Probabilistic processors possibly pack potent punch

http://arstechnica.com/hardware/news/2010/08/probabilistic-processors-possibly-potent.ars

by coderdude • 15 years ago

62 20 15 years ago

Possibly this may go the same way as the last outing of this idea, which can be seen, no joke, in fuzzy logic rice cookers and toasters and not many other places. Maybe.

psyklic2• 15 years ago

I wouldn't be so dismissive of this technology. The key is that it uses significantly less power than conventional circuit elements.

For instance, this concept has been demonstrated to be great at decoding lossy video -- perfect for mobile devices. And, it is already demonstrated to work as part of an error correction circuit for flash memory.

According to Lyric, their flash error correction chip requires "30X lower cost to manufacture and 12X lower power consumption" -- pretty significant savings.

modeless• 15 years ago

Do you have a citation for the lossy video thing? Seems like it could be good for rendering graphics too. For a 12x power savings maybe I can live with my pixels coming out #00FE00 instead of #00FF00 (for example).

waratuman• 15 years ago

Wow, someone went for alliteration!

jacques_chester3• 15 years ago

Always Aim to Alliterate, Says Stan.

Eliezer• 15 years ago

I always avoid excessive alliteration as it often annoys an otherwise attentive audience.

jacques_chester3• 15 years ago

I wish Jon Stokes had written this article.

caf• 15 years ago

If it lives up to the hype, it would be useful for some kinds of cryptanalysis.

ChuckMcM2• 15 years ago

When I saw the pitch deck for these guys I must admit I didn't get it. From what I could see it was "gee you can do divide in analog instantly!" which is to say that they had re-discovered analog computers. Now, don't get me wrong, an HDL for designing analog computers and a way to plug them into a digital stored program computer could be hella cool, but it read too much like someone simply not remembering the past.

That being said, and the fact that most 'analog' stuff is done in a DSP these days anyway, it would be fascinating if someone came up with the analog equivalent to a CLB in an FPGA and an HDL for describing non-linear computation (something the original analog computers could not do).

Its not clear at all however that these are the droids I was thinking of though. There is a lot of unused 130nm fab capacity though, so for a leading edge idea that could be implemented on trailing edge technology there should be a window.

jwm• 15 years ago

> it would be fascinating if someone came up with the analog equivalent to a CLB in an FPGA and an HDL for describing non-linear computation

What you have described do indeed exist as Field Programmable Analog Arrays (FPAAs).

The Wikipedia article (http://en.wikipedia.org/wiki/FPAA) gives a good overview of them, but basically they consist of multiple configurable analog blocks (CABs), which can be configured to perform some analog operation on a signal, and multiple CABs can be connected together to form a signal path. All the signal paths and CAB parameters are defined by the digitally loaded configuration. Very interesting!

The one's I have briefly used (many years ago) were the Anadigm FPAAs. Examples of the operations the CABs (or "CAMs") can do are signal filtering, rectification, addition, multiplication, comparison and integration/differentiation over time (http://www.anadigm.com/_doc/PR021100-0024.pdf). These devices to me are really targeted at analog signal processing applications (audio, instrumentation etc). If I was an EE (which I am not) I might be able to provide a decent evaluation of them, but they seemed like they would be pretty useful for this kind of thing.

My project using them was to get the FPAAs to perform some simple physics calculations, based on previous work by another student. One example was modelling the height of a moving projectile under gravity. I can't remember the specifics (sorry!) but input voltages were used to specify the equation parameters (mass, initial force), the CABs transformed these voltages according to the given motion equation and the output voltage was the height at time t. And it worked ok! A computer used Digital-to-Analog converters to hold the input voltages steady for the FPAA circuits, and sampled the output using Analog-to-Digital converters.

While this worked for simple examples, the whole system was limited to 8-bit effective values by the Signal-to-Noise resolution of the equation signal path. While for the FPAA device itself has a high signal-to-noise ratio that effectively gives a smallish 20 bit resolution (~= SNR 120db), the extra wiring and components in the rest of my circuit added enough noise to lower this down to 8bit (~= SNR 48db). (Will happily admit I am no great circuitsmith:). Also there were some caveats like hard limits to the parameters of the CABs (restricted internally by the physical limits of the variable capacitors and resistors), which limit quantities used in the analog equations and restricts its general purposefulness.

