Xbox, Microsoft’s future-generation video-game console system, delivers a powerful and realistic gaming experience to the user. The dedicated console uses the latest electronics hardware and custom-created components to deliver the hottest technology to the gamer community. It is powered by an Intel 733-MHz processor and includes a custom-designed graphics processing unit (GPU) capable of processing more than one trillion operations per second.
The Xbox game controller features an eight-way directional pad, a left and right analog thumb-stick, and analog left and right shoulder triggers. It also has six pressure-sensitive analog buttons, two expansion slots for memory cards and other peripheral devices, and built-in rumble motors for user feedback.
Considering the challenge of manufacturing hundreds of thousands of game controllers at product release, testing both electronics hardware and software is crucial for a successful product launch. For that reason, end-of-line functional test stations for verifying product acceptance and reliability are important parts of a successful product launch.
The main challenges in developing any production-line functional tester are:
- Package as many parallel test scenarios as possible within the allowed production-line beat rate.
- Collect as much data as possible for later analysis to implement improvements in the production processes and the unit under test (UUT).
- Produce a simple and easy-to-use user interface with minimal manual operator requirements.
- Develop an advanced diagnostics mode to help the manufacturing team diagnose problems quickly on the production floor so corrective actions can be taken immediately and not affect final production.
All of these requirements typically are limited by the construction and maintenance costs of the functional test station. This is the real challenge to the test engineer—to incorporate as much testing as possible within the limited budget and production-line beat rate.
Functional Test Station
The Xbox-controller functional test station is used at the end of the production line to verify acceptance before packaging and shipping to the retailer. The system can test all device communications both at the protocol and the parametric test levels.
The station monitors all data packets to verify that controller functional messages are within a user-configurable specification. Signals also are monitored at the chip level by analyzing the raw electrical signals for rise and fall times, min and max voltage levels, and current draw.
A custom-built signal breakout and routing box sends and conditions signals to the National Instruments’ (NI) 5112 PXI Digitizer to perform the electrical tests. Figure 1 shows the block diagram of the test station.
An automated test sequence that can be set up, saved, and configured by authorized users runs the production-line tests. The functional tests are completed immediately after production to determine the pass/fail condition of each controller before shipping.
You simply follow the yellow regions by pressing buttons and moving analog controls through the defined regions. The regions turn green or red depending on whether the station recognizes that the yellow region has been activated within user-defined limits. Green indicates that the controller recognizes that this region has been activated, and red designates that there is no activation within a user configurable timeout limit.
More than 250 individual test parameters are recorded to a data file for each tested controller, and each of the up to 30 test stations is linked to a main server via a LAN for data management. The Xbox controller functional test stations can execute tests typically not performed in a production environment such as device compliance testing, yet all tests can be performed well within the beat rate of the production line.
To optimize throughput, the production-line tester bundles parametric tests in parallel with basic functional tests. Typical R&D parametric tests include verifying strict eye-pattern compliance with the proprietary digital communications protocol to a resolution of 400 ps using the PXI Digitizer.
Signal integrity tests, which verify that the bit time electrical signals are within a user-defined mask, are accomplished during button testing. Pass/fail results are displayed at the bottom of the screen in Figure 2. Charge calculations, voltage supply measurements (Vcc tests), and current measurements (current tests) also are made on each controller as the two rumble motors are cycled individually and then collectively.
Continuity tests (VBI tests) are performed on the controller PCB to verify that essential advanced video synchronization signals are enabled. A sampling rate of 2.5 GS/s is necessary to analyze the actual raw bit signaling waveform. This is accomplished using the digitizer in the random interleaved sampling (RIS) mode.
RIS-Based Signal Acquisition
RIS, or equivalent time sampling (ETS), refers to a method that samples repetitive signals in a manner that results in the perceived sampling rate being much faster than the actual sampling rate. This effect is achieved by triggering at different offset points on the incoming signal relative to the actual sample clock edges, then reconstructing the incoming signal by interleaving the different data captures to produce a higher resolution data capture. The limit of the perceived sampling rate then is restricted by the resolution of the time measurement, done via a time-to-digital converter (TDC), made from the initial trigger capture to the first data collection point. Digitizers with RIS capabilities provide an effective and lower cost solution for acquiring data at much faster acquisition rates than available on a scope.
Advanced Online Diagnostics Mode
When the end-of-line functional test station identifies possible production-line problems, the station serves as an advanced diagnostics system. This allows for faster on-site debugging of component batch failures and permits the resolution of problems in real time on the production floor. Then, problems can be immediately corrected and retested in the diagnostics mode to minimize production-line downtime.
With the diagnostics mode screen shown in Figure 3, you can manually operate each automated test and view the raw input data. The upper left corner allows you to press all digital buttons and monitor the response of the button press. Analog buttons and their corresponding values are shown in the lower left portion of the screen.
The software can hold min and max values as you go through the required range of motion and view the real-time data. Thumb-stick regions are broken down into an X-Y mapping and display min/max values. The data-packet values can be displayed as raw voltage or as 8-, 16-, 32-, or 64-bit values. The graph on the upper right corner shows the real-time data.
Conclusion
By developing the Xbox controller test system using National Instruments’ LabVIEW, the PXI platform, and Windows 2000, the functional test station is reliable, flexible, cost-effective, and easy to maintain and upgrade. As controllers roll off the production line, each completed test sends more than 250 data parameters per controller to a dedicated LAN server for post-test analysis to help improve both the production process and the UUT.
All systems are connected via a LAN in a seamless manner with all data stored on a main server and with the test station configured so that production lines are not affected during server downtime. The advanced RIS mode of the PXI digitizer allows data collection of the raw electrical bit signals at a rate of 2.5 GS/s. The PC environment has made the customization of the station straightforward for quick programming modifications to isolate potential problems in the production process.
About the Authors
Jeff Alexander is the lead test engineer on the Microsoft Xbox Gamepad and associated peripheral devices, responsible for developing and manufacturing test of all Xbox peripherals. He has an A.S. in avionics systems and a B.S. in electrical engineering from the University of Alaska.
Lokesh Duraiappah is a product manager at National Instruments. He joined the company in 1998 as an application engineer before moving to product management in the measurements group. Mr. Duraiappah received an A.B. in physics from the University of California, Berkeley and a Ph.D. in physics from the University of Texas.
Darren Scarfe is the engineering team leader in the Michigan office of VI Engineering and responsible for engineering and delivery of customized turnkey test systems for both R&D and manufacturing environments. He has a B.S. in theoretical physics from the University of Guelph, Canada and an M.S. in physics from the University of Waterloo, Canada and is working on a Ph.D. in physics at the University of Houston. VI Engineering, 37800 Hills Tech Dr., Farmington Hills, MI 48331, 248-489-1200, e-mail: [email protected]
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November 2001