TR10: Probabilistic ChipsContinued from page 1 By Erika Jonietz
Applications where the limits of human perception reduce the need for precision are perfectly suited to PCMOS designs, Palem says. In cell phones, laptop computers, and other mobile devices, graphics and sound processing consume a significant proportion of the battery power; Palem believes that PCMOS chips might increase battery life as much as tenfold without compromising the user's experience. PCMOS also has obvious applications in fields that employ probabilistic approaches, such as cryptography and machine learning. Algorithms used in these fields are typically designed to arrive quickly at an approximate answer. Since PCMOS chips do the same thing, they could achieve in hardware what must be done with software today--with a significant gain in both energy efficiency and speed. Palem envisions devices that use one or more PCMOS coprocessors to handle specialized tasks, such as encryption, while a traditional chip assists with other computing chores. Palem and his team have already built and started testing a cryptography engine. They are also designing a graphics engine and a chip that people could use to adjust the power consumption and performance of their cell phones: consumers might choose high video or call quality and consume more power or choose lower quality and save the battery. Palem is discussing plans for one or more startup companies to commercialize such PCMOS chips. Companies could launch as early as next year, and products might be available in three or four years. As silicon transistors become smaller, basic physics means they will become less reliable, says Shekhar Borkar, director of Intel's Microprocessor Technology Lab. "So what you're looking at is having a probability of getting the result you wanted," he says. In addition to developing hardware designs, Palem has created a probabilistic analogue to the Boolean algebra that is at the core of computational logic circuits; it is this probabilistic logic that Borkar believes could keep Moore's Law on track. Though he says that much work remains to be done, Borkar says Palem's research "has a very vast applicability in any digital electronics." If Palem's research plays out the way the optimists believe it will, he may have the rebel's ultimate satisfaction: seeing his heresy become dogma. |
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Moore's Law
12/22/2008
Massachusetts Institute of Technology
Comments
GaryB
02/19/2008
Posts:64
lenhamilton
02/25/2008
Posts:1
kitk
02/27/2008
Posts:65
Silacon
02/27/2008
Posts:46
carlii
02/27/2008
Posts:26
I'm afraid the result of video processing most definitely is a number! It is in fact a stream of numbers.
I don't know if Palem actually said what was written down by the author of this article or whether the author translated what Palem actually said into something else in an attempt to simplify for the readership or whether the author didn't actually understand themselves; but what what Palem is trying to convey is this:
In some applications 100% accuracy of the output of the digital electronics is not critical. In areas of video and audio small errors in the data streams - so long as they are not perceptible by the human senses - is acceptable.
On the other hand, applications such as flight control systems in fighter aircraft, if the digital systems outputted small errors then that would not be tolerated and could be fatal.
So depending on the application, the presence of a small amount of error on the output can be tolerated.
Now, like other engineers/experts in electronics and computing, I am initially sceptical. Why?
What Palam is talking about is reducing the voltage of operation of the electronics to the point where it fails to function correctly.
How does this translate into 'small' errors in the output? Why is it that the errors are small, why should those errors not be large?
He has demonstrated video using the concept where the errors in the data stream were not discernable.
As an electronics engineer, I'm extrapolating what I believe Palam is talking about.
Logic gates are made up of transistors.
A chip for processing video will be made up of tens of thousands, hundreds of thousands of logic gates. Reducing the voltage will mean that the transistors don't switch correctly, thus leading to logic gates ouputting errant values.
Let's suppose we're working with monochrome video, with 8 bits per pixel, giving 256 shades of grey to simply the discussion.
Those logic gates work together to generate a stream of values, each value being in the range of 0-255. A single errant bit change in an output value can cause the output to change from its correct value by 0 - 128.
For the errant value to be imperceptible, what you would like is the difference from correct to errant value to be small, perhaps 1 or 2.
It's small and you might not notice it when watching the video stream.
How can that be realised? That's the issue I have.
Anyone of those logic gates in the digital circuit could produce an errant output value, leading to a completely different value being output in the 8 bit data stream, not just errors of 1 or 2, but 128 too. And here we're only talking about a single bit being in error.
If more than one bit error occurs, then the error value is greater still.
So my question is, how has Palam managed to constrain the magnitude of the error to ensure that it is not perceptible?
That's the key to this whole thing. (which hasn't been even mentioned in the article)
If reducing the operating voltage results in errors being perceptible in the output data stream then it's useless.
Rich43
12/05/2008
Posts:2
rogkru
03/09/2009
Posts:4