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TEST & MEASUREMENT WORLD: Software wrapper links Matlab to instruments

Matlab is a popular computing environment for electrical engineers. Many use it to analyze data, although they often save the data using another program, then import the data into Matlab. Mike Flaherty, applications engineer at Agilent Technologies, wanted a direct programming interface from Matlab scripts to generate waveforms with an AWG (arbitrary waveform generator).

Flaherty needed Matlab scripts that generate numerous waveforms, including 7-bit Barker-coded radar pulses, and multitone signals. The software needed to work with two AWGs: one through Ethernet, the other through CompactPCI.

To provide an easy-to-understand programming interface, Agilent engineers developed several Matlab scripts to control the instruments. They used function names such as awg_open and awg_storewaveform.

A Matlab MEX file provides an interface between Matlab and LXI or CompactPCI instrument drivers. These scripts call a Matlab MEX file, written in C, that in turn calls IVI-C drivers for the instruments. Those drivers then call the protocol stacks for the Ethernet and CompactPCI I/O ports (Figure 1).

“The waveform generators are 100% code-compatible with this application,” said Flaherty. Flaherty also developed a user interface that lets users select signals from a menu, then select specific parameters. Using Matlab and Agilent Vee, he built prototypes of the user interface. He wanted to develop a compiled, stand-alone executable, though. Because Vee is an interpreted language, Agilent engineers ported the GUI and the control code to Microsoft C#. The waveform engine is still Matlab but is compiled and linked to the application when built.

“The key to the application is the Matlab interface,” explained Flaherty. “It communicates through a MEX file to an instrument’s IVI-C driver. It passes a resource string to a Compact- PCI or Ethernet stack.”

The ATE industry’s hybrid theory By S. Vidyasankar, Senior Research Analyst at Frost & Sullivan

The ATE industry’s “hybrid theory” is that sector’s most important trend: the introduction of hybrid systems that employ combinations of GPIB, VXI, PXI, and LXI interfaces. GPIB, the interface bus from the 1970s, is a low-cost architecture that is still widely used. When VXI was introduced in 1987, many thought its high-channel-count capability would replace GPIB. Yet, the older bus had a huge installed base that continues to grow. Similarly, when PXI appeared in the 1990s, many predicted the end of VXI. Instead, PXI is exploring new avenues and markets for growth rather than replacing VXI. PXI revenue worldwide will more than double from 2006 to 2010. VXI revenues will decline gradually, while the aerospace and defense segment will continue to sustain the market for VXI. LXI, introduced in 2005, is the hot topic now. The technology uses standard Ethernet LAN hardware and software to simplify communications for instrumentation that is now mostly GPIB. LXI will not make GPIB go away, however, but will extend the speed for instrument interconnections and provide synchronizing capabilities not available in the older bus. The most evident truth is that no single bus technology can solve every T&M application. These platforms are not competitive but rather are complementary. The trend towards the convergence of bus standards in hybrid test systems is likely to shape the future of the ATE market. Hybrid test systems contain multiple bus-connectivity solutions— GPIB, VXI, PXI, and LXI, as well as PXI Express and USB. Hybrid systems are especially handy when users cannot get the desired instrument capabilities in a preferred form factor. Cost reduction and performance improvements seem to be the main goal of the next-generation softwaredefined test systems. The mix-and-match approach lets users choose instruments based on capabilities and pricing options when designing or upgrading a test system. Hybrid test systems are becoming a reality, and test engineers and equipment vendors should embrace the coexistence of multiple platforms and understand the trade-offs of the platform options before designing new instruments and test systems. Vendors must cooperate and coexist in order to have a foothold in the industry in the future.