A while back, searching for technologies more adapted to creating a microprocessor with a customized instruction set, I came across the web site for Elixent. They have a chip which contains a microprocessor, plus a fabric, something like an FPGA, but in which the cells are not simple gates or look-up tables, but instead ALUs. Also, NEC and other companies have 'reconfigurable computing' chips with many small computers of a sort.
Are there other kinds of software-customizable chips out there that are very different from an FPGA?
John Savard
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Old fart time... See if you can find a data sheet for the AMD 2901 or 29116. The 2901 was a 4 bit ALU slice. The 29116 was 4 of them in one package. They were a great breakthrough for building microcoded machines.
For those not familiar with that technology, back in the
70s-80s, it was common to build CPUs by building a faster microcoded machine that actually implemented the "real" instructions. The Alto from Xerox PARC is a good example. (pre 2901. It used '181s, I think. Memory might be foggy by now.)
The ones I'm familiar with used a wide instruction word to simplify decoding. Each instruction included a next-instruction address. There was no adder on the PC register. Branching was by ORing bits into the bottom of the next-PC, often with a pipeline dalay stage to make life more "interesting" for the microcoder.
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Check out Mathstar. They have a fabric of ALU's MAC's and register files that runs at 1 GHz. The current chips d> A while back, searching for technologies more adapted to creating a
I looked at that and grocked as much as wanted in a few mins looking at the gif pics mostly.
1st impression you only get 1 Tensilaca cpu for your $ and its pretty humble at about 260MHz but has an embc rating of 4.6 or so right in there with most 200-400MHz embedded DSPs, cpus. How much is this $chip.
2nd the compiler flashes critical C areas into the side engine reducing maybe a few 100 instructionsinto 1 cycle. Then it jumps to the top of the list with rating of about 900 for 200x gain, right on top of TI and BOPs (RIP).
3rd they claim fpgas are pretty expensive, well a risc core with 1 BlockRam and needed LUTs seems to be in the order of $1 and falling or so depending on cpu design etc. FPGA RISC can have any co processor attached as desired with no limits on what it could do bar imagination and the FPGA limits, but you gotta design it yourself, right now, but who knows somebody might have a bright idea.
Now if somebody were to do this whole compiler thing using a soft FPGA core and auto magically take chunks of C code and convert to FPGA fabric on the fly, they would likely get just as good results, although they would have to do some work in the reconfigation aspect and justify the swap costs v deliverd gain.
Further you could replicate this thing as many times as the fabric allows and you could put in things which were never part of the C program in the 1st place, such as the I/O systems, memory controllers.
While these other NOT AN FPGAs are very interesting, you swap 1 set of limits that we know how to deal with, for another set of limits and far smaller market presence if any at all. Anyone remember BOPs, they got borged.
regards
johnjakson at usa dot com transputer2 at yahoo dot com
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