Design Of VISA Based On LXI

As the development of computer science and technology, LXI bus, which appliesInternet to measurement, has become a hot area of research in instrumentation.Integrating legacy instruments such as GPIB, VXI and PXI to LXI system to buildAutomatic Test System (ATS) based on LXI bus has become a new trend; it can fullytake the advantages of various legacy instruments’ functionalities and easily controlinstrumentation remotely. The key of building ATS based on LXI bus relies on VISAlibrary. To control standard LXI instruments and manipulate VXI and GPIB instrumentsthrough LXI-VXI and LXI-GPIB adapters, the thesis designed a VISA library usingANSI C language on Windows platform, distributing in the form of dynamic link library.The architecture especially the data structures internal determine the efficiency ofVISA library greatly, for they the foundations of VISA interface functions. According tothe specification of VISA library, the thesis designed varieties of data structures torepresent hardware resources in the system and interact with applications, includingresource structure, session structure, find list structure, event structure and so on.Resource structure intends to represent hardware resource, stored in the form of array inshared memory so that multiple processes can easily share data and communicate witheach other. The rest data structures are represented by links to search efficiently as wellas saving memory space.Resource manager plays a rather important role in VISA library, for it organizesand manipulates all the hardware and software resources. The key of resource managerdesign in the thesis relies on VXI-11network device discovery and VXI A24/A32address space allocation. The implementation of VXI-11network device discoverybases on open resource RPC library—oncrpc. The thesis designed the formats of VXI-11RPC calling and replying network data structures, gives the setting of key argumentsand the whole flow of development. Resource also allocate address space for VXI A24/A32devices, calculates the results and then writes them into the correspondingregisters, through this the addressing of A24/A32functionalities of VXI devices can beactivated.VISA interface functions are standard VPP functions, providing users a unifiedform of manipulating instruments. The implemented VISA functions in the thesis variesfrom resource opening and closing, resource finding, basic I/O operation, format I/Ooperation, memory I/O operation and so on. The thesis also designs varieties ofadvanced functions of VISA library, including attribute control, resource locking, andevent mechanism. VISA event mechanism is an important part of VISA library,implemented by multiple threads in the thesis with simplicity and high efficiency.To validate the VISA designed, the thesis adopts it to control LXI, VXI and GPIBdevices on Microsoft Visual Studio as well as NI LabWindows CVI environments. First,the core functions are tested individually, then test the whole functions on three differentdevices vary from LXI, GPIB and VXI buses. Finally, to test the performance of VISAlibrary, the thesis builds a test system using multiple LXI, VXI and GPIB instruments.Test results show the VISA library designed can manipulate LXI, VXI and GPIBdevices efficiently. The VISA library is interchangeable with VISA designed by otherinstrument vendors, applications can run without even recompilation. The VISA libraryconforms to VPP standard, reaching the design purposes.