By David Voss
Chips that change function on the fly will mean more versatile handhelds.
Late for an appointment, you grab your "personal information appliance." Prompted by your uttering the words "cell phone," the small gadget awakens and instantly programs itself for a mobile phone call. Done with the call, you say "translator," and the device rewires itself to translate the latest business news from Tokyo. Issue the command "map," and it reconfigures itself again to take a GPS reading and display your location in real time.
One reason that this type of versatility is not possible today is that handheld gadgets are typically built around highly optimized specialty chips that do one thing really well. These chips are fast and relatively cheap, but their circuits are literally written in stoneor at least in silicon. A multipurpose gadget would have to have many specialized chips--a costly and clumsy solution. Alternately, you could use a general-purpose microprocessor, like the one in your PC, but that would be slow as well as expensive. For these reasons, chip designers are turning increasingly to reconfigurable hardware--integrated circuits where the architecture of the internal logic elements can be arranged and rearranged on the fly to fit particular applications.
Dozens of academic research groups and startup companies are pursuing the ideal of the reconfigurable computer. One of the most promising approaches is a technology called "field-programmable gate arrays." The strategy is to build uniform arrays of thousands of logic elements, each of which can take on the personality of different, fundamental components of digital circuitry; the switches and wires can be reprogrammed to operate in any desired pattern, effectively rewiring a chip's circuitry on demand. A designer can download a new wiring pattern and store it in the chipÕs memory, where it can be easily accessed when needed. "This kind of reconfigurable logic is grabbing a larger and larger share of designs," says physicist Philip Kuekes of Hewlett-Packard Laboratories. "And it will get even bigger."
Basic reconfigurable circuits already play a huge role in telecommunications. For instance, relatively simple versions made by companies such as Xilinx and Altera are widely used for network routers and switches, enabling circuit designs to be easily updated electronically without replacing chips. In these early applications, however, the speed at which the chips reconfigure themselves is not critical.
To be quick enough for personal information devices, the chips will need to completely reconfigure themselves in a millisecond or less. "That kind of chameleon device would be the killer app of reconfigurable computing," says University of California, Berkeley, computer scientist John Wawrzynek. And Wawrzynek and other computer scientists believe that it could soon be within reach, as they continue to improve the speed and density of reconfigurable logic circuits. These experts predict that in the next couple of years reconfigurable systems will be used in cell phones to handle things like changes in telecommunications systems or standards as users travel between calling regions--or between countries. Wawrzynek says the technology's biggest impact may be that it allows devices to better handle streaming media.
Some computer researchers believe that the technology is poised for even larger things, like general computing. It is getting more expensive and difficult to pattern, or etch, the elaborate circuitry used in microprocessors; many experts have predicted that maintaining the current rate of putting more circuits into ever smaller spaces will, sometime in the next 10 to 15 years, result in features on microchips no bigger than a few atoms, which would demand a nearly impossible level of precision in fabricating circuitry. "We are not going to be able to afford to build the Pentium 27," says Seth Goldstein of Carnegie Mellon University. "We can't afford the precision." But as it turns out, reconfigurable chips don't need that type of precision, and Goldstein and others believe the technology could offer a viable strategy for building computers that function at the nanoscale level.
"We've now discovered molecules that act just like reconfigurable logic bits," says Hewlett-Packard's Kuekes. "We are proposing fairly simple devices that can be literally grown with chemistry. Then all the complexity will be downloaded into configuration bits once the structure is made." Kuekes expects this technology will come to fruition in about ten years, just about the time silicon will peter out. "Reconfigurable logic won't just be a good idea," says Kuekes. "It will be the only way to do computing in the future."