Obsolescence is the curse of electronics: no sooner have you bought a gadget than its hardware is outdated. A new, low cost type of microchip that can rearrange its design on the fly could change that. The logic gates on the chip can be reconfigured to implement an improved design as soon as it becomes available—the hardware equivalent of the software upgrades often pushed out to gadgets like phones.
Reprogrammable: This chip can be reconfigured to implement new designs, thus allowing device hardware to be upgraded.
The new chips—made by a startup called Tabula—are a cheaper, more powerful competitor to an existing type of reprogrammable chip known as a field programmable gate array (FPGA). FPGAs are sometimes shipped in finished devices when that is cheaper than building a new chip from scratch—usually things that are expensive and sell in low volumes such as CT scanners. More commonly, FPGAs simply provide a way to prototype a design before making a conventional fixed microchip.
If programmable chips were more powerful and less costly they could be used in more devices, in more creative ways, says Steve Teig, founder and chief technology officer of Tabula. His company's reprogrammable design is considerably smaller than that of an FPGA. "FPGAs are very expensive because they are large pieces of silicon," says Teig, "and silicon [wafer] costs roughly $1 billion an acre." The time it takes for signals to traverse the relatively large surface of an FPGA also limits its performance, he says.
"It's like being inside a very large, one story building—the miles of corridors slow you down," he says. As with a building, stacking layers of circuit on top of each other helps, by providing a shortcut between floors, says Teig. But unfortunately, the technology needed to build stacked, 3-D chips is still restricted to research labs. Instead Teig found a way to make a chip with just one level behave as if it were eight different ones stacked up. "Imagine you walked into the elevator in a building and then walked back out, and that I rearranged the furniture quickly while you were in there," says Teig. "You would have no way to tell you weren't on a different floor." Tabula's chips perform the same trick on the data they process, cycling between up to eight different layouts at up to 1.6 billion times per second (1.6 Gigahertz). Signals on the chip encounter those different designs in turn, as if they were hopping up a level onto a different chip entirely. "From its behavior, our [design] is indistinguishable from a stack of chips," says Teig, who calls the virtual chip layers "folds."
That brings speed advantages, because signals don't have to travel a long way across the surface of a chip to reach new part of circuit, as they do on an FPGA. When the chip loads a new fold, new circuitry appears in place of the old. Teig estimates that the footprint of a Tabula chip is less than a third of an equivalent FPGA, making it five times cheaper to make, while providing more than double the density of logic and roughly four times the performance.
As with FPGAs, Tabula's chips contain arrays of many identical basic building blocks that can be programmed to implement any logic function. A memory store on the chip manages the different configurations that the chip cycles through.
Teig's approach makes sense, says Andre DeHon, who researches reconfigurable hardware at the University of Pennsylvania and has experimented with similar designs himself. Most of the area on an FPGA chip is made up of the wiring needed to connect the elements that do the work, he says. "This new type of design can run faster and avoids parts just sitting there while signals run down long paths."
Tabula could push reconfigurable silicon to displace conventional, fixed design chips in more places, says DeHon. Making a custom chip requires a guarantee of a few million units, says DeHon, and hence an upfront cost of several million dollars. "It's a matter of moving the crossover point between the cost of that and the cost of reconfigurable technology."
Making the reconfigurable approach cheaper could enable even consumer electronics to ship with programmable chips, making it possible for them to be upgraded with new design tweaks. That approach is currently used only in some expensive equipment such as cell-phone base stations. "Sony could say, 'look at what our competitor Toshiba did', and upgrade the chips inside their TVs to provide new features," says Teig. "Getting to digital cameras or TVs is definitely within reach."
However, Rich Wawzyrniak, who tracks FPGAs and related technology for analyst firm Semico Research, points out that there are limitations to this approach. "The power consumption if these devices is relatively high, and likely too much for a device like a phone," he says.
But ultimately, says DeHon, reconfigurable chips should morph their design even more often, shifting their workings to match the task in hand in a blend of software and hardware. "These things are really platforms that can run any computation. The grand vision is that we come up with a way for a program's code to be mapped to the chip when it runs."
By Tom Simonite
From Technology Review