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Chuck Moore's GreenArrays chip? (He's also the guy behind Forth, the quintessential stack-based VM.) How's that working?


The very same. It's working really well—initially I was intimidated about the chips because of a few of the constraints the chip has in order to be as good as it is. Three challenges:

1) Figuring out how to work within the very low (but reasonable) amount of RAM each core has. They're independent computers, so each core needs to store its code and its data, all within 64 18-bit bytewords, which roughly corresponds to a tweet of information if you tweeted in UTF-8.

2) Dealing with the IDE: the IDE is attacking a problem nobody's solved: parallel compilation. That being said, it has been the second greatest challenge so far, after

3) Getting the hardware set up. My co-project-doer is light-years ahead of me in the EE department and makes most of the EE decisions, with some input from me about what capabilities the chip needs to have (a minimum amount of off-die RAM, say). Sourcing parts is something I would not have been able to do on my own, so I'd say this project requires a good deal of electronic literacy, if not dexterity.

That being said, though it's a bit of a prima-donna, it has every right and reason to be. It's an amazing, amazing chip. It's fast, powerful, unclocked, can work with all kinds of devices, is a crazy bargain both in hardware cost and in energy cost, and best of all, for me at least, an endless source of fun, hard problems. It's a fascinating chip.


It's great to see people using Chuck's work, and in particular it's wonderful to see your reaction. I think it would be easy to recoil at the strange tools, not to mention the difficulty of programming the thing. I agree it's a fascinating device.


Can you give a hint as to what we can expect to do with this chip?

I was a Forth enthusiast and read the book in OP (in early 2000's) and followed Chuck's work from afar, but I am not sure what exactly I could do with this chip, given its peculiar limitations.


With low RAM like that, what you want to do is math, not UI. That means electrical engineering or number crunching, AFAIK.

OK, so first, it has a lot of I/O ports of different kinds on just one chip. In a lab, you could run lots of analogue knobs and many servos attached to just one chip. This means a lot less hardware debugging, which should be a Godsend.

Another possibility is HPC. You can tile a motherboard with these, cool them all down to -50 very easily and cheaply, and then overclock them as you perform number crunching that you couldn't do with a GPU. After all, these cores are truly independent, and can therefore branch independently, unlike GPU cores. That opens the door to a wide variety of algorithms that aren't GPGPU accessible.


I've always thought it was a nifty chip, but one I couldn't think of an application for. Things like the 18-bit word size can throw some developers off -- the last time I looked at the chip some audio application guys were kvetching that they really need 24 bits for their applications. I'm skeptical that the architecture is a good fit for number crunching, but perhaps I'm just blind to all the numeric apps that 18-bit integers are nifty for.

yet like said at the beginning, it doesn't stop me from wishing I had an excuse to play with them. Blazing speed with lots of cores, there ought to be some applications that for that sort of parallel horsepower.


A very peculiar kind of number crunching that would be. With 64 words, that should be some finely selected numbers :)

I'd love to be able to do some useful work with that, of course.


Don't think of the F18 computers in isolation- think about doing stream processing with a network of them. You probably can't fit your application on one F18, but you could easily fit one or two functions in 64 words, especially given that a single machine word can contain up to four instructions.


It sure looks like a fine chip for a very small niche, but they don't even have floating point instructions AFAIK, so you'd have to emulate them in software. So I'm extremely skeptical about their number crunching capabilities.


No floating point. I believe design complexity of the chip would increase manifold if it was. Emulation is not an option too with those extremely limited resources (64 words of memory). The design philosophy of this chip is that 18 bits of integer precision should be enough for your applications, period. I just feel like I'm not smart enough to figure out how to fit a useful application into that.


By IDE, do you mean Color Forth? Are you using Color Forth? If that's totally wrong, could you talk more about the IDE anyway?


Yes, I'm using Color Forth. It's not the best part of the package...it took a really long time to learn, and I had to learn its keyboard layout to do so. My philosophy, in general, is, "do whatever you want, but don't change my editor or keyboard." After all, I spent several weeks being unable to type because I was learning Dvorak, years ago. And emacs had a steep learning curve too.

The UI, I have to say, would not pass Apple's muster. It is a completely different way of programming, and I preferred to program on paper for the longest time rather than learn all the weird controls.




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