the amount of data contained in a single display and combining the requirement of updating this amount of data at 30 Hz, it is clear to see why a Page 6

7 Each object is embedded in the data payload of a Fibre Channel frame. Object 0 contains the container header information. The container header is 22 bytes of data that describes the container and summarizes the objects that will follow. For example, information included in the header is a definition of the frame rate, the frame type, and the number of objects used in the container. The header also includes the Cyclic Redundancy Checking (CRC) value of the previous container. The container mapping to the Fibre Channel frames is shown in Figure 4 below. Figure 4 Container Maps to Fibre Channel Frames Testing individual End Systems Testing End Systems in the ARINC-818 network INDIVIDUAL END SYSTEM TESTING Avionics digital display systems are delivered to the airframe manufacturer from many suppliers. Each display specializes in a particular function for the aircraft (i.e. navigation, collision avoidance radar, health maintenance). Individual testing is required for display systems and data generator End Systems; therefore, an ARINC-818 test system must be able to simulate the data source and/or simulate the digital display. Testing associated with ARINC-818 End Systems should answer the following questions. TESTING ARINC-818 Testing is a critical element in the process of integrating any avionics system. It is important to completely understand the behavior of each individual component and the whole system during normal operations, as well as behaviors and reactions to system faults. Testing is required to understand the movement of data over the ARINC-818 network as well as understanding the data that is being passed. Testing occurs in two phases: Page 7 Do the source data End System ports transmit correct containers at the appropriate synchronization intervals? How many transmit errors are produced over a long time period? Does the display receive and process objects correctly? How does the display system react to receiving incorrect objects, frames with protocol errors, CRC errors, or frames with bad data in them? Is the End System s redundancy management and integrity checking working?

8 NETWORK SYSTEM TESTS Individual End Systems are eventually integrated into an avionics ARINC-818 network. Effective testing is required during integration to ensure that the End System operates efficiently. This type of testing requires that the test equipment is placed in-line between the data source, and the digital display. Network frame flow testing reveals flaws in the system design and implementation. Testing associated with checking the ARINC-818 network frame flow includes the following. formats, but cannot decipher Fibre Channel protocol or network timing errors. An ARINC-818 test system requires the use of interfaces specifically designed for Fibre Channel and digital display applications. This system will perform all of the necessary protocol analysis, and have the capability of examining the Fibre Channel link information and object frame data in the payload in real time. We have found that there are currently only two commercial manufacturers of these products available. Monitoring each End System for frame errors associated with frame movement over the network. Checking the deterministic flow of containers from the End System source. Checking the redundancy of the network (if implemented). Checking the ARINC-818 network reaction and tolerance of errors. CHOOSING AN ARINC-818 TEST SYSTEM There are commercially available Fibre Channel protocol analyzers and digital frame grabber interfaces that can perform various degrees of ARINC-818 testing. Fibre Channel protocol analyzers are effective for testing Fibre Channel protocol errors only; they are not capable of monitoring objects within the Fibre Channel data payload of the frame in real time. Likewise, digital frame grabbers can display at various Page 8 The test system should perform the following three types of tests. 1. Traffic generation 2. Traffic monitoring 3. Digital display (receive) operation TRAFFIC GENERATION Traffic Generation is the ability to produce Digital Display containers from a single port, or redundant ports. The Containers will be sent using a Fibre Channel network to a Digital Display End System. It is important to test multiple types of container frames, and the ability to generate payload (display) data.

9 The setup of the Virtual Link for simulation will include the following actions: Constructing Object 0 Header Constructing Object 1, 2, or 3 Data Implementing the network connection (single or redundant) Sending objects with precise timing Fill words are used (most notably IDLES) to fill in the gaps between Fibre Channel frame transmissions. The number of IDLE fill words between the end of the frame and the start of the next frame is used to govern the vertical and horizontal synchronization characteristics of the frame. The data generation simulator must have the ability to adjust the number of IDLE fill words. The traffic generator needs to implement a robust scheduler capable of sequencing objects. The inter-message gaps between objects need to be programmable to a minimum of one (1) transmission word, 4 bytes, over the Fibre Channel network. This allows the test system to manipulate the digital display vertical and horizontal sync parameters and determining tolerances at various display rates. For example, consider a digital display that runs at 1024 rows by 768 pixels per row, 24 bits per pixel. The display operates at a 30Hz update rate, and it is a progressive scan device (every line is updated sequentially). ARINC-818 maps this display s Object 2 data elements onto 1536 Fibre Channel frames. Figure 6 illustrates the precise time sequence needed in order to maintain vertical and horizontal synchronization. Figure x 768, 30 Hz, 24-bit Page 9 The most flexible ARINC-818 traffic generation testers will be most capable of manipulating data at the Fibre Channel word level. In order to support multiple types of digital displays, the test equipment must have the ability to control the fill words used for timing. Error injection associated with traffic generation is important to determine how the display End System will behave in various error conditions. The types of error injection include the following. Fibre Channel frame level errors (CRC, wrong byte alignment, size) Incorrect container CRCs Incorrect sequencing of frames and objects A last important feature of the traffic generator is the ability to operate at non-standard Fibre Channel rates. As described previously, ARINC-818 uses a standard Fibre Channel rate (i.e., 1 Gbps, 2 Gbps ) and maps its objects to it. Fibre Channel fill words (IDLES) are used to adjust the timing to the specific display. There are digital displays made that expect digital data input at fixed rates, not corresponding to standard

