The littlest CPU

I may need to add a CPU to a design I am doing. I had rolled my own core once with a 16 bit data path and it worked out fairly well. But it was 600 LUT/FFs and I would like to use something smaller if possible. The target is a Lattice XP3 with about 3100 LUT/FFs and about 2000 are currently used. I believe that once I add the CPU core, I can take out a lot of the logic since it runs so slowly. The fastest parallel data rate is 8 kHz with some at 1 kHz and the rest at

100 Hz. I probably would have used a CPU to start with instead of the FPGA, but there was a possible need to handle higher speed signals which seems to have gone away.

I recall that someone had started a thread about serial implementations of processors that were supported by a C compiler. I don't think any ever turned up. But the OP had some other requirements that may have excluded a few very small designs. Are there any CPU cores, serial or parallel, that are significantly smaller than 600 LUT/FFs? The Lattice part has LUT memory even dual port, so that is not a constraint, the LUTs can be used for registers.

Rick

Reply to
rickman
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The Xilinx PicoBlaze is less than 100 LUTs plus one block ram. Someone has been working on a simple C compiler for the PicoBlaze, but I have not tried it yet. I have used the PicoBlaze in many projects and I am quite happy with it.

I have not used it, but Lattice has the Micro8. Have you looked at it? It has been mentioned here as the Lattice equivalent to the PicoBlaze.

Regards,

John McCaskill

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Reply to
John McCaskill

That should be less than 100 slices.

Regards,

John McCaskill

Reply to
John McCaskill

If a 8 bits CPU is fine you may want to see my site. There is VHDL or verilog design. For this CPU it is easy to find free or non free tools. All is discussed in detail at:

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"I used 8051 from

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The VHDL code has been translated to verilog to avoid mix languages simulation. The cpu is also slightly modified to be able to use XILINX memories: for ROM I use..."

Reply to
beky4kr

im OP

hi I may have different interests, yes smallest nonserialized CPU as for your current task is one of the wishes, and here also there is no one definitive winner

pico paco blazes and mico8 are out of the question, most others are too large

i have used cut AVR core in XP3 but i dont recall the lut count

Antti

Reply to
Antti

I would suggest you check out one of the many free PIC cores available on the web. The reason for suggesting PIC is that it is accompanied by a processional IDE from Microchip. Developing a processor is easy and the web is full of wonderful and clever implementation but at the end of the day if you have to develop some software you need a good IDE.

I just tried a quick push-button synthesis of a 16C54,

*********************************************** Device Utilization for LFXP3C/PQFP208 *********************************************** Resource Used Avail Utilization

----------------------------------------------- LUTs 374 3072 12.17% Flipflops 83 3072 2.70% Block RAMs 0 6 0.00% IOs 67 136 49.26%

-----------------------------------------------

Hans

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Reply to
HT-Lab

Have you tabulated your findings anywhere? The last time I did a survey of ARM7 processors, I put it all into a spread sheet and posted it on the web. I think it was useful for a while, but the market overtook it and I couldn't keep up!

I read your thread about the serial processor and it was interesting. I think my project actually has the time to use such a processor, but I think you never found one that met your requirements.

I am not looking for a large address space, but I would like for it to be able to read data from an SD card. My design uses FPGAs both on the application board and the test fixture. Ultimately I want the test fixture to be able to read a programming file from an SD card and configure the target FGPA without a programming cable.

Of all the suggestions, so far the PIC sounds like the best one. I couldn't find a C compiler for the picoblaze or the pacoblaze. There is mention of someone creating one, but the web site is no longer accessible.

Rick

Reply to
rickman

Still, that's 200 LUTs which is very small. But I can't find a C compiler for it.

Rick

Reply to
rickman

You can find a download link here :

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Disclaimer : I never used it myself

Josep

Reply to
Josep Duran

Maybe something worth checking:

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From the above website:

  1. The ZPU is now open source. See ZPU mailing list for more details. 2. BSD license for HDL implementations--no hiccups when using in proprietary commercial products. Under the open source royalty free license, there are no limits on what type of technology (FPGA, anti-fuse, or ASIC) in which the ZPU can be implemented. 3. GPL license for architecture, documentation and tools 4. Completely FPGA brand and type neutral implementation 5. 298 LUT @ 125 MHz after P&R with 16 bit datapath and 4kBytes BRAM 6. 442 LUT @ 95 MHz after P&R with 32 bit datapath and 32kBytes BRAM 7. Codesize 80% of ARM thumb 8. Configurable 16/32 bit datapath 9. GCC toolchain(GDB, newlib, libstdc++) 10. Debugging via simulator or GDB stubs 11. HDL simulation feedback to simulator for powerful profiling capabilities 12. Eclipse ZPU plug-in 13. eCos embedded operating system support.

Henri

Reply to
Henri

e

details.

RAM

RAM

eh this is still on my MUST evaluate plan :)

80% of THUMB? that nice also, i just made my first THUMB assembly program Atmel dataflash bootstrap loader, its about 60 bytes of code (thumb) would be fun to compare if that optimized to max thumb code still compacts on zpu :) my code is really funky it loads 1 32 bit constant and constructs all other constants, also uses lower port of io address as mask constant, etc..

Antti

Reply to
Antti

I'm pretty impressed. Small, fast and with GCC support!

Rick

Reply to
rickman

Related to this 'serial' processor design, (probably should be better called 'most compact'?), I spotted a reference in a larger CPU released recently, that mentioned it had Quad-SPI SRAM support - so it looks like SRAM will soon be added to the already-available Quad-SPI FLASH memory. (There is a 32K SPI SRAM out, but this is not quad) Such a device would also help those 'needing more SRAM' in their FPGAs...

-jg

Reply to
Jim Granville

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