Some of the things analog computers can do are interesting, like "instant" multiplication and division. However the difficulty of keeping thermally and electromagnetically induced noise low to get a high resolution signal (e.g. pushing past SNR 120db) in analog systems is one of the reasons why we don't really see them being used in computation any more. This is also one of the reasons why digital circuits are much much easier to work with as you no longer (really) have to worry about noise affecting accuracy, from the transistor level up to the PCB or long cable level.

This kind of thing explains the low 8-bit resolution from the device in the article.

> The technology allows a resolution of about 8 bits; that is, they can discriminate between about 2^8 = 256 different values (different probabilities) between 0 and VDD

High resolution analog seems to be just hard to do in practice.

(Aside: Also if you take with the width of the known universe, and discretize this distance by Planck length intervals, you only need ~220 bits to represent the position of an object on this line. So only ~3*220 bits for (x,y,z). Binary rules!)

So, I'm more of an digital fan for general purpose computing myself:) However analog computers are hella cool all the same.

EDIT: This post is long. You'll have to excuse the fact that I was finally happy for some information from the old undergrad thesis to see the light of day. TLDR: Analog computers are cool, but it seems they are limited in resolution and general configurability. Use FPGAs or GPUs or even poor old CPUs instead.

EDIT2: Rereading your post, maybe you were thinking about some kind of FPGA+FPAA hybrid? An FPGA, but with some with analog blocks and ADCs, DACs inside?

ChuckMcM2• 15 years ago

A mix of FPAAs and FPGAs, rather than all FPGAs or all FPAA. The DSP elements in newish FPGAs is a nod in this direction.

High resolution analog seems to be just hard to do in practice.

That is exactly the challenging bit. And something I was trying to figure out if Lyric had actually made an improvement on. If you could do computation in an analog matrix and still pull 32 bits reliably out of it, that would be something new.

jbri• 15 years ago

Analog electronics have been used for simulation for a long time. Mainly for simulation of analog components.

But trying to use an analog processor for discrete computation? While it could work, part of the point of digital electronics is that you can build in error-correction at every single gate to mitigate the effects of not using ideal zero-resistance electrical components. In order to do that with an analog machine you'd either need to sample-then-recreate (essentially making it a digital-logic circuit) or have accurate knowledge of how much voltage is being dropped at each point (which is influenced by environmental factors such as ambient temperature).

arethuza• 15 years ago

Analog computers used to come in various forms - including hydraulic. I once worked for an engineering Prof who had spent a lot of time using hydraulic analog computers to "solve" systems of equations modeling various kinds of real world systems.

One thing that I thought was particularly neat is that he had spent time using a hydraulic analog computer to model the flow of fluid through building walls....

aidenn02• 15 years ago

I can see it as potentially useful in mobile devices, since it sounds like it's a trade-off of engineering time (analog circuits are much harder to get right) vs. power consumption, and mobile has such large volume that engineering costs can become a rounding-error.

I'm slightly concerned about per-unit cost since I'm assuming testing yields is going to be much harder. Digital behaves in well-understood ways across temperature and voltage ranges; analog is not as well understood.

[edit] I see they are claiming 30x smaller footprint, which will help, since they can be very aggressive about rejecting chips, but still I wonder if fabs that mainly do digital are setup to test something like this.

aidenn02• 15 years ago

My biggest reason for thinking this won't make inroads into HPC is that they talk about "Up to 1000x improvement over x86 calculations" well that means they need to get it to market and adopted before we have 256 or 512 x86 cores in a single socket, which isn't that far away, and would reduce their advantage to "Up to 4-8x" which is not nearly as impressive.

pygy_• 15 years ago

These chips are also very energetically efficient, and I can't see why moore's law wouldn't apply to them too. You could build a 256 core probabilistic processor as well.

RiderOfGiraffes• 15 years ago

Here are the submissions from seven months ago:

http://news.ycombinator.com/item?id=1619515

http://news.ycombinator.com/item?id=1616800

I provide this purely for reference, because as so often happens, it sank without trace then, but it's getting noticed and some commentary now.

markkat• 15 years ago

I really expected to find some mention of quantum computing in this article. Could probability of spin states (or some other state) be used in this paradigm?

Probabilistic processors possibly pack potent punch

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