VXI: THE TEST PLATFORM OF THE FUTURE?

1 VXI: THE TEST PLATFORM OF THE future ? Charles Greenberg EADS North America Defense Test & Services 4 Goodyear St. Irvine, CA 92618 (949) 859-8999 - As VME Extensions for Instrumentation (VXI) turns 20 years old, its relevance for new applications is tested in the presence of the alternatives. This paper looks at the past successes and failures of the VXI PLATFORM , and then looks at present and future applications with respect to how well the standard holds up. Finally, this paper examines recent VME enhancements, including VITA-41, also known as VXS, to extend the applicability of the VXI PLATFORM , looking forward to the next twenty years.

2 introduction As part of the research for this paper, I visited with Robert (Wade) Lowdermilk and Anthony Estrada of BAE Systems in San Diego, California. Their company uses VXI extensively to build Synthetic Instruments (SI) and test systems, so they seemed like natural people to talk with about the future of the VXI bus. When I informed them of the proposed title of this paper: VXI: The Test PLATFORM of the future ,Wade laughed and quipped that he did not think that it would win the Best Paper award. Wade explained that the BAE Systems strategy was to replace their VXI instruments, one by one, with PXI instruments in PXI-VXI carriers, as suitable PXI instruments became available.

3 Eventually, when all of the instruments in the system were in the PXI format, they would switch over to a PXI chassis altogether. Needless to say, the BAE Systems meeting that day cured me of any thoughts that I had of this paper being a simple task. Was the nearly 20 year old VXI PLATFORM , even including its recent VME64 speed enhancement, going to be replaced with a newer architecture like PXI or LXI? To answer this question, we will need to observe the successes and failures of the VXI PLATFORM , compare it to some of the newer platforms, and, if the VXI PLATFORM has a few deficits but is otherwise found to still be relevant, suggest any changes necessary to make VXI the premier modular test PLATFORM for another 20 years or more.

4 SUCCESSES AND FAILURES OF VXI The story of VXI began in the mid-1980 s just as the first Navy CASS systems were being designed using VME instruments built in a special form factor that was similar to that of the yet-to-be-defined C-sized VXI module. In 1987, the VXIbus Consortium, consisting of a group of interested companies including HP (now Agilent), Tektronix, Racal Instruments (now EADS North America Defense Test & Services), Colorado Data Systems, and Wavetek (now Fluke), was created to fill the need for an open industry standard. The standard was created to meet the consortium s stated goals as listed below in Table 1:Table 1: Goals of VXI [1] Goal # Goal Description 1 Capability of handling demanding electronic test problems 2 Open standard to all designers/ manufacturers3 Interoperability with modules that would work together seamlessly 4 Ability to reduce the size of current instrumentation 5 Ability to increase the speed of Automatic Test Equipment (ATE) systems 6 Cost-effective ATE solutionIn the 19 years since the creation of VXI, the achievement of these goals is apparent for the 1-4244-0052-X/06/$ 2006 IEEE664most part.

5 The following sections contain brief assessments of how successful the VXI bus was at achieving each of the goals listed in Table 1. Goal 1: Handling Demanding Electronic Test Problems The key word here is demanding. The message here is that the VXI PLATFORM is not for everybody. It was never intended as a solution for the not-so-tough electronics problems that are out there. There is a premium to pay for usage of the PLATFORM , making it out of the question for some low-end test applications. But what exactly do demanding electronic test problems consist of and how well has the VXI PLATFORM been used to solve them? For this analysis, I will focus on two specific demanding areas in three different problem categories of electronics test: 1.

6 Re-hosting a legacy military test system 2. Building a test system with Synthetic Instruments (SI) Re-Hosting a Legacy Military Test System There are numerous examples of aging military test systems that needed modernization. System designers switched from standalone boxes to VXI instruments as part of a solution, usually combined with non-modular instruments such as oscilloscopes. VXI instruments were used for many reasons, but usually these reasons include the following: Maintainability: VXI is at its best when a low Mean Time to Repair (MTTR) is a must, as it is for mission-critical military testing. All VXI modules are plug-ins with front access for easy module and cable removal and replacement.

7 Even VXI chassis power supplies, fans and system monitors are frequently designed to be pluggable and spare-able for low MTTR. Compact Rack Footprint: VXI allows up to twelve C-sized instruments to fit into 7-9U (1U = vertical space) of rack space, more if mezzanine modules are used with VXI carriers. VXI modules have a space advantage over racked, standalone boxes because the backplane eliminates redundant power supplies, cabling, connectors, and cooling systems while doing away with front panel controls. Well-Defined Hardware/Software Integration: With the VXI bus hardware PLATFORM with its well-defined power and cooling specs along with commonly available VXIplug&play, IVI and VISA software tools, the integration task becomes straightforward and predictable.

8 Inherent Scalability: VXI modules tend to use backplane mechanisms that allow automatic setup of master/slave modes which allow channels of functionality to be added or subtracted at will. Availability of Top-Notch Instruments:A wide selection of high-performance instruments, mainframes and switching is available: o From analog to digital to microwave plus a vast selection of switching o From an estimated 80 different hardware manufacturers These are some of the reasons given for using VXI instrumentation and switching in the Joint Services Agile Rapid Global Combat Support (ARGCS) demonstration system. This system is designed to run Test Program Sets (TPS) from CASS, TETS, IFTE, ESTS and potentially other test systems.

9 The ARGCS system designers couldn t just procure all of the legacy instruments and assemble them into one gigantic tester that ran all legacy TPS. They needed a single core set of instruments and switching that was flexible enough to run legacy TPS from all supported legacy systems. ARGCS Core Instruments The digital and analog instruments for the ARGCS system needed to fit in a minimal footprint yet run TPS written for legacy systems that used different instruments. This means that all pre-existing measurement, stimulus, and signal switching capability had to be duplicated in the core instrument set. The solution required state of the art technology to produce measurements that could duplicate the functionality, accuracy, resolution and bandwidth 665of the legacy systems.

10 To achieve this, two principles were used: Extra Dynamic Range: There are too many legacy measurement ranges in existence to duplicate them all on a single instrument. This necessitates using different ranges, but ranges that had more resolution than the preceding systems had. Some examples of this are in the table below: Table 2: Comparison of ARGCS Dynamic Ranges to Those of Previous Test Systems Instrument Type Legacy Specs ARGCS Specs Waveform Generator 12-bit 125 MS/s 16-bit 200 MS/s Digitizer 8-bit 1 GS/s 10-bit 2GS/s Digital Multimeter +/- Million counts +/- 24 Million counts Extensions to Commercial-Off-the- Shelf (COTS) Hardware: The 340 mm ( ) depth of the VXI module gave ARGCS hardware designers room to extend the performance of COTS hardware (Digital Multimeters, Digitizers, Waveform Generators, etc.)