Abstract: Facing the severe challenges posed by modern high-tech weaponry to the testing field, this paper analyzes the shortcomings of current mainstream military testing system structures and proposes a multi-bus integrated automatic testing system structure based on LXI. The paper focuses on the implementation methods of integrating instruments from different buses and the technical solutions for synchronous triggering of different interface modules. To achieve interchangeability of functionally similar modules on different buses, the system's software structure framework is presented according to the IVI specification. Keywords: LXI; multiple bus fusion; automatic test system; IEEE1588; IVI-COM [b][align=center]Building a Multiple Bus Fusion Automatic Test System Based on LXI Cheng Jin-jun, Xiao Ming-qing[/align][/b] Abstract: The high-tech weaponry has brought forward critical requirements for test systems. The shortage of the dominant test system is analyzed; the multiple bus fusion test system is designed based on LXI. The implementation mechanism of the multiple bus fusion is expressed, and the synchronization and triggering of various instruments are given in this paper. The system software framework is shown based on the IVI specification, thus the system is interchangeable. Key words: LXI; multiple bus fusion; automatic test system; IEEE1588; IVI-COM 1 Introduction With the shift of the PLA's strategic guidance towards informatization, high technology is widely used throughout the entire life cycle of weapons and equipment, leading to a rapid increase in the complexity of weapons and equipment. Traditional single-bus-based test system architectures are becoming increasingly inadequate to meet the maintenance and support requirements of weaponry and equipment, primarily in the following aspects: 1) The single communication interface of the test system cannot meet the needs of weaponry and equipment for multi-digital interface communication. To enable weaponry and equipment to possess high-performance combat capabilities, the latest research results in modern computer technology, electronic technology, and communication technology are often applied. The interfaces between weaponry and equipment and the outside world typically include multiple types such as 1553B, RS422, and RS232, resulting in diverse interface forms. The test system needs to be configured with multiple communication bus interfaces to meet the testing requirements of weaponry and equipment. 2) Single-bus measurement instruments have limited functional coverage. Due to the numerous test items and complex test parameters of weaponry and equipment, the demand for test resources is relatively broad, and the frequency coverage of measurement devices needs to range from low frequency and radio frequency to microwave. However, the current mainstream military test instrument buses (such as the VXI bus) have limited support for radio frequency and microwave measurement instruments due to structural and instrument module limitations. In this area, GPIB bus instruments exhibit superior performance. 3) The test system structure is constrained. Due to limitations in the data acquisition capabilities of measurement modules and the testing environment, testing systems typically require triggering instrument modules on different buses to simultaneously initiate a test in order to complete the measurement task. Testing systems often lack a unified triggering structure to meet these requirements. 4) Poor portability and difficulty in updating and upgrading testing systems. Currently, there is a lack of interoperability between testing systems of different military branches and maintenance levels. This situation severely affects the allocation of testing resources, the generation of test sequences, and the retrieval of test results. The main factor affecting the interoperability of testing equipment is the wide variety of bus types and their incompatibility. Given that building a testing system using a single bus is insufficient to meet the testing needs of weaponry, combining the advantages of multiple instrument buses and constructing an automated testing system based on multiple digital interface buses has become one of the development trends in the military testing field. Definition of an automated testing system with multi-bus fusion: The testing system contains two or more digital interface buses, and different buses can achieve mechanical compatibility, electrical compatibility, functional compatibility, and operational compatibility. Different buses achieve mechanical and electrical compatibility through interface adapters; communication between different types of instruments on different buses can mask the differences in I/O interfaces, achieving "bus I/O transparency"; functional differences between similar instruments on different buses can mask the differences in functions, achieving "resource and function transparency," ultimately achieving operational and functional compatibility and meeting the interoperability and interchangeability requirements of the test system for measuring instruments on different buses. 