ARINC-818 测试的航电应用

ARINC-818 TESTING FOR AVIONICS APPLICATIONSKen BissonAIM-USA34 Country RdE Hampstead, NH 03826(603) 378-0957bisson@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 utilizea common link and protocols that supports high-bandwidth data specifically for digital video applications. Aerospace applications currently utilize 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. 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.INTRODUCTIONAvionics 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 the 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 high-bandwidth video data in commercial aircraft applications. The ARINC-818 Specification is based on the Fibre Channel standard (FC). Fibre Channel combines the ability of moving large amounts of high-bandwidth data like computer busses, 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 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 Airbus on its A400M program.ARINC-818 OVERVIEWThere are three reasons why ARINC-818 is a great fit for avionics applications:o Simple to implemento Fast and scalableo Separates physical protocol from application protocolARINC-818 defines an application protocol working on a Fibre Channel closed network topology. In order to understand ARINC-818, onemust also understand Fibre Channel. Likewise, when performing testing of ARINC-818 applications, it is essential to understand and be able to perform Fibre Channel testing as well.Fibre Channel separates functional areas into layers. There are five (5) layers illustrated in Figure 1.FC-AV is the Upper Layer protocol defined in layer 4. ARINC-818 further refines the FC-AV definition.Simple to ImplementThe primary elements of the ARINC-818 topology are End Systems, which are networked together in a point-to-point 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-to-point connections.The physical interface for a Fibre Channel port is simplex, unidirectional, serial connections. One line for transmit, another for receive. These are lightweight, and easy and maintain. 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 is 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 ScalableFibre Channel is extremely fast. Currently, 1, 2, and 4 Gbps speeds are all in use today. 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 high-bandwidth display applications.Avionics applications 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 the provisions for future upgrades. Figure 2 shows the relationship between the various display resolutions and data bandwidth [1].Figure 2 – Video Display ResolutionsSeparates physical protocol from application protocolThe 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 Upper Layer Protocol 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 ChannelAs 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 specificFC-0 Physical: Cabling, connectorsFC-1 Transmission Protocol: Encoding, word transmission, error detectionFC-2 Protocol: Frame layout, flow control, class of service FC-3 Common Services: Frame layout, flow control, class of serviceFC-4 Mapping of Protocols: Application protocol mapping to Fibre ChannelFigure 1 – Fibre Channel Layerscontrol information is added to the packet. The combination of the control information and the data is called a frame. For Fibre Channel a frame has 24 bytes of control information (header) and anywhere from 0 to 2112 bytes of payload (pure data containing the user information). If a packet of user information is too large to send in one frame, then multiple frames must be grouped together and this forms a sequence.Besides frames of data, Fibre Channel also identifies other types of data to be sent over the link. This type of data is called ordered sets. Ordered sets are Fibre Channel’s mechanism to perform control and signaling functions over the simplex transmission link. There are three (3) types of Ordered Sets:o Frame delimiters – identify start/end of frameso Signals – indicate events or actionso 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 6 ordered sets (most likely fill words) between the transmissions of frames. The most common fill word is an IDLE. Figure 3 shows the FibreARINC-818ARINC-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 2 dimensional image made up multiple rows of individual pixel data that display horizontally in a visible display. Digital display formats vary by the amount of rows, the number of rows, and the amount of bits per pixel. For example, an SVGA PC display is 1280 rows x 800 pixels in a row. The bits per pixel usually identifies the color resolution. So, the amount of data needed to generate a single 1280x800 frames with 16-bits per pixel color is 1.6 Mbytes. 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 have to be ordered in the same fashion. In addition to the data, there are timing elements that must be met. Digital Display must be synch’ed vertically and horizontally. There must be an identifiable, consistent timing pattern associated with the display of each consecutive row (horizontal sync) and also every time the display data reaches the bottom of the display it starts again at the top. For example, a common vertical sync 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 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 (4) types of objects:o Object 0: Ancilliary Datao Object 1: Audio Datao Object 2: Video Data (Progressive Scan)o 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 4 shows how a single container and its objects are defined.