10 Fibre Channel rates. It is important for the traffic generator to be able to adjust its baud rate to these non-standard rates. Although these types of displays do not adhere to the ARINC-818 Specification, they are common, commercially available products. IN-LINE TRAFFIC MONITORING Traffic monitoring is the ability to look at and capture all frames of data traversing the network. The ability to monitor traffic in chronological order, including IDLES, is important for monitoring anomalies. A complete analysis of the network can be accomplished by looking at the traffic over time. This information will yield how efficiently containers travel over the network. It is equally important for measuring an End System s adherence to ARINC-818 timing specifications for the particular digital display type. For monitoring tests, the test system needs to have a programmable capture mode. This provides the ability to begin capturing data based on an event. The event can be an error condition, a specific start of frame, or even a portion of digital data embedded within the payload. Programmable capture enables trapping infrequent errors so that network behavior that prompts these errors can be analyzed and repaired. Monitoring operational tests need to have the capability of storing data for long captures over time. ARINC-818 applications generate a lot of data, so the capability of filtering some of the data in hardware before archiving is needed. A test system that can store gigabytes of data onto a disk file for later review is vital. Archived disk files can be analyzed in detail, post operation. DIGITAL DISPLAY RECEIVE OPERATIONS The receive operational testing consists of receiving digital display frames from a Fibre Channel port just like an End System. These tests can be conducted by simulating the display End System, or by shadowing the actual receiving digital display End System. Shadowing simply means connecting to the same physical port connection as the receiver End System using a network splitter or tap, and acquiring the incoming frames simultaneously with the receiver End System. For receive testing, only the digital data frames are received. This is different from the Monitoring tests described previously where every frame and Fibre Channel fill word is captured. The intent of the receive operations testing is to gather and display the container information. Each incoming container is checked for CRC errors and statistics are kept of these error conditions. Receive operations tests can examine the ARINC-818 protocol by displaying the data visually. The test system must mimic the actual display, or be programmable to mimic the display attributes (i.e., VGA, XGA, DVI ). The ability of the test system to look at the data contained within the payload to verify its integrity is the important test function. Page 10

11 CONCLUSION ARINC-818 is a new Specification for implementing a digital display network in avionics applications. The ARINC-818 Specification is based on a Fibre Channel network architecture. Fibre Channel defines the topology and implementation of the network. ARINC-818 defines the protocol that defines the digital display information and its mapping to Fibre Channel. These standards specifically address moving high bandwidth, low latency data reliably and with determinism. These are key requirements for avionics communications. ARINC-818 test systems need to verify and monitor the behavior of the ARINC-818 network which requires doing more than just examining the digital display. Tests include traffic generation, chronological monitoring, and simulating End Systems receiving ARINC-818 containers. These tests require Fibre Channel testing, as well as checking the integrity of the digital display data. It is most important to look at timing within the network. The efficiency of the data traversing the ARINC-818 network is more important than the simple measurement of protocol faults that occur over time. REFERENCES ARINC Specification 818, Avionics Digital Video Bus, High Data Rate. ANSI INCITS (R1999), Information Technology - Fibre Channel - Physical and Signaling Interface (FC-PH) (formerly ANSI X (R1999)) (includes supplements). ANSI INCITS , Information technology -Fibre Channel - Audio Video (FC- AV). [1] Kembel, Robert W., Fibre Channel A Comprehensive Introduction, Northwest Learning Associates, [2] Avionics Digital Video Bus, High Data Rate Draft 3 of project Paper 818, Airlines Electronic Engineering Committee, June 24, [3] Information Technology Fibre Channel Audio Video (FC-AV), T11/Project D/1.3, NCITS, May 1, [4] Kelley, Timothy, ARINC 818 Becomes the New Protocol Standard for High- Performance Video Systems, Great River Technology, COTS Journal, December 2006, [5] What is Fibre Channel, Ancot Corporation, Page 11

12 [6] Fibre Channel Speed Chart, Fibre Channel Industry Association, [7] fcxplorer User s Manual, AIT, Version 2.0, Rev B, January [8] fcxplorer Software Library Reference Manual, AIT, Version 2.0, Rev A, December Page 12