Driving the Xbox 360-with feedback - Embedded.com

Driving the Xbox 360–with feedback

As video game developers aim to give users a more realistic experience, more interactive peripherals are being created to stimulate users' senses. Sight and sound, the two senses typically associated with video games, are being used to near full advantage thanks to improvements in both video and audio technology (3D games are in the works). Touch is the next sense on Xbox 360 game developers' radar, as evidenced by the introduction of Microsoft's Xbox 360 Wireless Racing Wheel, a wireless steering wheel controller designed to mimic the sensations of quick turns, rough terrain and high-impact crashes using Force Feedback technology.

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The two primary hardware components in the game controller are the dashboard with steering wheel controller, and the gas and brake pedal unit. A plastic clamp anchors the dashboard to a table. Based on my experience playing with … er, testing … the unit, I understand the need to anchor the dashboard–the twists and turns become increasingly intense as you drive some of the advanced race courses. The steering wheel is wireless, except for an Ethernet-style (four-wire) interface connecting the wheel to the pedal unit.

Unpacking the device, you can feel the weight of the main steering console, which is much more substantial than other video game controllers. The wheel itself is well-crafted–it feels a lot more like a real racecar steering wheel than, say, the steering wheel on my 1999 Mazda Protégé! The consensus among colleagues is that Microsoft's Xbox 360 and peripherals are mechanically sound hardware–quite good for a software company.

Upon taking apart the many layers of plastic that comprise the steering wheel controller, the main PCB is exposed. There are three large ICs, two with Microsoft markings, and a third, the Atmel AT91SAM7S32. The interesting parts are the Microsoft parts. Obviously Microsoft does not make chips, so whose ICs are they? We asked the good people of Semiconductor Insights to de-encapsulate (or decap) the devices to find out.

Bluetooth allows wireless control of the Xbox 360 driving experience.

Looking first at the shielded wireless device labeled “Microsoft X80199,” it is revealed to be a National Semiconductor LMX420CL. Further inspection of the die reveals RF and analog circuitry, as well as a significant amount of logic. From the FCC filings associated with this device, the 2.4-GHz band is mentioned as the communications frequency, so this device is indeed a Bluetooth transceiver. This device cannot be found on the National Semiconductor Web site, but could be similar to their other LMX labeled Bluetooth offerings.

The second Microsoft die, labeled “X81376,” contains another National Semiconductor device, the SC14470C mixed-signal microcontroller. This is one of two microcontrollers on the PCB, combining with the Atmel AT91SAM7 to provide the processing power for the steering wheel.

A peek back into the Under the Hood archives finds these same two National Semiconductor parts in another Xbox 360 peripheral: the Guitar Hero III Les Paul wireless controller featured in a teardown in February. And according to Portelligent, these same devices are also found in the simpler Microsoft Xbox 360 wireless controller. These two parts form an integrated Bluetooth and baseband processor communications set, with the microcontroller providing the logic to process the data from the regular buttons, take in the information provided by the other microcontroller and instruct the transceiver on communications with the game console.

It seems that these two parts are hand-picked by Microsoft for all their Bluetooth communications with the Xbox 360 game consoles. A huge design win for National, especially as they are a smaller player in the Bluetooth arena. Their capability in providing the full solution of microcontroller and transceiver–with the inevitable software support–probably helped their cause.

The extra processing horsepower comes from the Atmel AT91SAM7S32 microcontroller. The SAM7 series from Atmel comes with a 32-bit ARM7TDMI Thumb processor core, while this particular model comes with 32 KB of flash memory and 8 KB of SRAM. The major role of this microcontroller is to handle the complex motor control that is required to provide the “force feedback” that makes the user experience so realistic. The AT91SAM7 device may also control the power management of the steering wheel. This becomes more important than in other wireless controllers, as the steering wheel contains more active motor control while still running on a battery pack.

Finding this Atmel ARM-based device does bring to mind the current talks surrounding a possible acquisition of the microcontroller business of Atmel by Microchip Technology. When it comes to the 32-bit market, Microchip has clearly bet on the MIPS processor architecture while Atmel has embraced the ARM architecture for their 32-bit offerings, including the new Cortex-M3 device. Will both 32-bit architectures be able to survive in a single company? It's hard to believe they will–Bernie Cole provides further analysis on this potential merger online.

The pedal unit, when torn down, exposes a very simple design. The two pedals are mounted on springs that rotate around points. At the two points are two potentiometers that change the monitored voltage. So the four wire interface actually contains the supply voltage, ground and the two potentiometer output voltages that represent the gas and brake values. There are no active components in the pedal unit.

As for the rest of the ICs on the main PCB, two Analog Devices operational amplifiers (AD8692 and AD8694) and a quad analog switch/multiplexer from ON Semiconductor (MC14016B) are used to control and boost the analog signals from the pedal unit, as well as other motor control signals. A Monolithic Power Systems step-down converter (MP1591) reduces the high voltage from the battery pack to the 2.5 V that can be further reduced for the logic area of the two microcontrollers (the AT91SAM7 has a core voltage of 1.8 V).

All these electronics, and an attention to mechanical design, bring home a truly unique video-game driving experience. With the touch sense explored in driving games, what's next–smell? Ahh, imagine the aroma of burning rubber, fuel spills and new car leather.


Steve Bitton is a technology analyst at TechOnline, a division of TechInsights. He has a bachelor's of applied science in electrical engineering from Queen's University (Kingston, Ontario).

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