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, frame type, number of objects that are used in the container. The header also includes the CRC value of the previous container. Figure 5 illustrates the container mapping to the Fibre Channel frames [2].TESTING ARINC-818Testing is a critical element for 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 will occur in two phases:o Testing individual End Systemso Testing End Systems in the ARINC-818NetworkIndividual End System TestingAvionics Digital Display Systems are delivered tothe airframe manufacturer from many suppliers. Each Display specializes in a particular functionfor the aircraft (i.e. Navigation, Collision Avoidance Radar, Health Maintenance). Individual testing is required for the 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 include:o Do the Source data End System portstransmit correct containers at appropriate sync intervals?o How many transmit errors are producedover a long time period?o Does the Display receive and processobjects correctly?o How does the Display System react toreceiving incorrect Objects, frames with protocol errors, CRC errors, or frames with bad data in them?Network System TestsIndividual End Systems are eventually integrated into an avionics ARINC-818 network. Effective testing is required during integration to insure 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 include:o Monitoring each End System for frameerrors associated with frame movement over the network.o Checking the deterministic flow ofcontainers from the End System source. o Checking the redundancy of the network(if implemented). o Checking the ARINC-818 networkreaction and tolerance of errors.CHOOSING AN ARINC-818 TESTSYSTEMThere 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 formats, but cannot decipher Fibre Channel protocol or network timing errors.An ARINC-818 test system requires the use of interfaces specifically designed for FibreVideo FrameContainerFigure 5 – Container maps to Fibre Channel framesChannel 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. I have found that there are currently only two (2) commercial manufacturers of these products available.The Test System will perform 3 different types of tests. These are:1. Traffic Generation2. Traffic Monitoring3. Digital Display OperationTraffic GenerationTraffic 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. The setup of the Virtual Link for simulation will include the following actions:o Constructing Object 0 Headero Constructing Object 1, 2, or 3 Datao Implementing the Network connection (single or redundant)o Sending objects with precise timingThe traffic generator needs to implement a robust scheduler capable of sequencing objects. The intermessage gaps between Objects needs to be programmable to a minimum of one (1) transmission word, 4 bytes, over the Fibre Channel network. This enables manipulating 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 2s onto 1536 Fibre Channel frames. Figure 6 illustrates the precise time sequence in order to maintain vertical and horizontal sync.Fill words are used (most notably IDLES) to fill in the gaps between Fibre Channel frame transmissions. The amount of IDLE fill words between the End of Frame (EOF) and the start of the next frame (SOF), is used to govern the vertical and horizontal sync characteristics of the frame. The data generation simulator must have the ability to adjust the number of IDLE fill words. 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 see how the Display End System will behave to various error conditions. The types of error injection include:o Fibre Channel Frame level errors (CRC, wrong byte alignment, size)o Incorrect Container CRCso Incorrect sequencing of frames andObjectsFigure 6 – 1024x768, 30 Hz, 24-bitA 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. 1Gbps, 2Gbps…) 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 to Fibre Channel. It is important for the Traffic Generator to be able to adjust its baud rate to these non-standard rates. These types of displays do not adhere to the ARINC-818 Specification, but they are common, commercially available products.In-line Traffic MonitoringTraffic 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 Systems’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.The Monitor 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. Atest system that can store gigabytes of data ontoa disk file for later review is vital. Archived disk files can be analyzed in detail, post operation. Receive OperationsThe 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 errors conditions.The 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.CONCLUSIONARINC-818 is a new Specification forimplementing a Digital Display network in Avionicsapplications. The ARINC-818 Specification isbased on a Fibre Channel network architecture.Fibre Channel defines the topology andimplementation of the network. ARINC-818defines the protocol that defines the digital displayinformation and its mapping to Fibre Channel.These standards specifically address movinghigh-bandwidth, low latency data, reliability andwith determinism. These are key requirements forAvionics communications.ARINC-818 Test Systems need to verify andmonitor the behavior of the ARINC-818 networkwhich requires doing more than just examining thedigital display. Tests include traffic generation,chronological monitoring, and simulating EndSystems receiving ARINC-818 containers. Thesetests require Fibre Channel testing, as well as justchecking the integrity of the digital display data. Itis most important to look at timing within thenetwork. The efficiency of the data traversing theARINC-818 network is more important than thesimple measurement of protocol faults that occurover time.References[1] Avionics Digital Video Bus, High Data Rate– Draft 3of project Paper 818, Airlines ElectronicEngineering Committee, June 24, 2006, page 4.[2] Avionics Digital Video Bus, High Data Rate– Draft 3of project Paper 818, Airlines ElectronicEngineering Committee, June 24, 2006, page 9.[3] Avionics Digital Video Bus, High Data Rate– Draft 3of project Paper 818, Airlines ElectronicEngineering Committee, June 24, 2006.[4] ANSI INCITS 230-1994 (R1999), InformationTechnology - Fibre Channel - Physical andSignaling Interface (FC-P H) (formerly ANSIX3.230-1994 (R1999)) (includes supplements)[5] ANSI INCITS 356-2002, Information technology -Fibre Channel - Audio Video (FC-AV)[6] Kembel, Robert W., “Fibre Channel AComprehensive Introduction”,Northwest LearningAssociates, 2002.[7] Information Technology – Fibre Channel – AudioVideo (FC-AV), T11/Project 1305-D/1.3, NCITS,May 1, 2000.[8] Kelley, Timothy, “ARINC 818 Becomes the NewProtocol Standard for High-Performance VideoSystems”, Great River Technology, COTS Journal,December 2006, /home/article.php?id=100602&pg=1.[9] Fibre Channel Speed Chart, Fibre Channel IndustryAssociation,/OVERVIEW/Roadmap.html.。