Look Out for PCs in ATE

PCs tackling the ATE market have for the most part avoided challenging traditional production-floor ATE. Instead, they have taken up posts at the product design phase, where you can complete much of your work on a PC, then submit your design data to remote servers to run long simulations and generate the test patterns needed to program production ATE.

To evaluate a CPLD design, for example, you can submit your design to Xilinx’s WebFitter over the Internet. All you need is a browser that supports Javascript 1.2, frames, and Secure Sockets Layer encryption—either Netscape Navigator 4 or Microsoft Internet Explorer 4 running on a Windows 95 PC is adequate. Xilinx servers do the computational heavy lifting, determining whether your design fits within a CPLD, for example, and inserting the boundary-scan chains that you’ll use to test and program the devices on the production floor.

PCs in the Field and the Factory
For field-service ATE, Geotest offers ruggedized PC-based ATE to the military, which is emphasizing the procurement of commercial-off-the-shelf (COTS) products in an effort to cut costs. One such product is the US Army’s AN/TSM-205 Guided Missile System Test for the Apache Weapon system (Fig. 1), which includes conformally coated PC-based instruments. Because of the harsh environments faced by this equipment, a touch-screen display replaces a traditional PC’s keyboard and monitor.

At the design and field-service phases, throughput often takes lower priority than other concerns. When you’re designing a chip, you can turn your attention to other projects during the hours or days you spend waiting for a fault simulation to run. For ATE headed for the battlefield, portability, reliability, and functionality are more critical than whether it takes milliseconds or seconds to get answers. Consequently, PC architectures have been accepted by the military either as the complete computer engine for a tester like Geotest’s or as the user interface for simulators that might get farmed out to a mix of RISC and CISC processors on a LAN or over the Internet.

On the factory floor, however, PCs have been slow to catch on, other than as after-the-fact processors of test data and generators of test reports. That’s changing, though, as evidenced by two presentations at the 1998 International Test Conference, where Credence Systems and Teradyne presented papers on PC-based production ATE.

Driving this focus on PCs is the increasing speed of Intel processors running Windows NT, which are closing the gap with RISC processors running under Unix. And if RISC/Unix systems retain a slight edge, it’s often insignificant in ATE applications. After all, says Teradyne engineer Dan Proskauer, “If you need a supercomputer to run your ATE, then there is something wrong with your software architecture.”

Further, programmers are familiar with the Windows development environment and can more readily customize code than they can using Unix. Finally, the Windows Socket TCP/IP programming interface enables Windows computers to blend smoothly into an otherwise all-Unix environment.

Nevertheless, Windows suffers a poor reputation as a real-time operating system—it can respond quickly to humans but falls short on hardware-driven tasks. Credence engineer John Oonk reported in his ITC presentation1 that he noticed this limitation when evaluating a PC ATE architecture. His goal was to network a Windows NT user interface with test hardware as part of Credence’s Kalos, a 50-MHz system that can simultaneously test 16 flash memory devices. Although he found that network data rates were acceptable, latencies—from 1 to 1.5 ms—would preclude direct PC control of tester hardware over the Ethernet.

Credence took a divide-and-conquer approach, running user interfaces under NT (Fig. 2). To drive the test hardware, Credence chose an Intel 80960 controller for each test channel memory-mapped to the hardware it controls. To provide a TCP/IP interface at the test-hardware end, Credence employed Wind River Systems’ VxWorks real-time operating system, making it unnecessary to develop network sockets and task-management functions from scratch. VxWorks features preemptive multitasking—the highest-priority task runs to completion.

Oonk reports that the VxWorks approach is superior even to Unix, which, like NT, employs time-slicing schedulers. Emphasizing the importance of software components working together, Oonk said the selection of VxWorks resulted in part because it is supported by an NT-based development system.

Applications as Components
Windows NT and VxWorks represent software components that Credence used in its Kalos product. Teradyne engineer Dan Proskauer in his ITC presentation2 took the component model to a lower level as he described the implementation of Teradyne’s IG-XL, the programming language originally designed for the company’s Integra J750 microcontroller tester. For Proskauer, the components include operating-system controls as well as applications.

According to Proskauer, “Software components on the Unix platform are scarce and expensive in contrast with the PC platform. For example, we have employed a Unix third-party schmoo package that cost $60,000 plus $1,500 per copy shipped. A similar Windows package costs $200.” The fact that Pentium-based Windows NT systems have closed the performance gap relative to Unix RISC workstations enabled Proskauer to take advantage of the lower costs of Windows software.

Windows NT supports the software component model through its DCOM Distributed Common Object Model) and OLE (Object Linking and Embedding) standards. Although COM and OLE objects are relatively complex—because they must support application objects like Word and Excel files—the ActiveX subset proves useful for building applications without document overhead, Proskauer says. A programmer can drag an ActiveX control from a Visual Basic tool palette and into an application.

Figure 3 shows a waveform display invoked by an ActiveX control in IG-XL. Although the ATE vendor handles most programming chores, ATE customers familiar with Windows drag-and-drop operations can customize the programs to meet their specific manufacturing and production-test requirements.

Excel forms much of the user interface of IG-XL, so those familiar with device test and Excel can use the system immediately. Proskauer says this approach enables ATE vendors to add value by solving device-test problems instead of implementing data-processing and data-storage functions. “We’ve written spreadsheet engines,” he says, “but that’s about as far from value-added as an ATE vendor can get. Microsoft has an entire software team working on the performance and feature set of the calculation engine in Excel. An ATE company cannot commit this kind of resources to what amounts to only a small part of its product.” T&MW

FOOTNOTES
1. Oonk, John, “Leveraging New Standards In ATE Software,” Proceedings, International Test Conference, Washington, DC, 1998, p. 606.

2. Proskauer, Dan, “High Quality, Easy to Use, On Time ATE Software...Can it Be Done?” Proceedings, International Test Conference, Washington, DC, 1998, p. 597.