2 Overall Framework of the Test System 2.1 Multi-Bus Integrated Test System Architecture The test system built on LXI can better meet the construction requirements of an automated test system integrating multiple buses. The system structure diagram is shown in Figure 1. LXI (LAN eXtension for Instrument) is an extension of LAN local area network technology in the instrument field. LXI instruments are new instruments strictly based on IEEE 802.3, TCP/IP, network bus, web browser, IVI-COM driver, clock synchronization protocol (IEEE 1588), and standard module size. LXI modules use a standard web browser to achieve information browsing and program control, and communicate in IVI-COM format, facilitating system integration and interchangeability of similar instruments. [align=center]Figure 1 Overall Structure of an LXI-Based Multi-Bus Fusion Automated Test System[/align] In Figure 1, the system connects various instrument bus modules via LXI. VXI, PXI, and GPIB bus modules become components of the system through interface adapters. The computer controller, under the control of the operating system, acts as the instruction executor for the entire test system. The operating system provides file management, memory management, user interface message response, test result output and printing, and system I/O request processing services for the multi-bus fusion automated test system. At the system I/O layer, multi-bus mechanical and electrical compatibility adapters are interconnected with the system I/O interface, providing multiple test bus interfaces. The system I/O interface also controls the "synchronous trigger control logic," realizing the synchronous triggering of different bus test resources. With the cooperation of software resources, it meets the system's requirement for simultaneous measurement of multiple signals. The multi-bus fusion operation compatibility and functional compatibility layer mainly includes: the system I/O bus driver layer, the multi-bus test resource interchange driver layer, the signal virtual resource requirement to physical resource configuration mapping layer, and the signal-oriented virtual instrument layer. The system I/O interface connects to various instrument backplane buses (VXI, PXI, GPIB, etc.) via the LXI instrument connection bus, on which measuring instruments are mounted. Test interface adapters connect to the measuring instruments. These adapters facilitate signal cross-linking between the measuring instruments and the unit under test, performing impedance matching transformation on input and output signals, and handling signal attenuation and level conversion. The application software for the multi-bus integrated test system runs on the multi-bus test resource fusion layer. This layer does not contain specific physical resource information and its program code is written according to a signal-oriented and test-demand-oriented model. The mapping from virtual test resources to specific physical devices is implemented in the multi-bus test resource fusion layer. To ensure a good human-machine interface for the multi-bus integrated weapon equipment test system, the system is equipped with human-machine interfaces such as a monitor, keyboard, and mouse, as well as output devices such as a printer. 2.2 Multi-bus Mechanical and Electrical Compatibility Implementation Scheme To integrate different test bus modules into the LXI test system, two technical solutions are available: developing bridge adapters and interface adapters. The bridge adapter consists of an LXI interface and a specific bus interface. The LXI interface implements all LXI interface requirements, including network protocol support, web page browsing and instrument control, LAN configuration initialization, and IVI driver. Specific hardware and software interface requirements are implemented at the specific bus interface end of the bridge adapter. For example, if an LXI bridge adapter connects to a GPIB instrument, the bridge adapter must not only support both LXI and GPIB interfaces but also have the ability to map software commands from the LXI end to the GPIB end. Interface adapters completely convert non-LXI bus interfaces to LXI interfaces. Unlike bridge adapters, through interface adapters, the host can directly access and control non-LXI instruments using instrument drivers and web pages, without requiring mapping of control and communication mechanisms or VISA resources between the interface adapter and non-LXI instruments. In multi-bus converged test systems, to avoid significant changes to the original VXI, PXI, and GPIB system architecture, LXI-based multi-bus converged test systems use bridge adapter mechanisms to seamlessly integrate existing bus instruments. For example, for VXI bus modules, the EX2500 LXI-VXI Slot 0 Interface can be used to convert LXI instrument operation commands based on the TCP/IP protocol into signal drive logic on the VXI instrument backplane. With this structure, the existing VXI test system, as a subsystem of the system, only requires minor modifications to the Agilent IO Library interface configuration, while the system hardware and test software remain unchanged. 2.3 System Synchronization and Triggering Structure Synchronization and triggering between different bus instruments is a crucial aspect that must be considered in multi-bus integrated automatic test systems. Due to the significant differences in synchronization and triggering mechanisms among different test buses, implementing synchronization and triggering in multi-bus integrated automatic test systems is quite difficult. To meet the system's high-precision triggering error requirements, the system adopts a triggering structure combining LXI precision clock triggering (IEEE1588) and LXI hardware triggering, as shown in Figure 2. IEEE1588 provides a high-precision synchronization clock for the system, and LXI TRIGGERING provides unified event triggering with minimal phase difference for each bus module. The system's trigger hub is the EX2100. [align=center]Figure 2 Trigger Structure of Multi-Bus Integrated Automatic Test System[/align] In the multi-bus integrated automatic test system studied in this paper, since the trigger signal levels of VXI, PXI, and GPIB modules do not match the trigger level of LXI's LVDS (Low Voltage Differential Signal), the system uses different bus trigger signal adapters to convert the LVDS signal of LXI TRIGGERING into a level signal compatible with the triggering of VXI, PXI, GPIB, and other modules. Since not all existing VXI and PXI modules have trigger terminals compatible with LXI TRIGGERING on their front panels, when the trigger accuracy requirement is not high, the zero-slot controller of the VXI and PXI subsystems maps the IEEE1588 time trigger of the LXI system to the event triggering logic of the system, driving the TTL or ECL trigger signal lines on the bus backplane to achieve system synchronization. 