Are neuromorphic chips a dead end?

Read a recent article about Intel’s Pohoiki Beach neuromorphic system and their Loihi chips, that has scaled up to 8M neurons in IEEE Spectrum (Intel’s neuromorphic system hits 8 M neurons). In the last month or so I wrote up about a two startups one of which seemed (?) to be working on a neuromorphic chip development (see my Photonics computing sees the light of day post).

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I’ve been writing about neuromorphic chips since 2011, 8 long years (see IBM SyNAPSE chip post from 2011 or search my site for “neuromorphic”) and none have been successfully reached the market. The problems with neurmorphic architectures have always been twofold, scaling AND software.

Scaling up neurons

The human brain has ~86B neurons (see wikipedia human brain article). So, 8 million neuromorphic neurons is great, but it’s about 10K X too few. And that doesn’t count the connections between neurons. Some human neurons have over 1000 connections between nerve cells (can’t seem to find this reference anymore?).

To get from a single chip with 125K neurons to their 8M neuron system, Intel took 64 chips and put them on a couple of boards. To scale that to 86B or so would take ~690, 000 of their neuromorphic chips. Now, no one can say if there’s not some level below 85B neuromorphic neurons, that could support a useful AI solution, but the scaling problem still exists.

Then there’s the synapse connections between neuromorphic neurons problem. The article says that Loihi chips are connected in a heirarchical routing network, which implies to me that there are switches and master switches (and maybe a really big master switch) in their 8M neuromorphic neuron system. Adding another 4 orders of magnitude more neuromorphic neurons to this may be impossible or at least may require another 4 sets of progressively larger switches to be added to their interconnect network. There’s a question of how many hops and the resultant latency in connecting two neuromorphic neurons together but that seems to be the least of the problem with neuromorphic architectures.

Missing software abstractions

The first time I heard about neuromorphic chips I asked what the software looks like and the only thing I heard was that it was complex and not very user friendly and they didn’t want to talk about it.

I keep asking about software for neuromorphic chips and still haven’t gotten a decent answer. So, what’s the problem. In today’s day and age, software is easy to do, relatively inexpensive to produce and can range from spaghetti code to a hierarchical masterpieces, so there’s plenty of room to innovate here.

But whenever I talk to engineers about what the software looks like, it almost seems like a software version of an early plug board unit-record computer (essentially card sorters). Only instead of wires, you have software neuromorphic network connections and instead of electro-magnetic devices, one has software spiking neuromorphic neuron hardware.

The way we left plugboards behind was by building up hardware abstractions such as adders, shifters, multipliers, etc. and moving away from punch cards as a storage medium. Somewhere along this transition, we created programing languages like (macro) Assemblers, COBOL, FORTRAN, LISP, etc. It’s the software languages that brought computing out of the labs and into the market.

It’s been at least 8 years now, and yet, no-one has built a spiking neuromorphic computer language yet. Why not?

I think the problem is there’s no level of abstraction above a neuron. Where’s the aritmetic logic unit (ALU) or register equivalents in neuromorphic computers? They don’t exist as far as I can see.

Until we can come up with some higher levels of abstraction, coding neuromorphic chips is going to be an engineering problem not a commercial endeavor.

But neuromorphism has advantages

The IEEE article states a couple of advantages for neuromorphic computing: less energy to perform inferencing (and possibly training) and the ability to train on incremental data rather than having to train across whole datasets again.

Yes these are great, but there’s a gaggle of startups (e.g., see New GraphCore GC2 chip…, AI processing at the edge, TPU and HW-SW innovation) going after the energy problem in AI DL using Von Neumann architectures.

And the incremental training issue doesn’t seem any easier when you have ~80B neurons, with an occasional 1000s of connections between them to adjust correctly. From my perspective, its training advantage seems illusory at best.

Another advantage of neuromorphism is that it simulates the real analog logic of a human brain. Again, that’s great but a brain takes ~22 years to train (college level). Maybe because neuromorphic chips are electronic perhaps training can be done 100 times faster. But there’s still the software issue

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I hate to be the bearer of bad news. There’s been some major R&D spend on neuromorphism and it continues today with no abatement.

I just think we’d all be better served figuring out how to program the beast than on –spending more to develop more chip hardware..

This is hard for me to say, as I have always been a proponent of hardware innovation. It’s just that neuromorphic software tools don’t exist yet. And I’m afraid, I don’t see any easy way forward to make any progress on this.

Comments?.

Picture credit(s):

• IEEE Spectrum Intel’s neuromorphic system hits 8M neurons… article
• Wikipedia article on ALU
• Wikipedia article on plugboard computers