Low cost and/or small size CPU in an FPGA

On a sunny day (Wed, 24 Apr 2013 07:36:29 -0600) it happened hamilton wrote in :

Depends on the number of gates, logical units, not on the number of pins. It is relatively easy to write your own processor (clone), look here:

under processors for what people have done and made available.

Anywhere near that number of pins yes.

There are very cheap simple Altera FPGA boards on ebay too I have seen (have not tried those).

'Processor' is not always needed in FPGA, the idea is just to do things with logic that can run concurrently (sat at the same time) that otherwise have to be done sequentially. No latency, CPUs always have (instruction) latency.

hamilton schrieb:

Hello,

if we only look for the needed pins, these CPUs would fit: separate 8 bit data and 16 bit address bus separate 16 bit data and 16 bit address bus separate 16 bit data and 20 bit address bus multiplexed 16 bit data and address bus multiplexed 16 bit data and 32 bit address bus multiplexed 32 bit data and address bus

The number of gates necessary depends on the size of the instruction set. A RISC CPU with serial processing in the ALU would be slow but small.

Bye

AFAIR the i8080A was ~6000 transistors. Modern 8bit core like PIC18 or AVR is ~200000 transistors. This gives the ballpark of gate number.

Unlikely.

Vladimir Vassilevsky DSP and Mixed Signal Designs

I think limiting factor is usually memory, not the cpu

guess you could do something with an external serial flash some of them a quite fast, and it wouldn't take much logic to take advantage of the read address auto increment

-Lasse

Ok, my goal.

I need a uP and some logic, but I would like to do it with one part.

208 pins just won't fit into my package.

Thanks

hamilton

I've used the Picoblaze CPU from Xilinx in several projects. AFAIK that is the smallest useful FPGA cpu.

--
Failure does not prove something is impossible, failure simply 
indicates you are not using the right tools... 
nico@nctdevpuntnl (punt=.) 
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Have you looked at any of the FPGA lines yet? If package is a big deal, you need to pull up some data sheets and check out the packages.

The parts I have used or will be using are the XP from Lattice in the

100 pin QFP and the iCE40 also from Lattice in several useful packages. The iCE40 data sheet shows a 32 pin QFN, an 84 pin QFN and 100 and 144 pin QFP. Everything else is some fine pitch BGA which I prefer not to use because of the small drills and fine pitch required of the PCBs.

Xilinx and Altera may have some parts in non-BGA packages too, I'm not so familiar with those lines. Both of the Lattice families I mention have on chip Flash or one time programmable memory. That saves a chip or two for programming.

--

Rick

BTW, you might want to post this to comp.lang.forth They discuss MISC often there.

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Rick

ADUC702x has a quite simple programmable array (just combinatorial IIRC).

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John Devereux

I want to thank everyone that made suggestions.

I have discovered the SAM4S 120Mhz processor in a 48-pin package.

The I/O pins may be able to do in software what I wanted the logic to do on a slower processor.

I can create a 100nSec pulse in software.

hamilton