3 Software Structure of the Test System To achieve multi-bus integration of instruments with different buses, the test software should have the following functions: 1) The I/O differences of different bus instruments are transparent to the upper-layer application program. The system should not exhibit I/O differences in the operation of instruments on different buses. Instrument configuration, control, and data reading share the same functions. Test data and bus information from different bus resources do not require conversion, achieving "bus I/O transparency," which is the first level of multi-bus integration. 2) Buses with similar functions but different bus interfaces can be interchanged, achieving "resource function transparency," which is the second level of multi-bus instrument integration. According to the above functional requirements, the software of the multi-bus integrated test system consists of four parts: the VXI-11 communication protocol transmission layer, the VISA layer of the underlying I/O software, the IVI driver layer, and the application software layer. The system software hierarchy diagram is shown in Figure 3, which is a detailed representation of the software part in Figure 1. [align=center] Figure 3 Software structure of the multi-bus integrated test system[/align] The VXI-11 specification developed by the VXI Alliance defines the standard for network instruments to communicate with controllers via TCP/IP. Currently, the VXI-11 specification has evolved into the communication standard for Ethernet-based instruments. The existing I/O interface software VISA library encapsulates the VXI-11 standard as a subset of it. The VISA architecture shields the I/O differences between instruments operating on different buses, providing a unified set of underlying I/O control functions for instrument driver development. The system achieves "bus I/O transparency" across multiple buses at the VISA layer. Considering that similar instruments have largely the same functionality, each type of instrument can be encapsulated into a COM component during driver design. Through the isolation of COM components, the test application does not need to concern itself with the underlying instrument driver implementation; it can directly call the COM component's interface to control the instrument. The IVI configuration server manages the configuration of the COM components and stores configuration information. The COM components used in the driver are standard and completely consistent for drivers of similar instruments; instrument interchangeability can be achieved simply by changing the driver's configuration information in the configuration server. In addition to the IVI-COM driver, IVI-C is also an instrument driver model suitable for LXI architectures. The system achieves "resource and function compatibility" for similar instruments on different buses at the IVI layer. The system's application development environment offers multiple options, including VB, VC++, and LabVIEW, all of which provide IVI-COM API function calls and compilation. 4. Conclusion With the rapid development of computer, electronic, and communication technologies, this paper constructs a multi-bus integrated automatic test system based on LXI to meet the demands of weaponry testing. The system effectively meets the needs of current weaponry maintenance and support, and is suitable for building test systems with complex testing resource requirements. The multi-bus integrated test system is easy to build, highly interchangeable, and open, effectively integrating outdated testing equipment. In test system development practice, with only minor changes to the interface configuration, a general-purpose missile test system based on the VXI bus can be easily integrated into the multi-bus integrated test system constructed in this paper. Without increasing military funding, the overall performance of the system is significantly improved due to the integration of multiple bus resources. The authors' innovations are: 1) Driven by the testing needs of modern weaponry, a new structural form of automatic test system—the multi-bus integrated automatic test system—is proposed, and its definition is given. 2) The newly introduced LXI bus in the testing field is applied to the multi-bus integrated automatic test system, and the implementation method of system integration is given. References [1] LXI Consortium. LXI Standard Rev. 1.1[S], August 28, 2006. [2] MIKE DEWEY. Integrating LXI Devices Into Hybrid Test Systems[EB/OL]. www.LXIconneXion.com. [3] Cheng Siyi, Xiao Mingqing, Zheng Xin. Future Development Prospects of Military Test Systems[J], Microcomputer Information, 2006, 4-1: 170-173. [4] Liu Duxi, Ma Jun, Xu Jianshe et al. Research on LXI Bus and its Key Technologies for Instrument-Level Interchange[J], Science Technology and Engineering, 2006.5. [5] Dirk S.Mohl. 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